Internet DRAFT - draft-chunduri-isis-extended-sequence-no-tlv
draft-chunduri-isis-extended-sequence-no-tlv
Working Group U. Chunduri
Internet-Draft W. Lu
Intended status: Standards Track A. Tian
Expires: July 22, 2013 Ericsson Inc.
N. Shen
Cisco Systems, Inc.
January 18, 2013
IS-IS Extended Sequence number TLV
draft-chunduri-isis-extended-sequence-no-tlv-04
Abstract
This document defines Extended Sequence number TLV to protect
Intermediate System to Intermediate System (IS-IS) PDUs from replay
attacks.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on July 22, 2013.
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
1.2. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Replay attacks and Impact on IS-IS networks . . . . . . . . . 4
2.1. Impact of Replays . . . . . . . . . . . . . . . . . . . . 4
3. Extended Sequence Number TLV . . . . . . . . . . . . . . . . . 5
3.1. Sequence Number Wrap . . . . . . . . . . . . . . . . . . . 6
4. Mechanism and Packet Encoding . . . . . . . . . . . . . . . . 7
4.1. IIHs . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.2. SNPs . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.2.1. CSNPs . . . . . . . . . . . . . . . . . . . . . . . . 7
4.2.2. PSNPs . . . . . . . . . . . . . . . . . . . . . . . . 8
5. Backward Compatibility and Deployment . . . . . . . . . . . . 8
5.1. IIH and SNPs . . . . . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
9. Appendix A . . . . . . . . . . . . . . . . . . . . . . . . . . 9
9.1. Appendix A.1 . . . . . . . . . . . . . . . . . . . . . . . 10
9.2. Appendix A.2 . . . . . . . . . . . . . . . . . . . . . . . 10
10. Appendix B . . . . . . . . . . . . . . . . . . . . . . . . . . 10
10.1. Operational/Implementation consideration . . . . . . . . . 10
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
11.1. Normative References . . . . . . . . . . . . . . . . . . . 11
11.2. Informative References . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
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1. Introduction
With the rapid development of new data center infrastructures, due to
its flexibility and scalability attributes, IS-IS has been adopted
widely in various L2 and L3 routing deployment of the data centers
for critical business operations. At the meantime the SDN-enabled
networks even though put more power to Internet applications and also
make network management easier, it does raise the security
requirement of network routing infrastructure to another level.
A replayed IS-IS PDU can potentially cause many problems in the IS-IS
networks ranging from bouncing adjacencies to black hole or even some
form of Denial of Service (DoS) attacks as explained in Section 2.
This problem is also discussed in security consideration section, in
the context of cryptographic authentication work as described in
[RFC5304] and in [RFC5310].
Currently, there is no mechanism to protect IS-IS HELLO PDUs (IIHs)
and Sequence number PDUs (SNPs) from the replay attacks. However,
Link State PDUs (LSPs) have sequence number in the LSP header as
defined in [RFC1195], with which it can effectively mitigate the
intra-session replay attacks. But, LSPs are still susceptible to
inter-session replay attacks.
This document defines Extended Sequence number (ESN) TLV to protect
Intermediate System to Intermediate System (IS-IS) PDUs from replay
attacks.
The new ESN TLV defined here thwart these threats and can be deployed
with authentication mechanism as specified in [RFC5304] and in
[RFC5310] for a more secure network.
Replay attacks can be effectively mitigated by deploying a group key
management protocol (being developed as defined in [I-D.yeung-g-
ikev2] and [I-D.hartman-karp-mrkmp]) with a frequent key change
policy. Currently, there is no such mechanism defined for IS-IS.
Even if such a mechanism is defined, usage of this TLV can be helpful
to avoid replays before the keys are changed.
Also, it is believed, even when such key management system is
deployed, there always will be some manual key based systems that co-
exist with KMP (Key Management Protocol) based systems. The ESN TLV
defined in this document is more helpful for such deployments.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
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document are to be interpreted as described in RFC 2119 [RFC2119].
1.2. Acronyms
CSNP - Complete Sequence Number PDU
ESN - Extended Sequence Number
IIH - IS-IS Hello PDU
KMP - Key Management Protocol (auto key management)
LSP - IS-IS Link State PDU
MKM - Manual Key management Protocols
PDU - Protocol Data Unit
PSNP - Partial Sequence Number PDU
SNP - Sequence Number PDU
2. Replay attacks and Impact on IS-IS networks
This section explains the replay attacks and the applicability of the
same for IS-IS networks. 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
mitigate this threat completely. This has been described in detail
in "Replay Attacks" section of KARP IS-IS gap analysis document
[I-D.chunduri-karp-is-is-gap-analysis].
