Network Working Group                                          J. Uttaro
Internet-Draft                                                      AT&T
Updates: 5575bis (if approved)                                J. Alcaide
Intended status: Standards Track                             C. Filsfils
Expires: November 10, 2019 January 9, 2020                                        D. Smith
                                                                   Cisco
                                                            P. Mohapatra
                                                        Sproute Networks
                                                             May 9,
                                                            July 8, 2019

        Revised Validation Procedure for BGP Flow Specifications
                   draft-ietf-idr-bgp-flowspec-oid-08
                   draft-ietf-idr-bgp-flowspec-oid-09

Abstract

   This document describes a modification to the validation procedure
   defined in RFC 5575bis for the dissemination of BGP flow
   specifications. Flow
   Specifications.  RFC 5575bis requires that the originator of the flow
   specification Flow
   Specification matches the originator of the best-match unicast route
   for the destination prefix embedded in the flow specification. Flow Specification.  This
   allows only BGP speakers within the data forwarding path (such as
   autonomous system border routers) to originate BGP flow
   specifications. Flow
   Specifications.  Though it is possible to disseminate such flow
   specifications Flow
   Specifications directly from border routers, it may be operationally
   cumbersome in an autonomous system with a large number of border
   routers having complex BGP policies.  The modification proposed
   herein enables flow specifications Flow Specifications to be originated from a
   centralized BGP route controller.

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
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   This Internet-Draft will expire on November 10, 2019. January 9, 2020.

Copyright Notice

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   document authors.  All rights reserved.

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Table of Contents

   1.  Requirements Language . . . . . . . . . . . . . . . . . . . .   2
   2.  Motivation  .  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Introduction  Motivation  . . . . . . . . . . . . . . . . . . . . . . . .   4 .   3
   4.  Revised Validation Procedure  . . . . . . . . . . . . . . . .   5
     4.1.  Revision of Route Feasibility . . . . . . . . . . . . . .   5
     4.2.  Revision of AS_PATH Validation  . . . . . . . . . . . . .   6
   5.  Other RFC5575bis Considerations . . . . . . . . . . . . . . .   7
   6.  Topology Considerations . . . . . . . . . . . . . . . . . . .   8
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   6.   9
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   7.   9
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   8.  10
   10. Normative References  . . . . . . . . . . . . . . . . . . . .   7  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8  10

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].

2.  Motivation

   Step (a) of the validation procedure in [RFC5575bis], section 6 is  Introduction

   [RFC5575bis] defined with the underlying assumption that the flow specification
   NLRI traverses the same path, in the inter-domain and intra-domain
   route distribution graph, as a new BGP [RFC4271] capability that of the longest-match unicast route
   for the destination prefix embedded can be used
   to distribute traffic Flow Specifications amongst BGP speakers in the flow specification.

   In the case
   support of inter-domain traffic filtering, for example, the flow
   specification originator at the egress border routers filtering.  The primary intention of ASN1 (RTR-D
   and RTR-E in figure 1) matches the EBGP neighbor that advertised [RFC5575bis]
   is to enable downstream autonomous systems to signal traffic
   filtering policies to upstream autonomous systems.  In this way,
   traffic is filtered closer to the
   longest match destination prefix (RTR-F source and RTR-G respectively).
   Similarly, at the ingress border routers of ASN1 (RTR-A and RTR-B in
   figure 1), upstream autonomous
   system(s) avoid carrying the flow specification originator matches traffic to the egress IBGP
   border routers downstream autonomous
   system only to be discarded.  [RFC5575bis] also enables more granular
   traffic filtering based upon upper layer protocol information (e.g.,
   protocol port numbers) as opposed to coarse IP destination prefix-
   based filtering.  Flow specification NLRIs received from a BGP peer
   are subject to validity checks before being considered feasible and
   subsequently installed within the respective Adj-RIB-In.

   The validation procedure defined within [RFC5575bis] requires that had advertised
   the originator of the Flow Specification NLRI matches the originator
   of the best-match unicast route for the best-
   match destination prefix (RTR-D and RTR-E respectively). embedded
   in the Flow Specification.  This allows only BGP speakers within the
   data forwarding path (such as autonomous system border routers) to
   originate BGP Flow Specification NLRIs.  Though it is
   true even when ingress possible to
   disseminate such Flow Specification NLRIs directly from border
   routers, it may be operationally cumbersome in an autonomous system
   with a large number of border routers select paths having complex BGP policies.

