draft-ietf-v6ops-icmpv6-filtering-recs-03.txt   rfc4890.txt 
IPv6 Operations E. Davies Network Working Group E. Davies
Internet-Draft Consultant Request for Comments: 4890 Consultant
Intended status: Informational J. Mohacsi Category: Informational J. Mohacsi
Expires: August 17, 2007 NIIF/HUNGARNET NIIF/HUNGARNET
February 13, 2007
Recommendations for Filtering ICMPv6 Messages in Firewalls Recommendations for Filtering ICMPv6 Messages in Firewalls
draft-ietf-v6ops-icmpv6-filtering-recs-03.txt
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Abstract Abstract
In networks supporting IPv6 the Internet Control Message Protocol In networks supporting IPv6, the Internet Control Message Protocol
version 6 (ICMPv6) plays a fundamental role with a large number of version 6 (ICMPv6) plays a fundamental role with a large number of
functions, and a correspondingly large number of message types and functions, and a correspondingly large number of message types and
options. ICMPv6 is essential to the functioning of IPv6 but there options. ICMPv6 is essential to the functioning of IPv6, but there
are a number of security risks associated with uncontrolled are a number of security risks associated with uncontrolled
forwarding of ICMPv6 messages. Filtering strategies designed for the forwarding of ICMPv6 messages. Filtering strategies designed for the
corresponding protocol, ICMP, in IPv4 networks are not directly corresponding protocol, ICMP, in IPv4 networks are not directly
applicable, because these strategies are intended to accommodate a applicable, because these strategies are intended to accommodate a
useful auxiliary protocol that may not be required for correct useful auxiliary protocol that may not be required for correct
functioning. functioning.
This document provides some recommendations for ICMPv6 firewall This document provides some recommendations for ICMPv6 firewall
filter configuration that will allow propagation of ICMPv6 messages filter configuration that will allow propagation of ICMPv6 messages
that are needed to maintain the functioning of the network but drop that are needed to maintain the functioning of the network but drop
messages which are potential security risks. messages that are potential security risks.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Classifying ICMPv6 Messages . . . . . . . . . . . . . . . . . 6 2. Classifying ICMPv6 Messages . . . . . . . . . . . . . . . . . 6
2.1. Error and Informational ICMPv6 Messages . . . . . . . . . 6 2.1. Error and Informational ICMPv6 Messages . . . . . . . . . 6
2.2. Addressing of ICMPv6 . . . . . . . . . . . . . . . . . . . 7 2.2. Addressing of ICMPv6 . . . . . . . . . . . . . . . . . . . 6
2.3. Network Topology and Address Scopes . . . . . . . . . . . 7 2.3. Network Topology and Address Scopes . . . . . . . . . . . 7
2.4. Role in Establishing and Maintaining Communication . . . . 8 2.4. Role in Establishing and Maintaining Communication . . . . 7
3. Security Considerations . . . . . . . . . . . . . . . . . . . 8 3. Security Considerations . . . . . . . . . . . . . . . . . . . 8
3.1. Denial of Service Attacks . . . . . . . . . . . . . . . . 9 3.1. Denial-of-Service Attacks . . . . . . . . . . . . . . . . 9
3.2. Probing . . . . . . . . . . . . . . . . . . . . . . . . . 9 3.2. Probing . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.3. Redirection Attacks . . . . . . . . . . . . . . . . . . . 10 3.3. Redirection Attacks . . . . . . . . . . . . . . . . . . . . 9
3.4. Renumbering Attacks . . . . . . . . . . . . . . . . . . . 10 3.4. Renumbering Attacks . . . . . . . . . . . . . . . . . . . 10
3.5. Problems Resulting from ICMPv6 Transparency . . . . . . . 10 3.5. Problems Resulting from ICMPv6 Transparency . . . . . . . 10
4. Filtering Recommendations . . . . . . . . . . . . . . . . . . 10 4. Filtering Recommendations . . . . . . . . . . . . . . . . . . 10
4.1. Common Considerations . . . . . . . . . . . . . . . . . . 11 4.1. Common Considerations . . . . . . . . . . . . . . . . . . 11
4.2. Interaction of Link Local Messages with 4.2. Interaction of Link-Local Messages with
Firewall/Routers and Firewall/Bridges . . . . . . . . . . 12 Firewall/Routers and Firewall/Bridges . . . . . . . . . . 12
4.3. Recommendations for ICMPv6 Transit Traffic . . . . . . . . 13 4.3. Recommendations for ICMPv6 Transit Traffic . . . . . . . . 13
4.3.1. Traffic that Must Not be Dropped . . . . . . . . . . . 13 4.3.1. Traffic That Must Not Be Dropped . . . . . . . . . . . 14
4.3.2. Traffic that Normally Should Not be Dropped . . . . . 14 4.3.2. Traffic That Normally Should Not Be Dropped . . . . . 14
4.3.3. Traffic that will be Dropped Anyway - No Special 4.3.3. Traffic That Will Be Dropped Anyway -- No Special
Attention Needed . . . . . . . . . . . . . . . . . . . 14 Attention Needed . . . . . . . . . . . . . . . . . . . 15
4.3.4. Traffic for which a Policy Should be Defined . . . . . 15 4.3.4. Traffic for Which a Policy Should Be Defined . . . . . 16
4.3.5. Traffic which Should be Dropped Unless a Good Case 4.3.5. Traffic That Should Be Dropped Unless a Good Case
can be Made . . . . . . . . . . . . . . . . . . . . . 16 Can Be Made . . . . . . . . . . . . . . . . . . . . . 17
4.4. Recommendations for ICMPv6 Local Configuration Traffic . . 17 4.4. Recommendations for ICMPv6 Local Configuration Traffic . . 18
4.4.1. Traffic that Must Not be Dropped . . . . . . . . . . . 17 4.4.1. Traffic That Must Not Be Dropped . . . . . . . . . . . 18
4.4.2. Traffic that Normally Should Not be Dropped . . . . . 18 4.4.2. Traffic That Normally Should Not Be Dropped . . . . . 19
4.4.3. Traffic that will be Dropped Anyway - No Special 4.4.3. Traffic That Will Be Dropped Anyway -- No Special
Attention Needed . . . . . . . . . . . . . . . . . . . 18 Attention Needed . . . . . . . . . . . . . . . . . . . 19
4.4.4. Traffic for which a Policy Should be Defined . . . . . 19 4.4.4. Traffic for Which a Policy Should Be Defined . . . . . 20
4.4.5. Traffic which Should be Dropped Unless a Good Case 4.4.5. Traffic That Should Be Dropped Unless a Good Case
can be Made . . . . . . . . . . . . . . . . . . . . . 19 Can Be Made . . . . . . . . . . . . . . . . . . . . . 21
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 21
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 20 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20 6.1. Normative References . . . . . . . . . . . . . . . . . . . 21
7.1. Normative References . . . . . . . . . . . . . . . . . . . 20 6.2. Informative References . . . . . . . . . . . . . . . . . . 22
7.2. Informative References . . . . . . . . . . . . . . . . . . 21 Appendix A. Notes on Individual ICMPv6 Messages . . . . . . . . . 24
Appendix A. Notes on Individual ICMPv6 Messages . . . . . . . . . 22 A.1. Destination Unreachable Error Message . . . . . . . . . . 24
A.1. Destination Unreachable Error Message . . . . . . . . . . 22 A.2. Packet Too Big Error Message . . . . . . . . . . . . . . . 24
A.2. Packet Too Big Error Message . . . . . . . . . . . . . . . 22 A.3. Time Exceeded Error Message . . . . . . . . . . . . . . . 25
A.3. Time Exceeded Error Message . . . . . . . . . . . . . . . 23 A.4. Parameter Problem Error Message . . . . . . . . . . . . . 25
A.4. Parameter Problem Error Message . . . . . . . . . . . . . 23 A.5. ICMPv6 Echo Request and Echo Response . . . . . . . . . . 26
A.5. ICMPv6 Echo Request and Echo Response . . . . . . . . . . 24
A.6. Neighbor Solicitation and Neighbor Advertisement A.6. Neighbor Solicitation and Neighbor Advertisement
Messages . . . . . . . . . . . . . . . . . . . . . . . . . 24 Messages . . . . . . . . . . . . . . . . . . . . . . . . . 26
A.7. Router Solicitation and Router Advertisement Messages . . 25 A.7. Router Solicitation and Router Advertisement Messages . . 27
A.8. Redirect Messages . . . . . . . . . . . . . . . . . . . . 25 A.8. Redirect Messages . . . . . . . . . . . . . . . . . . . . 27
A.9. SEND Certificate Path Messages . . . . . . . . . . . . . . 25 A.9. SEND Certificate Path Messages . . . . . . . . . . . . . . 27
A.10. Multicast Listener Discovery Messages . . . . . . . . . . 25 A.10. Multicast Listener Discovery Messages . . . . . . . . . . 27
A.11. Multicast Router Discovery Messages . . . . . . . . . . . 26 A.11. Multicast Router Discovery Messages . . . . . . . . . . . 28
A.12. Router Renumbering Messages . . . . . . . . . . . . . . . 26 A.12. Router Renumbering Messages . . . . . . . . . . . . . . . 28
A.13. Node Information Query and Reply . . . . . . . . . . . . . 26 A.13. Node Information Query and Reply . . . . . . . . . . . . . 28
A.14. Mobile IPv6 Messages . . . . . . . . . . . . . . . . . . . 26 A.14. Mobile IPv6 Messages . . . . . . . . . . . . . . . . . . . 28
A.15. Unused and Experimental Messages . . . . . . . . . . . . . 27 A.15. Unused and Experimental Messages . . . . . . . . . . . . . 29
Appendix B. Example Script to Configure ICMPv6 Firewall Rules . . 28 Appendix B. Example Script to Configure ICMPv6 Firewall Rules . . 30
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 35
Intellectual Property and Copyright Statements . . . . . . . . . . 36
1. Introduction 1. Introduction
When a network supports IPv6 [RFC2460], the Internet Control Message When a network supports IPv6 [RFC2460], the Internet Control Message
Protocol version 6 (ICMPv6) [RFC4443] plays a fundamental role Protocol version 6 (ICMPv6) [RFC4443] plays a fundamental role
including being an essential component in establishing and including being an essential component in establishing and
maintaining communications both at the interface level and for maintaining communications both at the interface level and for
sessions to remote nodes. This means that overly aggressive sessions to remote nodes. This means that overly aggressive
filtering of ICMPv6 by firewalls may have a detrimental effect on the filtering of ICMPv6 by firewalls may have a detrimental effect on the
establishment and maintenance of IPv6 communications. On the other establishment and maintenance of IPv6 communications. On the other
hand, allowing indiscriminate passage of all ICMPv6 messages can be a hand, allowing indiscriminate passage of all ICMPv6 messages can be a
major security risk. This document recommends a set of rules which major security risk. This document recommends a set of rules that
seek to balance effective IPv6 communication against the needs of seek to balance effective IPv6 communication against the needs of
site security. site security.
In a few cases the appropriate rules will depend on whether the In a few cases, the appropriate rules will depend on whether the
firewall is protecting firewall is protecting
o an individual host, o an individual host,
o an end site where all ICMPv6 messages originate or terminate o an end site where all ICMPv6 messages originate or terminate
within the site, or within the site, or
o a transit site such as an Internet Service Provider's site where o a transit site such as an Internet Service Provider's site where
some ICMPv6 messages will be passing through. some ICMPv6 messages will be passing through.
The document suggests alternative rules appropriate to each situation The document suggests alternative rules appropriate to each situation
where it is relevant. It also notes some situations where where it is relevant. It also notes some situations where
alternative rules could be adopted according to the nature of the alternative rules could be adopted according to the nature of the
work being carried out on the site and consequent security policies. work being carried out on the site and consequent security policies.
In general Internet Service Providers should not filter ICMPv6 In general, Internet Service Providers should not filter ICMPv6
messages transiting their sites so that all the necessary messages transiting their sites so that all the necessary
communication elements are available to their customers to decide and communication elements are available to their customers to decide and
filter according to their policy. filter according to their policy.
Readers familiar with ICMPv6 can skip to the recommended filtering Readers familiar with ICMPv6 can skip to the recommended filtering
rules in Section 4 and an example configuration script for Linux rules in Section 4 and an example configuration script for Linux
netfilter in Appendix B. Netfilter in Appendix B.
