draft-ietf-intarea-router-alert-considerations-10.txt   rfc6398.txt 
Network Working Group F. Le Faucheur, Ed. Internet Engineering Task Force (IETF) F. Le Faucheur, Ed.
Internet-Draft Cisco Request for Comments: 6398 Cisco
Updates: 2113,2711 (if approved) August 2, 2011 BCP: 168 October 2011
Intended status: BCP Updates: 2113, 2711
Expires: February 3, 2012 Category: Best Current Practice
ISSN: 2070-1721
IP Router Alert Considerations and Usage IP Router Alert Considerations and Usage
draft-ietf-intarea-router-alert-considerations-10
Abstract Abstract
The IP Router Alert Option is an IP option that alerts transit The IP Router Alert Option is an IP option that alerts transit
routers to more closely examine the contents of an IP packet. routers to more closely examine the contents of an IP packet. The
Resource reSerVation Protocol (RSVP), Pragmatic General Multicast Resource reSerVation Protocol (RSVP), Pragmatic General Multicast
(PGM), Internet Group Management Protocol (IGMP), Multicast Listener (PGM), the Internet Group Management Protocol (IGMP), Multicast
Discovery (MLD), Multicast Router Discovery (MRD) and General Listener Discovery (MLD), Multicast Router Discovery (MRD), and
Internet Signalling Transport (GIST) are some of the protocols that General Internet Signaling Transport (GIST) are some of the protocols
make use of the IP Router Alert Option. This document discusses that make use of the IP Router Alert Option. This document discusses
security aspects and usage guidelines around the use of the current security aspects and usage guidelines around the use of the current
IP Router Alert Option thereby updating RFC2113 and RFC2711. IP Router Alert Option, thereby updating RFC 2113 and RFC 2711.
Specifically, it provides recommendation against using the Router Specifically, it provides recommendations against using the Router
Alert in the end-to-end open Internet as well as identify controlled Alert in the end-to-end open Internet and identifies controlled
environments where protocols depending on Router Alert can be used environments where protocols depending on Router Alert can be used
safely. It also provides recommendation about protection approaches safely. It also provides recommendations about protection approaches
for Service Providers. Finally it provides brief guidelines for for service providers. Finally, it provides brief guidelines for
Router Alert implementation on routers. Router Alert implementation on routers.
Status of this Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering This memo documents an Internet Best Current Practice.
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
BCPs is available in Section 2 of RFC 5741.
This Internet-Draft will expire on February 3, 2012. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6398.
Copyright Notice Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction ....................................................3
1.1. Conventions Used in This Document . . . . . . . . . . . . 3 2. Terminology .....................................................4
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1. Conventions Used in This Document ..........................4
3. Security Concerns of Router Alert . . . . . . . . . . . . . . 6 3. Security Concerns of Router Alert ...............................5
4. Guidelines for use of Router Alert . . . . . . . . . . . . . . 9 4. Guidelines for Use of Router Alert ..............................7
4.1. Use of Router Alert End-to-End In the Internet (Router 4.1. Use of Router Alert End to End in the Internet
Alert in Peer Model) . . . . . . . . . . . . . . . . . . . 9 (Router Alert in Peer Model) ...............................7
4.2. Use of Router Alert In Controlled Environments . . . . . . 10 4.2. Use of Router Alert in Controlled Environments .............9
4.2.1. Use of Router Alert Within an Administrative Domain . 10 4.2.1. Use of Router Alert within an Administrative
4.2.2. Use of Router Alert In Overlay Model . . . . . . . . . 12 Domain ..............................................9
4.3. Router Alert Protection Approaches for Service 4.2.2. Use of Router Alert in Overlay Model ...............11
Providers . . . . . . . . . . . . . . . . . . . . . . . . 15 4.3. Router Alert Protection Approaches for Service Providers ..13
5. Guidelines for Router Alert Implementation . . . . . . . . . . 17 5. Guidelines for Router Alert Implementation .....................15
6. Security Considerations . . . . . . . . . . . . . . . . . . . 18 6. Security Considerations ........................................16
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 7. Contributors ...................................................16
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 20 8. Acknowledgments ................................................16
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 21 9. References .....................................................17
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22 9.1. Normative References ......................................17
10.1. Normative References . . . . . . . . . . . . . . . . . . . 22 9.2. Informative References ....................................17
10.2. Informative References . . . . . . . . . . . . . . . . . . 22
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 24
1. Terminology
For readability, this document uses the following loosely defined
terms:
o Fast path : Hardware or Application Specific Integrated Circuit
(ASIC) processing path for packets. This is the nominal
processing path within a router for IP datagrams.
o Slow path : Software processing path for packets. This is a sub-
nominal processing path for packets that require special
processing or differ from assumptions made in fast path
heuristics.
o Next level protocol: the protocol transported in the IP datagram.
In IPv4 [RFC0791], the next level protocol is identified by the
IANA protocol number conveyed in the 8-bit "Protocol" field in the
IPv4 header. In IPv6 [RFC2460], the next level protocol is
identified by the IANA protocol number conveyed in the 8-bit "Next
Header" field in the IPv6 header.
1.1. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. Introduction 1. Introduction
[RFC2113] and [RFC2711] respectively define the IPv4 and IPv6 Router [RFC2113] and [RFC2711] define the IPv4 and IPv6 Router Alert Options
Alert Option (RAO). In this document, we collectively refer to those (RAOs), respectively. In this document, we collectively refer to
as the IP Router Alert. The IP Router Alert Option is an IP option those options as the IP Router Alert. The IP Router Alert Option is
that alerts transit routers to more closely examine the contents of an IP option that alerts transit routers to more closely examine the
an IP packet. contents of an IP packet.
Some of the protocols that make use of the IP Router Alert are the
Resource reSerVation Protocol (RSVP) ([RFC2205], [RFC3175], Resource reSerVation Protocol (RSVP) ([RFC2205], [RFC3175],
[RFC3209]), Pragmatic General Multicast (PGM) ([RFC3208]), Internet [RFC3209]), Pragmatic General Multicast (PGM) ([RFC3208]), the
Group Management Protocol (IGMP) ([RFC3376]), Multicast Listener Internet Group Management Protocol (IGMP) ([RFC3376]), Multicast
Discovery (MLD) ([RFC2710], [RFC3810]), Multicast Router Discovery Listener Discovery (MLD) ([RFC2710], [RFC3810]), Multicast Router
(MRD) ([RFC4286]) and NSIS General Internet Signalling Transport Discovery (MRD) ([RFC4286]), and Next Steps in Signaling (NSIS)
(GIST) ([RFC5971]) are some of the protocols that make use of the IP General Internet Signaling Transport (GIST) ([RFC5971]).
Router Alert.
Section 3 describes the security concerns associated with the use of Section 3 describes the security concerns associated with the use of
the Router Alert Option. the Router Alert Option.
Section 4 provides guidelines for the use of Router Alert. More Section 4 provides guidelines for the use of Router Alert. More
specifically, Section 4.1 recommends that Router Alert not be used specifically, Section 4.1 recommends that Router Alert not be used
for end to end applications over the Internet, while Section 4.2 for end-to-end applications over the Internet, while Section 4.2
presents controlled environments where applications/protocols relying presents controlled environments where applications/protocols relying
on IP Router Alert can be deployed effectively and safely. on IP Router Alert can be deployed effectively and safely.
