OSPFv2 manual keys: Security Extension for OSPFv2 When Using Manual Key Management

Internet Engineering Task Force (IETF)                         M. Bhatia
Request for Comments: 7474                                Ionos Networks
Updates: 2328, 5709                                           S. Hartman
Category: Standards Track                              Painless Security
ISSN: 2070-1721                                                 D. Zhang
                                           Huawei Technologies Co., Ltd.
                                                          A. Lindem, Ed.
                                                                   Cisco
                                                              April 2015


     Security Extension for OSPFv2 When Using Manual Key Management

Abstract

   The current OSPFv2 cryptographic authentication mechanism as defined
   in RFCs 2328 and 5709 is vulnerable to both inter-session and intra-
   session replay attacks when using manual keying.  Additionally, the
   existing cryptographic authentication mechanism does not cover the IP
   header.  This omission can be exploited to carry out various types of
   attacks.

   This document defines changes to the authentication sequence number
   mechanism that will protect OSPFv2 from both inter-session and intra-
   session replay attacks when using manual keys for securing OSPFv2
   protocol packets.  Additionally, we also describe some changes in the
   cryptographic hash computation that will eliminate attacks resulting
   from OSPFv2 not protecting the IP header.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7474.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   2.  Replay Protection Using Extended Sequence Numbers . . . . . .   4
   3.  OSPF Packet Extensions  . . . . . . . . . . . . . . . . . . .   5
   4.  OSPF Packet Key Selection . . . . . . . . . . . . . . . . . .   6
     4.1.  Key Selection for Unicast OSPF Packet Transmission  . . .   7
     4.2.  Key Selection for Multicast OSPF Packet Transmission  . .   8
     4.3.  Key Selection for OSPF Packet Reception . . . . . . . . .   8
   5.  Securing the IP Header  . . . . . . . . . . . . . . . . . . .   9
   6.  Mitigating Cross-Protocol Attacks . . . . . . . . . . . . . .  10
   7.  Backward Compatibility  . . . . . . . . . . . . . . . . . . .  11
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  12
     10.2.  Informative References . . . . . . . . . . . . . . . . .  12
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   The OSPFv2 cryptographic authentication mechanism as described in
   [RFC2328] uses per-packet sequence numbers to provide protection
   against replay attacks.  The sequence numbers increase monotonically
   so that attempts to replay stale packets can be thwarted.  The
   sequence number values are maintained as a part of neighbor adjacency
   state.  Therefore, if an adjacency is taken down, the associated
   sequence numbers get reinitialized and neighbor adjacency formation
   starts over again.  Additionally, the cryptographic authentication
   mechanism does not specify how to deal with the rollover of a
   sequence number when its value wraps.  These omissions can be
   exploited by attackers to implement various replay attacks
   ([RFC6039]).  In order to address these issues, we define extensions
   to the authentication sequence number mechanism.

   The cryptographic authentication as described in [RFC2328] and later
   updated in [RFC5709] does not include the IP header.  This omission
   can be exploited to launch several attacks as the source address in
   the IP header is not protected.  The OSPF specification, for
   broadcast and NBMA (Non-Broadcast Multi-Access) networks, requires
   implementations to use the source address in the IP header to
   determine the neighbor from which the packet was received.  Changing
   the IP source address of a packet to a conflicting IP address can be
   exploited to produce a number of denial-of-service attacks [RFC6039].
   If the packet is interpreted as coming from a different neighbor, the
   received sequence number state for that neighbor may be incorrectly
   updated.  This attack may disrupt communication with a legitimate
   neighbor.  Hello packets may be reflected to cause a neighbor to
   appear to have one-way communication.  Additionally, Database
   Description packets may be reflected in cases where the per-packet
   sequence numbers are sufficiently divergent in order to disrupt an
   adjacency [RFC6863].  This is the IP-layer issue described in point
   18 in Section 4 of [RFC6862].

