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Versions: (draft-chunduri-isis-extended-sequence-no-tlv) 00 01 02 03 04 05 06 RFC 7602

Working Group                                                U. Chunduri
Internet-Draft                                                     W. Lu
Intended status: Standards Track                                 A. Tian
Expires: October 24, 2015                                  Ericsson Inc.
                                                                 N. Shen
                                                     Cisco Systems, Inc.
                                                          April 22, 2015


                   IS-IS Extended Sequence number TLV
              draft-ietf-isis-extended-sequence-no-tlv-06

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
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   This Internet-Draft will expire on October 24, 2015.

Copyright Notice

   Copyright (c) 2015 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  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Extended Sequence Number TLV  . . . . . . . . . . . . . . . .   4
     3.1.  Sequence Number Wrap  . . . . . . . . . . . . . . . . . .   5
   4.  Mechanism and Packet Encoding . . . . . . . . . . . . . . . .   6
     4.1.  IIHs  . . . . . . . . . . . . . . . . . . . . . . . . . .   6
     4.2.  SNPs  . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Backward Compatibility and Deployment . . . . . . . . . . . .   6
     5.1.  IIH and SNPs  . . . . . . . . . . . . . . . . . . . . . .   7
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   8.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   8
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   8
     10.2.  Informative References . . . . . . . . . . . . . . . . .   8
   Appendix A.  ESSN Encoding Mechanisms . . . . . . . . . . . . . .   9
     A.1.  Using Timestamp . . . . . . . . . . . . . . . . . . . . .   9
     A.2.  Using Non-Volatile Storage  . . . . . . . . . . . . . . .  10
   Appendix B.  Operational/Implementation consideration . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   With the rapid development of new data center infrastructures, due to
   its flexibility and scalability attributes, Intermediate System to
   Intermediate System (IS-IS, [ISO10589]) has been adopted widely
   in various L2/L3 routing and switching deployment of the data centers
   and for critical business operations.  Also, while technologies such
   as Software Defined Networks (SDN) may improve network management and
   enable new applications, their use also has an effect on the security
   requirements of the routing infrastructure.

   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 a 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

   IS      -  Intermediate System

   KMP     -  Key Management Protocol (auto key management)




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   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

   Replaying a captured protocol packet to cause damage is a common
   threat for any protocol.  Securing the packet with cryptographic
   authentication information alone cannot mitigate this threat
   completely.  This section explains the replay attacks and the
   applicability of the same for each IS-IS PDU.

2.1.  IIHs

   When an adjacency is brought up an IS sends an IIH packet with an
   empty neighbor list (TLV 6), which can be sent with or without
   authentication information.  Packets can be replayed later on the
   broadcast network which may cause all ISes to bounce the adjacency,
   thus churning the network.  Note that mitigating replay is only
   possible when authentication information is present.

2.2.  LSPs

   Normal operation of the IS-IS update Process as specified in
   [ISO10589] provides timely recovery from all LSP replay
   attacks.  Therefore the use of the extensions defined in this
   document are prohibited in LSPs.  Further discussion of the
   vulnerability of LSPs to replay attacks can be found in [I-D.ietf-
   karp-isis-analysis].

2.3.  SNPs

   A replayed CSNP can result in the sending of unnecessary PSNPs on a
   given link.  A replayed CSNP or PSNP can result in unnecessary LSP
   flooding 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.



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   x CODE - 11.

   x LENGTH - total length of the value field, which is 12 bytes.

   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 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 be present only in any IIH
   and SNP PDUs.  A PDU with multiple ESN TLVs is invalid and MUST be
   discarded on receipt.

   The 64 bit ESSN MUST be non-zero and MUST contain ever increasing
   number whenever it is changed due any situation as specified in
   Section 3.1.  Encoding the 64-bit unsigned integer ESSN value is a
   local matter and implementations MAY use one of the alternatives
   provided in Appendix A.  Effectively, for each PDU which contains the
   ESN TLV the 96 bit unsigned integer value consisting of the 64 bit
   ESSN and 32 bit Packet Sequence Number (PSN) - where ESSN is the
   higher order 64 bits - MUST be greater than the most recently
   received value in a PDU of the same type originated by the same IS.

3.1.  Sequence Number Wrap

   If the 32-bit Packet Sequence Number in ESN TLV wraps or for the cold
   restart of the router, the 64-bit ESSN value MUST be set higher than
   the previous value.  IS-IS implementations MAY use guidelines
   provided in Appendix A for accomplishing this.