   This document describes a modification to the [RFC5575bis] validation
   procedure allowing Flow Specification NLRIs to be originated from different
   egress a
   centralized BGP route controller within the local autonomous system
   that is not in the data forwarding path.  While the proposed
   modification cannot be used for inter-domain coordination of traffic
   filtering, it greatly simplifies distribution of intra-domain traffic
   filtering policies within an autonomous system which has a large
   number of border routers as best path based upon IGP distance (as an
   example, RTR-A chooses RTR-D's path as best; RTR-B chooses RTR-E as having complex BGP policies.  By relaxing
   the best path).

                     / - - - - - - - - - - - - -  -
                     |           ASN1              |
                       +-------+        +-------+
                     | validation procedure for iBGP, the proposed modification allows
   Flow Specifications to be distributed in a standard and scalable
   manner throughout an autonomous system.

3.  Motivation

   Step (a) of the validation procedure in [RFC5575bis], section 6 is
   defined with the underlying assumption that the Flow Specification
   NLRI traverses the same path, in the inter-domain and intra-domain
   route distribution graph, as that of the longest-match unicast route
   for the destination prefix embedded in the Flow Specification.

   In the case of inter-domain traffic filtering, the Flow Specification
   originator at the egress border routers of an AS (e.g.  RTR-D and
   RTR-E of ASN1 in figure 1) matches the eBGP neighbor that advertised
   the longest match destination prefix (see RTR-F and RTR-G
   respectively in figure 1).  Similarly, at the ingress border routers
   of ASN (see RTR-A and RTR-B of ASN1 in figure 1), the Flow
   Specification originator matches the egress iBGP border routers that
   had advertised the unicast route for the best-match destination
   prefix (see RTR-D and RTR-E respectively in figure 1).  This is true
   even when ingress border routers select paths from different egress
   border routers as best path based upon IGP distance.  For example, in
   figure 1:

      RTR-A chooses RTR-D's path as best

      RTR-B chooses RTR-E as the best path

                     / - - - - - - - - - - - - -  -
                     |           ASN1              |
                       +-------+        +-------+
                     | |       |        |       |  |
                       | RTR-A |        | RTR-B |
                     | |       |        |       |  |
                       +-------+        +-------+
                     |       \           /         |
                        IBGP
                        iBGP  \         / IBGP iBGP
                     |         \       /           |
                               +-------+
                     |         |       |           |
                               | RTR-C |
                     |         |  RC   |           |
                               +-------+
                     |           /   \             |
                                /     \
                     |   IBGP   iBGP  /       \ IBGP iBGP      |
                       +-------+        +-------+
                     | | RTR-D |        | RTR-E |  |
                       |       |        |       |
                     | |       |        |       |  |
                       +-------+        +-------+
                     |     |                 |     |
                      - - -|- - - - - - - - -|- - -/
                           | EBGP       EBGP eBGP       eBGP |
                      - - -|- - - - - - - - -|- - -/
                     |     |                 |     |
                       +-------+        +-------+
                     | |       |        |       |  |
                       | RTR-F |        | RTR-G |
                     | |       |        |       |  |
                       +-------+        +-------+
                     |           ASN2              |
                     / - - - - - - - - - - - - -  -

                                 Figure 1

   It is highly desirable that each ASN is able to protect itself
   independently from network security attacks using the BGP flow
   specification NLRI for intra-domain purposes only.  Network operators
   often deploy a dedicated Security Operations Center (SOC) within
   their ASN to monitor and detect such security attacks.  To mitigate
   attacks in a scalable intra-domain manner, operators require the
   ability to originate intra-domain flow specification NLRIs from a
   central BGP route controller that is not within the data forwarding
   plane.  In this way, operators can direct border routers within their
   ASN with specific attack mitigation actions (drop the traffic,
   forward to a clean-pipe center, etc.).  To originate a flow
   specification NLRI, a central BGP route controller must set itself as
   the originator in the flowspec NLRI.  This is necessary given the
   route controller is originating the flow specification not reflecting
   it, and to avoid the complexity of having to determine the egress
   border router whose path was chosen as the best in each of the
   ingress border routers.  It thus becomes necessary to modify step (a)
   of the [RFC5575bis] validation procedure such that an IBGP peer that
   is not within the data forwarding plane may originate flow
   specification NLRIs.

