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Versions: (RFC 3682) 00 01 02 03 04 05 06 07
08 09 10 RFC 5082
Routing WG V. Gill
Internet-Draft J. Heasley
Obsoletes: 3682 (if approved) D. Meyer
Intended status: Standards Track P. Savola, Ed.
Expires: June 16, 2007 C. Pignataro
December 13, 2006
The Generalized TTL Security Mechanism (GTSM)
draft-ietf-rtgwg-rfc3682bis-08.txt
Status of this Memo
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Copyright Notice
Copyright (C) The IETF Trust (2006).
Abstract
The use of a packet's Time to Live (TTL) (IPv4) or Hop Limit (IPv6)
to verify whether the packet was originated by an adjacent node on a
connected link has been used in many recent protocols. This document
generalizes this technique. This document obsoletes RFC 3682.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Assumptions Underlying GTSM . . . . . . . . . . . . . . . . . 3
2.1. GTSM Negotiation . . . . . . . . . . . . . . . . . . . . . 4
2.2. Assumptions on Attack Sophistication . . . . . . . . . . . 4
3. GTSM Procedure . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 7
5.1. TTL (Hop Limit) Spoofing . . . . . . . . . . . . . . . . . 7
5.2. Tunneled Packets . . . . . . . . . . . . . . . . . . . . . 7
5.2.1. IP Tunneled over IP . . . . . . . . . . . . . . . . . 8
5.2.2. IP Tunneled over MPLS . . . . . . . . . . . . . . . . 9
5.3. Onlink Attackers . . . . . . . . . . . . . . . . . . . . . 11
5.4. Fragmentation Considerations . . . . . . . . . . . . . . . 11
5.5. Multi-Hop Protocol Sessions . . . . . . . . . . . . . . . 12
6. Applicability Statement . . . . . . . . . . . . . . . . . . . 12
6.1. Backwards Compatibility . . . . . . . . . . . . . . . . . 12
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
8.1. Normative References . . . . . . . . . . . . . . . . . . . 13
8.2. Informative References . . . . . . . . . . . . . . . . . . 14
Appendix A. Multi-hop GTSM . . . . . . . . . . . . . . . . . . . 14
Appendix B. Changes Since RFC3682 . . . . . . . . . . . . . . . 14
Appendix C. Draft Changelog . . . . . . . . . . . . . . . . . . 14
Appendix C.1. Changes between -07 and -08 . . . . . . . . . . . . 15
Appendix C.2. Changes between -06 and -07 . . . . . . . . . . . . 15
Appendix C.3. Changes between -05 and -06 . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16
Intellectual Property and Copyright Statements . . . . . . . . . . 17
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1. Introduction
The Generalized TTL Security Mechanism (GTSM) is designed to protect
a router's IP based control plane from CPU-utilization based attacks.
In particular, while cryptographic techniques can protect the router-
based infrastructure (e.g., BGP [RFC4271], [RFC4272]) from a wide
variety of attacks, many attacks based on CPU overload can be
prevented by the simple mechanism described in this document. Note
that the same technique protects against other scarce-resource
attacks involving a router's CPU, such as attacks against processor-
line card bandwidth.
GTSM is based on the fact that the vast majority of protocol peerings
are established between routers that are adjacent. Thus most
protocol peerings are either directly between connected interfaces or
at the worst case, are between loopback and loopback, with static
routes to loopbacks. Since TTL spoofing is considered nearly
impossible, a mechanism based on an expected TTL value can provide a
simple and reasonably robust defense from infrastructure attacks
based on forged protocol packets from outside the network. Note,
however, that GTSM is not a substitute for authentication mechanisms.
In particular, it does not secure against insider on-the-wire
attacks, such as packet spoofing or replay.
Finally, the GTSM mechanism is equally applicable to both TTL (IPv4)
and Hop Limit (IPv6), and from the perspective of GTSM, TTL and Hop
Limit have identical semantics. As a result, in the remainder of
this document the term "TTL" is used to refer to both TTL or Hop
Limit (as appropriate).
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 RFC 2119 [RFC2119].
2. Assumptions Underlying GTSM
GTSM is predicated upon the following assumptions:
1. The vast majority of protocol peerings are between adjacent
routers.
2. Service providers may or may not configure strict ingress
filtering [RFC3704] on non-trusted links. If maximal protection
is desired, such filtering is necessary as described in
Section 2.2.