Section 4.3 provides recommendations on protection approaches to be Section 4.3 provides recommendations on protection approaches to be
used by Service Providers in order to protect their network from used by service providers in order to protect their network from
Router Alert based attacks. Router-Alert-based attacks.
Finally, Section 5 provides generic recommendations for router Finally, Section 5 provides generic recommendations for router
implementation of Router Alert aiming at increasing protection implementation of Router Alert, aiming at increasing protection
against attacks. against attacks.
The present document discusses considerations and practices based on This document discusses considerations and practices based on the
the current specification of IP Router Alert ([RFC2113], [RFC2711]). current specifications of IP Router Alert ([RFC2113], [RFC2711]).
Possible future enhancements to the specification of IP Router Alert Possible future enhancements to the specifications of IP Router Alert
(in view of reducing the security risks associated with the use of IP (in view of reducing the security risks associated with the use of IP
Router Alert) are outside the scope of this document. One such Router Alert) are outside the scope of this document. One such
proposal is discussed in [I-D.narayanan-rtg-router-alert-extension] proposal is discussed in [RAO-EXT], but at the time of this writing,
but at the time of this writing, the IETF has not adopted any the IETF has not adopted any extensions for this purpose.
extensions for this purpose.
The IPv6 base specification [RFC2460] defines the hop-by-hop option The IPv6 base specification [RFC2460] defines the hop-by-hop options
extension header. The hop-by-hop option header is used to carry extension header. The hop-by-hop options header is used to carry
optional information that must be examined by every node along a optional information that must be examined by every node along a
packet's delivery path. The IPv6 Router Alert Option is one packet's delivery path. The IPv6 Router Alert Option is one
particular hop by hop option. Similar security concerns to those particular hop-by-hop option. Similar security concerns to those
discussed in the present document for the IPv6 Router Alert apply discussed in this document for the IPv6 Router Alert apply more
more generically to the concept of IPv6 hop-by-hop option extension generically to the concept of the IPv6 hop-by-hop options extension
header. However, addressing the broader concept of IPv6 hop-by-hop header. However, thoroughly addressing the broader concept of the
option thoroughly would require additional material so as to cover IPv6 hop-by-hop option would require additional material so as to
additional considerations associated with it (such as the attacks cover additional considerations associated with it (e.g., the
effectiveness depending on how many options are included and on the effectiveness of the attack could depend on how many options are
range from to which the option-type value belongs, etc.), so this is included and on the range to which the option-type value belongs), so
kept outside the scope of the present document. A detailed this is kept outside the scope of this document. A detailed
discussion about security risks and proposed remedies associated with discussion about security risks and proposed remedies associated with
IPv6 hop-by-hop option can be found in [I-D.krishnan-ipv6-hopbyhop]. the IPv6 hop-by-hop option can be found in [IPv6-HOPBYHOP].
The IPv4 base specification [RFC0791] defines a general notion of The IPv4 base specification [RFC0791] defines a general notion of
IPv4 options that can be included in the IPv4 header (without IPv4 options that can be included in the IPv4 header (without
distinguishing between hop-by-hop versus end-to-end option). The distinguishing between the hop-by-hop and end-to-end options). The
IPv4 Router Alert Option is one particular IPv4 option. Similar IPv4 Router Alert Option is one particular IPv4 option. Security
security concerns to those discussed in the present document for the concerns similar to those discussed in this document for the IPv4
IPv4 Router Alert apply more generically to the concept of IPv4 Router Alert apply more generically to the concept of the IPv4
option. However, addressing the security concerns of the broader option. However, thoroughly addressing the security concerns of the
concept of IPv4 option thoroughly is kept outside the scope of the broader concept of the IPv4 option is kept outside the scope of this
present document because it would require additional material so as document, because it would require additional material so as to cover
to cover additional considerations associated with it (such as lack additional considerations associated with it (such as lack of option
of option ordering, etc.), and because other IPv4 options are often ordering, etc.), and because other IPv4 options are often blocked in
blocked in firewalls and not very widely used, so the practical risks firewalls and not very widely used, so the practical risks they
they present are largely non-existent. present are largely nonexistent.
2. Terminology
For readability, this document uses the following loosely defined
terms:
o Fast path: Hardware or Application-Specific Integrated Circuit
(ASIC) processing path for packets. This is the nominal
processing path within a router for IP datagrams.
o Slow path: Software processing path for packets. This is a sub-
nominal processing path for packets that require special
processing or differ from assumptions made in fast-path
heuristics.
o Next level protocol: The protocol transported in the IP datagram.
In IPv4 [RFC0791], the next level protocol is identified by the
IANA protocol number conveyed in the 8-bit "Protocol" field in the
IPv4 header. In IPv6 [RFC2460], the next level protocol is
identified by the IANA protocol number conveyed in the 8-bit "Next
Header" field in the IPv6 header.
2.1. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
3. Security Concerns of Router Alert 3. Security Concerns of Router Alert
The IP Router Alert Option is defined ([RFC2113], [RFC2711]) as a The IP Router Alert Option is defined ([RFC2113], [RFC2711]) as a
mechanism that alerts transit routers to more closely examine the mechanism that alerts transit routers to more closely examine the
contents of an IP packet. [RFC4081] and [RFC2711] mention the contents of an IP packet. [RFC4081] and [RFC2711] mention the
security risks associated with the use of the IP Router Alert: security risks associated with the use of the IP Router Alert:
flooding a router with bogus (or simply undesired) IP datagrams which flooding a router with bogus (or simply undesired) IP datagrams that
contain the IP Router Alert could impact operation of the router in contain the IP Router Alert could impact operation of the router in
undesirable ways. For example, if the router punts the datagrams undesirable ways. For example, if the router punts the datagrams
containing the IP Router Alert Option to the slow path, such an containing the IP Router Alert Option to the slow path, such an
attack could consume a significant share of the router's slow path attack could consume a significant share of the router's slow path
and could also lead to packet drops in the slow path (affecting and could also lead to packet drops in the slow path (affecting
operation of all other applications and protocols operating in the operation of all other applications and protocols operating in the
slow path) thereby resulting in a denial of service (DoS) slow path), thereby resulting in a denial of service (DoS)
([RFC4732]). ([RFC4732]).
Furthermore, [RFC2113] specifies no (and [RFC2711] specifies very Furthermore, [RFC2113] specifies no (and [RFC2711] specifies a very
limited) mechanism for identifying different users of IP Router limited) mechanism for identifying different users of IP Router
Alert. As a result, many fast switching implementations of IP Router Alert. As a result, many fast switching implementations of IP Router
Alert punt most/all packets marked with IP Router Alert into the slow Alert punt most/all packets marked with IP Router Alert into the slow
path (unless configured to systematically ignore or drop all Router path (unless configured to systematically ignore or drop all Router
Alert packets). However, some existing deployed IP routers can and Alert packets). However, some existing deployed IP routers can and
do process IP packets containing the Router Alert Option inside the do process IP packets containing the Router Alert Option inside the
Fast Path. fast path.