3.  Introduction

   [RFC5575bis] defined a new BGP capability that can be used to
   distribute traffic flow specifications amongst BGP speakers in
   support of traffic filtering.  The primary intention of [RFC5575bis]
   is to enable downstream autonomous systems to signal traffic
   filtering policies to upstream autonomous systems.  In this way,
   traffic is filtered closer to the source and the upstream autonomous
   system(s) avoid carrying the traffic to the downstream autonomous
   system only to be discarded.  [RFC5575bis] also enables more granular
   traffic filtering based upon upper layer protocol information (e.g.,
   protocol port numbers) as opposed to coarse IP destination prefix-
   based filtering.  Flow specification NLRIs received from a BGP peer
   are subject to validity checks before being considered feasible and
   subsequently installed within the respective Adj-RIB-In.  The
   validation procedure defined within [RFC5575bis] requires that the
   originator of the flow specification NLRI matches the originator of
   the best-match unicast route for the destination prefix embedded in
   the flow specification.  This allows only BGP speakers [RFC4271]
   within the data forwarding path (such as autonomous system border
   routers) to originate BGP flow specification NLRIs.  Though it  -

                                 Figure 1

   It is
   possible highly desirable that the mechanisms exist to disseminate such flow specification NLRIs directly protect each ASN
   independently from
   border routers, it may be operationally cumbersome in an autonomous
   system with a large number of border routers having complex network security attacks using the BGP
   policies.  This document describes Flow
   Specification NLRI for intra-domain purposes only.  Network operators
   often deploy a modification dedicated Security Operations Center (SOC) within
   their ASN to monitor and detect such security attacks.  To mitigate
   attacks within a domain (AS or group of ASes), operators require the [RFC5575bis]
   validation procedure allowing flow specification NLRIs
   ability to be
   originated originate intra-domain Flow Specification NLRIs from a centralized
   central BGP route controller within the local
   autonomous system that is not in within the data forwarding path.  While
   plane.  In this way, operators can direct border routers within their
   ASN with specific attack mitigation actions (drop the
   proposed modification cannot be used for inter-domain coordination of
   traffic filtering, it greatly simplifies distribution traffic,
   forward to a clean-pipe center, etc.).

   To originate a Flow Specification NLRI, a central BGP route
   controller must set itself as the originator in the Flow
   Specification NLRI.  This is necessary given the route controller is
   originating the Flow Specification rather than reflecting it, and to
   avoid the complexity of intra-domain
   traffic filtering policies having to determine the egress border router
   whose path was chosen as the best in an autonomous system with a large
   number each of the ingress border routers having complex BGP policies.  By relaxing
   routers.  Thus, it is necessary to modify step (a) of the
   [RFC5575bis] validation procedure for IBGP, the proposed modification allows
   flow specifications to be distributed in a standard and scalable
   manner throughout such that an autonomous system. iBGP peer that is not
   within the data forwarding plane may originate Flow Specification
   NLRIs.

4.  Revised Validation Procedure

4.1.  Revision of Route Feasibility

   Step (a) of the validation procedure specified in [RFC5575bis],
   section 6 is redefined as follows:

   a.  One of the following conditions MUST hold true.

       *

       1.  The originator of the flow specification Flow Specification matches the
           originator of the best-match unicast route for the
           destination prefix embedded in the flow specification.

       * Flow Specification.

       2.  The AS_PATH attribute of the flow specification Flow Specification does not
           contain AS_SET and/or AS_SEQUENCE segments.

   An

           1.  This condition SHOULD be enabled by default.  This
               default behavior should validate an empty AS_PATH.

           2.  This condition MAY be disabled by configuration on a BGP
               speaker.

           3.  As an exception to this rule, a given AS_PATH without with AS_SET
               and/or AS_SEQUENCE segments indicates MAY be validated by policy.

   Explanation:

      In this context, an empty AS_PATH means that
   the flow specification was originated inside it does not have
      AS_SET and/or AS_SEQUENCE segments, and local domain means the
      local AS [RFC4271] or inside the local confederation of ASes (in the case
      that the local AS belongs to a confederation of ASes) [RFC5065]. ASes [RFC5065]).

      Thus, receiving a Flow Specification with an empty AS_PATH
      indicates that the Flow Specification was originated inside the
      local domain.

