draft-ietf-intarea-router-alert-considerations-06.txt   draft-ietf-intarea-router-alert-considerations-07.txt 
Network Working Group F. Le Faucheur, Ed. Network Working Group F. Le Faucheur, Ed.
Internet-Draft Cisco Internet-Draft Cisco
Intended status: BCP July 5, 2011 Intended status: BCP July 25, 2011
Expires: January 6, 2012 Expires: January 26, 2012
IP Router Alert Considerations and Usage IP Router Alert Considerations and Usage
draft-ietf-intarea-router-alert-considerations-06 draft-ietf-intarea-router-alert-considerations-07
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.
Resource reSerVation Protocol (RSVP), Pragmatic General Multicast Resource reSerVation Protocol (RSVP), Pragmatic General Multicast
(PGM), Internet Group Management Protocol (IGMP), Multicast Listener (PGM), Internet Group Management Protocol (IGMP), Multicast Listener
Discovery (MLD), Multicast Router Discovery (MRD) and General Discovery (MLD), Multicast Router Discovery (MRD) and General
Internet Signalling Transport (GIST) are some of the protocols that Internet Signalling Transport (GIST) are some of the protocols that
make use of the IP Router Alert option. This document discusses 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. Specifically, it provides recommendation IP Router Alert Option. Specifically, it provides recommendation
against using the Router Alert in the end-to-end open Internet as against using the Router Alert in the end-to-end open Internet as
well as identify controlled environments where protocols depending on well as identify controlled environments where protocols depending on
Router Alert can be used safely. It also provides recommendation Router Alert can be used safely. It also provides recommendation
about protection approaches for Service Providers. Finally it about protection approaches for Service Providers. Finally it
provides brief guidelines for Router Alert implementation on routers. provides brief guidelines for Router Alert implementation on routers.
Status of this Memo Status of this Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
skipping to change at page 1, line 43 skipping to change at page 1, line 43
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 6, 2012. This Internet-Draft will expire on January 26, 2012.
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
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
10.1. Normative References . . . . . . . . . . . . . . . . . . . 22 10.1. Normative References . . . . . . . . . . . . . . . . . . . 22
10.2. Informative References . . . . . . . . . . . . . . . . . . 22 10.2. Informative References . . . . . . . . . . . . . . . . . . 22
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 24 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 24
1. Terminology 1. Terminology
For readability, this document uses the following loosely defined For readability, this document uses the following loosely defined
terms: terms:
o Slow path : Software processing path for packets 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 Fast path : ASIC/Hardware processing path for packets 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. o Next level protocol: the protocol transported in the IP datagram.
In IPv4 [RFC0791], the next level protocol is identified by the In IPv4 [RFC0791], the next level protocol is identified by the
IANA protocol number conveyed in the 8-bit "Protocol" field in the IANA protocol number conveyed in the 8-bit "Protocol" field in the
IPv4 header. In IPv6 [RFC2460], the next level protocol is IPv4 header. In IPv6 [RFC2460], the next level protocol is
identified by the IANA protocol number conveyed in the 8-bit "Next identified by the IANA protocol number conveyed in the 8-bit "Next
Header" field in the IPv6 header. Header" field in the IPv6 header.
1.1. Conventions Used in This Document 1.1. Conventions Used in This Document
skipping to change at page 4, line 22 skipping to change at page 4, line 22
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]), Internet
Group Management Protocol (IGMP) ([RFC3376]), Multicast Listener Group Management Protocol (IGMP) ([RFC3376]), Multicast Listener
Discovery (MLD) ([RFC2710], [RFC3810]), Multicast Router Discovery Discovery (MLD) ([RFC2710], [RFC3810]), Multicast Router Discovery
(MRD) ([RFC4286]) and NSIS General Internet Signalling Transport (MRD) ([RFC4286]) and NSIS General Internet Signalling Transport
(GIST) ([RFC5971]) are some of the protocols that make use of the IP (GIST) ([RFC5971]) are some of the protocols that make use of the IP
Router Alert. 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.
skipping to change at page 6, line 7 skipping to change at page 6, line 7
option. However, addressing the security concerns of the broader option. However, addressing the security concerns of the broader
concept of IPv4 option thoroughly is kept outside the scope of the concept of IPv4 option thoroughly is kept outside the scope of the
present document because it would require additional material so as present document because it would require additional material so as
to cover additional considerations associated with it (such as lack to cover additional considerations associated with it (such as lack
of option ordering, etc.), and because other IPv4 options are often of option ordering, etc.), and because other IPv4 options are often
blocked in firewalls and not very widely used, so the practical risks blocked in firewalls and not very widely used, so the practical risks
they present are largely non-existent. they present are largely non-existent.
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 which
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 (thus, 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). slow path) thereby resulting in a denial of service (DoS)
([RFC4732]).