Some IP Router Alert implementations are able to take into account Some IP Router Alert implementations are able to take into account
the next level protocol as a discriminator for the punting decision the next level protocol as a discriminator for the punting decision
for different protocols using IP Router Alert. However, this still for different protocols using IP Router Alert. However, this still
only allows very coarse triage among various protocols using IP only allows very coarse triage among various protocols using IP
Router Alert for two reasons. First, the next level protocol is the Router Alert, for two reasons. First, the next level protocol is the
same when IP Router Alert is used for different applications of the same when IP Router Alert is used for different applications of the
same protocol (e.g., RSVP vs. RSVP-TE), or when IP Router Alert is same protocol (e.g., RSVP vs. RSVP - Traffic Engineering (RSVP-TE)),
used for different contexts of the same application (e.g., different or when IP Router Alert is used for different contexts of the same
levels of RSVP aggregation [RFC3175]). Thus, it is not always application (e.g., different levels of RSVP aggregation [RFC3175]).
possible to achieve the necessary triage in the fast path across IP Thus, it is not always possible to achieve the necessary triage in
Router Alert packets from different applications or from different the fast path across IP Router Alert packets from different
contexts of an application. Secondly, some protocols requiring applications or from different contexts of an application. Secondly,
punting might be carried over a transport protocol (e.g., TCP or UDP) some protocols requiring punting might be carried over a transport
possibly because they require the services of that transport protocol (e.g., TCP or UDP), possibly because (1) they require the
protocol, possibly because the protocol does not justify allocation services of that transport protocol, (2) the protocol does not
of a scarce next level protocol value or possibly because not relying justify allocation of a scarce next level protocol value, or (3) not
on a very widely deployed transport protocol is likely to result in relying on a very widely deployed transport protocol is likely to
deployment issues due to common middlebox behaviors (e.g. Firewalls result in deployment issues due to common middlebox behaviors (e.g.,
or NATs discarding packets of "unknown" protocols). Thus, firewalls or NATs discarding packets of "unknown" protocols). Thus,
considering the next level protocol alone in the fast path is not considering the next level protocol alone in the fast path is not
sufficient to allow triage in the fast path of IP Router Alert sufficient to allow triage in the fast path of IP Router Alert
packets from different protocols sharing the same transport protocol. packets from different protocols sharing the same transport protocol.
Therefore, it is generally not possible to ensure that only the IP Therefore, it is generally not possible to ensure that only the IP
Router Alert packets for next level protocols of interest are punted Router Alert packets for next level protocols of interest are punted
to the slow path while other IP Router Alert packets are efficiently to the slow path while other IP Router Alert packets are efficiently
forwarded (i.e., in fast path). forwarded (i.e., in the fast path).
Some IP Router Alert implementations are able to take into account Some IP Router Alert implementations are able to take into account
the value field inside the router alert option. However, only one the Value field inside the Router Alert Option. However, only one
value (zero) was defined in [RFC2113] and no IANA registry for IPv4 value (zero) was defined in [RFC2113], and no IANA registry for IPv4
Router Alert values was available until recently ([RFC5350]). So Router Alert values was available until recently ([RFC5350]). So
this did not allow most IPv4 Router Alert implementation to support this did not allow most IPv4 Router Alert implementations to support
useful classification based on the value field in the fast path. useful classification based on the Value field in the fast path.
Also, while [RFC2113] states that unknown values should be ignored Also, while [RFC2113] states that unknown values should be ignored
(i.e. The packets should be forwarded as normal IP traffic), it has (i.e., the packets should be forwarded as normal IP traffic), it has
been reported that some existing implementations simply ignore the been reported that some existing implementations simply ignore the
value field completely (i.e. Process any packet with an IPv4 Router Value field completely (i.e., process any packet with an IPv4 Router
Alert regardless of its option value). An IANA registry for further Alert regardless of its option value). An IANA registry for further
allocation of IPv4 Router Alert values has been introduced recently allocation of IPv4 Router Alert values has been introduced recently
([RFC5350]) but this would only allow coarse-grain classification, if ([RFC5350]), but this would only allow coarse-grain classification,
supported by implementations. For IPv6, [RFC2711] states that "the if supported by implementations. For IPv6, [RFC2711] states that
value field can be used by an implementation to speed processing of "the Value field can be used by an implementation to speed processing
the datagram within the transit router" and defines an IANA registry of the datagram within the transit router" and defines an IANA
for these values. But again, this only allows coarse-grain registry for these values. But again, this only allows coarse-grain
classification. Besides, some existing IPv6 Router Alert classification. Besides, some existing IPv6 Router Alert
implementations are reported to depart from that behavior. implementations are reported to depart from that behavior.
[RFC2711] mentions that limiting, by rate or some other means, the [RFC2711] mentions that limiting, by rate or some other means, the
use of IP Router Alert Option is a way of protecting against a use of the IP Router Alert Option is a way of protecting against a
potential attack. However, if rate limiting is used as a protection potential attack. However, if rate limiting is used as a protection
mechanism, but if the granularity of the rate limiting is not fine mechanism, but if the granularity of the rate limiting is not fine
enough to distinguish among IP Router Alert packet of interest from enough to distinguish IP Router Alert packets of interest from
unwanted IP Router Alert packet, a IP Router Alert attack could still unwanted IP Router Alert packets, an IP Router Alert attack could
severely degrade operation of protocols of interest that depend on still severely degrade operation of protocols of interest that depend
the use of IP Router Alert. on the use of IP Router Alert.
In a nutshell, the IP router alert option does not provide a In a nutshell, the IP Router Alert Option does not provide a
convenient universal mechanism to accurately and reliably distinguish convenient universal mechanism to accurately and reliably distinguish
between IP Router Alert packets of interest and unwanted IP Router between IP Router Alert packets of interest and unwanted IP Router
Alert packets. This, in turn, creates a security concern when IP Alert packets. This, in turn, creates a security concern when the IP
Router Alert Option is used, because, short of appropriate router Router Alert Option is used, because, short of appropriate router-
implementation specific mechanisms, the router slow path is at risk implementation-specific mechanisms, the router slow path is at risk
of being flooded by unwanted traffic. of being flooded by unwanted traffic.
Note that service providers commonly allow external parties to Note that service providers commonly allow external parties to
communicate with a control plane application in their routers, such communicate with a control plane application in their routers, such
as with BGP peering. Depending on the actual environment and BGP as with BGP peering. Depending on the actual environment and BGP
security practices, the resulting DoS attack vector is similar, or security practices, with BGP peering, the resulting DoS attack vector
somewhat less serious, with BGP peering than with Router Alert Option is similar to or somewhat less serious than it would be with the
for a number of reasons that include: Router Alert Option for a number of reasons, including the following:
o With BGP, edge routers only exchange control plane information o With BGP, edge routers only exchange control plane information
with pre-identified peers and can easily filter out any control with pre-identified peers and can easily filter out any control
plane traffic coming from other peers or non-authenticated peers, plane traffic coming from other peers or non-authenticated peers,
while the Router-Alert option can be received in a datagram with while the Router Alert Option can be received in a datagram with
any source address and any destination source. However, we note any source address and any destination address. However, we note
that effectiveness of such BGP filtering is dependent on proper that the effectiveness of such BGP filtering is dependent on
security practices; poor BGP security practices (such as proper security practices; poor BGP security practices (such as
infrequent or inexistent update of BGP peers authentication keys) infrequent or nonexistent update of BGP peers' authentication
create vulnerabilities through which the BGP authentication keys) create vulnerabilities through which the BGP authentication
mechanisms can be compromised. mechanisms can be compromised.