2.1. Impact of Replays
At the time of adjacency bring up an IS sends IIH packet with empty
neighbor list (TLV 6) and with or with out 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.
Today Link State PDUs (LSPs) have intra-session replay protection as
LSP header contains 32-bit sequence number which is verified for
every received PDU against the local LSP database. But, if the key
is not changed, an adversary can cause an inter-session replay attack
by replaying a old LSP with higher sequence number and fewer prefixes
or fewer adjacencies. This forces the receiver to accept and remove
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the routes from the routing table, which eventually causes traffic
disruption to those prefixes. The more common pre-conditions for
inter-session replay attacks with LSPs and the current in-built
recovery mechanism, have been discussed in details in Section 2.3.1.1
of KARP IS-IS gap analysis document [I-D.chunduri-karp-is-is-gap-
analysis]. This document does not propose any solution to completely
mitigate the replay threat for LSPs as network can still recover
reliably after processing a disruptive reply.
In broadcast networks a replayed Complete Sequence Number PDU (CSNP)
can force the receiver to request Partial Sequence Number PDU (PSNP)
in the network and similarly, a replayed PSNP can cause unnecessary
LSP flood in the network.
Please refer KARP IS-IS gap analysis document for further details.
3. Extended Sequence Number TLV
The Extended Sequence Number (ESN) TLV is composed of 1 octet for the
Type, 1 octet that specifies the number of bytes in the Value field
and a 12 byte Value field. This TLV is defined only for IIH and SNP
PDUs.
x CODE - TBD.
x LENGTH - total length of the value field, which is 12 bytes and
applicable for IIH and SNP PDUs.
x Value - 64-bit Extended Session Sequence Number (ESSN), which is
present for all IS-IS PDUs followed 32 bit monotonically increasing
per Packet Sequence Number (PSN).
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+
| Type |
+-+-+-+-+-+-+-+-+
| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extended Session Sequence Number (High Order 32 Bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extended Session Sequence Number (Low Order 32 Bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Packet Sequence Number (32 Bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Extended Sequence Number (ESN) TLV
The Extended Sequence Number (ESN) TLV Type is TBD. Please refer to
IANA Considerations, in Section 6 for more details. Length indicates
the length of the value field; which is 12 bytes for IIH and SNP
PDUs.
In order to provide protection against both inter-session and intra-
session replay attacks, the IS-IS Extended Session Sequence Number
(ESSN) is defined a 64-bits value; the value MUST contain ever
increasing number in IIH and SNP PDUs whenever it is changed due any
situation as specified in Section 3.1.
The 32-bit Packet Sequence Number (PSN) MUST be set and increase
monotonically for IIH or SNP PDUs sent by IS-IS node. Upon
reception, the Packet Sequence number MUST be greater than the last
sequence number in the IIH or SNP PDUs accepted from the sending
IS-IS node. Otherwise, the IIH or SNP PDU is considered as replayed
PDU and dropped.
The ESN TLV defined here is optional. The ESN TLV MAY present only
in any IIH and SNP PDUs. If present and authentication is in use
this TLV MUST be included as part of the authentication data to
calculate the digest. A sender MUST only transmit a single ESN TLV
in a IS-IS PDU.
3.1. Sequence Number Wrap
If the 32-bit Packet Sequence Number in ESN TLV wraps; or session is
refreshed; or even for the cold restarts the 64-bit ESSN value MUST
be set higher than the previous value. IS-IS implementations MAY use
guidelines provided in Section 9 for accomplishing this.
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4. Mechanism and Packet Encoding
The ESN TLV defined in this document is optional and the encoding and
decoding of this TLV in each IS-IS PDU is as detailed below. Also
refer, when to ignore processing of the ESN TLV as described in
Section 5 for appropriate operation in the face of legacy node(s) in
the network with out having this capability.
4.1. IIHs
The IIH ESN TLV information is maintained per IS-IS interface and per
level. For a broadcast interface, it can have two sets of ESN TLV
information, if the circuit belongs to both level-1 and level-2. For
point-to-point (P2P) interface, only one ESN TLV information is
needed. This TLV information can be maintained as part of the
adjacency state.
While transmitting, the 64-bit ESSN MUST always be started with a non
zero number and MAY use the guidelines as specified in Section 9 to
encode this 64-bit value. The 32-bit PSN starts from 1 and increases
monotonically for every subsequent PDU.
