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Versions: 00 01 02 03 04 05 06 rfc7602                                  
Working Group                                                U. Chunduri
Internet-Draft                                                     W. Lu
Intended status: Standards Track                                 A. Tian
Expires: July 29, 2014                                     Ericsson Inc.
                                                                 N. Shen
                                                     Cisco Systems, Inc.
                                                        January 25, 2014


                   IS-IS Extended Sequence number TLV
              draft-ietf-isis-extended-sequence-no-tlv-01

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 29, 2014.

Copyright Notice

   Copyright (c) 2014 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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   include Simplified BSD License text as described in Section 4.e of




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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
     1.2.  Acronyms  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Replay attacks and Impact on IS-IS networks . . . . . . . . .   4
     2.1.  IIHs  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  LSPs  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.3.  SNPs  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Extended Sequence Number TLV  . . . . . . . . . . . . . . . .   5
     3.1.  Sequence Number Wrap  . . . . . . . . . . . . . . . . . .   6
   4.  Mechanism and Packet Encoding . . . . . . . . . . . . . . . .   6
     4.1.  IIHs  . . . . . . . . . . . . . . . . . . . . . . . . . .   6
     4.2.  SNPs  . . . . . . . . . . . . . . . . . . . . . . . . . .   7
       4.2.1.  CSNPs . . . . . . . . . . . . . . . . . . . . . . . .   7
       4.2.2.  PSNPs . . . . . . . . . . . . . . . . . . . . . . . .   7
   5.  Backward Compatibility and Deployment . . . . . . . . . . . .   7
     5.1.  IIH and SNPs  . . . . . . . . . . . . . . . . . . . . . .   8
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   9.  Appendix A  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     9.1.  Appendix A.1  . . . . . . . . . . . . . . . . . . . . . .   9
     9.2.  Appendix A.2  . . . . . . . . . . . . . . . . . . . . . .   9
   10. Appendix B  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     10.1.  Operational/Implementation consideration . . . . . . . .  10
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  10
     11.2.  Informative References . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

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



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   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 [ISO10589], 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
   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




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   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

   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 section explains the replay attacks and the
   applicability of the same for each IS-IS PDU.

2.1.  IIHs

   At the time of adjacency bring up an IS sends IIH packet with empty
   neighbor list (TLV 6) and with or without 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.

2.2.  LSPs

   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
   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 "Replay
   Attacks" Section of KARP IS-IS gap analysis document [I-D.ietf-karp-
   isis-analysis].

   This document does not propose any solution to completely mitigate
   the replay threat for LSPs as its perceived that network can still
   recover from the short-lived disruption, reliably after processing a
   reply.







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2.3.  SNPs

   In broadcast networks a replayed Complete Sequence Number PDU (CSNP)
   can force the receiver to request Partial Sequence Number PDU (PSNP)
   on a given link and similarly, based on the link type a replayed CSNP
   /PSNP can cause unnecessary LSP flood on the link.

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
   followed by a 32 bit monotonically increasing per Packet Sequence
   Number (PSN).

        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.

   The ESN TLV defined here is optional.  Though this is an optional
   TLV, this can be mandatory on a link when 'verify' mode is enabled as
   specified in Section 5.1.  The ESN TLV MAY present only in any IIH
   and SNP PDUs.  If present and authentication is in use this TLV MUST



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   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.

   In order to provide protection against both inter-session and intra-
   session replay attacks, the IS-IS Extended Session Sequence Number
   (ESSN) is defined as a 64-bits value; the value MUST contain ever
   increasing number whenever it is changed due any situation as
   specified in Section 3.1.  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.  While
   receiving, the 64-bit ESSN MUST always be either same or higher than
   the stored value corresponding to the PDU and the combined unsigned
   96 bit value (where ESSN is the 64 MSBs) MUST be greater than the
   previously received value.

   The 32-bit Packet Sequence Number (PSN) MUST be set and increase
   monotonically.  Upon reception, if ESSN field is unchanged, the
   Packet Sequence number MUST be greater than the last sequence number
   in the corresponding IIH or SNP PDUs accepted from the sending IS-IS
   node.  Otherwise, the IIH or SNP PDU is considered as replayed PDU
   and dropped.

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.

4.  Mechanism and Packet Encoding

   The encoding and decoding of ESN TLV in each IS-IS PDU as applicable
   is 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 without having this capability.

4.1.  IIHs

   The IIH ESN TLV information is maintained per IS-IS link and per
   level.  For a broadcast link, it can have two sets of ESN TLV
   information, if the circuit belongs to both level-1 and level-2.  For
   a point-to-point (P2P) link, only one ESN TLV information is needed.
   The procedure for encoding, verification and sequence number wrap
   scenarios are explained in Section 3.  If the received PDU is
   accepted then the stored value should be updated with the last
   received IIH PDU's ESN TLV information.





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   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, CSNP ESN TLV information is maintained per
   level and per link.  The procedure for encoding, verification and
   sequence number wrap scenarios are explained in Section 3 and a
   separate CSNP ESN TLV information should be used per link.  In case
   of DIS change the new DIS is free to start using an ESN, totally
   independent of what was used by its predecessor DIS.

   In P2P networks, CSNP ESN TLV information is maintained per link
   similar to IIH ESN TLV information.  The procedure for encoding,
   verification and sequence number wrap scenarios are similar as
   explained in Section 3, and a 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 link similar to CSNP ESN TLV information.  The
   procedure for encoding, verification and sequence number wrap
   scenarios are explained in Section 3 and a 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 its 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



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   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 its 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).  Once 'verify' mode is set for an
   interface all the IIH and SNP PDUs being sent and received MUST
   contain the ESN TLV and any single PDU sent without the ESN TLV
   becomes a potential replay candidate and MUST be dropped.  This way
   deployment can be done in 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.







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8.  Acknowledgements

   As some sort of sequence number mechanism to thwart protocol replays
   is a old mechanism, authors of this document do not make any claims
   on the originality of the overall protection idea 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, whenever 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.

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



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   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.

11.  References

11.1.  Normative References

   [ISO10589]
              International Organization for Standardization,
              "Intermediate system to intermediate system intra-domain-
              routing routine information exchange protocol for use in
              conjunction with the protocol for providing the
              connectionless-mode Network Service (ISO 8473)", ISO/
              IEC 10589:2002, Second Edition, Nov. 2002.

   [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.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-isis-analysis]
              Chunduri, U., Tian, A., and W. Lu, "KARP IS-IS security
              analysis", draft-ietf-karp-isis-analysis-00 (work in
              progress), March 2013.




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   [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-05 (work in progress), May 2013.

   [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.

   [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










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   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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