KARPRouting Working Group U. Chunduri
Internet-Draft A. Tian
Intended status: Informational W. Lu
Expires: August 9, 2014 March 12, 2015 Ericsson Inc.,
September 8, 2014
KARP IS-IS security analysis
This document analyzes the threats applicable for Intermediate system
to Intermediate system (IS-IS) routing protocol and security gaps
according to the KARP Design Guide. This document also provides
specific requirements to address the gaps with both manual and auto
key management protocols.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
1.2. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Current State . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Key Usage . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1.1. Sub network Independent . . . . . . . . . . . . . . . 4
2.1.2. Sub network dependent . . . . . . . . . . . . . . . . 4
2.2. Key Agility . . . . . . . . . . . . . . . . . . . . . . . 5
2.3. Security Issues . . . . . . . . . . . . . . . . . . . . . 5
2.3.1. Replay Attacks . . . . . . . . . . . . . . . . . . . 5
184.108.40.206. Current Recovery mechanism for LSPs . . . . . . . 6
2.3.2. Spoofing Attacks . . . . . . . . . . . . . . . . . . 7
2.3.3. DoS Attacks . . . . . . . . . . . . . . . . . . . . . 8
3. Gap Analysis and Security Requirements . . . . . . . . . . . 8
3.1. Manual Key Management . . . . . . . . . . . . . . . . . . 8
3.2. Key Management Protocols . . . . . . . . . . . . . . . . 9
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
7.1. Normative References . . . . . . . . . . . . . . . . . . 10
7.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
This document analyzes the current state of Intermediate system to
Intermediate system (IS-IS) protocol according to the requirements
set forth in [RFC6518] for both manual and auto key management
With currently published work, IS-IS meets some of the requirements
expected from a manually keyed routing protocol. Integrity
protection is expanded with more cryptographic algorithms and also
limited algorithm agility (HMAC-SHA family) is provided with
[RFC5310]. Basic form of Intra-connection re-keying capability is
provided by the specification [RFC5310] with some gaps as explained
in Section 3.
This draft summarizes the current state of cryptographic key usage in
IS-IS protocol and several previous efforts to analyze IS-IS
security. This includes base IS-IS specification [RFC1195],
[RFC5304], [RFC5310] and the OPSEC working group document [RFC6039].
Authors would like to acknowledge all the previous work done in the
This document also analyzes applicability of various threats as
described in [RFC6862] to IS-IS, lists gaps and provide specific
recommendations to thwart the applicable threats for both manual
keying and for auto key management mechanisms.
1.1. Requirements Language
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].
DoS - Denial of Service.
IGP - Interior Gateway Protocol.
IIH - IS-IS HELLO PDU.
IPv4 - Internet Protocol version 4.
KMP - Key Management Protocol (auto key management).
LSP - IS-IS Link State PDU.
MKM - Manual Key management Protocols.
NONCE - Number Once.
SA - Security Association.
SNP - Sequence number PDU.
2. Current State
IS-IS is specified in International Standards Organization (ISO)
10589, with extensions to support Internet Protocol version 4 (IPv4)
described in [RFC1195]. The specification includes an authentication
mechanism that allows for any authentication algorithm and also
specifies the algorithm for clear text passwords. Further [RFC5304]
extends the authentication mechanism to work with HMAC-MD5 and also
modifies the base protocol for more effectiveness. [RFC5310]
provides algorithm agility, with new generic crypto authentication
mechanism (CRYPTO_AUTH) for IS-IS. The CRYPTO_AUTH also introduces
Key ID mechanism that map to unique IS-IS Security Associations
The following sections describe the current authentication key usage
for various IS-IS messages, current key change methodologies and the
various potential security threats.
2.1. Key Usage
IS-IS can be provisioned with a per interface, peer-to-peer key for
IS-IS HELLO PDUs (IIH) and a group key for Link State PDUs (LSPs) and
Sequence number PDUs (SNPs). If provisioned, IIH packets potentially
can use the same group key used for LSPs and SNPs.
2.1.1. Sub network Independent
Link State PDUs, Complete and partial Sequence Number PDUs come under
Sub network Independent messages. For protecting Level-1 SNPs and
Level-1 LSPs, provisioned Area Authentication key is used. Level-2
SNPs as well as Level-2 LSPs use the provisioned domain
Since authentication is performed on the LSPs transmitted by an IS,
rather than on the LSP packets transmitted to a specific neighbor, it
is implied that all the ISes within a single flooding domain must be
configured with the same key in order for authentication to work
correctly. This is also true for SNP packets, though they are
limited to link local scope in broadcast networks.