o with BGP Peering, the control plane hole is only open on the edge o With BGP peering, the control plane hole is only open on the edge
routers, and core routers are completely isolated from any direct routers, and core routers are completely isolated from any direct
control plane exchange with entities outside the administrative control plane exchange with entities outside the administrative
domain. Thus, with BGP, a DoS attack would only affect the edge domain. Thus, with BGP, a DoS attack would only affect the edge
routers, while with Router Alert Option, the attack could routers, while with the Router Alert Option, the attack could
propagate to core routers. However, in some BGP environments, the propagate to core routers. However, in some BGP environments, the
distinction between edge and core routers is not strict, and many/ distinction between edge and core routers is not strict, and many/
most/all routers act as both edge and core routers; in such BGP most/all routers act as both edge and core routers; in such BGP
environments, a large part of the network is exposed to direct environments, a large part of the network is exposed to direct
control plane exchanges with entities outside the administrative control plane exchanges with entities outside the administrative
domain (as it would be with Router Alert). domain (as it would be with Router Alert).
o with BGP, the BGP policy control would typically prevent re- o With BGP, the BGP policy control would typically prevent re-
injection of undesirable information out of the attacked device, injection of undesirable information out of the attacked device,
while with the Router-Alert option, the non-filtered attacking while with the Router Alert Option, the non-filtered attacking
messages would typically be forwarded downstream. However, we messages would typically be forwarded downstream. However, we
note that there has been real life occurrences of situations where note that there have been real-life occurrences of situations
incorrect information was propagated through the BGP system, where incorrect information was propagated through the BGP system,
causing quite widespread problems. causing widespread problems.
4. Guidelines for use of Router Alert 4. Guidelines for Use of Router Alert
4.1. Use of Router Alert End-to-End In the Internet (Router Alert in 4.1. Use of Router Alert End to End in the Internet (Router Alert in
Peer Model) Peer Model)
Because of the security concerns associated with Router Alert Because of the security concerns associated with Router Alert
discussed in Section 3, network operators SHOULD actively protect discussed in Section 3, network operators SHOULD actively protect
themselves against externally generated IP Router Alert packets. themselves against externally generated IP Router Alert packets.
Because there is no convenient universal mechanisms to triage between Because there are no convenient universal mechanisms to triage
desired and undesired router alert packets, network operators between desired and undesired Router Alert packets, network operators
currently often protect themselves in ways that isolate them from currently often protect themselves in ways that isolate them from
externally generated IP Router Alert packets. This might be achieved externally generated IP Router Alert packets. This might be achieved
by tunneling IP Router Alert packets [RFC6178] so that the IP Router by tunneling IP Router Alert packets [RFC6178] so that the IP Router
Alert Option is hidden through that network, or it might be achieved Alert Option is hidden through that network, or it might be achieved
via mechanisms resulting in occasional (e.g., rate limiting) or via mechanisms resulting in occasional (e.g., rate limiting) or
systematic drop of IP Router Alert packets. systematic drop of IP Router Alert packets.
Thus, applications and protocols SHOULD NOT be deployed with a Thus, applications and protocols SHOULD NOT be deployed with a
dependency on processing of the Router Alert Option (as currently dependency on processing of the Router Alert Option (as currently
specified) across independent administrative domains in the Internet. specified) across independent administrative domains in the Internet.
Figure 1 illustrates such a hypothetical use of Router Alert end-to- Figure 1 illustrates such a hypothetical use of Router Alert end to
end in the Internet. We refer to such a model of Router Alert Option end in the Internet. We refer to such a model of Router Alert Option
use as a "Peer Model" Router Alert Option use, since core routers in use as a "Peer Model" Router Alert Option use, since core routers in
different administrative domains would partake in processing of different administrative domains would partake in processing of
Router Alert Option datagrams associated with the same signalling Router Alert Option datagrams associated with the same signaling
flow. flow.
-------- -------- -------- -------- -------- -------- -------- --------
/ A \ / B \ / C \ / D \ / A \ / B \ / C \ / D \
| (*) | | (*) | | (*) | | (*) | | (*) | | (*) | | (*) | | (*) |
| | |<============>| |<=============>| |<=============>| | | | | |<============>| |<=============>| |<=============>| | |
| - | | - | | - | | - | | - | | - | | - | | - |
\ / \ / \ / \ / \ / \ / \ / \ /
-------- -------- -------- -------- -------- -------- -------- --------
(*) closer examination of Router Alert Option datagrams (*) closer examination of Router Alert Option datagrams
<==> flow of Router Alert Option datagrams <==> flow of Router Alert Option datagrams
Figure 1: Use of Router Alert End-to-End in the Open Internet (Router Figure 1: Use of Router Alert End to End in the Open Internet
Alert in Peer Model) (Router Alert in Peer Model)
While this recommendation is framed here specifically in the context While this recommendation is framed here specifically in the context
of router alert, the fundamental security risk that network operators of Router Alert, the fundamental security risk that network operators
want to preclude is to allow devices/protocols that are outside of want to preclude is to allow devices/protocols that are outside of
their administrative domain (and therefore not controlled) to tap their administrative domain (and therefore not controlled) to tap
into the control plane of their core routers. Whether this control into the control plane of their core routers. Similar security
plane access is provided through router alert option or would be concerns would probably result whether this control plane access is
provided by any other mechanism (e.g. Deep packet inspection) provided through the Router Alert Option or provided by any other
probably results in similar security concerns. In other words, the mechanism (e.g., deep packet inspection). In other words, the
fundamental security concern is associated with the notion of end to fundamental security concern is associated with the notion of end-to-
end signaling in a Peer Model across domains in the Internet. As a end signaling in a Peer Model across domains in the Internet. As a
result, it is expected that network operators would typically not result, it is expected that network operators would typically not
want to have their core routers partake in end-to-end signalling with want to have their core routers partake in end-to-end signaling with
external uncontrolled devices through the open Internet, and external uncontrolled devices through the open Internet, and
therefore prevent deployment of end to end signalling in a Peer model therefore prevent deployment of end-to-end signaling in a Peer Model
through their network (regardless of whether that signalling uses through their network (regardless of whether that signaling uses
Router Alert or not). Router Alert or not).
4.2. Use of Router Alert In Controlled Environments 4.2. Use of Router Alert in Controlled Environments
4.2.1. Use of Router Alert Within an Administrative Domain 4.2.1. Use of Router Alert within an Administrative Domain
In some controlled environments, such as within a given In some controlled environments, such as within a given
Administrative Domain, the network administrator can determine that administrative domain, the network administrator can determine that
IP Router Alert packets will only be received from trusted well- IP Router Alert packets will only be received from trusted well-
behaved devices or can establish that specific protection mechanisms behaved devices or can establish that specific protection mechanisms
(e.g., RAO filtering and rate-limiting) against the plausible RAO- (e.g., RAO filtering and rate limiting) against the plausible RAO-
based DoS attacks are sufficient. In that case, an application based DoS attacks are sufficient. In that case, an application
relying on exchange and handling of RAO packets (e.g., RSVP) can be relying on exchange and handling of RAO packets (e.g., RSVP) can be
safely deployed within the controlled network. A private enterprise safely deployed within the controlled network. A private enterprise
network firewalled from the Internet and using RSVP reservations for network firewalled from the Internet and using RSVP reservations for
voice and video flows might be an example of such controlled voice and video flows might be an example of such a controlled
environment. Such an environment is illustrated in Figure 2. environment. Such an environment is illustrated in Figure 2.