      With this the above modification to the [RFC5575bis] validation
      procedure, it is now
   possible for an IBGP a BGP peer within the local domain that is not within
      the data forwarding path
   to can originate flow specification NLRIs.  This applies whether the AS
   belongs or not to a confederation of ASes.  Checking the (newly
   introduced) second condition above MAY be disabled by configuration
   on a BGP speaker.  However, it SHOULD be enabled by default. Flow Specification.

      Disabling the new condition above (a.2.2) may be a good practice
      when the administrator operator knows with certainty that there are is not flow specification NLRI a Flow
      Specification originated inside the local AS (or local confederation).  The default
   behavior is thus domain.

      Also, policy may be useful to validate an empty AS_PATH.  In this context, an
   empty AS_PATH means that it does not have AS_SET and/or AS_SEQUENCE
   segments.  Optionally, an implementation MAY also validate a specific set of non-empty AS_PATH.
      AS_PATHs (a.2.3).  For instance, example, it could validate a flowspec NLRI Flow
      Specification whose AS_PATH contains only an AS_SEQUENCE of with ASes
      that are all known (via
   configuration) to belong to the same administrative domain.

   Further,

4.2.  Revision of AS_PATH Validation

   [RFC5575bis] states that "BGP (flow specification) states:

   o  BGP implementations MUST also enforce that the AS_PATH attribute
      of a route received via the External Border Gateway Protocol (EBGP)
      (eBGP) contains the neighboring AS in the left-most position of
      the AS_PATH attribute". attribute.

   This rule is not valid for all topologies.  For example, it prevents the exchange of BGP flow specification Flow Specification NLRIs at
   Internet exchanges with BGP route servers.  Therefore, this document
   also redefines the [RFC5575bis] AS_PATH validation procedure
   referenced above as follows:

   o  BGP flow specification Flow Specification implementations MUST enforce that the last AS
   added within in
      the left-most position of the AS_PATH attribute of a EBGP learned flow
   specification NLRI MUST match Flow
      Specification route received via the External Border Gateway
      Protocol (eBGP) matches the last AS added within in the left-most position of the
      AS_PATH attribute of the best-match unicast route for the
      destination prefix embedded in the flow specification. Flow Specification NLRI.

   Explanation:

      For clarity, the AS in the left-most position of the AS_PATH means
      the AS that was last added to the AS_SEQUENCE.

      This proposed modification enables the exchange of BGP flow specification Flow
      Specification NLRIs at Internet exchanges with BGP route servers
      while at the same time, for security reasons, prevents an EBGP eBGP
      peer from advertising an inter-domain flow
   specification Flow Specification for a
      destination prefix that it does not provide reachability
      information for.  Note, comparing

      Comparing only the last ASes added is sufficient for EBGP eBGP learned flow specification
      Flow Specification NLRIs.  Requiring a full AS_PATH match would
      limit origination of inter-
   domain flow specifications inter-domain Flow Specifications to the
      origin (or first) AS of the best-
   match best-match unicast route for the destination
      prefix embedded in the Flow Specification only.  As such, a full
      AS_PATH validity check may prevent transit ASes from originating
      inter-domain Flow Specifications, which is not desirable.

      Redefinition of this AS_PATH validation rule for a Flow
      Specification does not mean that the original rule in [RFC5575bis]
      cannot be enforced as well.  Its enforcement remains optional per
      [RFC4271].  That is, we can enforce the first AS in the AS_PATH to
      be the same as the neighbor AS for any address-family route
      (including a Flow Specification).

      Using the new rule to validate a Flow Specification received from
      an Internal Border Gateway Protocol (iBGP) peer is out of the
      scope of this document.  Note that in most scenarios such
      validation would be redundant.

      Using the new rule to validate a Flow Specification route received
      from an External Border Gateway Protocol (eBGP) peer belonging to
      the same local domain (in the case that the local AS belongs to a
      confederation of ASes) is out of the scope of this document.  Note
      that although it's possible, its utility is dubious.

5.  Other RFC5575bis Considerations

   This section clarifies some of the terminology and rules referenced
   in [RFC5575bis].  Namely:

   o  [RFC5575bis] references "the best-match unicast route for the
      destination prefix embedded in the Flow Specification".  For
      clarity, this route is defined hereby as the best path of the
      unicast network with the longer prefix-length that covers the
      destination prefix embedded in the Flow Specification.

   Explanation:

      We consider only the best-match network and we do not consider
      unicast route for non-best paths (even if it is received from the destination prefix embedded in same peer
      as the flow
   specification only.  As such, Flow Specification).

   o  If a full AS_PATH validity check may
   prevent transit ASes from originating inter-domain flow
   specifications, which is not desirable.