ICMPv6 has a large number of functions defined in a number of sub- ICMPv6 has a large number of functions defined in a number of sub-
protocols, and there are a correspondingly large number of messages protocols, and there are a correspondingly large number of messages
and options within these messages. The functions currently defined and options within these messages. The functions currently defined
fall into a number of categories: fall into a number of categories:
Returning Error Messages Returning Error Messages
* Returning error messages to the source if a packet could not * Returning error messages to the source if a packet could not
be delivered. Four different error messages, each with a be delivered. Four different error messages, each with a
number of sub-types are specified in [RFC4443]. number of sub-types, are specified in [RFC4443].
Connection Checking Connection Checking
* Simple monitoring of connectivity through echo requests and * Simple monitoring of connectivity through echo requests and
responses used by the ping and traceroute utilities. The responses used by the ping and traceroute utilities. The
Echo Request and Echo Response messages are specified in Echo Request and Echo Response messages are specified in
[RFC4443]. [RFC4443].
Discovery Functions Discovery Functions
* Finding neighbors (both routers and hosts) connected to the * Finding neighbors (both routers and hosts) connected to the
same link and determining their IP and link layer addresses. same link and determining their IP and link layer addresses.
These messages are also used to check the uniqueness of any These messages are also used to check the uniqueness of any
addresses that an interface proposes to use (Duplicate addresses that an interface proposes to use (Duplicate
Address Detection - DAD). Four messages - Neighbor Address Detection - DAD). Four messages -- Neighbor
Solicitation (NS), Neighbor Advertisement (NA), Router Solicitation (NS), Neighbor Advertisement (NA), Router
Solicitation (RS) and Router Advertisement (RA) - are Solicitation (RS) and Router Advertisement (RA) -- are
specified in [RFC2461]. specified in [RFC2461].
* Ensuring that neighbors remain reachable using the same IP * Ensuring that neighbors remain reachable using the same IP
and link layer addresses after initial discovery (Neighbor and link layer addresses after initial discovery (Neighbor
Unreachability Discovery - NUD) and notifying neighbors of Unreachability Discovery - NUD) and notifying neighbors of
changes to link layer addresses. Uses NS and NA [RFC2461]. changes to link layer addresses. Uses NS and NA [RFC2461].
* Finding routers and determining how to obtain IP addresses * Finding routers and determining how to obtain IP addresses
to join the subnets supported by the routers. Uses RS and to join the subnets supported by the routers. Uses RS and
RA [RFC2461]. RA [RFC2461].
* If stateless auto-configuration of hosts is enabled,
* If stateless autoconfiguration of hosts is enabled,
communicating prefixes and other configuration information communicating prefixes and other configuration information
(including the link Maximum Transfer Unit (MTU) and (including the link Maximum Transmission Unit (MTU) and
suggested hop limit default) from routers to hosts. Uses RS suggested hop limit default) from routers to hosts. Uses RS
and RA [RFC2462]. and RA [RFC2462].
* Using SEcure Neighbor Discovery (SEND) to authenticate a
router attached to a link, the Certificate Path Solicitation * When using SEcure Neighbor Discovery (SEND) to authenticate
and Advertisement messages specified in [RFC3971] are used a router attached to a link, the Certificate Path
by hosts to retrieve the trust chain between a trust anchor Solicitation and Advertisement messages specified in
and the router certificate from the router. [RFC3971] are used by hosts to retrieve the certificates
* Determining the Maximum Transmission Unit (MTU) along a documenting the trust chain between a trust anchor and the
path. The Packet Too Big error message is essential to this router from the router.
function [RFC1981].
* Determining the MTU along a path. The Packet Too Big error
message is essential to this function [RFC1981].
* Providing a means to discover the IPv6 addresses associated * Providing a means to discover the IPv6 addresses associated
with the link layer address of an interface (the inverse of with the link layer address of an interface (the inverse of
Neighbor Discovery, where the link layer address is Neighbor Discovery, where the link layer address is
discovered given an IPv6 address). Two messages, Inverse discovered given an IPv6 address). Two messages, Inverse
Neighbor Discovery Solicitation and Advertisement messages Neighbor Discovery Solicitation and Advertisement messages,
are specified in [RFC3122]. are specified in [RFC3122].
* Communicating which multicast groups have listeners on a * Communicating which multicast groups have listeners on a
link to the multicast capable routers connected to the link. link to the multicast capable routers connected to the link.
Uses messages Multicast Listener Query, Multicast Listener Uses messages Multicast Listener Query, Multicast Listener
Report (two versions) and Multicast Listener Done (version 1 Report (two versions), and Multicast Listener Done (protocol
only) as specified in Multicast Listener Discovery MLDv1 version 1 only) as specified in Multicast Listener Discovery
[RFC2710] and MLDv2[RFC3810]. MLDv1 [RFC2710] and MLDv2 [RFC3810].
* Discovering multicast routers attached to the local link. * Discovering multicast routers attached to the local link.
Uses messages Multicast Router Advertisement, Multicast Uses messages Multicast Router Advertisement, Multicast
Router Solicitation and Multicast Router Termination as Router Solicitation, and Multicast Router Termination as
specified in Multicast Router Discovery [RFC4286]. specified in Multicast Router Discovery [RFC4286].
Reconfiguration Functions Reconfiguration Functions
* Redirecting packets to a more appropriate router on the * Redirecting packets to a more appropriate router on the
local link for the destination address or pointing out that local link for the destination address or pointing out that
a destination is actually on the local link even if it is a destination is actually on the local link even if it is
not obvious from the IP address (where a link supports not obvious from the IP address (where a link supports
multiple subnets). The Redirect message is specified in multiple subnets). The Redirect message is specified in
[RFC2461]. [RFC2461].
* Supporting renumbering of networks by allowing the prefixes * Supporting renumbering of networks by allowing the prefixes
advertised by routers to be altered. Uses NS, NA, RS and RA advertised by routers to be altered. Uses NS, NA, RS and RA
together with the Router Renumbering message specified in together with the Router Renumbering message specified in
[RFC2894]. [RFC2894].
Mobile IPv6 Support Mobile IPv6 Support
* Providing support for some aspects of Mobile IPv6 especially * Providing support for some aspects of Mobile IPv6 especially
dealing with the IPv6 Mobile Home Agent functionality dealing with the IPv6 Mobile Home Agent functionality
provided in routers and needed to support a Mobile node provided in routers and needed to support a Mobile node
homed on the link. The Home Agent Address Discovery Request homed on the link. The Home Agent Address Discovery Request
and Reply; and Mobile Prefix Solicitation and Advertisement and Reply and the Mobile Prefix Solicitation and
messages are specified in [RFC3775] Advertisement messages are specified in [RFC3775].
Experimental Extensions Experimental Extensions
* An experimental extension to ICMPv6 specifies the ICMP Node * An experimental extension to ICMPv6 specifies the ICMP Node
Information Query and Response messages which can be used to Information Query and Response messages that can be used to
retrieve some basic information about nodes [RFC4620]. retrieve some basic information about nodes [RFC4620].
* The SEAmless IP MOBility (seamoby) working group specified a
pair of experimental protocols which use an ICMPv6 message * The SEAmless IP MOBility (SEAMOBY) working group specified a
pair of experimental protocols that use an ICMPv6 message
specified in [RFC4065] to help in locating an access router specified in [RFC4065] to help in locating an access router
and moving the attachment point of a mobile node from one and moving the attachment point of a mobile node from one
access router to another. access router to another.
Many of these messages should only be used in a link-local context Many of these messages should only be used in a link-local context
rather than end-to-end, and filters need to be concerned with the rather than end-to-end, and filters need to be concerned with the
type of addresses in ICMPv6 packets as well as the specific source type of addresses in ICMPv6 packets as well as the specific source
and destination addresses. and destination addresses.
Compared with the corresponding IPv4 protocol, ICMP, ICMPv6 cannot be Compared with the corresponding IPv4 protocol, ICMP, ICMPv6 cannot be
treated as an auxiliary function with packets that can be dropped in treated as an auxiliary function with packets that can be dropped in
most cases without damaging the functionality of the network. This most cases without damaging the functionality of the network. This
means that firewall filters for ICMPv6 have to be more carefully means that firewall filters for ICMPv6 have to be more carefully
configured than was the case for ICMP, where typically a small set of configured than was the case for ICMP, where typically a small set of
blanket rules could be applied. blanket rules could be applied.
2. Classifying ICMPv6 Messages 2. Classifying ICMPv6 Messages
2.1. Error and Informational ICMPv6 Messages 2.1. Error and Informational ICMPv6 Messages
ICMPv6 messages contain an eight bit Type field interpreted as an ICMPv6 messages contain an eight-bit Type field interpreted as an
integer between 0 and 255. Messages with Type values less than or integer between 0 and 255. Messages with Type values less than or
equal to 127 are Error Messages. The remainder are Informational equal to 127 are Error messages. The remainder are Informational
Messages. In general terms, Error Messages with well-known messages. In general terms, Error messages with well-known
(standardized) Type values would normally be expected to be allowed (standardized) Type values would normally be expected to be allowed
to be sent to or pass through firewalls, and may be essential to the to be sent to or pass through firewalls, and may be essential to the
establishment and maintenance of communications (see Section 2.4) establishment and maintenance of communications (see Section 2.4)
whereas Informational Messages will generally be the subject of whereas Informational messages will generally be the subject of
policy rules, and those passing through end site firewalls can, in policy rules, and those passing through end site firewalls can, in
many but by no means all cases, be dropped without damaging IPv6 many but by no means all cases, be dropped without damaging IPv6
communications. communications.
2.2. Addressing of ICMPv6 2.2. Addressing of ICMPv6
ICMPv6 messages are sent using various kinds of source and ICMPv6 messages are sent using various kinds of source and
destination address types. The source address is usually a unicast destination address types and scopes. The source address is usually
address, but during address autoconfiguration message exchanges, the a unicast address, but during address autoconfiguration message
unspecified address :: is also used as a source address [RFC2462]. exchanges, the unspecified address (::) is also used as a source
address [RFC2462].
Multicast Listener Discovery (MLD) Report and Done messages are sent Multicast Listener Discovery (MLD) Report and Done messages are sent
with a link-local address as the IPv6 source address, if a valid with a link-local address as the IPv6 source address, if a valid
address is available on the interface. If a valid link-local address address is available on the interface. If a valid link-local address
is not available (e.g., one has not been configured), the message is is not available (e.g., one has not been configured), the message is
sent with the unspecified address (::) as the IPv6 source address. sent with the unspecified address (::) as the IPv6 source address.
Subsequently the node will generate new MLD Report messages with Subsequently, the node will generate new MLD Report messages with
proper link-local source address once it has been configured proper link-local source address once it has been configured
[RFC3590]. [RFC3590].
The destination address can be either a well-known multicast address, The destination address can be either a well-known multicast address,
a generated multicast address such as the solicited-node multicast a generated multicast address such as the solicited-node multicast
address, an anycast address or a unicast address. While many ICMPv6 address, an anycast address, or a unicast address. While many ICMPv6
messages use multicast addresses most of the time, some also use messages use multicast addresses most of the time, some also use
unicast addresses. For instance, the Router Advertisement messages unicast addresses. For instance, the Router Advertisement messages
are sent to the all-nodes multicast address when unsolicited, but can are sent to the all-nodes multicast address when unsolicited, but can
also be sent to a unicast address in response to a specific Router also be sent to a unicast address in response to a specific Router
Solicitation, although this is rarely seen in current Solicitation, although this is rarely seen in current
implementations. implementations.
2.3. Network Topology and Address Scopes 2.3. Network Topology and Address Scopes
ICMPv6 messages can be classified according to whether they are meant ICMPv6 messages can be classified according to whether they are meant
for end-to-end communications or communications within a link. There for end-to-end communications or local communications within a link.
are also messages that we can classify as 'any-to-end', which can be There are also messages that we can classify as 'any-to-end', which
sent from any point within a path back to the source; typically these can be sent from any point within a path back to the source;
are used to announce an error in processing the original packet. For typically, these are used to announce an error in processing the
instance, the address resolution messages are solely for local original packet. For instance, the address resolution messages are
communications [RFC2461], whereas the Destination Unreachable solely for local communications [RFC2461], whereas the Destination
messages are any-to-end in nature. Generally end-to-end and any-to- Unreachable messages are any-to-end in nature. Generally, end-to-end
end messages might be expected to pass through firewalls depending on and any-to-end messages might be expected to pass through firewalls
policies but local communications must not. depending on policies but local communications must not.