------------------------- -------- -------- ------------------------- -------- --------
/ A \ / B \ / C \ / A \ / B \ / C \
| (*) (*) | -- | | | | | (*) (*) | -- | | | |
| | |<============>| | |--|FW|--| |--------| | | | |<============>| | |--|FW|--| |--------| |
| - - | -- | | | | | - - | -- | | | |
\ / \ / \ / \ / \ / \ /
------------------------- -------- -------- ------------------------- -------- --------
(*) closer examination of Router Alert Option datagrams (*) closer examination of Router Alert Option datagrams
<==> flow of Router Alert Option datagrams <==> flow of Router Alert Option datagrams
FW Firewall FW: Firewall
Figure 2: Use of Router Alert Within an Administrative Domain Figure 2: Use of Router Alert within an Administrative Domain -
Private Enterprise Network Firewalled from the Internet
and Using RSVP Reservations
In some controlled environments, several Administrative Domains have In some controlled environments, several administrative domains have
a special relationship whereby they cooperate very tightly and a special relationship whereby they cooperate very tightly and
effectively operate as a single trust domain. In that case, one effectively operate as a single trust domain. In that case, one
domain is willing to trust another with respect to the traffic domain is willing to trust another with respect to the traffic
injected across the boundary. In other words, a downstream domain is injected across the boundary. In other words, a downstream domain is
willing to trust that the traffic injected at the boundary has been willing to trust that the traffic injected at the boundary has been
properly validated/filtered by the upstream domain. Where it has properly validated/filtered by the upstream domain. Where it has
been established that such trust can be applied to router alert been established that such trust can be applied to Router Alert
option packets, an application relying on exchange and handling of Option packets, an application relying on exchange and handling of
RAO packets (e.g., RSVP) can be safely deployed within such a RAO packets (e.g., RSVP) can be safely deployed within such a
controlled environment. The entity within a company responsible for controlled environment. The entity within a company responsible for
operating multimedia endpoints and the entity within the same company operating multimedia endpoints and the entity within the same company
responsible for operating the network might be an example of such responsible for operating the network might be an example of such a
controlled environment. For example, they might collaborate so that controlled environment. For example, they might collaborate so that
RSVP reservations can be used for video flows from endpoints to RSVP reservations can be used for video flows from endpoints to
endpoints through the network. endpoints through the network.
In some environments, the network administrator can reliably ensure In some environments, the network administrator can reliably ensure
that router alert packets from any untrusted device (e.g., from that Router Alert packets from any untrusted device (e.g., from
external routers) are prevented from entering a trusted area (e.g., external routers) are prevented from entering a trusted area (e.g.,
the internal routers). For example, this might be achieved by the internal routers). For example, this might be achieved by
ensuring that routers straddling the trust boundary (e.g., edge ensuring that routers straddling the trust boundary (e.g., edge
routers) always encapsulate those packets (without setting IP Router routers) always encapsulate those packets (without setting IP Router
Alert -or equivalent- in the encapsulating header) through the Alert -or equivalent- in the encapsulating header) through the
trusted area (as discussed in [RFC6178]). In such environments, the trusted area (as discussed in [RFC6178]). In such environments, the
risks of DoS attacks through the IP Router Alert vector is removed in risks of DoS attacks through the IP Router Alert vector are removed
the trusted area (or greatly reduced) even if IP Router Alert is used (or greatly reduced) in the trusted area even if IP Router Alert is
inside the trusted area (say for RSVP-TE). Thus an application used inside the trusted area (say, for RSVP-TE). Thus, an
relying on IP Router Alert can be safely deployed within the trusted application relying on IP Router Alert can be safely deployed within
area. A Service Provider running RSVP-TE within his network might be the trusted area. A service provider running RSVP-TE within its
an example of such protected environment. Such an environment is network might be an example of such a protected environment. Such an
illustrated in Figure 3. environment is illustrated in Figure 3.
-------- -------------------------- -------- -------- -------------------------- --------
/ A \ / B \ / C \ / A \ / B \ / C \
| | | (*) (*) | | | | | | (*) (*) | | |
| |-------TT | |<=============>| | TT------- | | | |-------TT | |<=============>| | TT------- | |
| | | - - | | | | | | - - | | |
\ / \ / \ / \ / \ / \ /
-------- -------------------------- -------- -------- -------------------------- --------
(*) closer examination of Router Alert Option datagrams (*) closer examination of Router Alert Option datagrams
<==> flow of Router Alert Option datagrams <==> flow of Router Alert Option datagrams
TT Tunneling of Router Alert Option datagrams TT: Tunneling of Router Alert Option datagrams
Figure 3: Use of Router Alert Within an Administrative Domain Figure 3: Use of Router Alert within an Administrative Domain -
Service Provider Running RSVP-TE within Its Network
4.2.2. Use of Router Alert In Overlay Model 4.2.2. Use of Router Alert in Overlay Model
In some controlled environment: In some controlled environment:
o the sites of a network A are interconnected through a service o The sites of a network A are interconnected through a service
provider network B provider network B.
o the service provider network B protects itself from IP Router o The service provider network B protects itself from IP Router
Alert messages without dropping those when they transit over the Alert messages without dropping those messages when they transit
transit network (for example using mechanisms discussed in over the network (for example, using mechanisms discussed in
[RFC6178]) [RFC6178]).
In such controlled environment, an application relying on exchange In such a controlled environment, an application relying on exchange
and handling of RAO packets (e.g., RSVP) in the network A sites (but and handling of RAO packets (e.g., RSVP) in the network A sites (but
not inside network B) can be safely deployed. We refer to such a not inside network B) can be safely deployed. We refer to such a
deployment as a use of Router Alert in a Water-Tight Overlay. deployment as a use of Router Alert in a Water-Tight Overlay --
"Overlay" because Router Alert Option datagrams are used in network A "Overlay", because Router Alert Option datagrams are used in network
on top of, and completely transparently to, network B. "Water-Tight" A on top of, and completely transparently to, network B; and
because router alert option datagrams from A cannot leak inside "Water-Tight", because Router Alert Option datagrams from network A
network B. A private enterprise intranet realised as a Virtual cannot leak inside network B. A private enterprise intranet realized
Private Network (VPN) over a Service Provider network, and using RSVP as a Virtual Private Network (VPN) over a service provider network
to perform reservations within the enterprise sites for voice and and using RSVP to perform reservations within the enterprise sites
video flows might be an example of such controlled environment. Such for voice and video flows might be an example of such a controlled
an environment is illustrated in Figure 4. environment. Such an environment is illustrated in Figure 4.
-------- -------- -------- --------
/ A \ / A \ / A \ / A \
| (*) | | (*) | | (*) | | (*) |
| | |<=====================================>| | | | | |<=====================================>| | |
| - | | - | | - | | - |
\ / \ / \ / \ /
-------- -------- -------- --------
\ / \ /
\ ------------------------- / \ ------------------------- /
\ / B \ / \ / B \ /
\| |/ \| |/
TT TT TT TT
| | | |
\ / \ /
------------------------- -------------------------
(*) closer examination of Router Alert Option datagrams (*) closer examination of Router Alert Option datagrams
<==> flow of Router Alert Option datagrams <==> flow of Router Alert Option datagrams
TT Tunneling of Router Alert Option datagrams TT: Tunneling of Router Alert Option datagrams
Figure 4: Use of Router Alert In Water-tight Overlay Figure 4: Use of Router Alert in Water-Tight Overlay
In the controlled environment described above, an application relying In the controlled environment described above, an application relying
on exchange and handling of RAO packets (e.g. RSVP-TE) in the on exchange and handling of RAO packets (e.g., RSVP-TE) in the
service provider network B (but not in network A) can also be safely service provider network B (but not in network A) can also be safely
deployed simultaneously. Such an environment with independent, deployed simultaneously. Such an environment with independent,
isolated, deployment of router alert in overlay at two levels is isolated deployment of Router Alert in overlay at two levels is
illustrated in Figure 5. illustrated in Figure 5.