   [RFC2328] states that implementations MUST offer keyed MD5
   authentication.  It is likely that this will be deprecated in favor
   of the stronger algorithms described in [RFC5709] and required in
   [RFC6094].

   This document defines a few simple changes to the cryptographic
   authentication mechanism, as currently described in [RFC5709], to
   prevent such IP-layer attacks.

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].

   When used in lowercase, these words convey their typical use in
   common language, and are not to be interpreted as described in RFC
   2119 [RFC2119].

2.  Replay Protection Using Extended Sequence Numbers

   In order to provide replay protection against both inter-session and
   intra-session replay attacks, the OSPFv2 sequence number is expanded
   to 64 bits with the least significant 32-bit value containing a
   strictly increasing sequence number and the most significant 32-bit
   value containing the boot count.  OSPFv2 implementations are required
   to retain the boot count in non-volatile storage for the deployment
   life of the OSPF router.  The requirement to preserve the boot count
   is also placed on SNMP agents by the SNMPv3 security architecture
   (refer to snmpEngineBoots in Section 2.2 of [RFC3414]).

   Since there is no room in the OSPFv2 packet for a 64-bit sequence
   number, it will occupy the 8 octets following the OSPFv2 packet and
   MUST be included when calculating the OSPFv2 packet digest.  These
   additional 8 octets are not included in the OSPFv2 packet header
   length but are included in the OSPFv2 header Authentication Data
   length and the IPv4 packet header length.

   The lower-order 32-bit sequence number MUST be incremented for every
   OSPF packet sent by the OSPF router.  Upon reception, the sequence
   number MUST be greater than the sequence number in the last OSPF
   packet of that type accepted from the sending OSPF neighbor.
   Otherwise, the OSPF packet is considered a replayed packet and
   dropped.  OSPF packets of different types may arrive out of order if
   they are prioritized as recommended in [RFC4222].

   OSPF routers implementing this specification MUST use available
   mechanisms to preserve the sequence number's strictly increasing
   property for the deployed life of the OSPFv2 router (including cold
   restarts).  This is achieved by maintaining a boot count in non-
   volatile storage and incrementing it each time the OSPF router loses
   its prior sequence number state.  The SNMPv3 snmpEngineBoots variable
   [RFC3414] MAY be used for this purpose.  However, maintaining a
   separate boot count solely for OSPF sequence numbers has the
   advantage of decoupling SNMP reinitialization and OSPF
   reinitialization.  Also, in the rare event that the lower-order
   32-bit sequence number wraps, the boot count can be incremented to
   preserve the strictly increasing property of the aggregate sequence
   number.  Hence, a separate OSPF boot count is RECOMMENDED.

3.  OSPF Packet Extensions

   The OSPF packet header includes an authentication type field, and 64
   bits of data for use by the appropriate authentication scheme
   (determined by the type field).  Authentication types 0, 1, and 2 are
   defined [RFC2328].  This section defines Authentication type 3.

   When using this authentication scheme, the 64-bit Authentication
   field (as defined in Appendix D.3 of [RFC2328]) in the OSPF packet
   header (as defined in Appendix A.3.1 of [RFC2328] and [RFC6549]) is
   changed as shown in Figure 1.  The sequence number is removed and the
   Key ID is extended to 32 bits and moved to the former position of the
   sequence number.

   Additionally, the 64-bit sequence number is moved to the first 64
   bits following the OSPFv2 packet and is protected by the
   authentication digest.  These additional 64 bits or 8 octets are
   included in the IP header length but not the OSPF header packet
   length.

   Finally, the 0 field at the start of the OSPFv2 header authentication
   is extended from 16 bits to 24 bits.