Local communications will use link-local addresses in many cases but Local communications will use link-local addresses in many cases but
may also use global unicast addresses when configuring global may also use global unicast addresses when configuring global
addresses, for example. Also some ICMPv6 messages used in local addresses, for example. Also, some ICMPv6 messages used in local
communications may contravene the usual rules requiring compatible communications may contravene the usual rules requiring compatible
scopes for source and destination addresses. scopes for source and destination addresses.
2.4. Role in Establishing and Maintaining Communication 2.4. Role in Establishing and Maintaining Communication
Many ICMPv6 messages have a role in establishing or maintaining Many ICMPv6 messages have a role in establishing or maintaining
communications to and from the firewall and such messages have to be communications to and from the firewall and such messages have to be
accepted by firewalls for local delivery. Generally a firewall will accepted by firewalls for local delivery. Generally, a firewall will
also be acting as a router so that all the messages that might be also be acting as a router so that all the messages that might be
used in configuring a router interface need to be accepted and used in configuring a router interface need to be accepted and
generated. These messages should not transit through a firewall that generated. These messages should not transit through a firewall that
is also acting as a router as they are normally intended for use is also acting as a router as they are normally intended for use
within a link. within a link.
On the other hand, most ICMPv6 error messages traveling end-to-end or On the other hand, most ICMPv6 error messages traveling end-to-end or
any-to-end are essential to the establishment and maintenance of any-to-end are essential to the establishment and maintenance of
communications. These messages must be passed through firewalls and communications. These messages must be passed through firewalls and
might also be sent to and from firewalls to assist with establishment might also be sent to and from firewalls to assist with establishment
and maintenance of communications. For example the Packet Too Big and maintenance of communications. For example, the Packet Too Big
error message is needed to determine the MTU along a path both when a error message is needed to determine the MTU along a path both when a
communication session is established initially and later if the path communication session is established initially and later if the path
is rerouted during the session. is rerouted during the session.
The remaining ICMPv6 messages which are not associated with The remaining ICMPv6 messages that are not associated with
communication establishment or maintenance will normally be communication establishment or maintenance will normally be
legitimately attempting to pass through a firewall from inside to out legitimately attempting to pass through a firewall from inside to out
or vice versa, but in most cases decisions as to whether to allow or vice versa, but in most cases decisions as to whether or not to
them to pass or not can be made on the basis of local policy without allow them to pass can be made on the basis of local policy without
interfering with IPv6 communications. interfering with IPv6 communications.
The filtering rules for the various message roles will generally be The filtering rules for the various message roles will generally be
different. different.
3. Security Considerations 3. Security Considerations
This memo recommends filtering configurations for firewalls designed This memo recommends filtering configurations for firewalls designed
to minimize the security vulnerabilities that can arise in using the to minimize the security vulnerabilities that can arise in using the
many different sub-protocols of ICMPv6 in support of IPv6 many different sub-protocols of ICMPv6 in support of IPv6
communication. communication.
A major concern is that it is generally not possible to use IPsec or A major concern is that it is generally not possible to use IPsec or
other means to authenticate the sender and validate the contents of other means to authenticate the sender and validate the contents of
many ICMPv6 messages. To a large extent this is because a site can many ICMPv6 messages. To a large extent, this is because a site can
legitimately expect to receive certain error and other messages from legitimately expect to receive certain error and other messages from
almost any location in the wider Internet, and these messages may almost any location in the wider Internet, and these messages may
occur as a result of the first message sent to a destination. occur as a result of the first message sent to a destination.
Establishing security associations with all possible sources of Establishing security associations with all possible sources of
ICMPv6 messages is therefore impossible. ICMPv6 messages is therefore impossible.
The inability to establish security associations to protect some The inability to establish security associations to protect some
messages that are needed to establish and maintain communications messages that are needed to establish and maintain communications
means that alternative means have to used to reduce the vulnerability means that alternative means have to be used to reduce the
of sites to ICMPv6 based attacks. The most common way of doing this vulnerability of sites to ICMPv6-based attacks. The most common way
is to establish strict filtering policies in site firewalls to limit of doing this is to establish strict filtering policies in site
the unauthenticated ICMPv6 messages that can pass between the site firewalls to limit the unauthenticated ICMPv6 messages that can pass
and the wider Internet. This makes control of ICMPv6 filtering a between the site and the wider Internet. This makes control of
delicate balance between protecting the site by dropping some of the ICMPv6 filtering a delicate balance between protecting the site by
ICMPv6 traffic passing through the firewall and allowing enough of dropping some of the ICMPv6 traffic passing through the firewall and
the traffic through to make sure that efficient communication can be allowing enough of the traffic through to make sure that efficient
established. communication can be established.
SEND [RFC3971] has been specified as a means to improve the security SEND [RFC3971] has been specified as a means to improve the security
of local ICMPv6 communications. SEND sidesteps security association of local ICMPv6 communications. SEND sidesteps security association
bootstrapping problems that would result if IPsec was used. SEND bootstrapping problems that would result if IPsec was used. SEND
affects only link local messages and does not limit the filtering affects only link-local messages and does not limit the filtering
which firewalls can apply and its role in security is therefore not that firewalls can apply, and its role in security is therefore not
discussed further in this document. discussed further in this document.
Firewalls will normally be used to monitor ICMPv6 to control the Firewalls will normally be used to monitor ICMPv6 to control the
following security concerns: following security concerns:
3.1. Denial of Service Attacks 3.1. Denial-of-Service Attacks
ICMPv6 can be used to cause a Denial of Service(DoS) in a number of ICMPv6 can be used to cause a denial of service (DoS) in a number of
ways, including simply sending excessive numbers of ICMPv6 packets to ways, including simply sending excessive numbers of ICMPv6 packets to
destinations in the site and sending error messages which disrupt destinations in the site and sending error messages that disrupt
established communications by causing sessions to be dropped. Also established communications by causing sessions to be dropped. Also,
if spurious communication establishment or maintenance messages can if spurious communication establishment or maintenance messages can
be infiltrated on to a link it might be possible to invalidate be infiltrated onto a link, it might be possible to invalidate
legitimate addresses or disable interfaces. legitimate addresses or disable interfaces.
3.2. Probing 3.2. Probing
A major security consideration is preventing attackers probing the A major security consideration is preventing attackers from probing
site to determine the topology and identify hosts that might be the site to determine the topology and identify hosts that might be
vulnerable to attack. Carefully crafted but, often, malformed vulnerable to attack. Carefully crafted but, often, malformed
messages can be used to provoke ICMPv6 responses from hosts thereby messages can be used to provoke ICMPv6 responses from hosts thereby
informing attackers of potential targets for future attacks. However informing attackers of potential targets for future attacks.
the very large address space of IPv6 makes probing a less effective However, the very large address space of IPv6 makes probing a less
weapon as compared with IPv4 provided that addresses are not effective weapon as compared with IPv4 provided that addresses are
allocated in an easily guessable fashion. This subject is explored not allocated in an easily guessable fashion. This subject is
in more depth in [I-D.ietf-v6ops-scanning-implications]. explored in more depth in [SCAN-IMP].
3.3. Redirection Attacks 3.3. Redirection Attacks
A redirection attack could be used by a malicious sender to perform A redirection attack could be used by a malicious sender to perform
man-in-the-middle attacks or divert packets either to a malicious man-in-the-middle attacks or divert packets either to a malicious
monitor or to cause DoS by blackholing the packets. These attacks monitor or to cause DoS by blackholing the packets. These attacks
would normally have to be carried out locally on a link using the would normally have to be carried out locally on a link using the
Redirect message. Administrators need to decide if the improvement Redirect message. Administrators need to decide if the improvement
in efficiency from using Redirect messages is worth the risk of in efficiency from using Redirect messages is worth the risk of
malicious use. Factors to consider include the physical security of malicious use. Factors to consider include the physical security of
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link in a secure building with complex addressing and redundant link in a secure building with complex addressing and redundant
routers, the efficiency gains might well outweigh the small risk of a routers, the efficiency gains might well outweigh the small risk of a
rogue node being connected. rogue node being connected.
3.4. Renumbering Attacks 3.4. Renumbering Attacks
Spurious Renumbering messages can lead to the disruption of a site. Spurious Renumbering messages can lead to the disruption of a site.
Although Renumbering messages are required to be authenticated with Although Renumbering messages are required to be authenticated with
IPsec, so that it is difficult to carry out such attacks in practice, IPsec, so that it is difficult to carry out such attacks in practice,
they should not be allowed through a site boundary firewall. On the they should not be allowed through a site boundary firewall. On the
other hand a site may employ multiple "layers" of firewall. In this other hand, a site may employ multiple "layers" of firewalls. In
case Renumbering messages might be expected to be allowed to transit this case, Renumbering messages might be expected to be allowed to
interior firewalls but not pass across the outer boundary. transit interior firewalls but not pass across the outer boundary.
3.5. Problems Resulting from ICMPv6 Transparency 3.5. Problems Resulting from ICMPv6 Transparency
Because some ICMPv6 error packets need to be passed through a Because some ICMPv6 error packets need to be passed through a
firewall in both directions, malicious users can potentially use firewall in both directions, malicious users can potentially use
these messages to communicate between inside and outside, bypassing these messages to communicate between inside and outside, bypassing
administrative inspection. For example it might be possible to carry administrative inspection. For example, it might be possible to
out a covert conversation through the payload of ICMPv6 error carry out a covert conversation through the payload of ICMPv6 error
messages or tunnel inappropriate encapsulated IP packets in ICMPv6 messages or tunnel inappropriate encapsulated IP packets in ICMPv6
error messages. This problem can be alleviated by filtering ICMPv6 error messages. This problem can be alleviated by filtering ICMPv6
errors using a deep packet inspection mechanism to ensure that the errors using a deep packet inspection mechanism to ensure that the
packet carried as a payload is associated with legitimate traffic to packet carried as a payload is associated with legitimate traffic to
or from the protected network. or from the protected network.
4. Filtering Recommendations 4. Filtering Recommendations
When designing firewall filtering rules for ICMPv6, the rules can be When designing firewall filtering rules for ICMPv6, the rules can be
divided into two classes: divided into two classes:
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messages or tunnel inappropriate encapsulated IP packets in ICMPv6 messages or tunnel inappropriate encapsulated IP packets in ICMPv6
error messages. This problem can be alleviated by filtering ICMPv6 error messages. This problem can be alleviated by filtering ICMPv6
errors using a deep packet inspection mechanism to ensure that the errors using a deep packet inspection mechanism to ensure that the
packet carried as a payload is associated with legitimate traffic to packet carried as a payload is associated with legitimate traffic to
or from the protected network. or from the protected network.
4. Filtering Recommendations 4. Filtering Recommendations
When designing firewall filtering rules for ICMPv6, the rules can be When designing firewall filtering rules for ICMPv6, the rules can be
divided into two classes: divided into two classes:
o Rules for ICMPv6 traffic transiting the firewall, with some minor o Rules for ICMPv6 traffic transiting the firewall, with some minor
variations for variations for
* firewalls protecting end sites or individual hosts, and * firewalls protecting end sites or individual hosts, and
* firewalls protecting transit sites * firewalls protecting transit sites
o Rules for ICMPv6 directed to interfaces on the firewall o Rules for ICMPv6 directed to interfaces on the firewall
Firewalls integrated with an individual host ("end host firewalls") Firewalls integrated with an individual host ("end host firewalls")
can be treated as end site firewalls but the special considerations can be treated as end site firewalls, but the special considerations
discussed in Section 4.2 may be relevant because the firewall is not discussed in Section 4.2 may be relevant because the firewall is not
a router. a router.