-------- -------- -------- --------
/ A \ / A \ / A \ / A \
| (*) | | (*) | | (*) | | (*) |
| | |<=====================================>| | | | | |<=====================================>| | |
| - | | - | | - | | - |
\ / \ / \ / \ /
-------- -------- -------- --------
\ / \ /
\ ------------------------- / \ ------------------------- /
\ / B \ / \ / B \ /
\| (*) (*) |/ \| (*) (*) |/
TT | |<============>| | TT TT | |<============>| | TT
| - - | | - - |
\ / \ /
------------------------- -------------------------
(*) closer examination of Router Alert Option datagrams (*) closer examination of Router Alert Option datagrams
<==> flow of Router Alert Option datagrams <==> flow of Router Alert Option datagrams
TT Tunneling of Router Alert Option datagrams TT: Tunneling of Router Alert Option datagrams
Figure 5: Use of Router Alert In Water-tight Overlay at Two Levels Figure 5: Use of Router Alert in Water-Tight Overlay at Two Levels
In some controlled environment: In some controlled environment:
o the sites of a network A are interconnected through a service o The sites of a network A are interconnected through a service
provider network B provider network B.
o the service provider B processes router alert packets on the edge o The service provider B processes Router Alert packets on the edge
routers and protect these edge routers against RAO based attacks routers and protects these edge routers against RAO-based attacks
using mechanisms such as (possibly per port) RAO rate limiting and using mechanisms such as (possibly per port) RAO rate limiting and
filtering filtering.
o the service provider network B protects its core routers from o The service provider network B protects its core routers from
Router Alert messages without dropping those when they transit Router Alert messages without dropping those messages when they
over the transit network (for example using mechanisms discussed transit over the network (for example, using mechanisms discussed
in [RFC6178]) in [RFC6178]).
In such controlled environment, an application relying on exchange In such a controlled environment, an application relying on exchange
and handling of RAO packets (e.g., RSVP) in the network A sites and and handling of RAO packets (e.g., RSVP) in the network A sites and
in network B Edges (but not in the core of network B) can be safely in network B's edges (but not in the core of network B) can be safely
deployed. We refer to such a deployment as a use of Router Alert in deployed. We refer to such a deployment as a use of Router Alert in
a Leak-Controlled Overlay. "Overlay" because Router Alert Option a Leak-Controlled Overlay -- "Overlay", because Router Alert Option
datagrams are used in network A on top of, and completely datagrams are used in network A on top of, and completely
transparently to, network B core. "Leak-Controlled" because router transparently to, network B's core; and "Leak-Controlled", because
alert option datagrams from A leak inside network B's B edges but not Router Alert Option datagrams from network A leak inside network B's
inside network B's core. A private enterprise intranet, whose sites edges but not inside network B's core. A private enterprise
are interconnected through a Service Prover network, using RSVP for intranet, whose sites are interconnected through a service provider
voice and video within network A sites as well as on Network B's edge network, using RSVP for voice and video within network A sites as
to extend the reservation onto the attachment links between A and B well as on network B's edge to extend the reservation onto the
(as specified in [RFC6016]) might be an example of such controlled attachment links between networks A and B (as specified in
environment. Such an environment is illustrated in Figure 4. [RFC6016]), might be an example of such a controlled environment.
Such an environment is illustrated in Figure 6.
-------- -------- -------- --------
/ A \ / A \ / A \ / A \
| | | | | | | |
| | ------------------------ | | | | ------------------------ | |
| (*) | /(*) (*) \ | (*) | | (*) | /(*) (*) \ | (*) |
| | |<======>| |<============>| |<=========>| | | | | |<======>| |<============>| |<=========>| | |
| - | | - - | | - | | - | | - - | | - |
\ / | \ - - / | \ / \ / | \ - - / | \ /
-------- | TT-| | | |-TT | -------- -------- | TT-| | | |-TT | --------
| - - | | - - |
\ / \ /
------------------------ ------------------------
(*) closer examination of Router Alert Option datagrams (*) closer examination of Router Alert Option datagrams
<==> flow of Router Alert Option datagrams <==> flow of Router Alert Option datagrams
TT Tunneling of Router Alert Option datagrams TT: Tunneling of Router Alert Option datagrams
Figure 6: Use of Router Alert In Leak-Controlled Overlay Figure 6: Use of Router Alert in Leak-Controlled Overlay
4.3. Router Alert Protection Approaches for Service Providers 4.3. Router Alert Protection Approaches for Service Providers
Section 3 discusses the security risks associated with the use of the Section 3 discusses the security risks associated with the use of the
IP Router Alert and how it opens up a DoS vector in the router IP Router Alert and how it opens up a DoS vector in the router
control plane. Thus, a Service Provider MUST implement strong control plane. Thus, a service provider MUST implement strong
protection of his network against attacks based on IP Router Alert. protection of its network against attacks based on IP Router Alert.
As discussed in Section 4.2.2 some applications can benefit from the As discussed in Section 4.2.2, some applications can benefit from the
use of IP Router Alert packets in an Overlay model (i.e. Where use of IP Router Alert packets in an Overlay Model (i.e., where
Router Alert packets are exchanged transparently on top of a Service Router Alert packets are exchanged transparently on top of a service
Provider). Thus, a Service Provider protecting his network from provider). Thus, a service provider protecting its network from
attacks based on IP Router Alert SHOULD use mechanisms that avoid (or attacks based on IP Router Alert SHOULD use mechanisms that avoid (or
at least minimize) dropping of end to end IP Router Alert packets at least minimize) the dropping of end-to-end IP Router Alert packets
(other than those involved in an attack). (other than those involved in an attack).
For example, if the Service Provider does not run any protocol For example, if the service provider does not run any protocol
depending on IP Router Alert within his network, he might elect to depending on IP Router Alert within its network, it might elect to
simply turn-off punting/processing of IP Router Alert packet on his simply turn off punting/processing of IP Router Alert packets on its
routers; this will ensure that end-to-end IP Router Alert packet routers; this will ensure that end-to-end IP Router Alert packets
transit transparently and safely through his network. transit transparently and safely through its network.
As another example, using protection mechanisms such selective As another example, using protection mechanisms such as selective
filtering and rate-limiting (that Section 5 suggests be supported by filtering and rate limiting (which Section 5 suggests be supported by
IP Router Alert implementations) a Service Provider can protect the IP Router Alert implementations), a service provider can protect the
operation of a protocol depending on IP Router Alert within his operation of a protocol depending on IP Router Alert within its
network (e.g., RSVP-TE) while at the same time transporting IP Router network (e.g., RSVP-TE) while at the same time transporting IP Router
Alert packets carrying another protocol that might be used end to Alert packets carrying another protocol that might be used end to
end. Note that the Service Provider might additionally use protocol end. Note that the service provider might additionally use protocol-
specific mechanisms that reduce the dependency on Router Alert for specific mechanisms that reduce the dependency on Router Alert for
operation of this protocol inside the Service Provider environment; operation of this protocol inside the service provider environment;
use of RSVP refresh reduction mechanisms ([RFC2961]) would be an use of RSVP refresh reduction mechanisms ([RFC2961]) would be an
example of such mechanisms in the case where the Service Provider is example of such mechanisms in the case where the service provider is
running RSVP-TE within his network since this allows refresh of running RSVP-TE within its network, since this allows the refresh of
existing Path and Resv states without use of the IP Router Alert existing Path and Resv states without the use of the IP Router Alert
Option. Option.