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3. Use of GTSM is OPTIONAL, and can be configured on a per-peer
(group) basis.
4. The peer routers both implement GTSM.
5. The router supports a method to use separate resource pools
(e.g., queues, processing quotas) for differently classified
traffic.
Note that this document does not prescribe further restrictions that
a router may apply to the packets not matching the GTSM filtering
rules, such as dropping packets that do not match any configured
protocol session and rate-limiting the rest. This document also does
not suggest the actual means of resource separation, as those are
hardware and implementation-specific.
The possibility of denial-of-service (DoS) attack prevention,
however, is based on the assumption that packet classification and
separation of their paths is done before they go through a scarce
resource in the system. In practice, this means that, the closer
GTSM processing is done to the line-rate hardware, the more resistant
the system is to the DoS attacks.
2.1. GTSM Negotiation
This document assumes that, when used with existing protocols, GTSM
will be manually configured between protocol peers. That is, no
automatic GTSM capability negotiation, such as is provided by RFC
3392 [RFC3392] is assumed or defined.
If a new protocol is designed with built-in GTSM support, then it is
recommended that procedures are always used for sending and
validating received protocol packets (GTSM is always on, see for
example [RFC2461]). If, however, dynamic negotiation of GTSM support
is necessary, protocol messages used for such negotiation MUST be
authenticated using other security mechanisms to prevent DoS attacks.
Also note that this specification does not offer a generic GTSM
capability negotiation mechanism, so messages of the protocol
augmented with the GTSM behavior will need to be used if dynamic
negotiation is deemed necessary.
2.2. Assumptions on Attack Sophistication
Throughout this document, we assume that potential attackers have
evolved in both sophistication and access to the point that they can
send control traffic to a protocol session, and that this traffic
appears to be valid control traffic (i.e., has the source/destination
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of configured peer routers).
We also assume that each router in the path between the attacker and
the victim protocol speaker decrements TTL properly (clearly, if
either the path or the adjacent peer is compromised, then there are
worse problems to worry about).
For maximal protection, ingress filtering should be applied before
the packet goes through the scarce resource. Otherwise an attacker
directly connected to one interface could disturb a GTSM-protected
session on the same or another interface. Interfaces which aren't
configured with this filtering (e.g., backbone links) are assumed to
not have such attackers (i.e., trusted).
As a specific instance of such interfaces, we assume that tunnels are
not a back-door for allowing TTL-spoofing on protocol packets for a
GTSM-protected peering session with a directly connected neighbor.
We assume that: 1) there are no tunneled packets terminating on the
router, 2) tunnels terminating on the router are assumed to be secure
and endpoints are trusted, 3) tunnel decapsulation includes source
address spoofing prevention [RFC3704], or 4) the GTSM-enabled session
does not allow protocol packets coming from a tunnel.
Since the vast majority of peerings are between adjacent routers, we
can set the TTL on the protocol packets to 255 (the maximum possible
for IP) and then reject any protocol packets that come in from
configured peers which do NOT have an inbound TTL of 255.
GTSM can be disabled for applications such as route-servers and other
multi-hop peerings. In the event that an attack comes in from a
compromised multi-hop peering, that peering can be shut down.
3. GTSM Procedure
If GTSM is not built into the protocol and used as an additional
feature (e.g., for BGP, LDP, or MSDP), it SHOULD NOT be enabled by
default in order to be backward-compatible with the unmodified
protocol.
If GTSM is enabled for a protocol session, the following steps are
added to the IP packet sending and reception procedures:
Sending protocol packets:
The TTL field in all IP packets used for transmission of
messages associated with GTSM-enabled protocol sessions MUST be
set to 255. This also applies to related error handling
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messages associated with said session, such as TCP RSTs or ICMP
errors.
On some architectures, the TTL of control plane originated
traffic is under some configurations decremented in the
forwarding plane. The TTL of GTSM-enabled sessions MUST NOT be
decremented.
Receiving protocol packets:
The GTSM packet identification step associates each received
packet addressed to the router's control plane with one of the
following three trustworthiness categories:
+ Unknown: these are packets that cannot be associated with
any registered GTSM-enabled session, and hence GTSM cannot
make any judgement on the level of risk associated with
them.
+ Trusted: these are packets that have been identified as
belonging to one of the GTSM-enabled sessions, and their TTL
values are within the expected range.