This section suggests some common considerations which should be This section suggests some common considerations that should be borne
borne in mind when designing filtering rules and then categorizes the in mind when designing filtering rules and then categorizes the rules
rules for each class. The categories are: for each class. The categories are:
o Messages that must not be dropped: usually because establishment o Messages that must not be dropped: usually because establishment
or maintenance of communications will be prevented or severely or maintenance of communications will be prevented or severely
impacted. impacted.
o Messages that should not be dropped: administrators need to have a o Messages that should not be dropped: administrators need to have a
very good reason for dropping this category very good reason for dropping this category.
o Messages that may be dropped in firewall/routers, but these o Messages that may be dropped in firewall/routers, but these
messages may already be targeted to drop for other reasons, (e.g., messages may already be targeted to drop for other reasons (e.g.,
because they are using link-local addresses), or because the because they are using link-local addresses) or because the
protocol specification would cause the messages to be rejected if protocol specification would cause the messages to be rejected if
they had passed through a router. Special considerations apply to they had passed through a router. Special considerations apply to
transit traffic if the firewall is not a router as discussed in transit traffic if the firewall is not a router as discussed in
Section 4.2. Section 4.2.
o Messages that administrators may or may not want to drop depending o Messages that administrators may or may not want to drop depending
on local policy. on local policy.
o Messages that administrators should consider dropping (e.g., ICMP o Messages that administrators should consider dropping (e.g., ICMP
node information name lookup queries) node information name lookup queries).
More detailed analysis of each of the message types can be found in More detailed analysis of each of the message types can be found in
Appendix A. Appendix A.
4.1. Common Considerations 4.1. Common Considerations
Depending on the classification of the message to be filtered (see Depending on the classification of the message to be filtered (see
Section 2), ICMPv6 messages should be filtered based on the ICMPv6 Section 2), ICMPv6 messages should be filtered based on the ICMPv6
type of the message and the type (unicast, multicast, etc.) and scope type of the message and the type (unicast, multicast, etc.) and scope
(link-local, global unicast, etc) of source and destination (link-local, global unicast, etc.) of source and destination
addresses. In some cases it may be desirable to filter on the Code addresses. In some cases, it may be desirable to filter on the Code
field of ICMPv6 error messages. field of ICMPv6 error messages.
Messages that can be authenticated on delivery, probably because they Messages that can be authenticated on delivery, probably because they
contain an IPsec AH header or ESP header with authentication, may be contain an IPsec AH header or ESP header with authentication, may be
subject to less strict policies than messages that cannot be subject to less strict policies than messages that cannot be
authenticated. In the remainder of this section, we are generally authenticated. In the remainder of this section, we are generally
considering what should be configured for unauthenticated messages. considering what should be configured for unauthenticated messages.
In many cases it is not realistic to expect more than a tiny fraction In many cases, it is not realistic to expect more than a tiny
of the messages to be authenticated. fraction of the messages to be authenticated.
Where messages are not essential to the establishment or maintenance Where messages are not essential to the establishment or maintenance
of communications, local policy can be used to determine whether a of communications, local policy can be used to determine whether a
message should be allowed or dropped. message should be allowed or dropped.
Depending on the capabilities of the firewall being configured, it Depending on the capabilities of the firewall being configured, it
may be possible for the firewall to maintain state about packets that may be possible for the firewall to maintain state about packets that
may result in error messages being returned or about ICMPv6 packets may result in error messages being returned or about ICMPv6 packets
(e.g., Echo Requests) that are expected to receive a specific (e.g., Echo Requests) that are expected to receive a specific
response. This state may allow the firewall to perform more precise response. This state may allow the firewall to perform more precise
checks based on this state, and to apply limits on the number of checks based on this state, and to apply limits on the number of
ICMPv6 packets accepted incoming or outgoing as a result of a packet ICMPv6 packets accepted incoming or outgoing as a result of a packet
traveling in the opposite direction. The capabilities of firewalls traveling in the opposite direction. The capabilities of firewalls
to perform such stateful packet inspection vary from model to model, to perform such stateful packet inspection vary from model to model,
and it is not assumed that firewalls are uniformly capable in this and it is not assumed that firewalls are uniformly capable in this
respect. respect.
Firewalls which are able to perform deep packet inspection may be Firewalls that are able to perform deep packet inspection may be able
able to check the header fields in the start of the errored packet to check the header fields in the start of the errored packet that is
which is carried by ICMPv6 error messages. If the embedded packet carried by ICMPv6 error messages. If the embedded packet has a
has a source address which does not match the destination of the source address that does not match the destination of the error
error message the packet can be dropped. This provides a partial message, the packet can be dropped. This provides a partial defense
defense against some possible attacks on TCP that use spoofed ICMPv6 against some possible attacks on TCP that use spoofed ICMPv6 error
error messages, but the checks can also be carried out at the messages, but the checks can also be carried out at the destination.
destination. For further information on these attacks see For further information on these attacks see [ICMP-ATTACKS].
[I-D.ietf-tcpm-icmp-attacks].
In general, the scopes of source and destination addresses of ICMPv6 In general, the scopes of source and destination addresses of ICMPv6
messages should be matched, and packets with mismatched addresses messages should be matched, and packets with mismatched addresses
should be dropped if they attempt to transit a router. However some should be dropped if they attempt to transit a router. However, some
of the address configuration messages carried locally on a link may of the address configuration messages carried locally on a link may
legitimately have mismatched addresses. Node implementations must legitimately have mismatched addresses. Node implementations must
accept these messages delivered locally on a link and administrators accept these messages delivered locally on a link, and administrators
should be aware that they can exist. should be aware that they can exist.
ICMPv6 messages transiting firewalls inbound to a site may be treated ICMPv6 messages transiting firewalls inbound to a site may be treated
differently depending on whether they addressed to a node on the site differently depending on whether they are addressed to a node on the
or to some other node. For end sites packets addressed to nodes not site or to some other node. For end sites, packets addressed to
on the site should be dropped but would generally be forwarded by nodes not on the site should be dropped, but would generally be
firewalls on transit sites. forwarded by firewalls on transit sites.
4.2. Interaction of Link Local Messages with Firewall/Routers and 4.2. Interaction of Link-Local Messages with Firewall/Routers and
Firewall/Bridges Firewall/Bridges
Firewalls can be implemented both as IP routers (firewall/routers) Firewalls can be implemented both as IP routers (firewall/routers)
and as link layer bridges (e.g., Ethernet bridges) that are and as link layer bridges (e.g., Ethernet bridges) that are
transparent to the IP layer although they will actually be inspecting transparent to the IP layer although they will actually be inspecting
the IP packets as they pass through (firewall/bridges). the IP packets as they pass through (firewall/bridges).
Many of the messages used for establishment and maintenance of Many of the messages used for establishment and maintenance of
communications on the local link will be sent with link-local communications on the local link will be sent with link-local
addresses for at least one of their source and destination. Routers addresses for at least one of their source and destination. Routers
conforming to the IPv6 standards will not forward these packets; conforming to the IPv6 standards will not forward these packets;
there is no need to configure additional rules to prevent these there is no need to configure additional rules to prevent these
packets traversing a firewall/router, although administrators may packets traversing a firewall/router, although administrators may
wish to configure rules that would drop these packets for insurance wish to configure rules that would drop these packets for insurance
and as a means of monitoring for attacks. Also the specifications of and as a means of monitoring for attacks. Also, the specifications
ICMPv6 messages intended for use only on the local link specify of ICMPv6 messages intended for use only on the local link specify
various measures which would allow receivers to detect if the message various measures that would allow receivers to detect if the message
had passed through a router, including: had passed through a router, including:
o Requiring that the hop limit in the IPv6 header is set to 255 on o Requiring that the hop limit in the IPv6 header is set to 255 on
transmission. Receivers verify that the hop limit is still 255, transmission. Receivers verify that the hop limit is still 255,
to ensure that the packet has not passed through a router. to ensure that the packet has not passed through a router.
o Checking that the source address is a link-local unicast address. o Checking that the source address is a link-local unicast address.
Accordingly it is not essential to configure firewall/router rules to
drop out-of-specification packets of these types. If they have non- Accordingly, it is not essential to configure firewall/router rules
link-local source and destination addresses, allowing them to to drop out-of-specification packets of these types. If they have
non-link-local source and destination addresses, allowing them to
traverse the firewall/router, they would be rejected because of the traverse the firewall/router, they would be rejected because of the
checks performed at the destination. Again, firewall administrators checks performed at the destination. Again, firewall administrators
may still wish to configure rules to log or drop such out-of- may still wish to configure rules to log or drop such out-of-
specification packets. specification packets.
For firewall/bridges, slightly different considerations apply. The For firewall/bridges, slightly different considerations apply. The
physical links on either side of the firewall/bridge are treated as a physical links on either side of the firewall/bridge are treated as a
single logical link for the purposes of IP. Hence the link local single logical link for the purposes of IP. Hence, the link local
messages used for discovery functions on the link must be allowed to messages used for discovery functions on the link must be allowed to
transit the transparent bridge. Administrators should assure for transit the transparent bridge. Administrators should ensures that
themselves that routers and hosts attached to the link containing the routers and hosts attached to the link containing the firewall/bridge
firewall/bridge are built to the correct specifications so that out- are built to the correct specifications so that out-of-specification
of-specification packets are actually dropped as described in the packets are actually dropped as described in the earlier part of this
earlier part of this section. section.
An end host firewall can generally be thought of as a special case of An end host firewall can generally be thought of as a special case of
a firewall/bridge but the only link local messages that need to be a firewall/bridge, but the only link-local messages that need to be
allowed through are those directed to the host's interface. allowed through are those directed to the host's interface.
4.3. Recommendations for ICMPv6 Transit Traffic 4.3. Recommendations for ICMPv6 Transit Traffic
This section recommends rules that should be applied to ICMPv6 This section recommends rules that should be applied to ICMPv6
traffic attempting to transit a firewall. traffic attempting to transit a firewall.
4.3.1. Traffic that Must Not be Dropped 4.3.1. Traffic That Must Not Be Dropped
Error messages that are essential to the establishment and Error messages that are essential to the establishment and
maintenance of communications: maintenance of communications:
o Destination Unreachable (Type 1) - All codes o Destination Unreachable (Type 1) - All codes
o Packet Too Big (Type 2) o Packet Too Big (Type 2)
o Time Exceeded (Type 3) - Code 0 only o Time Exceeded (Type 3) - Code 0 only
o Parameter Problem (Type 4) - Codes 1 and 2 only o Parameter Problem (Type 4) - Codes 1 and 2 only
Appendix A.4 suggests some more specific checks that could be Appendix A.4 suggests some more specific checks that could be
performed on Parameter Problem messages if a firewall has the performed on Parameter Problem messages if a firewall has the
necessary packet inspection capabilities. necessary packet inspection capabilities.
Connectivity checking messages: Connectivity checking messages:
o Echo Request (Type 128) o Echo Request (Type 128)
o Echo Response (Type 129) o Echo Response (Type 129)
For Teredo tunneling [RFC4380] to IPv6 nodes on the site to be For Teredo tunneling [RFC4380] to IPv6 nodes on the site to be
possible, it is essential that the connectivity checking messages are possible, it is essential that the connectivity checking messages are
allowed through the firewall. It has been common practice in IPv4 allowed through the firewall. It has been common practice in IPv4
networks to drop Echo Request messages in firewalls to minimize the networks to drop Echo Request messages in firewalls to minimize the
risk of scanning attacks on the protected network. As discussed in risk of scanning attacks on the protected network. As discussed in
Section 3.2, the risks from port scanning in an IPv6 network are much Section 3.2, the risks from port scanning in an IPv6 network are much
less severe and it is not necessary to filter IPv6 Echo Request less severe, and it is not necessary to filter IPv6 Echo Request
messages. messages.
4.3.2. Traffic that Normally Should Not be Dropped 4.3.2. Traffic That Normally Should Not Be Dropped
Error messages other than those listed in Section 4.3.1:
Error messages other than those listed in Section 4.3.1
o Time Exceeded (Type 3) - Code 1 o Time Exceeded (Type 3) - Code 1
o Parameter Problem (Type 4) - Code 0 o Parameter Problem (Type 4) - Code 0
Mobile IPv6 messages that are needed to assist mobility: Mobile IPv6 messages that are needed to assist mobility:
o Home Agent Address Discovery Request (Type 144) o Home Agent Address Discovery Request (Type 144)
o Home Agent Address Discovery Reply (Type 145) o Home Agent Address Discovery Reply (Type 145)
o Mobile Prefix Solicitation (Type 146) o Mobile Prefix Solicitation (Type 146)
o Mobile Prefix Advertisement(Type 147) o Mobile Prefix Advertisement(Type 147)
Administrators may wish to apply more selective rules as described in Administrators may wish to apply more selective rules as described in
Appendix A.14 depending on whether the site is catering for mobile Appendix A.14 depending on whether the site is catering for mobile
nodes which would normally be at home on the site and/or foreign nodes that would normally be at home on the site and/or foreign
mobile nodes roaming onto the site. mobile nodes roaming onto the site.
