draft-ietf-intarea-router-alert-considerations-05.txt   draft-ietf-intarea-router-alert-considerations-06.txt 
Network Working Group F. Le Faucheur, Ed. Network Working Group F. Le Faucheur, Ed.
Internet-Draft Cisco Internet-Draft Cisco
Intended status: BCP June 27, 2011 Intended status: BCP July 5, 2011
Expires: December 29, 2011 Expires: January 6, 2012
IP Router Alert Considerations and Usage IP Router Alert Considerations and Usage
draft-ietf-intarea-router-alert-considerations-05 draft-ietf-intarea-router-alert-considerations-06
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
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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 December 29, 2011. This Internet-Draft will expire on January 6, 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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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, assuming the router punts the undesirable ways. For example, if the router punts the datagrams
datagrams containing the IP Router Alert option to the slow path, containing the IP Router Alert option to the slow path, such an
such an attack could consume a significant share of the router's slow attack could consume a significant share of the router's slow path
path and could also lead to packet drops in the slow path (thus, and could also lead to packet drops in the slow path (thus, affecting
affecting operation of all other applications and protocols operating operation of all other applications and protocols operating in the
in the slow path). slow path).
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). Alert packets). However, some existing deployed IP routers can and
do process IP packets containing the Router Alert option inside the
Fast Path.
Some IP Router Alert implementations may be 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
levels of RSVP aggregation [RFC3175]). Thus, it is not possible to levels of RSVP aggregation [RFC3175]). Thus, it is not always
achieve the necessary triage in the fast path across IP Router Alert possible to achieve the necessary triage in the fast path across IP
packets from different applications or from different contexts of an Router Alert packets from different applications or from different
application. Secondly, some protocols requiring punting may be contexts of an application. Secondly, some protocols requiring
carried over a transport protocol (e.g., TCP or UDP) possibly because punting might be carried over a transport protocol (e.g., TCP or UDP)
they require the services of that transport protocol, possibly possibly because they require the services of that transport
because the protocol does not justify allocation of a scarce next protocol, possibly because the protocol does not justify allocation
level protocol value or possibly because not relying on a very widely of a scarce next level protocol value or possibly because not relying
deployed transport protocol is likely to result in deployment issues on a very widely deployed transport protocol is likely to result in
due to common middlebox behaviors (e.g. Firewalls or NATs discarding deployment issues due to common middlebox behaviors (e.g. Firewalls
packets of "unknown" protocols). Thus, considering the next level or NATs discarding packets of "unknown" protocols). Thus,
protocol does not allow triage in the fast path of IP Router Alert considering the next level protocol alone in the fast path is not
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 fast path).
Some IP Router Alert implementations may be 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 implementation 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, ([RFC5350]) but this would only allow coarse-grain classification, if
when, and if, supported by implementations. For IPv6, [RFC2711] supported by implementations. For IPv6, [RFC2711] states that "the
states that "the value field can be used by an implementation to value field can be used by an implementation to speed processing of
speed processing of the datagram within the transit router" and the datagram within the transit router" and defines an IANA registry
defines an IANA registry for these values. But again, this only for these values. But again, this only allows coarse-grain
allows coarse-grain classification. Besides, some existing IPv6 classification. Besides, some existing IPv6 Router Alert
Router Alert implementations are reported to depart from that implementations are reported to depart from that behavior.
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
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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 need to 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 may 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 may 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, it is RECOMMENDED that applications and protocols not be
deployed with a dependency on processing of the Router Alert option deployed with a dependency on processing of the Router Alert option
(as currently specified) across independent administrative domains in (as currently specified) across independent administrative domains in
the Internet. Figure 1 illustrates such a hypothetical use of Router the Internet. 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 end-to-end in the Internet. We refer to such a model of Router
Alert option use as a "Peer Model" Router Alert option use, since Alert option use as a "Peer Model" Router Alert option use, since
core routers in different administrative domains would partake in core routers in different administrative domains would partake in
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want to have their core routers partake in end-to-end signalling with want to have their core routers partake in end-to-end signalling 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 signalling in a Peer model
through their network (regardless of whether that signalling uses through their network (regardless of whether that signalling 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 Administrative In some controlled environments, such as within a given
Domain, the network administrator can determine that IP Router Alert Administrative Domain, the network administrator can determine that
packets will only be received from trusted well-behaved devices or IP Router Alert packets will only be received from trusted well-
can establish that specific protection mechanisms (e.g., RAO behaved devices or can establish that specific protection mechanisms
filtering and rate-limiting) against the plausible RAO-based DoS (e.g., RAO filtering and rate-limiting) against the plausible RAO-
attacks are sufficient. In that case, an application relying on based DoS attacks are sufficient. In that case, an application
exchange and handling of RAO packets (e.g., RSVP) MAY be safely relying on exchange and handling of RAO packets (e.g., RSVP) MAY be
deployed within the controlled network. A private enterprise network safely deployed within the controlled network. A private enterprise
firewalled from the Internet and using RSVP reservations for voice network firewalled from the Internet and using RSVP reservations for
and video flows may be an example of such controlled environment. voice and video flows might be an example of such controlled
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
skipping to change at page 11, line 14 skipping to change at page 11, line 14
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) MAY be safely deployed within such a RAO packets (e.g., RSVP) MAY 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 may be an example of such responsible for operating the network might be an example of such
controlled environment. For example, they may 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 may be achieved by ensuring the internal routers). For example, this might be achieved by
that routers straddling the trust boundary (e.g., edge routers) ensuring that routers straddling the trust boundary (e.g., edge
always encapsulate those packets (without setting IP Router Alert -or routers) always encapsulate those packets (without setting IP Router
equivalent- in the encapsulating header) through the trusted area (as Alert -or equivalent- in the encapsulating header) through the
discussed in [RFC6178]). In such environments, the risks of DOS trusted area (as discussed in [RFC6178]). In such environments, the
attacks through the IP Router Alert vector is removed in the trusted risks of DOS attacks through the IP Router Alert vector is removed in
area (or greatly reduced) even if IP Router Alert is used inside the the trusted area (or greatly reduced) even if IP Router Alert is used
trusted area (say for RSVP-TE). Thus an application relying on IP inside the trusted area (say for RSVP-TE). Thus an application
Router Alert MAY be safely deployed within the trusted area. A relying on IP Router Alert MAY be safely deployed within the trusted
Service Provider running RSVP-TE within his network may be an example area. A Service Provider running RSVP-TE within his network might be
of such protected environment. Such an environment is illustrated in an example of such protected environment. Such an environment is
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
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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, whose sites are
interconnected through a Service Prover network, and using RSVP to interconnected through a Service Prover network, and using RSVP to
perform reservations within the enterprise sites for voice and video perform reservations within the enterprise sites for voice and video
flows may be an example of such controlled environment. Such an flows might be an example of such controlled environment. Such an
environment is illustrated in Figure 4. environment is illustrated in Figure 4.