+ Dangerous: these are packets that have been identified as
belonging to one of the GTSM-enabled sessions, but their TTL
values are NOT within the expected range, and hence GTSM
believes there is a risk that the packets have been spoofed.
The exact policies applied to packets of different
classifications are not postulated in this document and are
expected to be configurable. Configurability is likely
necessary particular with the treatment of related messages
such as ICMP errors and TCP RSTs. It should be noted that
fragmentation may restrict the amount of information available
to the classification.
However, by default, the implementations:
+ SHOULD ensure that packets classified as Dangerous do not
compete for resources with packets classified as Trusted or
Unknown.
+ MUST NOT drop (as part of GTSM processing) packets
classified as Trusted or Unknown.
+ MAY drop packets classified as Dangerous.
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4. Acknowledgments
The use of the TTL field to protect BGP originated with many
different people, including Paul Traina and Jon Stewart. Ryan
McDowell also suggested a similar idea. Steve Bellovin, Jay
Borkenhagen, Randy Bush, Alfred Hoenes, Vern Paxon, Robert Raszuk and
Alex Zinin also provided useful feedback on earlier versions of this
document. David Ward provided insight on the generalization of the
original BGP-specific idea. Alex Zinin, Alia Atlas, and John Scudder
provided significant amount of feedback for the newer versions of the
document.
5. Security Considerations
GTSM is a simple procedure that protects single hop protocol
sessions, except in those cases in which the peer has been
compromised. In particular, it does not protect against the wide
range of on-the-wire attacks; protection from these attacks requires
more rigorous security mechanisms.
5.1. TTL (Hop Limit) Spoofing
The approach described here is based on the observation that a TTL
(or Hop Limit) value of 255 is non-trivial to spoof, since as the
packet passes through routers towards the destination, the TTL is
decremented by one per router. As a result, when a router receives a
packet, it may not be able to determine if the packet's IP address is
valid, but it can determine how many router hops away it is (again,
assuming none of the routers in the path are compromised in such a
way that they would reset the packet's TTL).
Note, however, that while engineering a packet's TTL such that it has
a particular value when sourced from an arbitrary location is
difficult (but not impossible), engineering a TTL value of 255 from
non-directly connected locations is not possible (again, assuming
none of the directly connected neighbors are compromised, the packet
hasn't been tunneled to the decapsulator, and the intervening routers
are operating in accordance with RFC 791 [RFC0791]).
5.2. Tunneled Packets
The security of any tunneling technique depends heavily on
authentication at the tunnel endpoints, as well as how the tunneled
packets are protected in flight. Such mechanisms are, however,
beyond the scope of this memo.
An exception to the observation that a packet with TTL of 255 is
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difficult to spoof may occur when a protocol packet is tunneled and
the tunnel is not integrity-protected (i.e., the lower layer is
compromised).
When the protocol packet is tunneled directly to the protocol peer
(the protocol peer is the decapsulator), the GTSM provides some
limited added protection as the security depends entirely on the
integrity of the tunnel.
For protocol adjacencies over a tunnel, if the tunnel itself is
deemed secure (e.g., the underlying infrastructure is deemed secure,
and the tunnel offers degrees of protection against spoofing such as
keys or cryptographic security), the GTSM can serve as a check that
the protocol packet did not originate beyond the head-end of the
tunnel. In addition, if the protocol peer can receive packets for
the GTSM-protected protocol session from outside the tunnel, the GTSM
can help thwart attacks from beyond the adjacent router.
When the tunnel tail-end decapsulates the protocol packet and then
IP-forwards the packet to a directly connected protocol peer, TTL is
decremented as described below. This means that the tunnel
decapsulator is the penultimate node from the GTSM-protected protocol
peer's perspective. As a result, the GTSM check protects from
attackers encapsulating packets to your peers. However, specific
cases arise when the connection from the tunnel decapsulator node to
the protocol peer is not an IP forwarding hop, where TTL-decrementing
does not happen (e.g., layer-2 tunneling, bridging, etc). In the
IPsec architecture [RFC4301], another example is the use of Bump-in-
the-Wire (BITW) [BITW].
5.2.1. IP Tunneled over IP
Protocol packets may be tunneled over IP directly to a protocol peer,
or to a decapsulator (tunnel endpoint) that then forwards the packet
to a directly connected protocol peer. Examples of tunneling IP over
IP include IP-in-IP [RFC2003], GRE [RFC2784], or various forms of
IPv6-in-IPv4 (e.g., [RFC4213]). These cases are depicted below.