Furthermore, [RFC2113] specifies no (and [RFC2711] specifies very Furthermore, [RFC2113] specifies no (and [RFC2711] specifies 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-TE), or when IP Router Alert is
used for different contexts of the same application (e.g., different used for different contexts of the same application (e.g., different
skipping to change at page 7, line 28 skipping to change at page 7, line 29
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, if
supported by implementations. For IPv6, [RFC2711] states that "the supported by implementations. For IPv6, [RFC2711] states that "the
value field can be used by an implementation to speed processing of value field can be used by an implementation to speed processing of
the datagram within the transit router" and defines an IANA registry the datagram within the transit router" and defines an IANA registry
for these values. But again, this only allows coarse-grain 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 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 among IP Router Alert packet of interest from
unwanted IP Router Alert packet, a IP Router Alert attack could still unwanted IP Router Alert packet, a IP Router Alert attack could still
severely degrade operation of protocols of interest that depend on severely degrade operation of protocols of interest that depend on
the use of IP Router Alert. 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 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, the resulting DoS attack vector is similar, or
somewhat less serious, with BGP peering than with Router Alert option somewhat less serious, with BGP peering than with Router Alert Option
for a number of reasons that include: for a number of reasons that include:
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 source. However, we note
that effectiveness of such BGP filtering is dependent on proper that effectiveness of such BGP filtering is dependent on proper
security practices; poor BGP security practices (such as security practices; poor BGP security practices (such as
infrequent or inexistent update of BGP peers authentication keys) infrequent or inexistent update of BGP peers authentication keys)
create vulnerabilities through which the BGP authentication 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 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
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note that there has been real life occurrences of situations where note that there has been real life occurrences of situations where
incorrect information was propagated through the BGP system, incorrect information was propagated through the BGP system,
causing quite widespread problems. causing quite 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 need to 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 is no convenient universal mechanisms to triage between
desired and undesired router alert packets, network operators 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, it is RECOMMENDED that applications and protocols not be Thus, applications and protocols SHOULD NOT be deployed with a
deployed with a dependency on processing of the Router Alert option dependency on processing of the Router Alert Option (as currently
(as currently specified) across independent administrative domains in specified) across independent administrative domains in the Internet.
the Internet. Figure 1 illustrates such a hypothetical use of Router Figure 1 illustrates such a hypothetical use of Router Alert end-to-
Alert end-to-end in the Internet. We refer to such a model of Router end in the Internet. We refer to such a model of Router Alert Option
Alert option use as a "Peer Model" Router Alert option use, since use as a "Peer Model" Router Alert Option use, since core routers in
core routers in different administrative domains would partake in different administrative domains would partake in processing of
processing of Router Alert option datagrams associated with the same Router Alert Option datagrams associated with the same signalling
signalling 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 (Router
Alert in Peer Model) 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. Whether this control
plane access is provided through router alert option or would be plane access is provided through router alert option or would be
skipping to change at page 10, line 40 skipping to change at page 10, line 40
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
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
skipping to change at page 11, line 27 skipping to change at page 11, line 27
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 is removed in
the trusted area (or greatly reduced) even if IP Router Alert is used the trusted area (or greatly reduced) even if IP Router Alert is used
inside the trusted area (say for RSVP-TE). Thus an application inside the trusted area (say for RSVP-TE). Thus an application
relying on IP Router Alert MAY be safely deployed within the trusted relying on IP Router Alert MAY be safely deployed within the trusted
area. A Service Provider running RSVP-TE within his network might be area. A Service Provider running RSVP-TE within his network might be
an example of such protected environment. Such an environment is an example of such protected environment. Such an environment is
illustrated in Figure 3. 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
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 when they transit over the
transit network (for example using mechanisms discussed in transit network (for example using mechanisms discussed in
[RFC6178]) [RFC6178])
In such controlled environment, an application relying on exchange In such 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) MAY be safely deployed. We refer to such a not inside network B) MAY 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 A
on top of, and completely transparently to, network B. "Water-Tight" on top of, and completely transparently to, network B. "Water-Tight"
because router alert option datagrams from A cannot leak inside because router alert option datagrams from A cannot leak inside
network B. A private enterprise intranet, whose sites are network B. A private enterprise intranet realised as a Virtual
interconnected through a Service Prover network, and using RSVP to Private Network (VPN) over a Service Provider network, and using RSVP
perform reservations within the enterprise sites for voice and video to perform reservations within the enterprise sites for voice and
flows might be an example of such controlled environment. Such an video flows might be an example of such controlled environment. Such
environment is illustrated in Figure 4. 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) MAY also be safely service provider network B (but not in network A) MAY 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.
skipping to change at page 14, line 21 skipping to change at page 14, line 21
-------- -------- -------- --------
\ / \ /
\ ------------------------- / \ ------------------------- /
\ / 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 protect these edge routers against RAO based attacks
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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 when they transit
over the transit network (for example using mechanisms discussed over the transit network (for example using mechanisms discussed
in [RFC6178]) in [RFC6178])
In such controlled environment, an application relying on exchange In such 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) MAY be safely in network B Edges (but not in the core of network B) MAY 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 core. "Leak-Controlled" because router
alert option datagrams from A leak inside network B's B edges but not alert option datagrams from A leak inside network B's B edges but not
inside network B's core. A private enterprise intranet, whose sites inside network B's core. A private enterprise intranet, whose sites
are interconnected through a Service Prover network, using RSVP for are interconnected through a Service Prover network, using RSVP for
voice and video within network A sites as well as on Network B's edge voice and video within network A sites as well as on Network B's edge
to extend the reservation onto the attachment links between A and B to extend the reservation onto the attachment links between A and B
(as specified in [RFC6016]) might be an example of such controlled (as specified in [RFC6016]) might be an example of such controlled
environment. Such an environment is illustrated in Figure 4. environment. Such an environment is illustrated in Figure 4.