As yet another example, using mechanisms such as those discussed in As yet another example, using mechanisms such as those discussed in
[RFC6178] a Service Provider can safely protect the operation of a [RFC6178], a service provider can safely protect the operation of a
protocol depending on IP Router Alert within his network (e.g., protocol depending on IP Router Alert within its network (e.g.,
RSVP-TE) while at the same time safely transporting IP Router Alert RSVP-TE) while at the same time safely transporting IP Router Alert
packets carrying another protocol that might be used end to end packets carrying another protocol that might be used end to end
(e.g., IPv4/IPv6 RSVP). We observe that while tunneling of Router (e.g., IPv4/IPv6 RSVP). We observe that while tunneling of Router
Alert Option datagrams over an MPLS backbone as discussed in Alert Option datagrams over an MPLS backbone as discussed in
[RFC6178] is well understood, tunneling Router Alert Option datagrams [RFC6178] is well understood, tunneling Router Alert Option datagrams
over an non-MPLS IP backbone presents a number of issues (and in over a non-MPLS IP backbone presents a number of issues (in
particular for determining where to forward the encapsulated particular, for determining where to forward the encapsulated
datagram) and is not common practice at the time of writing this datagram) and is not common practice at the time of writing this
document. document.
As a last resort, if the SP does not have any means to safely As a last resort, if the service provider does not have any means to
transport end to end IP Router Alert Option packets over his network, safely transport end-to-end IP Router Alert Option packets over its
the SP can drop those packets. It must be noted that this has the network, the service provider can drop those packets. It must be
undesirable consequence of preventing the use of the Router Alert noted that this has the undesirable consequence of preventing the use
Option in the Overlay Model on top of this network, and therefore of the Router Alert Option in the Overlay Model on top of that
prevents users of that network from deploying a number of valid network, and therefore prevents users of that network from deploying
applications/protocols in their environment. a number of valid applications/protocols in their environment.
5. Guidelines for Router Alert Implementation 5. Guidelines for Router Alert Implementation
A router implementation of IP Router Alert Option SHOULD include A router implementation of the IP Router Alert Option SHOULD include
protection mechanisms against Router Alert based DoS attacks protection mechanisms against Router-Alert-based DoS attacks as
appropriate for their targeted deployment environments. For example, appropriate for their targeted deployment environments. For example,
this can include ability on an edge router to "tunnel" IP Router this can include the ability of an edge router to "tunnel" received
Alert Option of received packets when forwarding those over the core IP Router Alert Option packets when forwarding those packets over the
as discussed in [RFC6178]. As another example, although not always core, as discussed in [RFC6178]. As another example, although not
available from current implementations, new implementations MAY always available from current implementations, new implementations
include protection mechanisms such as selective (possibly dynamic) MAY include protection mechanisms such as selective (possibly
filtering and rate-limiting of IP Router Alert Option packets. dynamic) filtering and rate limiting of IP Router Alert Option
packets.
In particular, router implementations of IP Router Alert Option In particular, router implementations of the IP Router Alert Option
SHOULD offer the configuration option simply to ignore the presence SHOULD offer the configuration option to simply ignore the presence
of "IP Router Alert" in IPv4 and IPv6 packets. As discussed in of "IP Router Alert" in IPv4 and IPv6 packets. As discussed in
Section 4.3, that permits IP Router Alert packets to transit a Section 4.3, that permits IP Router Alert packets to transit a
network segment without presenting an adverse operational security network segment without presenting an adverse operational security
risk to that particular network segment, provided the operator of risk to that particular network segment, provided the operator of
that network segment does not ever use the IP Router Alert messages that network segment does not ever use the IP Router Alert messages
for any purpose. for any purpose.
If an IP packet contains the IP Router Alert Option, but the next If an IP packet contains the IP Router Alert Option, but the next
level protocol is not explicitly identified as a protocol of interest level protocol is not explicitly identified as a protocol of interest
by the router examining the packet, the behavior is not explicitly by the router examining the packet, the behavior is not explicitly
defined by [RFC2113]. However, the behavior is implied and, for defined by [RFC2113]. However, the behavior is implied, and, for
example, the definition of RSVP in [RFC2205] assumes that the packet example, the definition of RSVP in [RFC2205] assumes that the packet
will be forwarded using normal forwarding based on the destination IP will be forwarded using normal forwarding based on the destination IP
address. Thus, a router implementation SHOULD forward within the address. Thus, a router implementation SHOULD forward within the
"fast path" (subject to all normal policies and forwarding rules) a "fast path" (subject to all normal policies and forwarding rules) a
packet carrying the IP Router Alert Option containing a next level packet carrying the IP Router Alert Option containing a next level
protocol that is not a protocol of interest to that router. The "not protocol that is not a protocol of interest to that router. The "not
punting" behavior protects the router from DoS attacks using IP punting" behavior protects the router from DoS attacks using IP
Router Alert packets of a protocol unknown to the router. The Router Alert packets of a protocol unknown to the router. The
"forwarding" behavior contributes to transparent end to end transport "forwarding" behavior contributes to transparent end-to-end transport
of IP Router Alert packets (e.g., to facilitate their use by end to of IP Router Alert packets (e.g., to facilitate their use by end-to-
end application). end applications).
Similarly, an implementation MAY support selective forwarding within Similarly, an implementation MAY support selective forwarding within
"the fast path" (subject to all normal policies and forwarding rules) the fast path (subject to all normal policies and forwarding rules)
or punting of a packet with the IP Router Alert Option, based on the or punting of a packet with the IP Router Alert Option, based on the
Value field of the Router Alert Option. This would allow router Value field of the Router Alert Option. This would allow router
protection against DoS attacks using IP Router Alert packets with protection against DoS attacks using IP Router Alert packets with a
value that is not relevant for that router (e.g. Nesting levels of value that is not relevant for that router (e.g., nesting levels of
Aggregated RSVP Reservation [RFC5350]). aggregated RSVP reservation [RFC5350]).
6. Security Considerations 6. Security Considerations
This document discusses security risks associated with current usage This document expands the security considerations of [RFC2113] and
of the IP Router Alert Option and associated practices. This [RFC2711], which define the IPv4 and IPv6 RAOs, respectively, by
document expands the security considerations of [RFC2113] and discussing security risks associated with usage of the current IP
[RFC2711], which defined the RAO, to discuss security risks Router Alert Option and associated practices. See [RFC4081] for
associated with current usage of the IP Router Alert Option and additional security considerations.
associated practices. See [RFC4081] for additional security
considerations.
7. IANA Considerations
None.