If multiple instances share the circuits as specified in [RFC6822],
instance specific authentication credentials can be used to protect
the LSPs and SNPs with in an area or domain. It is important to
note, [RFC6822] also allows usage of topology specific authentication
credentials with in an instance for the LSPs and SNPs.
2.1.2. Sub network dependent
IS-IS HELLO PDUs use the Link Level Authentication key, which may be
different from that of LSPs and SNPs. This could be particularly
true for point-to-point links. In broadcast networks it is possible
to provision the same common key used for LSPs and SNPs, to protect
IIH messages. This allows neighbor discovery and adjacency formation
with more than one neighbor on the same physical interface. If
multiple instances share the circuits as specified in [RFC6822],
instance specific authentication credentials can be used to protect
2.2. Key Agility
Key roll over without effecting the routing protocols operation in
general and IS-IS in particular, is necessary for effective key
management protocol integration.
Current HMAC-MD5 crypto authentication as defined in [RFC5304],
suggests a transition mode, so that ISes use a set of keys when
verifying the authentication value, to allow key changes. This
approach will allow changing the authentication key manually without
bringing down the adjacency and without dropping any control packet.
But, this can increase the load on control plane for the key
transition duration as each control packet may have to be verified by
more than one key and also allows to mount a potential Denial of
Service (DoS) attack in the transition duration.
The above situation is improved with the introduction of Key ID
mechanism as defined in [RFC5310]. With this, the receiver
determines the active security association (SA) by looking at the Key
ID field in the incoming PDU and need not try with other keys, when
the integrity check or digest verification fails. But, neither Key
co-ordination across the group nor exact key change mechanism is
clearly defined. [RFC5310] says: " Normally, an implementation would
allow the network operator to configure a set of keys in a key chain,
with each key in the chain having a fixed lifetime. The actual
operation of these mechanisms is outside the scope of this document."
2.3. Security Issues
The following section analyzes various security threats possible, in
the current state for IS-IS protocol.
2.3.1. Replay Attacks
Replaying a captured protocol packet to cause damage is a common
threat for any protocol. Securing the packet with cryptographic
authentication information alone can not cannot mitigate this threat
completely. Though this problem is more prevalent in broadcast
networks it is important to note, most of the IGP deployments use
P2P-over-lan [RFC5309], which makes an adversary replay 'easier' than
the traditional P2P networks
In intra-session replay attacks a secured protocol packet of the
current session is replayed, can cause damage, if there is no other
mechanism to confirm this is a replay packet. In inter-session
replay attacks, captured packet from one of the previous session can
be replayed to cause the damage. IS-IS packets are vulnerable to
both these attacks, as there is no sequence number verification for
IIH packets and SNP packets. Also with current manual key management
periodic key changes across the group are done rarely. Thus the
intra-connection and inter-connection replay requirements are not
IS-IS specifies the use of the HMAC-MD5 [RFC5304] and HMAC-SHA-1
family in [RFC5310], to protect IS-IS packets. An adversary could
replay old IIHs or replay old SNPs that would cause churn in the
network or bring down the adjacencies.
1. At the time of adjacency bring up an IS sends IIH packet with
empty neighbor list (TLV 6) and with the authentication
information as per provisioned authentication mechanism. If this
packet is replayed later on the broadcast network, all ISes in
the broadcast network can bounce the adjacency to create a huge
churn in the network.
2. Today LSPs have intra-session replay protection as LSP header
contains 32-bit sequence number which is verified for every
received packet against the local LSP database. But, if a node
in the network is out of service (is undergoing some sort of high
availability condition, or an upgrade) for more than LSP refresh
time and the rest of the network ages out the LSPs of the node
under consideration, an adversary can potentially plunge in
inter-session replay attacks in the network. If the key is not
changed in the above circumstances, attack can be launched by
replaying an old LSP with higher sequence number and fewer
prefixes or fewer adjacencies. This may force the receiver to
accept and remove the routes from the routing table, which
eventually causes traffic disruption to those prefixes. However,
as per the IS-IS specification there is a built-in recovery
mechanism for LSPs from inter-session replay attacks and it is
further discussed in Section 220.127.116.11.
3. In any IS-IS network (broadcast or otherwise), if an old and an
empty Complete Sequence Number packet (CSNP) is replayed this can
cause LSP flood in the network. Similarly a replayed Partial
Sequence Number packet (PSNP) can cause LSP flood in the
18.104.22.168. Current Recovery mechanism for LSPs
In the event of inter-session replay attack by an adversary, as LSP
with higher sequence number gets accepted, it also gets propagated
until it reaches the originating node of the LSP. The originator
recognizes the LSP is "newer" than in the local database and this
prompts the originator to flood a newer version of the LSP with
higher sequence number than the received. This newer version can
potentially replace any versions of the replayed LSP which may exist
in the network.