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |  Version #  |     Type        |       Packet length           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                          Router ID                            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                           Area ID                             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |           Checksum            | Instance ID   |  AuType       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                               0               | Auth Data Len |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         Key ID                                |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |                   OSPF Protocol Packet                        |
       ~                                                               ~
       |                                                               |
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     Sequence Number (Boot Count)                              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     Sequence Number (Strictly Increasing Packet Counter)      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       ~                Authentication Data                            ~
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           Figure 1: Extended Sequence Number Packet Extensions

4.  OSPF Packet Key Selection

   This section describes how this security solution selects long-lived
   keys from key tables.  [RFC7210].  In this context, we are selecting
   the key and corresponding Security Association (SA) as defined in
   Section 3.2 of [RFC5709].  Generally, a key used for OSPFv2 packet
   authentication should satisfy the following requirements:

   o  For packet transmission, the key validity interval as defined by
      SendLifetimeStart and SendLifetimeEnd must include the current
      time.

   o  For packet reception, the key validity interval as defined by
      AcceptLifetimeStart and AcceptLifetimeEnd must include the current
      time.

   o  The key must be valid for the desired security algorithm.

   In the remainder of this section, additional requirements for keys
   are enumerated for different scenarios.

4.1.  Key Selection for Unicast OSPF Packet Transmission

   Assume that a router R1 tries to send a unicast OSPF packet from its
   interface I1 to the interface I2 of a remote router R2 using security
   protocol P via interface I at time T.  First, consider the
   circumstances where R1 and R2 are not connected with a virtual link.
   R1 then needs to select a long-lived symmetric key from its key
   table.  Because the key should be shared by both R1 and R2 to protect
   the communication between I1 and I2, the key should satisfy the
   following requirements:

   o  The Peers field contains the area ID or, if no key containing the
      area ID is present, the string "all".

   o  The Direction field is either "out" or "both".

   o  The Interfaces field matches I1 or "all".

   o  If multiple keys match the Interface field, keys that explicitly
      match I1 should be preferred over keys matching "all".  If there
      are still multiple keys that match, the key with the most recent
      SendLifetimeStart will be selected.  This will facilitate graceful
      key rollover.

   o  The Key ID field in the OSPFv2 header (refer to Figure 1) will be
      set to the selected key's LocalKeyName.

   When R1 and R2 are connected to a virtual link, the Peers field must
   identify the virtual endpoint rather than the virtual link.  Since
   there may be virtual links to the same router, the transit area ID
   must be part of the identifier.  Hence, the key should satisfy the
   following requirements:

   o  The Peers field includes both the virtual endpoint's OSPF router
      ID and the transit area ID for the virtual link in the form of the
      transit area ID, followed by a colon, followed by the router ID.
      If no such key exists, then a key with the Peers field set to the
      transit area ID is used, followed by a key with the Peers field
      set to "all".

   o  The Interfaces field is not used for key selection on virtual
      links.

   o  The Direction field is either "out" or "both".

   o  If multiple keys match the Peers field, keys that explicitly match
      the router ID should be preferred, followed by keys with a transit
      area specified, followed by keys with the Peers field set to
      "all".  If there are still multiple keys that match, the key with
      the most recent SendLifetimeStart will be selected.  This will
      facilitate graceful key rollover.

   o  The Key ID field in the OSPFv2 header (refer to Figure 1) will be
      set to the selected key's LocalKeyName.

4.2.  Key Selection for Multicast OSPF Packet Transmission

   If a router R1 sends an OSPF packet from its interface I1 to a
   multicast address (i.e., AllSPFRouters or AllDRouters), it needs to
   select a key according to the following requirements:

   o  First, try a key with the Peers field containing the area ID to
      which the interface belongs.  If no key exists, try a key with the
      Peers field "all".

   o  The Interfaces field matches the interface over which the packet
      is sent or "all".

   o  The Direction field is either "out" or "both".

   o  If multiple keys match the Interface field, keys that explicitly
      match I1 should be preferred over keys matching "all".  If there
      are still multiple keys that match, the key with the most resent
      SendLifetimeStart will be selected.  This will facilitate graceful
      key rollover.

   o  The Key ID field in the OSPFv2 header (refer to Figure 1) will be
      set to the selected key's LocalKeyName.