4.3.3. Traffic that will be Dropped Anyway - No Special Attention 4.3.3. Traffic That Will Be Dropped Anyway -- No Special Attention
Needed Needed
The messages listed in this section are all involved with local The messages listed in this section are all involved with local
management of nodes connected to the logical link on which they were management of nodes connected to the logical link on which they were
initially transmitted. All these messages should never be propagated initially transmitted. All these messages should never be propagated
beyond the link on which they were initially transmitted. If the beyond the link on which they were initially transmitted. If the
firewall is a firewall/bridge rather than a firewall/router, these firewall is a firewall/bridge rather than a firewall/router, these
messages should be allowed to transit the firewall as they would be messages should be allowed to transit the firewall as they would be
intended for establishing communications between the two physical intended for establishing communications between the two physical
parts of the link that are bridged into a single logical link. parts of the link that are bridged into a single logical link.
During normal operations these messages will have destination During normal operations, these messages will have destination
addresses, mostly link local but in some cases global unicast addresses, mostly link local but in some cases global unicast
addresses, of interfaces on the local link. No special action is addresses, of interfaces on the local link. No special action is
needed to filter messages with link-local addresses in a firewall/ needed to filter messages with link-local addresses in a firewall/
router. As discussed in Section 4.1 these messages are specified so router. As discussed in Section 4.1, these messages are specified so
that either the receiver is able to check that the message has not that either the receiver is able to check that the message has not
passed through a router or it will be dropped at the first router it passed through a router or it will be dropped at the first router it
encounters. encounters.
Administrators may also wish to consider providing rules in firewall/ Administrators may also wish to consider providing rules in firewall/
routers to catch illegal packets sent with hop limit = 1 to avoid routers to catch illegal packets sent with hop limit = 1 to avoid
ICMPv6 Time Exceeded messages being generated for these packets. ICMPv6 Time Exceeded messages being generated for these packets.
Address Configuration and Router Selection messages (must be received Address Configuration and Router Selection messages (must be received
with hop limit = 255): with hop limit = 255):
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o Router Solicitation (Type 133) o Router Solicitation (Type 133)
o Router Advertisement (Type 134) o Router Advertisement (Type 134)
o Neighbor Solicitation (Type 135) o Neighbor Solicitation (Type 135)
o Neighbor Advertisement (Type 136) o Neighbor Advertisement (Type 136)
o Redirect (Type 137) o Redirect (Type 137)
o Inverse Neighbor Discovery Solicitation (Type 141) o Inverse Neighbor Discovery Solicitation (Type 141)
o Inverse Neighbor Discovery Advertisement (Type 142) o Inverse Neighbor Discovery Advertisement (Type 142)
Link-local multicast receiver notification messages (must have link- Link-local multicast receiver notification messages (must have link-
local source address): local source address):
o Listener Query (Type 130) o Listener Query (Type 130)
o Listener Report (Type 131) o Listener Report (Type 131)
o Listener Done (Type 132) o Listener Done (Type 132)
o Listener Report v2 (Type 143) o Listener Report v2 (Type 143)
SEND Certificate Path notification messages (must be received with SEND Certificate Path notification messages (must be received with
hop limit = 255): hop limit = 255):
o Certificate Path Solicitation (Type 148) o Certificate Path Solicitation (Type 148)
o Certificate Path Advertisement (type 149) o Certificate Path Advertisement (Type 149)
Multicast Router Discovery messages (must have link-local source Multicast Router Discovery messages (must have link-local source
address and hop limit = 1): address and hop limit = 1):
o Multicast Router Advertisement (Type 151) o Multicast Router Advertisement (Type 151)
o Multicast Router Solicitation (Type 152) o Multicast Router Solicitation (Type 152)
o Multicast Router Termination (Type 153) o Multicast Router Termination (Type 153)
4.3.4. Traffic for which a Policy Should be Defined 4.3.4. Traffic for Which a Policy Should Be Defined
The message type that the experimental Seamoby protocols are using The message type that the experimental Seamoby protocols are using
will be expected to have to cross site boundaries in normal will be expected to have to cross site boundaries in normal
operation. Transit sites must allow these messages to transit the operation. Transit sites must allow these messages to transit the
site. End site administrators should determine if they need to site. End site administrators should determine if they need to
support these experiments and otherwise messages of this type should support these experiments and otherwise messages of this type should
be dropped: be dropped:
o Seamoby Experimental (Type 150) o Seamoby Experimental (Type 150)
Error messages not currently defined by IANA: Error messages not currently defined by IANA:
o Unallocated Error messages (Types 5-99 and 102-126, inclusive) o Unallocated Error messages (Types 5-99 inclusive and 102-126
inclusive)
The base ICMPv6 specification suggests that error messages which are The base ICMPv6 specification suggests that error messages that are
not explicitly known to a node should be forwarded and passed to any not explicitly known to a node should be forwarded and passed to any
higher level protocol that might be able to interpret them. There is higher-level protocol that might be able to interpret them. There is
a small risk that such messages could be used to provide a covert a small risk that such messages could be used to provide a covert
channel or form part of a DoS attack. Administrators of end sites channel or form part of a DoS attack. Administrators of end sites
should be aware of this and determine whether they wish to allow should be aware of this and determine whether they wish to allow
these messages through the firewall. Firewalls protecting transit these messages through the firewall. Firewalls protecting transit
sites must allow all types of error messages to transit the site but sites must allow all types of error messages to transit the site but
may adopt different policies for error messages addressed to nodes may adopt different policies for error messages addressed to nodes
within the site. within the site.
All informational messages with types not explicitly assigned by All informational messages with types not explicitly assigned by
IANA, currently: IANA, currently:
skipping to change at page 16, line 40 skipping to change at page 17, line 15
messages through the firewall, relying on end hosts to drop messages through the firewall, relying on end hosts to drop
unrecognized messages, or drop all such messages at the firewall. unrecognized messages, or drop all such messages at the firewall.
Different policies could be adopted for inbound and outbound Different policies could be adopted for inbound and outbound
messages. messages.
If administrators choose to implement policies that drop currently If administrators choose to implement policies that drop currently
unallocated error or informational messages, it is important to unallocated error or informational messages, it is important to
review the set of messages affected in case new message types are review the set of messages affected in case new message types are
assigned by IANA. assigned by IANA.
4.3.5. Traffic which Should be Dropped Unless a Good Case can be Made 4.3.5. Traffic That Should Be Dropped Unless a Good Case Can Be Made
Node Information enquiry messages should generally not be forwarded Node Information enquiry messages should generally not be forwarded
across site boundaries. Some of these messages will be using non- across site boundaries. Some of these messages will be using non-
link-local unicast addresses so that they will not necessarily be link-local unicast addresses so that they will not necessarily be
dropped by address scope limiting rules: dropped by address scope limiting rules:
o Node Information Query (Type 139) o Node Information Query (Type 139)
o Node Information Response (Type 140) o Node Information Response (Type 140)
Router Renumbering messages should not be forwarded across site Router Renumbering messages should not be forwarded across site
boundaries. As originally specified, these messages may use a site boundaries. As originally specified, these messages may use a site
scope multicast address or a site local unicast address. They should scope multicast address or a site local unicast address. They should
be caught by standard rules that are intended to stop any packet with be caught by standard rules that are intended to stop any packet with
a multicast site scope or site local destination being forwarded a multicast site scope or site local destination being forwarded
across a site boundary provided these are correctly configured. across a site boundary provided these are correctly configured.
Since site local addresses have now been deprecated it seems likely Since site local addresses have now been deprecated, it seems likely
that changes may be made to allow the use of unique local addresses that changes may be made to allow the use of unique local addresses
or global unicast addresses. Should this happen, it will be or global unicast addresses. Should this happen, it will be
essential to explicitly filter these messages at site boundaries. If essential to explicitly filter these messages at site boundaries. If
a site has internal as well as boundary firewalls, individual a site has internal as well as boundary firewalls, individual
policies should be established for the internal firewalls depending policies should be established for the internal firewalls depending
on whether the site wishes to use Router Renumbering or not: on whether or not the site wishes to use Router Renumbering:
o Router Renumbering (Type 138) o Router Renumbering (Type 138)
Messages with types in the experimental allocations: Messages with types in the experimental allocations:
o Types 100, 101, 200 and 201.
o Types 100, 101, 200, and 201.
Messages using the extension type numbers until such time as ICMPv6 Messages using the extension type numbers until such time as ICMPv6
needs to use such extensions: needs to use such extensions:
o Types 127 and 255. o Types 127 and 255.
4.4. Recommendations for ICMPv6 Local Configuration Traffic 4.4. Recommendations for ICMPv6 Local Configuration Traffic
This section recommends filtering rules for ICMPv6 traffic addressed This section recommends filtering rules for ICMPv6 traffic addressed
to an interface on a firewall. For a small number of messages, the to an interface on a firewall. For a small number of messages, the
desired behavior may differ between interfaces on the site or private desired behavior may differ between interfaces on the site or private
side of the firewall and the those on the public Internet side of the side of the firewall and the those on the public Internet side of the
firewall. firewall.
skipping to change at page 17, line 31 skipping to change at page 18, line 13
o Types 127 and 255. o Types 127 and 255.
4.4. Recommendations for ICMPv6 Local Configuration Traffic 4.4. Recommendations for ICMPv6 Local Configuration Traffic
This section recommends filtering rules for ICMPv6 traffic addressed This section recommends filtering rules for ICMPv6 traffic addressed
to an interface on a firewall. For a small number of messages, the to an interface on a firewall. For a small number of messages, the
desired behavior may differ between interfaces on the site or private desired behavior may differ between interfaces on the site or private
side of the firewall and the those on the public Internet side of the side of the firewall and the those on the public Internet side of the
firewall. firewall.
4.4.1. Traffic that Must Not be Dropped 4.4.1. Traffic That Must Not Be Dropped
Error messages that are essential to the establishment and Error messages that are essential to the establishment and
maintenance of communications: maintenance of communications:
o Destination Unreachable (Type 1) - All codes o Destination Unreachable (Type 1) - All codes
o Packet Too Big (Type 2) o Packet Too Big (Type 2)
o Time Exceeded (Type 3) - Code 0 only o Time Exceeded (Type 3) - Code 0 only
o Parameter Problem (Type 4) - Codes 1 and 2 only o Parameter Problem (Type 4) - Codes 1 and 2 only
Connectivity checking messages: Connectivity checking messages:
o Echo Request (Type 128) o Echo Request (Type 128)
o Echo Response (Type 129) o Echo Response (Type 129)
As discussed in Section 4.3.1, dropping connectivity checking As discussed in Section 4.3.1, dropping connectivity checking
messages will prevent the firewall being the destination of a Teredo messages will prevent the firewall being the destination of a Teredo
tunnel and it is not considered necessary to disable connectivity tunnel and it is not considered necessary to disable connectivity
checking in IPv6 networks because port scanning is less of a security checking in IPv6 networks because port scanning is less of a security
risk. risk.
There are a number of other sets of messages which play a role in There are a number of other sets of messages that play a role in
configuring the node and maintaining unicast and multicast configuring the node and maintaining unicast and multicast
communications through the interfaces of a node. These messages must communications through the interfaces of a node. These messages must
not be dropped if the node is to successfully participate in an IPv6 not be dropped if the node is to successfully participate in an IPv6
network. The exception to this is the Redirect message for which an network. The exception to this is the Redirect message for which an
explicit policy decision should be taken (see Section 4.4.4). explicit policy decision should be taken (see Section 4.4.4).