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4.  Mechanism and Packet Encoding

   The encoding of ESN TLV in each applicable IS-IS PDU is detailed
   below.  Please refer to Section 5 for appropriate operations on how
   to inter-op with legacy node(s) that do not support the extensions
   defined in this document.  If the received PDU with ESN TLV is
   accepted then the stored value for the corresponding originator and
   PDU type MUST be updated with the latest value received.  Please note
   that level information is included in the PDU type.

4.1.  IIHs

   ESN TLV information is maintained for each type of IIH PDU being sent
   on a given circuit.  The procedures for encoding, verification and
   sequence number wrap scenarios are explained in Section 3.

4.2.  SNPs

   A separate CSNP/PSNP ESN TLV information is maintained per PDU type,
   per originator and per link.  The procedures for encoding,
   verification and sequence number wrap scenarios are explained in
   Section 3.

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 the 'send' and/or 'verify'
   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
   node to the last node in the network or all nodes of a particular LAN
   segment, where 'send' mode is configured.  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




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   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).  The "send" and "verify" modes described above can be set
   independently on each link and in the case of a broadcast network
   independently for each level.

   To introduce ESN support without disrupting operations, ISs on a
   given interface are first configured to operate in 'send' mode.  Once
   all routers operating on an interface are operating in 'send' mode
   'verify' mode can be enabled on each IS.  Once 'verify' mode is set
   for an interface all the IIH and SNP PDUs being sent on that
   interface MUST contain the ESN TLV.  Any such PDU received without an
   ESN TLV MUST be discarded when 'verify' mode is enabled.  Similarly,
   to safely disable ESN support on a link, 'verify' mode is disabled on
   all ISs on the link.  Once all routers operating on an interface are
   disabled from 'verify' mode 'send' mode can be disabled on each IS.
   Please refer Section 5 for considerations on enabling or disabling
   'verify' mode on all ISs on a link.

6.  IANA Considerations

   A new TLV code point is assigned by IANA from the IS-IS TLV
   Codepoints Registry as defined in this document, referred to as the
   "Extended Sequence Number" TLV, with the following attributes:


      Type  Description            IIH  LSP  SNP  Purge
      ----  ---------------------  ---  ---  ---  -----
      11    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].  If an adversary either does not forward the packets or
   delay the same as specified in Section 3.3 of [RFC6862], the
   mechanism specified in this document cannot mitigate those threats.
   Also some of the threats as specified in Section 2.3 of [I-D.ietf-
   karp-isis-analysis] are not addressable with ESN TLV as specified in
   this document.  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.  Contributors

   Authors would like to thank Les Ginsberg for his significant
   contribution in detailed reviews and suggestions.

9.  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 and Joel Halpern.  Thanks to Alia Atlas, Chris Hopps,
   Nevil Brownlee and Adam W.  Montville for their reviews and
   suggestions during IESG directorate review.  Authors would also thank
   Christer Holmberg, Ben Campbell, Barry Leiba, Stephen Farrell and
   Alvaro Retana for their reviews on this document.

10.  References

10.1.  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.

10.2.  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-04 (work in
              progress), March 2015.




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   [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.

   [RFC6862]  Lebovitz, G., Bhatia, M., and B. Weis, "Keying and
              Authentication for Routing Protocols (KARP) Overview,
              Threats, and Requirements", RFC 6862, March 2013.

   [RFC7474]  Bhatia, M., Hartman, S., Zhang, D., and A. Lindem,
              "Security Extension for OSPFv2 When Using Manual Key
              Management", RFC 7474, April 2015.

Appendix A.  ESSN Encoding Mechanisms

   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.

A.1.  Using Timestamp

   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



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   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).

A.2.  Using Non-Volatile Storage

   One other mechanism for accomplishing this would be similar to the
   one as specified in [RFC7474], 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 8 of [RFC7474], if used is
   applicable here.  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 router hardware is upgraded such that the
   contents are lost, keys MUST be changed to prevent replay attacks.

Appendix B.  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.  Effective usage of the
   TLV defined in this document for operational issues MAY also need
   more system information before making concrete conclusions and
   defining all that information is beyond the scope of this document.

Authors' Addresses

   Uma Chunduri
   Ericsson Inc.
   300 Holger Way,
   San Jose, California  95134
   USA

   Phone: 408 750-5678
   Email: uma.chunduri@ericsson.com









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   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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