4.3.  Key Selection for OSPF Packet Reception

   When cryptographic authentication is used, the ID of the
   authentication key is included in the authentication field of the
   OSPF packet header.  Using this Key ID, it is straight forward for a
   receiver to locate the corresponding key.  The simple requirements
   are:

   o  The interface on which the key was received is associated with the
      key's interface.

   o  The Key ID obtained from the OSPFv2 packet header corresponds to
      the neighbor's PeerKeyName.  Since OSPFv2 keys are symmetric, the
      LocalKeyName and PeerKeyName for OSPFv2 keys will be identical.
      Hence, the Key ID will be used to select the correct local key.

   o  The Direction field is either "in" or "both".

   o  The Peers field matches as described in Sections Section 4.1 and
      Section 4.2.

5.  Securing the IP Header

   This document updates the definition of the Apad constant, as it is
   defined in [RFC5709], to include the IP source address from the IP
   header of the OSPFv2 protocol packet.  The overall cryptographic
   authentication process defined in [RFC5709] remains unchanged.  To
   reduce the potential for confusion, this section minimizes the
   repetition of text from RFC 5709 [RFC5709].  The changes are:

   RFC 5709, Section 3.3 describes how the cryptographic authentication
   must be computed.  In RFC 5709, the First-Hash includes the OSPF
   packet and Authentication Trailer.  With this specification, the
   64-bit sequence number will be included in the First-Hash along with
   the Authentication Trailer and OSPF packet.

   RFC 5709, Section 3.3 also requires the OSPFv2 packet's
   Authentication Trailer (which is the appendage described in RFC 2328,
   Appendix D.4.3, page 233, items (6)(a) and (6)(d)) to be filled with
   the value Apad.  Apad is a hexadecimal constant with the value
   0x878FE1F3 repeated (L/4) times, where L is the length of the hash
   being used and is measured in octets rather than bits.

   OSPF routers sending OSPF packets must initialize the first 4 octets
   of Apad to the value of the IP source address that would be used when
   sending the OSPFv2 packet.  The remainder of Apad will contain the
   value 0x878FE1F3 repeated (L - 4)/4 times, where L is the length of
   the hash, measured in octets.  The basic idea is to incorporate the
   IP source address from the IP header in the cryptographic
   authentication computation so that any change of IP source address in
   a replayed packet can be detected.

   When an OSPF packet is received, implementations MUST initialize the
   first 4 octets of Apad to the IP source address from the IP header of
   the incoming OSPFv2 packet.  The remainder of Apad will contain the
   value 0x878FE1F3 repeated (L - 4)/4 times, where L is the length of
   the hash, measured in octets.  Besides changing the value of Apad,
   this document does not introduce any other changes to the
   authentication mechanism described in [RFC5709].  This would prevent
   all attacks where a rogue OSPF router changes the IP source address
   of an OSPFv2 packet and replays it on the same multi-access interface
   or another interface since the IP source address is now included in
   the cryptographic hash computation and modification would result in
   the OSPFv2 packet being dropped due to an authentication failure.

6.  Mitigating Cross-Protocol Attacks

   In order to prevent cross-protocol replay attacks for protocols
   sharing common keys, the two-octet OSPFv2 Cryptographic Protocol ID
   is appended to the authentication key prior to use.  Refer to the
   IANA Considerations (Section 9).