Address Configuration and Router Selection messages: Address Configuration and Router Selection messages:
o Router Solicitation (Type 133) o Router Solicitation (Type 133)
o Router Advertisement (Type 134) o Router Advertisement (Type 134)
o Neighbor Solicitation (Type 135) o Neighbor Solicitation (Type 135)
o Neighbor Advertisement (Type 136) o Neighbor Advertisement (Type 136)
o Inverse Neighbor Discovery Solicitation (Type 141) o Inverse Neighbor Discovery Solicitation (Type 141)
o Inverse Neighbor Discovery Advertisement (Type 142) o Inverse Neighbor Discovery Advertisement (Type 142)
Link-Local Multicast Receiver Notification messages:
Link-local multicast receiver notification messages:
o Listener Query (Type 130) o Listener Query (Type 130)
o Listener Report (Type 131) o Listener Report (Type 131)
o Listener Done (Type 132) o Listener Done (Type 132)
o Listener Report v2 (Type 143) o Listener Report v2 (Type 143)
SEND Certificate Path notification messages: SEND Certificate Path Notification messages:
o Certificate Path Solicitation (Type 148) o Certificate Path Solicitation (Type 148)
o Certificate Path Advertisement (type 149) o Certificate Path Advertisement (Type 149)
Multicast Router Discovery messages : Multicast Router Discovery messages :
o Multicast Router Advertisement (Type 151) o Multicast Router Advertisement (Type 151)
o Multicast Router Solicitation (Type 152) o Multicast Router Solicitation (Type 152)
o Multicast Router Termination (Type 153) o Multicast Router Termination (Type 153)
4.4.2. Traffic that Normally Should Not be Dropped 4.4.2. Traffic That Normally Should Not Be Dropped
Error messages other than those listed in Section 4.4.1: Error messages other than those listed in Section 4.4.1:
o Time Exceeded (Type 3) - Code 1 o Time Exceeded (Type 3) - Code 1
o Parameter Problem (Type 4) - Code 0 o Parameter Problem (Type 4) - Code 0
4.4.3. Traffic that will be Dropped Anyway - No Special Attention 4.4.3. Traffic That Will Be Dropped Anyway -- No Special Attention
Needed Needed
Router Renumbering messages must be authenticated using IPsec, so it Router Renumbering messages must be authenticated using IPsec, so it
is not essential to filter these messages even if they are not is not essential to filter these messages even if they are not
allowed at the firewall/router: allowed at the firewall/router:
o Router Renumbering (Type 138) o Router Renumbering (Type 138)
Mobile IPv6 messages that are needed to assist mobility: Mobile IPv6 messages that are needed to assist mobility:
o Home Agent Address Discovery Request (Type 144) o Home Agent Address Discovery Request (Type 144)
o Home Agent Address Discovery Reply (Type 145) o Home Agent Address Discovery Reply (Type 145)
o Mobile Prefix Solicitation (Type 146) o Mobile Prefix Solicitation (Type 146)
o Mobile Prefix Advertisement(Type 147) o Mobile Prefix Advertisement(Type 147)
It may be desirable to drop these messages, especially on public It may be desirable to drop these messages, especially on public
interfaces, if the firewall is not also providing mobile Home Agent interfaces, if the firewall is not also providing mobile home agent
services, but they will be ignored otherwise. services, but they will be ignored otherwise.
The message used by the experimental Seamoby protocols may be dropped The message used by the experimental Seamoby protocols may be dropped
but will be ignored if the service is not implemented: but will be ignored if the service is not implemented:
o Seamoby Experimental (Type 150) o Seamoby Experimental (Type 150)
4.4.4. Traffic for which a Policy Should be Defined 4.4.4. Traffic for Which a Policy Should Be Defined
Redirect messages provide a significant security risk, and
administrators should take a case-by-case approach to whether
firewalls, routers in general, and other nodes should accept these
messages:
Redirect messages provide a significant security risk and
administrators should take a case-by-case view of whether firewalls,
routers in general and other nodes should accept these messages:
o Redirect (Type 137) o Redirect (Type 137)
Conformant nodes must provide configuration controls which allow
nodes to control their behavior with respect to Redirect messages so Conformant nodes must provide configuration controls that allow nodes
that it should only be necessary to install specific filtering rules to control their behavior with respect to Redirect messages so that
under special circumstances, such as if Redirect messages are it should only be necessary to install specific filtering rules under
accepted on private interfaces but not public ones. special circumstances, such as if Redirect messages are accepted on
private interfaces but not public ones.
If a node implements the experimental Node Information service, the If a node implements the experimental Node Information service, the
administrator needs to make an explicit decision as to whether the administrator needs to make an explicit decision as to whether the
node should respond to or accept Node Information messages on each node should respond to or accept Node Information messages on each
interface: interface:
o Node Information Query (Type 139) o Node Information Query (Type 139)
o Node Information Response (Type 140) o Node Information Response (Type 140)
It may be possible to disable the service on the node if it is not It may be possible to disable the service on the node if it is not
wanted in which case these messages will be ignored and no filtering wanted, in which case these messages will be ignored and no filtering
is necessary. is necessary.
Error messages not currently defined by IANA: Error messages not currently defined by IANA:
o Unallocated Error messages (Types 5-99 and 102-126, inclusive)
The base ICMPv6 specification suggests that error messages which are o Unallocated Error messages (Types 5-99 inclusive and 102-126
inclusive)
The base ICMPv6 specification suggests that error messages that are
not explicitly known to a node should be forwarded and passed to any not explicitly known to a node should be forwarded and passed to any
higher level protocol that might be able to interpret them. There is higher-level protocol that might be able to interpret them. There is
a small risk that such messages could be used to provide a covert a small risk that such messages could be used to provide a covert
channel or form part of a DoS attack. Administrators should be aware channel or form part of a DoS attack. Administrators should be aware
of this and determine whether they wish to allow these messages to be of this and determine whether they wish to allow these messages to be
sent to the firewall. sent to the firewall.
4.4.5. Traffic which Should be Dropped Unless a Good Case can be Made 4.4.5. Traffic That Should Be Dropped Unless a Good Case Can Be Made
Messages with types in the experimental allocations: Messages with types in the experimental allocations:
o Types 100, 101, 200 and 201.
o Types 100, 101, 200, and 201.
Messages using the extension type numbers until such time as ICMPv6 Messages using the extension type numbers until such time as ICMPv6
needs to use such extensions: needs to use such extensions:
o Types 127 and 255. o Types 127 and 255.
All informational messages with types not explicitly assigned by All informational messages with types not explicitly assigned by
IANA, currently: IANA, currently:
o Types 154 - 199 inclusive and 202 - 254 inclusive. o Types 154 - 199 inclusive and 202 - 254 inclusive.
Note that the base ICMPv6 specification requires that received Note that the base ICMPv6 specification requires that received
informational messages with unknown types must be silently discarded. informational messages with unknown types must be silently discarded.
5. IANA Considerations 5. Acknowledgements
There are no IANA considerations defined in this document.
6. Acknowledgements
Pekka Savola created the original IPv6 Security Overview document Pekka Savola created the original IPv6 Security Overview document,
which contained suggestions for ICMPv6 filter setups. This which contained suggestions for ICMPv6 filter setups. This
information has been incorporated into this document. He has also information has been incorporated into this document. He has also
provided important comments. Some analysis of the classification of provided important comments. Some analysis of the classification of
ICMPv6 messages and the term 'any-to-end' were used by Jari Arkko in ICMPv6 messages and the term 'any-to-end' were used by Jari Arkko in
a draft relating to ICMPv6 and IKE. a document relating to ICMPv6 and IKE.
The Netfilter configuration script in Appendix C was contributed by The Netfilter configuration script in Appendix B was contributed by
Suresh Krishnan. Suresh Krishnan.
7. References 6. References
7.1. Normative References 6.1. Normative References
[RFC1981] McCann, J., Deering, S., and J. Mogul, "Path MTU Discovery [RFC1981] McCann, J., Deering, S., and J. Mogul, "Path MTU
for IP version 6", RFC 1981, August 1996. Discovery for IP version 6", RFC 1981, August 1996.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol,
(IPv6) Specification", RFC 2460, December 1998. Version 6 (IPv6) Specification", RFC 2460,
December 1998.
[RFC2461] Narten, T., Nordmark, E., and W. Simpson, "Neighbor [RFC2461] Narten, T., Nordmark, E., and W. Simpson, "Neighbor
Discovery for IP Version 6 (IPv6)", RFC 2461, Discovery for IP Version 6 (IPv6)", RFC 2461,
December 1998. December 1998.
[RFC2462] Thomson, S. and T. Narten, "IPv6 Stateless Address [RFC2462] Thomson, S. and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998. Autoconfiguration", RFC 2462, December 1998.
[RFC2710] Deering, S., Fenner, W., and B. Haberman, "Multicast [RFC2710] Deering, S., Fenner, W., and B. Haberman, "Multicast
Listener Discovery (MLD) for IPv6", RFC 2710, Listener Discovery (MLD) for IPv6", RFC 2710,
October 1999. October 1999.
[RFC2894] Crawford, M., "Router Renumbering for IPv6", RFC 2894, [RFC2894] Crawford, M., "Router Renumbering for IPv6",
August 2000. RFC 2894, August 2000.
[RFC3122] Conta, A., "Extensions to IPv6 Neighbor Discovery for [RFC3122] Conta, A., "Extensions to IPv6 Neighbor Discovery for
Inverse Discovery Specification", RFC 3122, June 2001. Inverse Discovery Specification", RFC 3122,
June 2001.
[RFC3590] Haberman, B., "Source Address Selection for the Multicast [RFC3590] Haberman, B., "Source Address Selection for the
Listener Discovery (MLD) Protocol", RFC 3590, Multicast Listener Discovery (MLD) Protocol",
September 2003. RFC 3590, September 2003.
[RFC3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support [RFC3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility
in IPv6", RFC 3775, June 2004. Support in IPv6", RFC 3775, June 2004.
[RFC3810] Vida, R. and L. Costa, "Multicast Listener Discovery [RFC3810] Vida, R. and L. Costa, "Multicast Listener Discovery
Version 2 (MLDv2) for IPv6", RFC 3810, June 2004. Version 2 (MLDv2) for IPv6", RFC 3810, June 2004.
[RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure [RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander,
Neighbor Discovery (SEND)", RFC 3971, March 2005. "SEcure Neighbor Discovery (SEND)", RFC 3971,
March 2005.
[RFC4065] Kempf, J., "Instructions for Seamoby and Experimental [RFC4065] Kempf, J., "Instructions for Seamoby and Experimental
Mobility Protocol IANA Allocations", RFC 4065, July 2005. Mobility Protocol IANA Allocations", RFC 4065,
July 2005.
[RFC4286] Haberman, B. and J. Martin, "Multicast Router Discovery", [RFC4286] Haberman, B. and J. Martin, "Multicast Router
RFC 4286, December 2005. Discovery", RFC 4286, December 2005.
[RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control [RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet
Message Protocol (ICMPv6) for the Internet Protocol Control Message Protocol (ICMPv6) for the Internet
Version 6 (IPv6) Specification", RFC 4443, March 2006. Protocol Version 6 (IPv6) Specification", RFC 4443,
March 2006.
[RFC4620] Crawford, M. and B. Haberman, "IPv6 Node Information [RFC4620] Crawford, M. and B. Haberman, "IPv6 Node Information
Queries", RFC 4620, August 2006. Queries", RFC 4620, August 2006.
7.2. Informative References 6.2. Informative References
[I-D.ietf-tcpm-icmp-attacks]
Gont, F., "ICMP attacks against TCP",
draft-ietf-tcpm-icmp-attacks-01 (work in progress),
October 2006.
[I-D.ietf-v6ops-scanning-implications] [ICMP-ATTACKS] Gont, F., "ICMP attacks against TCP", Work
Chown, T., "IPv6 Implications for Network Scanning", in Progress, October 2006.
draft-ietf-v6ops-scanning-implications-01 (work in
progress), October 2006.
[RFC3041] Narten, T. and R. Draves, "Privacy Extensions for [RFC3041] Narten, T. and R. Draves, "Privacy Extensions for
Stateless Address Autoconfiguration in IPv6", RFC 3041, Stateless Address Autoconfiguration in IPv6",
January 2001. RFC 3041, January 2001.
[RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through
Network Address Translations (NATs)", RFC 4380, Network Address Translations (NATs)", RFC 4380,
February 2006. February 2006.
[netfilter] [SCAN-IMP] Chown, T., "IPv6 Implications for Network Scanning",
netfilter.org, "The netfilter.org project", Firewalling, Work in Progress, March 2007.
NAT and Packet Mangling for Linux , 2006,
<http://www.netfilter.org/>. [netfilter] netfilter.org, "The netfilter.org project",
Firewalling, NAT and Packet Mangling for Linux ,
2006, <http://www.netfilter.org/>.