But in the above process, depending on where in the network the
replay is initiated, how quick the nodes in the network react to the
replayed LSP and also how different the content in the accepted LSP
determines the damage caused by the replayed LSP.
2.3.2. Spoofing Attacks
IS-IS shares the same key between all neighbors in an area or in a
domain to protect the LSP, SNP packets and in broadcast networks even
IIH packets. False advertisement by a router is not within scope of
the KARP work. However, given the wide sharing of keys as described
above, there is a significant risk that an attacker can compromise a
key from one device, and use it to falsely participate in the
routing, possibly even in a very separate part of the network.
If the same underlying topology is shared across multiple instances
to transport routing/application information as defined in [RFC6822],
it is necessary to use different authentication credentials for
different instances. In this connection, based on the deployment
considerations, if certain topologies in a particular IS-IS instance
require more protection from spoofing attacks and less exposure,
topology specific authentication credentials can be used for LSPs and
SNPs as facilitated in [RFC6822].
Currently possession of the key itself is used as authentication
check and there is no identity check done separately. Spoofing
occurs when an illegitimate device assumes the identity of a
legitimate one. An attacker can use spoofing as a means for
launching various types of attacks. For example:
1. The attacker can send out unrealistic routing information that
might cause the disruption of network services such as block
2. A rogue system having access to the common key used to protect
the LSP, can send an LSP, setting the Remaining Lifetime field to
zero, and flooding it thereby initiating a purge. Subsequently,
this also can cause the sequence number of all the LSPs to
increase quickly to max out the sequence number space, which can
cause an IS to shut down for MaxAge + ZeroAgeLifetime period to
allow the old LSPs to age out in other ISes of the same flooding
2.3.3. DoS Attacks
Denial-of-service (DoS) attacks using the authentication mechanism is
possible and an attacker can send packets which can overwhelm the
security mechanism itself. An example is initiating an overwhelming
load of spoofed but integrity protected protocol packets, so that the
receiver needs to process the integrity check, only to discard the
packet. This can cause significant CPU usage. DoS attacks are not
generally preventable with in the routing protocol. As the attackers
are often remote, the DoS attacks are more damaging to area-scoped or
domain-scoped packet receivers than link-local scoped packet
3. Gap Analysis and Security Requirements
This section outlines the differences between the current state of
the IS-IS routing protocol and the desired state as specified in KARP
Design Guidelines [RFC6518]. The section focuses on where IS-IS
protocol fails to meet general requirements as specified in the
threats and requirements document.
This section also describes security requirements that should be met
by IS-IS implementations that are secured by manual as well as auto
key management protocols.
3.1. Manual Key Management
1. With CRYPTO_AUTH specification [RFC5310], IS-IS packets can be
protected with HMAC-SHA family of cryptographic algorithms. The
specification provides the limited algorithm agility (SHA
family). By using Key IDs, it also conceals the algorithm
information from the protected control messages.
2. Even though both intra and inter session replay attacks are best
prevented by deploying key management protocols with frequent key
change capability, basic constructs for sequence number should be
there in the protocol messages. So, some basic or extended
sequence number mechanism should be in place to protect IIH
packets and SNP packets. The sequence number should be increased
for each protocol packet. This allows mitigation of some of the
replay threats as mentioned in Section 2.3.1.
3. Any common key mechanism with keys shared across a group of
routers is susceptible to spoofing attacks caused by a malicious
router. Separate authentication check (apart from the integrity
check to verify the digest) with digital signatures as described
in [RFC2154], can effectively nullify this attack. But this
approach was never deployed and one can only assume due to
operational considerations at that time. The alternative
approach to thwart this threat would be by using the keys from
the group key management protocol. As the group key(s) are
generated by authenticating the member ISes in the group first,
and then periodically rekeyed, per packet identity or
authentication check may not be needed.
4. In general DoS attacks may not be preventable with mechanism from
routing protocols itself. But some form of Admin controlled
lists (ACLs) at the forwarding plane can reduce the damage.
There are some other forms the DoS attacks common to any protocol
are not in scope as per the section 3.3 in [RFC6862].
As discussed in Section 2.2, though Key ID mechanism in [RFC5310]
helps, better key co-ordination mechanism for key roll over is
desirable even with manual key management. But, it fell short of
specifying exact mechanism other than using key chains. The specific
a. Keys SHOULD be able to change without affecting the established
adjacency and even better without any control packet loss.
b. Keys SHOULD be able to change without effecting the protocol
operations, for example, LSP flooding should not be held for a
specific Key ID availability.
c. Any proposed mechanism SHOULD also be further incrementally
deployable with key management protocols.