   [RFC5709], Section 3.3 describes the mechanism to prepare the key
   used in the hash computation.  This document updates the text under
   "(1) PREPARATION OF KEY" as follows:

      The OSPFv2 Cryptographic Protocol ID is appended to the
      Authentication Key (K) yielding a Protocol-Specific Authentication
      Key (Ks).  In this application, Ko is always L octets long.  While
      [RFC2104] supports a key that is up to B octets long, this
      application uses L as the Ks length consistent with [RFC4822],
      [RFC5310], and [RFC5709].  According to [FIPS-198], Section 3,
      keys greater than L octets do not significantly increase the
      function strength.  Ks is computed as follows:

      If the Protocol-Specific Authentication Key (Ks) is L octets long,
      then Ko is equal to Ks.  If the Protocol-Specific Authentication
      Key (Ks) is more than L octets long, then Ko is set to H(Ks).  If
      the Protocol-Specific Authentication Key (Ks) is less than L
      octets long, then Ko is set to the Protocol-Specific
      Authentication Key (Ks) with zeros appended to the end of the
      Protocol-Specific Authentication Key (Ks) such that Ko is L octets
      long.

   Once the cryptographic key (Ko) used with the hash algorithm is
   derived, the rest of the authentication mechanism described in
   [RFC5709] remains unchanged other than one detail that was
   unspecified.  When XORing Ko and Ipad of Opad, Ko MUST be padded with
   zeros to the length of Ipad or Opad.  It is expected that
   implementations of [RFC5709] perform this padding implicitly.

7.  Backward Compatibility

   This security extension uses a new authentication type, AuType in the
   OSPFv2 header (refer to Figure 1).  When an OSPFv2 packet is received
   and the AuType doesn't match the configured authentication type for
   the interface, the OSPFv2 packet will be dropped as specified in RFC
   2328 [RFC2328].  This guarantees backward-compatible behavior
   consistent with any other authentication type mismatch.

8.  Security Considerations

   This document rectifies the manual key management procedure that
   currently exists within OSPFv2, as part of Phase 1 of the KARP
   Working Group.  Therefore, only the OSPFv2 manual key management
   mechanism is considered.  Any solution that takes advantage of the
   automatic key management mechanism is beyond the scope of this
   document.

   The described sequence number extension offers most of the benefits
   of more complicated mechanisms without their attendant challenges.
   There are, however, a couple drawbacks to this approach.  First, it
   requires the OSPF 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 or the OSPFv2 router is
   replaced, the authentication keys MUST be changed to prevent replay
   attacks.

   Second, if a router is taken out of service completely (either
   intentionally or due to a persistent failure), the potential exists
   for reestablishment of an OSPFv2 adjacency by replaying the entire
   OSPFv2 session establishment.  However, this scenario is extremely
   unlikely, since it would imply an identical OSPFv2 adjacency
   formation packet exchange.  Without adjacency formation, the replay
   of OSPFv2 hello packets alone for an OSPFv2 router that has been
   taken out of service should not result in any serious attack, as the
   only consequence is superfluous processing.  Of course, this attack
   could also be thwarted by changing the relevant manual keys.

   This document also provides a solution to prevent certain denial-of-
   service attacks that can be launched by changing the source address
   in the IP header of an OSPFv2 protocol packet.

   Using a single crypto sequence number can leave the router vulnerable
   to a replay attack where it uses the same source IP address on two
   different point-to-point unnumbered links.  In such environments
   where an attacker can actively tap the point-to-point links, it's
   recommended that the user employ different keys on each of those
   unnumbered IP interfaces.

9.  IANA Considerations

   This document registers a new code point from the "OSPF Shortest Path
   First (OSPF) Authentication Codes" registry:

   o  3 - Cryptographic Authentication with Extended Sequence Numbers.

   This document also registers a new code point from the
   "Authentication Cryptographic Protocol ID" registry defined under
   "Keying and Authentication for Routing Protocols (KARP) Parameters":

   o  3 - OSPFv2.

10.  References

10.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998,
              <http://www.rfc-editor.org/info/rfc2328>.

   [RFC5709]  Bhatia, M., Manral, V., Fanto, M., White, R., Barnes, M.,
              Li, T., and R. Atkinson, "OSPFv2 HMAC-SHA Cryptographic
              Authentication", RFC 5709, October 2009,
              <http://www.rfc-editor.org/info/rfc5709>.