Peer router ---------- Tunnel endpoint router and peer
TTL=255 [tunnel] [TTL=255 at ingress]
[TTL=255 at processing]
Peer router -------- Tunnel endpoint router ----- On-link peer
TTL=255 [tunnel] [TTL=255 at ingress] [TTL=254 at ingress]
[TTL=254 at egress]
In both cases, the encapsulator (origination tunnel endpoint) is the
(supposed) sending protocol peer. The TTL in the inner IP datagram
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can be set to 255, since RFC 2003 specifies the following behavior:
When encapsulating a datagram, the TTL in the inner IP
header is decremented by one if the tunneling is being
done as part of forwarding the datagram; otherwise, the
inner header TTL is not changed during encapsulation.
In the first case, the encapsulated packet is tunneled directly to
the protocol peer (also a tunnel endpoint), and therefore the
encapsulated packet's TTL can be received by the protocol peer with
an arbitrary value, including 255.
In the second case, the encapsulated packet is tunneled to a
decapsulator (tunnel endpoint) which then forwards it to a directly
connected protocol peer. For IP-in-IP tunnels, RFC 2003 specifies
the following decapsulator behaviour:
The TTL in the inner IP header is not changed when decapsulating.
If, after decapsulation, the inner datagram has TTL = 0, the
decapsulator MUST discard the datagram. If, after decapsulation,
the decapsulator forwards the datagram to one of its network
interfaces, it will decrement the TTL as a result of doing normal
IP forwarding. See also Section 4.4.
And similarly, for GRE tunnels, RFC 2784 specifies the following
decapsulator behaviour:
When a tunnel endpoint decapsulates a GRE packet which has an IPv4
packet as the payload, the destination address in the IPv4 payload
packet header MUST be used to forward the packet and the TTL of
the payload packet MUST be decremented.
Hence the inner IP packet header's TTL, as seen by the decapsulator,
can be set to an arbitrary value (in particular, 255). If the
decapsulator is also the protocol peer, it is possible to deliver the
protocol packet to it with a TTL of 255 (first case). On the other
hand, if the decapsulator needs to forward the protocol packet to a
directly connected protocol peer, the TTL will be decremented (second
case).
5.2.2. IP Tunneled over MPLS
Protocol packets may also be tunneled over MPLS Label Switched Paths
(LSPs) to a protocol peer. The following diagram depicts the
topology.
Peer router -------- LSP Termination router and peer
TTL=255 MPLS LSP [TTL=x at ingress]
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MPLS LSPs can operate in Uniform or Pipe tunneling models. The TTL
handling for these models is described in RFC 3443 [RFC3443] that
updates RFC 3032 [RFC3032] in regards to TTL processing in MPLS
networks. RFC 3443 specifies the TTL processing in both Uniform and
Pipe Models, which in turn can used with or without penultimate hop
popping (PHP). The TTL processing in these cases results in
different behaviors, and therefore are analyzed separately. Please
refer to Section 3.1 through Section 3.3 of RFC 3443.
The main difference from a TTL processing perspective between Uniform
and Pipe Models at the LSP termination node resides in how the
incoming TTL (iTTL) is determined. The tunneling model determines
the iTTL: For Uniform Model LSPs, the iTTL is the value of the TTL
field from the popped MPLS header (encapsulating header), whereas for
Pipe Model LSPs, the iTTL is the value of the TTL field from the
exposed header (encapsulated header).
For Uniform Model LSPs, RFC 3443 states that at ingress:
For each pushed Uniform Model label, the TTL is copied from the
label/IP-packet immediately underneath it.
From this point, the inner TTL (TTL of the tunneled IP datagram)
represents non-meaningful information, and at the egress node or
during PHP, the ingress TTL (iTTL) is equal to the TTL of the popped
MPLS header (see Section 3.1 of RFC 3443). In consequence, for
Uniform Model LSPs of more than one hop, the TTL at ingress (iTTL)
will be less than 255 (x <= 254), and as a result the check described
in Section 3 of this document will fail.
The TTL treatment is identical between Short Pipe Model LSPs without
PHP and Pipe Model LSPs (without PHP only). For these cases, RFC
3443 states that:
For each pushed Pipe Model or Short Pipe Model label, the TTL
field is set to a value configured by the network operator. In
most implementations, this value is set to 255 by default.