While receiving, the 64-bit ESSN MUST always be either same or higher
than the stored value in the adjacency state. Similarly, the 32-bit
PSN MUST be higher than the stored value in the adjacency state. If
the PDU is accepted then the adjacency state should be updated with
the last received IIH PDU's ESN TLV information.
For an adjacency refresh or the 32-bit PSN wrap the associated higher
order 64-bit ESSN MUST always be higher than the previous value and
the lower order 32-bit packet sequence number starts all over again.
4.2. SNPs
4.2.1. CSNPs
In broadcast networks, only Designated Intermediate System (DIS) CSNP
ESN TLV information is maintained per adjacency (per level) similar
to IIH ESN TLV information. The procedure for encoding, verification
and sequence number wrap scenarios are similar as explained in
Section 4.1, except separate DIS ESN TLV information should be used.
In case of DIS change all adjacencies in the broadcast network MUST
reflect new DIS's CSNP ESN TLV information in the adjacency and
should be used for encoding/verification.
In P2P networks, CSNP ESN TLV information is maintained per adjacency
similar to IIH ESN TLV information. The procedure for encoding,
verification and sequence number wrap scenarios are similar as
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explained in Section 4.1, except separate CSNP ESN TLV information
should be used.
4.2.2. PSNPs
In both broadcast and P2P networks, PSNP ESN TLV information is
maintained per adjacency (per level) similar to IIH ESN TLV
information. The procedure for encoding, verification and sequence
number wrap scenarios are similar as explained in Section 4.1, except
separate PSNP ESN TLV information should be used.
5. Backward Compatibility and Deployment
The implementation and deployment of the ESN TLV can be done to
support backward compatibility and gradual deployment in the network
without requiring a flag day. This feature can also be deployed for
the links in a certain area of the network where the maximum security
mechanism is needed, or it can be deployed for the entire network.
The implementation SHOULD allow the configuration of ESN TLV feature
on each IS-IS link level. The implementation SHOULD also allow
operators to control the configuration of 'send' and/or 'verify' the
feature of IS-IS PDUs for the links and for the node. In this
document, the 'send' operation is to include the ESN TLV in it's own
IS-IS PDUs; and the 'verify' operation is to process the ESN TLV in
the receiving IS-IS PDUs from neighbors.
In the face of an adversary doing an active attack, it is possible to
have inconsistent data view in the network, if there is a
considerable delay in enabling ESN TLV 'verify' operation from first
node to the last node in the network. This can happen primarily
because, replay PDUs can potentially be accepted by the nodes where
'verify' operation is still not provisioned at the time of the
attack. To minimize such a window it is recommended that
provisioning of 'verify' SHOULD be done in a timely fashion by the
network operators.
5.1. IIH and SNPs
On the link level, ESN TLV involves the IIH PDUs and SNPs (both CSNP
and PSNP). When the router software is upgraded to include this
feature, the network operators can configure the IS-IS to 'send' the
ESN TLV in it's IIH PDUs and SNPs for those IS-IS interfaces on the
IS-IS area or level. When all the routers attached to the link or
links have been upgraded with this feature, network operators can
start to configure 'verify' on the IS-IS interfaces for all the
routers sharing the same link(s). This way deployment can be done in
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per link basis in the network. The operators may decide to only
apply ESN TLV feature on some of the links in the network, or only on
their multi-access media links.
6. IANA Considerations
This document requests that IANA allocate from the IS-IS TLV
Codepoints Registry a new TLV, referred to as the "Extended Sequence
Number" TLV, with the following attributes:
Type Description IIH LSP SNP Purge
---- --------------------- --- --- --- -----
TBD ESN TLV Y N Y N
Figure 2: IS-IS Codepoints Registry Entry
7. Security Considerations
This document describes a mechanism to the replay attack threat as
discussed in the Security Considerations section of [RFC5304] and in
[RFC5310]. This document does not introduce any new security
concerns to IS-IS or any other specifications referenced in this
document.
8. Acknowledgements
The authors of this document do not make any claims on the
originality of the ideas described. Authors are thankful for the
review and the valuable feedback provided by Acee Lindem, Joel
Halpern and Les Ginsberg.
9. Appendix A
IS-IS nodes implementing this specification SHOULD use available
mechanisms to preserve the 64-bit Extended Session Sequence Number's
strictly increasing property, when ever it is changed for the
deployed life of the IS-IS node (including cold restarts).