8. Contributors
The contributors to this document (in addition to the editors) are:
o Reshad Rahman:
* Cisco Systems
* rrahman@cisco.com
o David Ward:
* Juniper Networks
* dward@juniper.net
o Ashok Narayanan:
* Cisco Systems 7. Contributors
* ashokn@cisco.com The contributors to this document (in addition to the editor) are:
o Adrian Farrel: Reshad Rahman
Cisco Systems
rrahman@cisco.com
* OldDog Consulting David Ward
Juniper Networks
dward@juniper.net
* adrian@olddog.co.uk Ashok Narayanan
Cisco Systems
ashokn@cisco.com
o Tony Li: Adrian Farrel
OldDog Consulting
adrian@olddog.co.uk
* tony.li@tony.li Tony Li
Cisco Systems
tony.li@tony.li
9. Acknowledgments 8. Acknowledgments
We would like to thank Dave Oran, Magnus Westerlund, John Scudder, The editor and contributors would like to thank Dave Oran, Magnus
Ron Bonica, Ross Callon, Alfred Hines, Carlos Pignataro, Roland Westerlund, John Scudder, Ron Bonica, Ross Callon, Alfred Hines,
Bless, Jari Arkko and Ran Atkinson for their comments. This document Carlos Pignataro, Roland Bless, Jari Arkko, and Ran Atkinson for
also benefited from discussions with Jukka Manner and Suresh their comments. This document also benefited from discussions with
Krishnan. The discussion about use of the value field in the IPv4 Jukka Manner and Suresh Krishnan. The discussion about use of the
Router Alert borrowed from a similar discussion in [RFC5971]. Value field in the IPv4 Router Alert is borrowed from a similar
discussion in [RFC5971].
10. References 9. References
10.1. Normative References 9.1. Normative References
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
September 1981. September 1981.
[RFC2113] Katz, D., "IP Router Alert Option", RFC 2113, [RFC2113] Katz, D., "IP Router Alert Option", RFC 2113,
February 1997. February 1997.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998. (IPv6) Specification", RFC 2460, December 1998.
[RFC2711] Partridge, C. and A. Jackson, "IPv6 Router Alert Option", [RFC2711] Partridge, C. and A. Jackson, "IPv6 Router Alert Option",
RFC 2711, October 1999. RFC 2711, October 1999.
[RFC5350] Manner, J. and A. McDonald, "IANA Considerations for the [RFC5350] Manner, J. and A. McDonald, "IANA Considerations for the
IPv4 and IPv6 Router Alert Options", RFC 5350, IPv4 and IPv6 Router Alert Options", RFC 5350,
September 2008. September 2008.
10.2. Informative References 9.2. Informative References
[I-D.krishnan-ipv6-hopbyhop]
Krishnan, S., "The case against Hop-by-Hop options",
draft-krishnan-ipv6-hopbyhop-05 (work in progress),
October 2010.
[I-D.narayanan-rtg-router-alert-extension] [IPv6-HOPBYHOP]
Narayanan, A., Faucheur, F., Ward, D., and R. Rahman, "IP Krishnan, S., "The case against Hop-by-Hop options", Work
Router Alert Option Extension", in Progress, October 2010.
draft-narayanan-rtg-router-alert-extension-00 (work in
progress), March 2009.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RAO-EXT] Narayanan, A., Le Faucheur, F., Ward, D., and R. Rahman,
Requirement Levels", BCP 14, RFC 2119, March 1997. "IP Router Alert Option Extension", Work in Progress,
March 2009.
[RFC2205] Braden, B., Zhang, L., Berson, S., Herzog, S., and S. [RFC2205] Braden, R., Ed., Zhang, L., Berson, S., Herzog, S., and S.
Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1 Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
Functional Specification", RFC 2205, September 1997. Functional Specification", RFC 2205, September 1997.
[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.
[RFC2961] Berger, L., Gan, D., Swallow, G., Pan, P., Tommasi, F., [RFC2961] Berger, L., Gan, D., Swallow, G., Pan, P., Tommasi, F.,
and S. Molendini, "RSVP Refresh Overhead Reduction and S. Molendini, "RSVP Refresh Overhead Reduction
Extensions", RFC 2961, April 2001. Extensions", RFC 2961, April 2001.
skipping to change at page 23, line 20 skipping to change at page 18, line 16
Lin, S., Leshchiner, D., Luby, M., Montgomery, T., Rizzo, Lin, S., Leshchiner, D., Luby, M., Montgomery, T., Rizzo,
L., Tweedly, A., Bhaskar, N., Edmonstone, R., L., Tweedly, A., Bhaskar, N., Edmonstone, R.,
Sumanasekera, R., and L. Vicisano, "PGM Reliable Transport Sumanasekera, R., and L. Vicisano, "PGM Reliable Transport
Protocol Specification", RFC 3208, December 2001. Protocol Specification", RFC 3208, December 2001.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001. Tunnels", RFC 3209, December 2001.
[RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A. [RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
Thyagarajan, "Internet Group Management Protocol, Version Thyagarajan, "Internet Group Management Protocol,
3", RFC 3376, October 2002. Version 3", RFC 3376, October 2002.
[RFC3810] Vida, R. and L. Costa, "Multicast Listener Discovery [RFC3810] Vida, R., Ed., and L. Costa, Ed., "Multicast Listener
Version 2 (MLDv2) for IPv6", RFC 3810, June 2004. Discovery Version 2 (MLDv2) for IPv6", RFC 3810,
June 2004.
[RFC4081] Tschofenig, H. and D. Kroeselberg, "Security Threats for [RFC4081] Tschofenig, H. and D. Kroeselberg, "Security Threats for
Next Steps in Signaling (NSIS)", RFC 4081, June 2005. Next Steps in Signaling (NSIS)", RFC 4081, June 2005.
[RFC4286] Haberman, B. and J. Martin, "Multicast Router Discovery", [RFC4286] Haberman, B. and J. Martin, "Multicast Router Discovery",
RFC 4286, December 2005. RFC 4286, December 2005.
[RFC4732] Handley, M., Rescorla, E., and IAB, "Internet Denial-of- [RFC4732] Handley, M., Ed., Rescorla, E., Ed., and IAB, "Internet
Service Considerations", RFC 4732, December 2006. Denial-of-Service Considerations", RFC 4732,
December 2006.
[RFC5971] Schulzrinne, H. and R. Hancock, "GIST: General Internet [RFC5971] Schulzrinne, H. and R. Hancock, "GIST: General Internet
Signalling Transport", RFC 5971, October 2010. Signalling Transport", RFC 5971, October 2010.
[RFC6016] Davie, B., Le Faucheur, F., and A. Narayanan, "Support for [RFC6016] Davie, B., Le Faucheur, F., and A. Narayanan, "Support for
the Resource Reservation Protocol (RSVP) in Layer 3 VPNs", the Resource Reservation Protocol (RSVP) in Layer 3 VPNs",
RFC 6016, October 2010. RFC 6016, October 2010.
[RFC6178] Smith, D., Mullooly, J., Jaeger, W., and T. Scholl, "Label [RFC6178] Smith, D., Mullooly, J., Jaeger, W., and T. Scholl, "Label
Edge Router Forwarding of IPv4 Option Packets", RFC 6178, Edge Router Forwarding of IPv4 Option Packets", RFC 6178,
skipping to change at page 24, line 14 skipping to change at page 19, line 14
Author's Address Author's Address
Francois Le Faucheur (editor) Francois Le Faucheur (editor)
Cisco Systems Cisco Systems
Greenside, 400 Avenue de Roumanille Greenside, 400 Avenue de Roumanille
Sophia Antipolis 06410 Sophia Antipolis 06410
France France
Phone: +33 4 97 23 26 19 Phone: +33 4 97 23 26 19
Email: flefauch@cisco.com EMail: flefauch@cisco.com
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