Appendix A. Notes on Individual ICMPv6 Messages Appendix A. Notes on Individual ICMPv6 Messages
A.1. Destination Unreachable Error Message A.1. Destination Unreachable Error Message
Destination Unreachable (Type 1) error messages [RFC4443] are sent Destination Unreachable (Type 1) error messages [RFC4443] are sent
any-to-end between unicast addresses. The message can be generated any-to-end between unicast addresses. The message can be generated
from any node which a packet traverses when the node is unable to from any node that a packet traverses when the node is unable to
forward the packet for any reason except congestion. forward the packet for any reason except congestion.
Destination Unreachable messages are useful for debugging but are Destination Unreachable messages are useful for debugging, but are
also important to speed up cycling through possible addresses, as also important to speed up cycling through possible addresses, as
they can avoid the need to wait through timeouts and hence can be they can avoid the need to wait through timeouts and hence can be
part of the process of establishing or maintaining communications. part of the process of establishing or maintaining communications.
It is a common practice in IPv4 to refrain from generating ICMP It is a common practice in IPv4 to refrain from generating ICMP
Destination Unreachable messages in an attempt to hide the networking Destination Unreachable messages in an attempt to hide the networking
topology and/or service structure. The same idea could be applied to topology and/or service structure. The same idea could be applied to
IPv6 but this can slow down connection if a host has multiple IPv6, but this can slow down connection if a host has multiple
addresses, some of which are deprecated, as they may be when using addresses, some of which are deprecated, as they may be when using
privacy addresses [RFC3041]. If policy allows the generation of privacy addresses [RFC3041]. If policy allows the generation of
ICMPv6 Destination Unreachable messages, it is important that nodes ICMPv6 Destination Unreachable messages, it is important that nodes
provide the correct reason code, one of: no route to destination, provide the correct reason code, one of: no route to destination,
administratively prohibited, beyond scope of source address, address administratively prohibited, beyond scope of source address, address
unreachable, port unreachable, source address failed ingress/egress unreachable, port unreachable, source address failed ingress/egress
policy, reject route to destination. policy, or reject route to destination.
A.2. Packet Too Big Error Message A.2. Packet Too Big Error Message
Packet Too Big (Type 2) error messages [RFC4443] are sent any-to-end Packet Too Big (Type 2) error messages [RFC4443] are sent any-to-end
between unicast addresses. The message can be generated from any between unicast addresses. The message can be generated from any
node which a packet traverses on the path when the node is unable to node that a packet traverses on the path when the node is unable to
forward the packet because the packet is too large for the MTU of the forward the packet because the packet is too large for the MTU of the
next link. This message is vital to the correct functioning of Path next link. This message is vital to the correct functioning of Path
MTU Discovery and hence is part of the establishment and maintenance MTU Discovery and hence is part of the establishment and maintenance
of communications. Since routers are not allowed to fragment of communications. Since routers are not allowed to fragment
packets, informing sources of the need to fragment large packets is packets, informing sources of the need to fragment large packets is
more important than for IPv4. If these messages are not generated more important than for IPv4. If these messages are not generated
when appropriate, hosts will continue to send packets which are too when appropriate, hosts will continue to send packets that are too
large or may assume that the route is congested. Effectively parts large or may assume that the route is congested. Effectively, parts
of the Internet will become inaccessible. of the Internet will become inaccessible.
If a network chooses to generate packets that are no larger than the If a network chooses to generate packets that are no larger than the
Guaranteed Minimum MTU (1280 octets) and the site's links to the Guaranteed Minimum MTU (1280 octets) and the site's links to the
wider internet have corresponding MTUs, Packet Too Big messages wider Internet have corresponding MTUs, Packet Too Big messages
should not be expected at the firewall and could be dropped if they should not be expected at the firewall and could be dropped if they
arrive. arrive.
A.3. Time Exceeded Error Message A.3. Time Exceeded Error Message
Time Exceeded (Type 3) error messages [RFC4443] can occur in two Time Exceeded (Type 3) error messages [RFC4443] can occur in two
contexts: contexts:
o Code 0 are generated at any node on the path being taken by the o Code 0 are generated at any node on the path being taken by the
packet and sent, any-to-end between unicast addresses, if the Hop packet and sent, any-to-end between unicast addresses, if the Hop
Limit value is decremented to zero at that node. Limit value is decremented to zero at that node.
o Code 1 messages are generated at the destination node and sent o Code 1 messages are generated at the destination node and sent
end-to-end between unicast addresses if all the segments of a end-to-end between unicast addresses if all the segments of a
fragmented message are not received within the reassembly time fragmented message are not received within the reassembly time
limit limit.
Code 0 messages can be needed as part of the establishment of Code 0 messages can be needed as part of the establishment of
communications if the path to a particular destination requires an communications if the path to a particular destination requires an
unusually large number of hops. unusually large number of hops.
Code 1 messages will generally only result from congestion in the Code 1 messages will generally only result from congestion in the
network and it is less essential to propagate these messages. network, and it is less essential to propagate these messages.
A.4. Parameter Problem Error Message A.4. Parameter Problem Error Message
The great majority of Parameter Problem (Type 4) error messages will The great majority of Parameter Problem (Type 4) error messages will
be generated by the destination node when processing destination be generated by the destination node when processing destination
options and other extension headers, and hence are sent end-to-end options and other extension headers, and hence are sent end-to-end
between unicast addresses. Exceptionally, these messages might be between unicast addresses. Exceptionally, these messages might be
generated by any node on the path if a faulty or unrecognized hop-by- generated by any node on the path if a faulty or unrecognized hop-by-
hop option is included or from any routing waypoint if there are hop option is included or from any routing waypoint if there are
faulty or unrecognized destination options associated with a Type 0 faulty or unrecognized destination options associated with a Type 0
routing header. In these cases the message will be sent any-to-end routing header. In these cases, the message will be sent any-to-end
using unicast source and destination addresses. using unicast source and destination addresses.
Parameter Problem Code 1 (Unrecognized Next Header) and Code 2 Parameter Problem Code 1 (Unrecognized Next Header) and Code 2
(Unrecognized IPv6 Option) messages may result if a node on the path (Unrecognized IPv6 Option) messages may result if a node on the path
(usually the destination) is unable to process a correctly formed (usually the destination) is unable to process a correctly formed
extension header or option. If these messages are not returned to extension header or option. If these messages are not returned to
the source communication cannot be established, as the source would the source, communication cannot be established, as the source would
need to adapt its choice of options probably because the destination need to adapt its choice of options probably because the destination
does not implement these capabilities. Hence these messages need to does not implement these capabilities. Hence, these messages need to
be generated and allowed for effective IPv6 communications. be generated and allowed for effective IPv6 communications.
Code 0 (Erroneous Header) messages indicate a malformed extension Code 0 (Erroneous Header) messages indicate a malformed extension
header generally as a result of incorrectly generated packets. Hence header generally as a result of incorrectly generated packets.
these messages are useful for debugging purposes but it is unlikely Hence, these messages are useful for debugging purposes, but it is
that a node generating such packets could establish communications unlikely that a node generating such packets could establish
without human intervention to correct the problem. communications without human intervention to correct the problem.
Code 2 messages, only, can be generated for packets with multicast Code 2 messages, only, can be generated for packets with multicast
destination addresses. destination addresses.
It is possible that attackers may seek to probe or scan a network by It is possible that attackers may seek to probe or scan a network by
deliberately generating packets with unknown extension headers or deliberately generating packets with unknown extension headers or
options, or faulty headers. If nodes generate Parameter Problem options or with faulty headers. If nodes generate Parameter Problem
error messages in all cases and these outgoing messages are allowed error messages in all cases and these outgoing messages are allowed
through firewalls, the attacker may be able to identify active through firewalls, the attacker may be able to identify active
addresses that can be probed further or learn about the network addresses that can be probed further or learn about the network
topology. The vulnerability could be mitigated whilst helping to topology. The vulnerability could be mitigated whilst helping to
establish communications if the firewall was able to examine such establish communications if the firewall was able to examine such
error messages in depth and was configured to only allow Parameter error messages in depth and was configured to only allow Parameter
Problem messages for headers which had been standardized but were not Problem messages for headers that had been standardized but were not
supported in the protected network. If the network administrator supported in the protected network. If the network administrator
believes that all nodes in the network support all legitimate believes that all nodes in the network support all legitimate
extension headers then it would be reasonable to drop all outgoing extension headers, then it would be reasonable to drop all outgoing
Parameter Problem messages. Note that this is not a major Parameter Problem messages. Note that this is not a major
vulnerability in a well-designed IPv6 network because of the vulnerability in a well-designed IPv6 network because of the
difficulties of performing scanning attacks (see Section 3.2). difficulties of performing scanning attacks (see Section 3.2).
A.5. ICMPv6 Echo Request and Echo Response A.5. ICMPv6 Echo Request and Echo Response
Echo Request (Type 128) uses unicast addresses as source addresses, Echo Request (Type 128) uses unicast addresses as source addresses,
but may be sent to any legal IPv6 address, including multicast and but may be sent to any legal IPv6 address, including multicast and
anycast addresses [RFC4443]. Echo Requests travel end-to-end. anycast addresses [RFC4443]. Echo Requests travel end-to-end.
Similarly Echo Responses (Type 129) travel end-to-end and would have Similarly, Echo Responses (Type 129) travel end-to-end and would have
a unicast address as destination and either a unicast or anycast a unicast address as destination and either a unicast or anycast
address as source. They are mainly used in combination for address as source. They are mainly used in combination for
monitoring and debugging connectivity. Their only role in monitoring and debugging connectivity. Their only role in
establishing communication is that they are required when verifying establishing communication is that they are required when verifying
connectivity through Teredo tunnels[RFC4380]: Teredo tunneling to connectivity through Teredo tunnels[RFC4380]: Teredo tunneling to
IPv6 nodes on the site will not be possible if these messages are IPv6 nodes on the site will not be possible if these messages are
blocked. It is not thought that there is a significant risk from blocked. It is not thought that there is a significant risk from
scanning attacks on a well-designed IPv6 network (see Section 3.2) scanning attacks on a well-designed IPv6 network (see Section 3.2),
and so connectivity checks should be allowed by default. and so connectivity checks should be allowed by default.
A.6. Neighbor Solicitation and Neighbor Advertisement Messages A.6. Neighbor Solicitation and Neighbor Advertisement Messages
ICMPv6 Neighbor Solicitation and Neighbor Advertisement (Type 135 and ICMPv6 Neighbor Solicitation and Neighbor Advertisement (Type 135 and
136) messages are essential to the establishment and maintenance of 136) messages are essential to the establishment and maintenance of
communications on the local link. Firewalls need to generate and communications on the local link. Firewalls need to generate and
accept these messages to allow them to establish and maintain accept these messages to allow them to establish and maintain
interfaces onto their connected links. interfaces onto their connected links.
Note that the address scopes of the source and destination addresses Note that the address scopes of the source and destination addresses
on Neighbor Solicitations and Neighbor Advertisements may not match. on Neighbor Solicitations and Neighbor Advertisements may not match.
The exact functions which these messages will be carrying out depends The exact functions that these messages will be carrying out depends
on the mechanism being used to configure IPv6 addresses on the link on the mechanism being used to configure IPv6 addresses on the link
(Stateless, Stateful or Static configuration). (Stateless, Stateful, or Static configuration).
A.7. Router Solicitation and Router Advertisement Messages A.7. Router Solicitation and Router Advertisement Messages
ICMPv6 Router Solicitation and Router Advertisement(Type 133 and 134) ICMPv6 Router Solicitation and Router Advertisement (Type 133 and
messages are essential to the establishment and maintenance of 134) messages are essential to the establishment and maintenance of
communications on the local link. Firewalls need to generate (since communications on the local link. Firewalls need to generate (since
the firewall will generally be behaving as a router) and accept these the firewall will generally be behaving as a router) and accept these
messages to allow them to establish and maintain interfaces onto messages to allow them to establish and maintain interfaces onto
their connected links. their connected links.
A.8. Redirect Messages A.8. Redirect Messages
ICMPv6 Redirect Messages(Type 137) are used on the local link to ICMPv6 Redirect Messages(Type 137) are used on the local link to
indicate that nodes are actually link-local and communications need indicate that nodes are actually link-local and communications need
not go via a router, or to indicate a more appropriate first hop not go via a router, or to indicate a more appropriate first-hop
router. Although they can be used to make communications more router. Although they can be used to make communications more
efficient, they are not essential to the establishment of efficient, they are not essential to the establishment of
communications and may be a security vulnerability, particularly if a communications and may be a security vulnerability, particularly if a
link is not physically secured. Conformant nodes are required to link is not physically secured. Conformant nodes are required to
provide configuration controls which suppress the generation of provide configuration controls that suppress the generation of
Redirect messages and allow them to be ignored on reception. Using Redirect messages and allow them to be ignored on reception. Using
Redirect messages on, for example, a wireless link without link level Redirect messages on, for example, a wireless link without link level
encryption/authentication is particularly hazardous because the link encryption/authentication is particularly hazardous because the link
is open to eavesdropping and packet injection. is open to eavesdropping and packet injection.