This Appendix provides only guidelines for achieving the same and
implementations can resort to any similar method as far as strictly
increasing property of the 64-bit ESSN in ESN TLV is maintained.
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9.1. Appendix A.1
One mechanism for accomplishing this is by encoding 64-bit ESSN as
system time represented in 64-bit unsigned integer value. This MAY
be similar to the system timestamp encoding for NTP long format as
defined in Appendix A.4 of [RFC5905]. New current time MAY be used
when the IS-IS node loses its sequence number state including in
Packet Sequence Number wrap scenarios.
Implementations MUST make sure while encoding the 64-bit ESN value
with current system time, it should not default to any previous value
or some default node time of the system; especially after cold
restarts or any other similar events. In general system time must be
preserved across cold restarts in order for this mechanism to be
feasible. One example of such implementation is to use a battery
backed real-time clock (RTC).
9.2. Appendix A.2
One other mechanism for accomplishing this would be similar to the
one as specified in [I-D.ietf-ospf-security-extension-manual-keying],
to use the 64-bit ESSN as a wrap/boot count stored in non-volatile
storage. This value is incremented anytime the IS-IS node loses its
sequence number state including in Packet Sequence Number wrap
scenarios.
The drawback of this approach per Section 6 of [I-D.ietf-ospf-
security-extension-manual-keying], if used is applicable here. The
only drawback is, it requires the IS-IS implementation to be able to
save its boot count in non-volatile storage. If the non-volatile
storage is ever repaired or upgraded such that the contents are lost,
keys MUST be changed to prevent replay attacks.
10. Appendix B
10.1. Operational/Implementation consideration
Since the ESN is maintained per interface, per level and per PDU
type, this scheme can be useful for monitoring the health of the
IS-IS adjacency. A Packet Sequence Number skip on IIH can be
recorded by the neighbors which can be used later to correlate with
adjacency state changes over the interface. For instance in a multi-
access media, all the neighbors have the skips from the same IIH
sender or only one neighbor has the Packet Sequence Number skips can
indicate completely different issues on the network.
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11. References
11.1. 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.
[RFC5905] Mills, D., Martin, J., Burbank, J., and W. Kasch, "Network
Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, June 2010.
11.2. Informative References
[I-D.chunduri-karp-is-is-gap-analysis]
Chunduri, U., Tian, A., and W. Lu, "KARP IS-IS security
gap analysis", draft-chunduri-karp-is-is-gap-analysis-03
(work in progress), October 2012.
[I-D.hartman-karp-mrkmp]
Hartman, S., Zhang, D., and G. Lebovitz, "Multicast Router
Key Management Protocol (MaRK)",
draft-hartman-karp-mrkmp-05 (work in progress),
September 2012.
[I-D.ietf-karp-threats-reqs]
Lebovitz, G., Bhatia, M., and B. Weis, "Keying and
Authentication for Routing Protocols (KARP) Overview,
Threats, and Requirements",
draft-ietf-karp-threats-reqs-07 (work in progress),
December 2012.
[I-D.ietf-ospf-security-extension-manual-keying]
Bhatia, M., Hartman, S., Zhang, D., and A. Lindem,
"Security Extension for OSPFv2 when using Manual Key
Management",
draft-ietf-ospf-security-extension-manual-keying-02 (work
in progress), April 2012.
[I-D.weis-gdoi-mac-tek]
Weis, B. and S. Rowles, "GDOI Generic Message
Authentication Code Policy", draft-weis-gdoi-mac-tek-03
(work in progress), September 2011.
[RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic
Authentication", RFC 5304, October 2008.
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[RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
and M. Fanto, "IS-IS Generic Cryptographic
Authentication", RFC 5310, February 2009.
[RFC6518] Lebovitz, G. and M. Bhatia, "Keying and Authentication for
Routing Protocols (KARP) Design Guidelines", RFC 6518,
February 2012.
Authors' Addresses
Uma Chunduri
Ericsson Inc.
300 Holger Way,
San Jose, California 95134
USA
Phone: 408 750-5678
Email: uma.chunduri@ericsson.com
Wenhu Lu
Ericsson Inc.
300 Holger Way,
San Jose, California 95134
USA
Email: wenhu.lu@ericsson.com
Albert Tian
Ericsson Inc.
300 Holger Way,
San Jose, California 95134
USA
Phone: 408 750-5210
Email: albert.tian@ericsson.com
Naiming Shen
Cisco Systems, Inc.
225 West Tasman Drive,
San Jose, California 95134
USA
Email: naiming@cisco.com
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