skipping to change at page 15, line 24 skipping to change at page 15, line 24
| | ------------------------ | | | | ------------------------ | |
| (*) | /(*) (*) \ | (*) | | (*) | /(*) (*) \ | (*) |
| | |<======>| |<============>| |<=========>| | | | | |<======>| |<============>| |<=========>| | |
| - | | - - | | - | | - | | - - | | - |
\ / | \ - - / | \ / \ / | \ - - / | \ /
-------- | 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, it is RECOMMENDED that a Service Provider control plane. Thus, it is RECOMMENDED that a Service Provider
implements strong protection of his network against attacks based on implements strong protection of his network against attacks based on
IP Router Alert. 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, it is RECOMMENDED that a Service Provider protects Provider). Thus, it is RECOMMENDED that a Service Provider protects
his network from attacks based on IP Router Alert using mechanisms his network from attacks based on IP Router Alert using mechanisms
that avoid (or at least minimize) dropping of end to end IP Router that avoid (or at least minimize) dropping of end to end IP Router
skipping to change at page 16, line 20 skipping to change at page 16, line 20
operation of a protocol depending on IP Router Alert within his operation of a protocol depending on IP Router Alert within his
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 his network since this allows refresh of
existing Path and Resv states without use of the IP Router Alert existing Path and Resv states without 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 his 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 an non-MPLS IP backbone presents a number of issues (and 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 SP does not have any means to safely
transport end to end IP Router Alert option packets over his network, transport end to end IP Router Alert Option packets over his network,
the SP MAY drop those packets. It must be noted that this has the the SP MAY drop those packets. It must be noted that this has the
undesirable consequence of preventing the use of the Router Alert undesirable consequence of preventing the use of the Router Alert
option in the Overlay Model on top of this network, and therefore Option in the Overlay Model on top of this network, and therefore
prevents users of that network from deploying a number of valid prevents users of that network from deploying a number of valid
applications/protocols in their environment. applications/protocols in their environment.
5. Guidelines for Router Alert Implementation 5. Guidelines for Router Alert Implementation
It is RECOMMENDED that router implementations of IP Router Alert It is RECOMMENDED that router implementations of IP Router Alert
option include protection mechanisms against Router Alert based DOS Option include protection mechanisms against Router Alert based DoS
attacks appropriate for their targeted deployment environments. For attacks appropriate for their targeted deployment environments. For
example, this can include ability on an edge router to "tunnel" IP example, this can include ability on an edge router to "tunnel" IP
Router Alert option of received packets when forwarding those over Router Alert Option of received packets when forwarding those over
the core as discussed in [RFC6178]. As another example, although not the core as discussed in [RFC6178]. As another example, although not
always available from current implementations, new implementations always available from current implementations, new implementations
MAY include protection mechanisms such as selective (possibly MAY include protection mechanisms such as selective (possibly
dynamic) filtering and rate-limiting of IP Router Alert option dynamic) filtering and rate-limiting of IP Router Alert Option
packets. packets.
In particular, it is RECOMMENDED that router implementations of IP In particular, it is RECOMMENDED that router implementations of IP
Router Alert option offer the configuration option simply to ignore Router Alert Option offer the configuration option simply to ignore
the presence of "IP Router Alert" in IPv4 and IPv6 packets. As the presence of "IP Router Alert" in IPv4 and IPv6 packets. As
discussed in Section 4.3, that permits IP Router Alert packets to discussed in Section 4.3, that permits IP Router Alert packets to
transit a network segment without presenting an adverse operational transit a network segment without presenting an adverse operational
security risk to that particular network segment, provided the security risk to that particular network segment, provided the
operator of that network segment does not ever use the IP Router operator of that network segment does not ever use the IP Router
Alert messages for any purpose. Alert messages 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 application).
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
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 discusses security risks associated with current usage
of the IP Router Alert Option and associated practices. of the IP Router Alert Option and associated practices.
7. IANA Considerations 7. IANA Considerations
skipping to change at page 20, line 27 skipping to change at page 20, line 27
* Juniper Networks * Juniper Networks
* dward@juniper.net * dward@juniper.net
o Ashok Narayanan: o Ashok Narayanan:
* Cisco Systems * Cisco Systems
* ashokn@cisco.com * ashokn@cisco.com
o Adrian Farrell: o Adrian Farrel:
* OldDog Consulting * OldDog Consulting
* adrian@olddog.co.uk * adrian@olddog.co.uk
o Tony Li: o Tony Li:
* tony.li@tony.li * tony.li@tony.li
9. Acknowledgments 9. Acknowledgments
skipping to change at page 23, line 32 skipping to change at page 23, line 32
[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.
[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-
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,
March 2011. March 2011.
 End of changes. 55 change blocks. 
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