-------- -------- -------- --------
/ A \ / A \ / A \ / A \
| (*) | | (*) | | (*) | | (*) |
| | |<=================================>| | | | | | |<=====================================>| | |
| - | | - | | - | | - |
\ / \ / \ / \ /
-------- -------- -------- --------
\ / \ /
\ ------------------------- / \ ------------------------- /
\ / B \ / \ / B \ /
\| |/ \| |/
TT TT TT TT
| | | |
\ / \ /
------------------------- -------------------------
skipping to change at page 14, line 7 skipping to change at page 14, line 7
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.
-------- -------- -------- --------
/ A \ / A \ / A \ / A \
| (*) | | (*) | | (*) | | (*) |
| | |<=================================>| | | | | | |<=====================================>| | |
| - | | - | | - | | - |
\ / \ / \ / \ /
-------- -------- -------- --------
\ / \ /
\ ------------------------- / \ ------------------------- /
\ / B \ / \ / B \ /
\| (*) (*) |/ \| (*) (*) |/
TT | |<============>| | TT TT | |<============>| | TT
| - - | | - - |
\ / \ /
------------------------- -------------------------
skipping to change at page 15, line 8 skipping to change at page 15, line 8
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]) may 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.
-------- -------- -------- --------
/ 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
skipping to change at page 15, line 49 skipping to change at page 15, line 49
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
Alert packets (other than those involved in an attack). Alert packets (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 may elect to depending on IP Router Alert within his network, he might elect to
simply turn-off punting/processing of IP Router Alert packet on his simply turn-off punting/processing of IP Router Alert packet on his
routers; this will ensure that end-to-end IP Router Alert packet routers; this will ensure that end-to-end IP Router Alert packet
transit transparently and safely through his network. transit transparently and safely through his network.
As another example, using protection mechanisms such selective As another example, using protection mechanisms such selective
filtering and rate-limiting (that Section 5 suggests be supported by filtering and rate-limiting (that 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 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 may be used end to end. Alert packets carrying another protocol that might be used end to
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 may be used end to end (e.g., packets carrying another protocol that might be used end to end
IPv4/IPv6 RSVP). We observe that while tunneling of Router Alert (e.g., IPv4/IPv6 RSVP). We observe that while tunneling of Router
option datagrams over an MPLS backbone as discussed in [RFC6178] is Alert option datagrams over an MPLS backbone as discussed in
well understood, tunneling Router Alert option datagrams over an non- [RFC6178] is well understood, tunneling Router Alert option datagrams
MPLS IP backbone presents a number of issues (and in particular for over an non-MPLS IP backbone presents a number of issues (and in
determining where to forward the encapsulated datagram) and is not particular for determining where to forward the encapsulated
common practice at the time of writing this document. datagram) and is not common practice at the time of writing this
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
skipping to change at page 17, line 18 skipping to change at page 17, line 18
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
Router Alert option offer the configuration option simply to ignore
the presence of "IP Router Alert" in IPv4 and IPv6 packets. As
discussed in Section 4.3, that permits IP Router Alert packets to
transit a network segment without presenting an adverse operational
security risk to that particular network segment, provided the
operator of that network segment does not ever use the IP Router
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
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* 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
We would like to thank Dave Oran, Magnus Westerlund, John Scudder, We would like to thank Dave Oran, Magnus Westerlund, John Scudder,
Ron Bonica, Ross Callon, Alfred Hines, Carlos Pignataro and Roland Ron Bonica, Ross Callon, Alfred Hines, Carlos Pignataro, Roland
Bless for their comments. This document also benefited from Bless, Jari Arkko and Ran Atkinson for their comments. This document
discussions with Jukka Manner and Suresh Krishnan. The discussion also benefited from discussions with Jukka Manner and Suresh
about use of the value field in the IPv4 Router Alert borrowed from a Krishnan. The discussion about use of the value field in the IPv4
similar discussion in [RFC5971]. Router Alert borrowed from a similar discussion in [RFC5971].
10. References 10. References
10.1. Normative References 10.1. 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.
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