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Versions: 00 01 02 03 04 draft-ietf-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.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on July 22, 2013.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   the Trust Legal Provisions and are provided without warranty as



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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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