3.2. Key Management Protocols
In broadcast deployments, the keys used for protecting IS-IS
protocols messages can, in particular, be group keys. A mechanism,
similar to as described in [I-D.weis-gdoi-mac-tek] can be used to
distribute group keys to a group of ISes in Level-1 area or Level-2
domain, using GDOI as specified in [RFC6407]. There are also similar
approaches with IKEv2 based group key management solutions, to
routing protocols as described in [I-D.yeung-g-ikev2] and [I-D
If a group key is used, the authentication granularity becomes group
membership of devices, not peer authentication between devices.
Group key management protocol deployed SHOULD be capable of
supporting rekeying support.
In some deployments, where IS-IS point-to-point (P2P) mode is used
for adjacency bring-up, sub network dependent messages (IIHs) can use
a different key shared between the two point-to-point peers, while
all other messages use a group key. When group keying mechanism is
deployed, even the P2P IIHs can be protected with the common group
keys. This approach facilitates one key management mechanism instead
of both pair-wise keying and group keying protocols to be deployed
together. If same circuits are shared across multiple instances, the
granularity of the group can become per instance for IIHs and per
instance/topology for LSPs and SNPs as specified in the [RFC6822].
Effective key change capability with in the routing protocol which
allows key roll over without impacting the routing protocol
operation, is one of the requirements for deploying any group key
mechanism. Once such mechanism is in place with deployment of group
key management protocol, IS-IS can be protected from various threats
not limited to intra and inter session replay attacks and spoofing
Specific use of crypto tables [I-D.ietf-karp-crypto-key-table] [RFC7210] should be defined for IS-IS
4. IANA Considerations
This document defines no new namespaces.
5. Security Considerations
This document is mostly about security considerations of IS-IS
protocol, lists potential threats and security requirements for
solving those threats. This document does not introduce any new
security threats for IS-IS protocol. For more detailed security
considerations please refer the Security Considerations section of
the KARP Design Guide [RFC6518] document as well as KARP threat
Authors would like to thank Joel Halpern for initial discussions on
this document and giving valuable review comments. Authors would
like to acknowledge Naiming Shen for reviewing and providing feedback
on this document.
7.1. Normative References
[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, December 1990.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic
Authentication", RFC 5304, October 2008.
[RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
and M. Fanto, "IS-IS Generic Cryptographic
Authentication", RFC 5310, February 2009.
7.2. Informative References
Hartman, S., Zhang, D., and G. Lebovitz, "Multicast Router
Key Management Protocol (MaRK)", draft-hartman-karp-
mrkmp-05 (work in progress), September 2012.
Housley, R., Polk, T., Hartman, S., and D. Zhang,
"Database of Long-Lived Symmetric Cryptographic Keys",
draft-ietf-karp-crypto-key-table-10 (work in progress),
Weis, B. and S. Rowles, "GDOI Generic Message
Authentication Code Policy", draft-weis-gdoi-mac-tek-03
(work in progress), September 2011.
Rowles, S., Yeung, A., Tran, P., and Y. Nir, "Group Key
Management using IKEv2", draft-yeung-g-ikev2-07 (work in
progress), November 2013.
[RFC2154] Murphy, S., Badger, M., and B. Wellington, "OSPF with
Digital Signatures", RFC 2154, June 1997.
[RFC4107] Bellovin, S. and R. Housley, "Guidelines for Cryptographic
Key Management", BCP 107, RFC 4107, June 2005.
[RFC5309] Shen, N. and A. Zinin, "Point-to-Point Operation over LAN
in Link State Routing Protocols", RFC 5309, October 2008.
[RFC6039] Manral, V., Bhatia, M., Jaeggli, J., and R. White, "Issues
with Existing Cryptographic Protection Methods for Routing
Protocols", RFC 6039, October 2010.
[RFC6407] Weis, B., Rowles, S., and T. Hardjono, "The Group Domain
of Interpretation", RFC 6407, October 2011.
[RFC6518] Lebovitz, G. and M. Bhatia, "Keying and Authentication for
Routing Protocols (KARP) Design Guidelines", RFC 6518,
[RFC6822] Previdi, S., Ginsberg, L., Shand, M., Roy, A., and D.
Ward, "IS-IS Multi-Instance", RFC 6822, December 2012.
[RFC6862] Lebovitz, G., Bhatia, M., and B. Weis, "Keying and
Authentication for Routing Protocols (KARP) Overview,
Threats, and Requirements", RFC 6862, March 2013.
[RFC7210] Housley, R., Polk, T., Hartman, S., and D. Zhang,
"Database of Long-Lived Symmetric Cryptographic Keys", RFC
7210, April 2014.
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