10.2.  Informative References

   [FIPS-198]
              US National Institute of Standards and Technology, "The
              Keyed-Hash Message Authentication Code (HMAC)", FIPS PUB
              198-1, July 2008.

   [RFC2104]  Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
              Hashing for Message Authentication", RFC 2104, February
              1997, <http://www.rfc-editor.org/info/rfc2104>.

   [RFC3414]  Blumenthal, U. and B. Wijnen, "User-based Security Model
              (USM) for version 3 of the Simple Network Management
              Protocol (SNMPv3)", STD 62, RFC 3414, December 2002,
              <http://www.rfc-editor.org/info/rfc3414>.

   [RFC4222]  Choudhury, G., Ed., "Prioritized Treatment of Specific
              OSPF Version 2 Packets and Congestion Avoidance", BCP 112,
              RFC 4222, October 2005,
              <http://www.rfc-editor.org/info/rfc4222>.

   [RFC4822]  Atkinson, R. and M. Fanto, "RIPv2 Cryptographic
              Authentication", RFC 4822, February 2007,
              <http://www.rfc-editor.org/info/rfc4822>.

   [RFC5310]  Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
              and M. Fanto, "IS-IS Generic Cryptographic
              Authentication", RFC 5310, February 2009,
              <http://www.rfc-editor.org/info/rfc5310>.

   [RFC6039]  Manral, V., Bhatia, M., Jaeggli, J., and R. White, "Issues
              with Existing Cryptographic Protection Methods for Routing
              Protocols", RFC 6039, October 2010,
              <http://www.rfc-editor.org/info/rfc6039>.

   [RFC6094]  Bhatia, M. and V. Manral, "Summary of Cryptographic
              Authentication Algorithm Implementation Requirements for
              Routing Protocols", RFC 6094, February 2011,
              <http://www.rfc-editor.org/info/rfc6094>.

   [RFC6549]  Lindem, A., Roy, A., and S. Mirtorabi, "OSPFv2 Multi-
              Instance Extensions", RFC 6549, March 2012,
              <http://www.rfc-editor.org/info/rfc6549>.

   [RFC6862]  Lebovitz, G., Bhatia, M., and B. Weis, "Keying and
              Authentication for Routing Protocols (KARP) Overview,
              Threats, and Requirements", RFC 6862, March 2013,
              <http://www.rfc-editor.org/info/rfc6862>.

   [RFC6863]  Hartman, S. and D. Zhang, "Analysis of OSPF Security
              According to the Keying and Authentication for Routing
              Protocols (KARP) Design Guide", RFC 6863, March 2013,
              <http://www.rfc-editor.org/info/rfc6863>.

   [RFC7210]  Housley, R., Polk, T., Hartman, S., and D. Zhang,
              "Database of Long-Lived Symmetric Cryptographic Keys", RFC
              7210, April 2014,
              <http://www.rfc-editor.org/info/rfc7210>.

Acknowledgments

   Thanks to Ran Atkinson for help in the analysis of errata for RFC
   6506, which led to clarifications in this document.

   Thanks to Gabi Nakibly for pointing out a possible attack on P2P
   links.

   Thanks to Suresh Krishnan for comments made during the Gen-Art
   review.  In particular, thanks for pointing out an ambiguity in the
   initialization of Apad.

   Thanks to Shaun Cooley for the security directorate review.

   Thanks to Adrian Farrel for comments during the IESG last call.

Authors' Addresses

   Manav Bhatia
   Ionos Networks
   Bangalore
   India

   EMail: manav@ionosnetworks.com


   Sam Hartman
   Painless Security

   EMail: hartmans-ietf@mit.edu


   Dacheng Zhang
   Huawei Technologies Co., Ltd.
   Beijing
   China

   EMail: dacheng.zhang@gmail.com


   Acee Lindem (editor)
   Cisco
   United States

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