In these models, the forwarding treatment at egress is based on the
tunneled packet as opposed to the encapsulation packet. The ingress
TTL (iTTL) is the value of the TTL field of the header that is
exposed, that is the tunneled IP datagram's TTL. The protocol
packet's TTL as seen be the LSP termination can therefore be set to
an arbitrary value (including 255). If the LSP termination router is
also the protocol peer, it is possible to deliver the protocol packet
with a TTL of 255 (x = 255).
Finally, for Short Pipe Model LSPs with PHP, the TTL of the tunneled
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packet is unchanged after the PHP operation. Therefore, the same
conclusions drawn regarding the Short Pipe Model LSPs without PHP and
Pipe Model LSPs (without PHP only) apply to this case. For Short
Pipe Model LSPs, the TTL at egress has the same value with or without
PHP.
In conclusion, GTSM-checks are possible for IP tunneled over Pipe
model LSPs, but not for IP tunneled over Uniform model LSPs.
Additionally, for all tunneling modes, if the LSP termination router
needs to forward the protocol packet to a directly connected protocol
peer, it is not possible to deliver the protocol packet to the
protocol peer with a TTL of 255. If the packet is further forwarded,
the outgoing TTL (oTTL) is calculated by decrementing iTTL by one.
5.3. Onlink Attackers
As described in Section 2, an attacker directly connected to one
interface can disturb a GTSM-protected session on the same or another
interface (by spoofing a GTSM peer's address) unless ingress
filtering has been applied on the connecting interface. As a result,
interfaces which do not include such protection need to be trusted
not to originate attacks on the router.
5.4. Fragmentation Considerations
As already mentioned, fragmentation may restrict the amount of
information available for classification. Since non-initial IP
fragments do not contain Layer 4 information, it is highly likely
that they cannot be associated with a registered GTSM-enabled
session. Following the receiving protocol procedures described in
Section 3, non-initial IP fragments would likely be classified with
Unknown trustworthiness. And since the IP packet would need to be
reassembled in order to be processed, the end result is that the
initial-fragment of a GTSM-enabled session effectively receives the
treatment of an Unknown-trustworthiness packet, and the complete
reassembled packet receives the aggregate of the Unknowns.
Further, reassembly requires to wait for all the fragments and
therefore likely invalidates or weakens the fifth assumption
presented in Section 2: it may not be possible to classify non-
initial fragments before going through a scarce resource in the
system, when fragments need to be buffered for reassembly and later
processed by a CPU. That is, when classification cannot be done with
the required granularity, non-initial fragments of GTSM-enabled
session packets would not use different resource pools.
Consequently, to get practical protection from fragment attacks,
operators may need to rate-limit or discard all received fragments.
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As such, it is highly recommended for GTSM-protected protocols to
avoid fragmentation and reassembly by manual MTU tuning, using
adaptive measures such as Path MTU Discovery (PMTUD), or any other
available method.
5.5. Multi-Hop Protocol Sessions
GTSM could possibly offer some small though difficult to quantify
degree of protection when used with multi-hop protocol sessions (see
Appendix A). In order to avoid having to quantify the degree of
protection and the resulting applicability of multi-hop, we only
describe the single-hop because its security properties are clearer.
6. Applicability Statement
GTSM is only applicable to environments with inherently limited
topologies (and is most effective in those cases where protocol peers
are directly connected). In particular, its application should be
limited to those cases in which protocol peers are directly
connected.
Experimentation on GTSM's applicability and security properties is
needed in multi-hop scenarios. The multi-hop scenarios where GTSM
might be applicable is expected to have the following
characteristics: the topology between peers is fairly static and well
known, and in which the intervening network (between the peers) is
trusted.
6.1. Backwards Compatibility
RFC 3682 did not specify how to handle "related messages" such as TCP
RSTs or ICMP errors. This specification mandates setting and
verifying TTL=255 of those as well as the main protocol packets.
Setting TTL=255 in related messages does not cause issues for RFC
3682 implementations.
Requiring TTL=255 in related messages may have impact with RFC 3682
implementations, depending on which default TTL the implementation
uses for originated packets; some implementations are known to use
255, while 64 or other values are also used. Related messages from
the latter category of RFC 3682 implementations would be classified
as Dangerous and treated as described in Section 3. This is not
believed to be a significant problem because protocols do not depend
on related messages (e.g., typically having a protocol exchange for
closing the session instead of doing a TCP-RST), and indeed the
delivery of related messages is not reliable. As such, related
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messages typically provide an optimization to shorten a protocol
keepalive timeout. Regardless of these issues, given that related
messages provide a significant attack vector to e.g., reset protocol
sessions, making this further restriction seems sensible.