A.9. SEND Certificate Path Messages A.9. SEND Certificate Path Messages
SEND [RFC3971] uses two messages (Certificate Path Solicitation and SEND [RFC3971] uses two messages (Certificate Path Solicitation and
Advertisement - Types 148 and 149) sent from nodes to supposed Advertisement - Types 148 and 149) sent from nodes to supposed
routers on the same local link to obtain a certificate path which routers on the same local link to obtain a certificate path that will
will allow the node to authenticate the router's claim to provide allow the node to authenticate the router's claim to provide routing
routing services for certain prefixes. If a link connected to a services for certain prefixes. If a link connected to a firewall/
firewall/router is using SEND, the firewall must be able to exchange router is using SEND, the firewall must be able to exchange these
these messages with nodes on the link that will use its routing messages with nodes on the link that will use its routing services.
services.
A.10. Multicast Listener Discovery Messages A.10. Multicast Listener Discovery Messages
Multicast Listener Discovery (MLD) version 1 [RFC2710] (Listener Multicast Listener Discovery (MLD) version 1 [RFC2710] (Listener
Query, Listener Report and Listener Done - Types 130, 131 and 132) Query, Listener Report, and Listener Done - Types 130, 131, and 132)
and version 2 [RFC3810] (Listener Query and Listener Report Version 2 and version 2 [RFC3810] (Listener Query and Listener Report version 2
- Types 130 and 143) messages are sent on the local link to - Types 130 and 143) messages are sent on the local link to
communicate between multicast capable routers and nodes which wish to communicate between multicast-capable routers and nodes that wish to
join or leave specific multicast groups. Firewalls need to be able join or leave specific multicast groups. Firewalls need to be able
to generate Listener messages in order to establish communications to generate Listener messages in order to establish communications
and may generate all the messages if they also provide multicast and may generate all the messages if they also provide multicast
routing services. routing services.
A.11. Multicast Router Discovery Messages A.11. Multicast Router Discovery Messages
Multicast Router Discovery [RFC4286] (Router Advertisement, Router Multicast Router Discovery [RFC4286] (Router Advertisement, Router
Solicitation and Router Termination - Types 151, 152 and 153) Solicitation, and Router Termination - Types 151, 152, and 153)
messages are sent by nodes on the local link to discover multicast messages are sent by nodes on the local link to discover multicast-
capable routers on the link, and by multicast capable routers to capable routers on the link, and by multicast-capable routers to
notify other nodes of their existence or change of state. Firewalls notify other nodes of their existence or change of state. Firewalls
which also act as multicast routers need to process these messages on that also act as multicast routers need to process these messages on
their interfaces. their interfaces.
A.12. Router Renumbering Messages A.12. Router Renumbering Messages
ICMPv6 Router Renumbering (Type 138) command messages can be received ICMPv6 Router Renumbering (Type 138) command messages can be received
and results messages sent by routers to change the prefixes which and results messages sent by routers to change the prefixes that they
they advertise as part of Stateless Address Configuration [RFC2461], advertise as part of Stateless Address Configuration [RFC2461],
[RFC2462]. These messages are sent end-to-end to either the all- [RFC2462]. These messages are sent end-to-end to either the all-
routers multicast address (site or local scope) or specific unicast routers multicast address (site or local scope) or specific unicast
addresses from a unicast address. addresses from a unicast address.
Router Renumbering messages are required to be protected by IPsec Router Renumbering messages are required to be protected by IPsec
authentication since they could be readily misused by attackers to authentication since they could be readily misused by attackers to
disrupt or divert site communications. Renumbering messages should disrupt or divert site communications. Renumbering messages should
generally be confined to sites for this reason. generally be confined to sites for this reason.
A.13. Node Information Query and Reply A.13. Node Information Query and Reply
ICMPv6 Node Information Query and Reply (Type 139 and 140) messages ICMPv6 Node Information Query and Reply (Type 139 and 140) messages
defined in [RFC4620] are sent end-to-end between unicast addresses, defined in [RFC4620] are sent end-to-end between unicast addresses,
and can also be sent to link-local multicast addresses. They can, in and they can also be sent to link-local multicast addresses. They
theory, be sent from any node to any other but it would generally not can, in theory, be sent from any node to any other, but it would
be desirable for nodes outside the local site to be able to send generally not be desirable for nodes outside the local site to be
queries to nodes within the site. Also these messages are not able to send queries to nodes within the site. Also, these messages
required to be authenticated. are not required to be authenticated.
A.14. Mobile IPv6 Messages A.14. Mobile IPv6 Messages
Mobile IPv6 [RFC3775] defines four ICMPv6 messages which are used to Mobile IPv6 [RFC3775] defines four ICMPv6 messages that are used to
support mobile operations: Home Agent Address Discovery Request, Home support mobile operations: Home Agent Address Discovery Request, Home
Agent Address Discovery Reply, Mobile Prefix Solicitation and ICMP Agent Address Discovery Reply, Mobile Prefix Solicitation, and ICMP
Mobile Prefix Advertisement(Type 144, 145, 146 and 147) messages. Mobile Prefix Advertisement (Type 144, 145, 146, and 147) messages.
These messages are sent end-to-end between unicast addresses of a These messages are sent end-to-end between unicast addresses of a
mobile node and its home agent. They must be expected to be sent mobile node and its home agent. They must be expected to be sent
from outside a site and must traverse site-boundary firewalls to from outside a site and must traverse site-boundary firewalls to
reach the home agent in order for Mobile IPv6 to function. The two reach the home agent in order for Mobile IPv6 to function. The two
Mobile prefix messages should be protected by the use of IPsec Mobile prefix messages should be protected by the use of IPsec
authentication. authentication.
o If the site provides home agents for mobile nodes, the firewall o If the site provides home agents for mobile nodes, the firewall
must allow incoming Home Agent Address Discovery Request and must allow incoming Home Agent Address Discovery Request and
Mobile Prefix Solicitation messages, and outgoing Home Agent Mobile Prefix Solicitation messages, and outgoing Home Agent
Address Discovery Reply and ICMP Mobile Prefix Advertisement Address Discovery Reply and ICMP Mobile Prefix Advertisement
messages. It may be desirable to limit the destination addresses messages. It may be desirable to limit the destination addresses
for the incoming messages to links that are known to support home for the incoming messages to links that are known to support home
agents. agents.
o If the site is prepared to host roaming mobile nodes, the firewall o If the site is prepared to host roaming mobile nodes, the firewall
must allow outgoing Home Agent Address Discovery Request and must allow outgoing Home Agent Address Discovery Request and
Mobile Prefix Solicitation messages, and incoming Home Agent Mobile Prefix Solicitation messages, and incoming Home Agent
Address Discovery Reply and ICMP Mobile Prefix Advertisement Address Discovery Reply and ICMP Mobile Prefix Advertisement
messages. messages.
o Administrators may find it desirable to prevent static nodes which
o Administrators may find it desirable to prevent static nodes that
are normally resident on the site from behaving as mobile nodes by are normally resident on the site from behaving as mobile nodes by
dropping Mobile IPv6 messages from these nodes. dropping Mobile IPv6 messages from these nodes.
A.15. Unused and Experimental Messages A.15. Unused and Experimental Messages
A large number of ICMPv6 Type values are currently unused. These A large number of ICMPv6 Type values are currently unused. These
values have not had a specific function registered with IANA. This values have not had a specific function registered with IANA. This
section describes how to treat messages which attempt to use these section describes how to treat messages that attempt to use these
Type values in a way of which the network administrator (and hence Type values in a way of which the network administrator (and hence
the firewall) is not aware. the firewall) is not aware.
[RFC4443] defines a number of experimental Type values for ICMPv6 [RFC4443] defines a number of experimental Type values for ICMPv6
Error and Informational messages, which could be used in site Error and Informational messages, which could be used in site-
specific ways. These values should be treated in the same way as specific ways. These messages should be dropped by transit networks
values which are not registered by IANA unless the network and at site edges. They should also not be propagated within sites
administrator is explicitly made aware of usage. unless the network administrator is explicitly made aware of usage.
The codes reserved for future extension of the ICMPv6 Type space The codes reserved for future extension of the ICMPv6 Type space
should currently be dropped as this functionality is as yet should currently be dropped as this functionality is as yet
undefined. undefined.
Any ICMPv6 Informational messages of which the firewall is not aware Any ICMPv6 Informational messages of which the firewall is not aware
should not be allowed to pass through the firewall or be accepted for should be allowed to transit through the firewall but should not be
local delivery on any of its interfaces. accepted for local delivery on any of its interfaces.
Any incoming ICMPv6 Error messages of which the firewall is not aware Unknown ICMPv6 Error messages should be allowed to pass through
may be allowed through the firewall in line with the specification in transit networks. At end site boundaries any incoming ICMPv6 Error
[RFC4443], which requests delivery of unknown error messages to messages of which the firewall is not aware may be allowed through
higher layer protocol processes. However, administrators may wish to the firewall in line with the specification in [RFC4443], which
disallow forwarding of these incoming messages as a potential requests delivery of unknown error messages to higher-layer protocol
security risk. Unknown outgoing Error messages should be dropped as processes. However, administrators may wish to disallow forwarding
the administrator should be aware of all messages that could be of these incoming messages as a potential security risk. Unknown
generated on the site. outgoing Error messages should be dropped as the administrator should
be aware of all messages that could be generated on the site.
Also the Seamoby working group has had an ICMPv6 message (Type 150) Also, the SEAMOBY working group has had an ICMPv6 message (Type 150)
allocated for experimental use in two protocols. This message is allocated for experimental use in two protocols. This message is
sent end-to-end and may need to pass through firewalls on sites that sent end-to-end and may need to pass through firewalls on sites that
are supporting the experimental protocols. are supporting the experimental protocols.
Appendix B. Example Script to Configure ICMPv6 Firewall Rules Appendix B. Example Script to Configure ICMPv6 Firewall Rules
This appendix contains an example script to implement most of the This appendix contains an example script to implement most of the
rules suggested in this document when using the Netfilter packet rules suggested in this document when using the Netfilter packet
filtering system for Linux [netfilter]. When used with IPv6, the filtering system for Linux [netfilter]. When used with IPv6, the
'ip6tables' command is used to configure packet filtering rules for 'ip6tables' command is used to configure packet filtering rules for
skipping to change at page 35, line 29 skipping to change at page 37, line 29
Example Netfilter Configuration Script for ICMPv6 Filtering Example Netfilter Configuration Script for ICMPv6 Filtering
Authors' Addresses Authors' Addresses
Elwyn B. Davies Elwyn B. Davies
Consultant Consultant
Soham, Cambs Soham, Cambs
UK UK
Phone: +44 7889 488 335 Phone: +44 7889 488 335
Email: elwynd@dial.pipex.com EMail: elwynd@dial.pipex.com
Janos Mohacsi Janos Mohacsi
NIIF/HUNGARNET NIIF/HUNGARNET
Victor Hugo u. 18-22 Victor Hugo u. 18-22
Budapest, H-1132 Budapest, H-1132
Hungary Hungary
Phone: +36 1 4503070 Phone: +36 1 4503070
Email: mohacsi@niif.hu EMail: mohacsi@niif.hu
Full Copyright Statement Full Copyright Statement
Copyright (C) The IETF Trust (2007). Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors contained in BCP 78, and except as set forth therein, the authors
retain all their rights. retain all their rights.
This document and the information contained herein are provided on an This document and the information contained herein are provided on an
skipping to change at page 36, line 45 skipping to change at page 38, line 45
such proprietary rights by implementers or users of this such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr. http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at this standard. Please address the information to the IETF at
ietf-ipr@ietf.org. ietf-ipr@ietf.org.
Acknowledgment Acknowledgement
Funding for the RFC Editor function is provided by the IETF Funding for the RFC Editor function is currently provided by the
Administrative Support Activity (IASA). Internet Society.
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