7. IANA Considerations
This document requires no action from IANA.
8. References
8.1. Normative References
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
September 1981.
[RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003,
October 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2461] Narten, T., Nordmark, E., and W. Simpson, "Neighbor
Discovery for IP Version 6 (IPv6)", RFC 2461,
December 1998.
[RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
March 2000.
[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, January 2001.
[RFC3392] Chandra, R. and J. Scudder, "Capabilities Advertisement
with BGP-4", RFC 3392, November 2002.
[RFC3443] Agarwal, P. and B. Akyol, "Time To Live (TTL) Processing
in Multi-Protocol Label Switching (MPLS) Networks",
RFC 3443, January 2003.
[RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms
for IPv6 Hosts and Routers", RFC 4213, October 2005.
[RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
Protocol 4 (BGP-4)", RFC 4271, January 2006.
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[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
8.2. Informative References
[BITW] "Thread: 'IP-in-IP, TTL decrementing when forwarding and
BITW' on int-area list, Message-ID:
<Pine.LNX.4.64.0606020830220.12705@netcore.fi>",
June 2006, <http://www1.ietf.org/mail-archive/web/
int-area/current/msg00267.html>.
[RFC3704] Baker, F. and P. Savola, "Ingress Filtering for Multihomed
Networks", BCP 84, RFC 3704, March 2004.
[RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis",
RFC 4272, January 2006.
Appendix A. Multi-hop GTSM
NOTE: This is a non-normative part of the specification.
The main applicability of GTSM is for directly connected peers. GTSM
could be used for non-directly connected sessions as well, where the
recipient would check that the TTL is within "TrustRadius" (e.g., 1)
of 255 instead of 255. As such deployment is expected to have a more
limited applicability and different security implications, it is not
specified in this document.
Appendix B. Changes Since RFC3682
o New text on GTSM applicability and use in new and existing
protocols.
o Explicitly require that related messages (e.g., TCP RSTs, ICMP
errors) must also be sent and checked to have TTL=255. See
Section 6.1 for discussion on backwards compatibility.
o Clarifications relating to security with tunneling.
o A significant number of editorial improvements and clarifications.
Appendix C. Draft Changelog
NOTE to the RFC-editor: please remove this section before
publication.
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Appendix C.1. Changes between -07 and -08
o Describe the assumption of ingress filtering to protect against
on-link attacks.
o Rewrite the IP over MPLS section based on the new MPLS TTL
handling procedure (from Carlos Pignataro) to get the details of
new MPLS architecture right.
o Rephrase IP over IP tunneling section a bit, to make distinction
between encapsulation and decapsulation behaviour clearer.
o Make it clearer in the tunneling section that unless the tunnel
peer is also the protocol peer, GTSM should be able to offer
protection.
o Describe better the applicability of GTSM when tunneling.
o Rephrase Multi-hop GTSM section to mainly refer to the difficult-
to-quantify security properties as a reason for exclusion at this
point.
o Some editorial updates.
Appendix C.2. Changes between -06 and -07
o Be more reserved about multi-hop security properties in section
'Multi-Hop Protocol Sessions'.
o Clarify IP-in-IP tunnel decapsulation/forwarding as decrementing
TTL.
o Add text on related messages backwards compatibility.
o Editorial updates.
Appendix C.3. Changes between -05 and -06
o Clarify the assumptions wrt. resource separation and protection
based on comments from Alex Zinin.
o Rewrite the GTSM procedure based on text from Alex Zinin.
o Reduce TrustRadius and multi-hop scenarios to a mention in an
Appendix.
o Describe TCP-RST, ICMP error and "related messages" handling.
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o Update the tunneling security considerations text.
o Editorial updates (e.g., shortening the abstract).
Authors' Addresses
Vijay Gill
Email: vijay@umbc.edu
John Heasley
Email: heas@shrubbery.net
David Meyer
Email: dmm@1-4-5.net
Pekka Savola (editor)
Espoo
Finland
Email: psavola@funet.fi
Carlos Pignataro
Email: cpignata@cisco.com
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