   This document also clarifies proper handling when the BGP flow
   specification Flow Specification does not embed a destination prefix component.  The
      component, then the default behavior SHOULD be not to perform any the
      validation procedure.
   Further, support procedures.

   Explanation:

      The reason for two-octet AS number space this is out of because the scope of best-match unicast route is not
      defined in this document. case.

   o  In the context of this context, document and [RFC5575bis], AS_PATH
      attribute is defined as the reconstructed AS
   Path path information (by
      combining AS_PATH and AS4_PATH attributes, if the BGP speaker is a
      NEW speaker and receives the route from an OLD speaker), according
      to section 4.2.3 of [RFC6793].

   [RFC5575bis] references "the best-match unicast route

   o  Support for the
   destination prefix embedded in the flow specification".  For clarity,
   this route two-octet AS only implementations is defined hereby as the best path out of the unicast network scope
      of this document (i.e. it's assumed that covers destination prefix embedded in the flow specification
   with the longer prefix-length.  In other words, we consider only the
   best-match network and we do not consider unicast non-best paths
   (even if it is received from the same peer than BGP speaker supports
      [RFC6793]).

6.  Topology Considerations

   [RFC5575bis] indicates that the flowspec route).

   Note that, per [RFC5575bis], originator may refer to the BGP
   ORIGINATOR_ID
   originator path attribute (ORIGINATOR_ID) or (if the attribute is not
   present) the transport address of the peer from which we received the
   update.  If the later, latter applies, a network must should be designed so it
   has a congruent topology.  Otherwise, using

   With the additional second condition (a.2) in the validation
   procedure, non-congruent topologies are supported within the local
   domain if the Flow Specification is originated within the local
   domain.

   Explanation:

      Consider the following scenarios without the second condition
      (a.2) being added to the validation procedure:

      1.  Consider a topology with two BGP speakers with two peering
          sessions between the same pair of BGP speakers, them, one for unicast and one for flowspec, will cause the flowspec validation
   procedure to fail.  Consider, for example, the case where a BGP route
   reflector receives the NLRIs from Flow
          Specification.  This is a route reflector client, thus not
   receiving non-congruent topology.  Let's
          assume that the ORIGINATOR_ID attribute.  If the speaker belongs to a
   confederation [RFC5065] and we are receiving attribute was not received (e.g.
          a flowspec route reflector receiving routes from
   different peers than its best match unicast route, clients).  In this
          case, the flowspec Flow Specification validation procedure will fail as well.
          because of the first condition (a.1).

      2.  Consider also a
   misconfiguration where flowspec address-family is not configured for topology with a particular peering between different member-AS (but it BGP speaker within a confederation
          of ASes, inside local AS X.  ORIGINATOR_ID attribute is
   configured for unicast).  Even if we receive not
          advertised within the flowspec route via a
   redundant peer, we may receive local domain.  Let's assume the unicast Flow
          Specification route is received from peer A and the flowspec best-match
          unicast route is received from different peers, peer B.  Both peers belong in
          local AS Y.  Both AS X and thus flowspec AS Y belong to the same local
          domain.  The Flow Specification validation procedure will fail.  Thus,
   with also
          fail because of the first condition (a.1).

      In the examples above, if Flow Specifications are originated in
      the same local domain, AS_PATH will not contain AS_SET and/or
      AS_SEQUENCE segments.  When the (newly introduced) second condition above applied,
   incongruent (a.2) in the
      validation procedure is used, the validation procedure will pass.
      Thus, non-congruent topologies are supported.

   Note that supported if the flowspec NLRI Flow
      Specification is learned from another AS (and thus originated in the AS_PATH same local domain.

      Even when the second condition (a.2) is not empty), used in the original validation procedures defined
      procedure, a Flow Specification originated in [RFC5575bis] still apply a different local
      domain needs a congruent topology.  AS_SEQUENCE is not empty and incongruent topologies may cause
      the first condition (a.1) in the validation rules procedure needs to be
      evaluated.  Because transport addresses for Flow Specification and
      unicast routes are different, the validation procedure will fail.

5.
      This is true both across domains and within domains.  Consider
      both cases:

      *  Consider the first example.  If the Flow Specification route is
         originated in another AS, the validation procedure will fail
         because the topology is non-congruent within the domain.

      *  Consider the second example and modify it so AS X and AS Y
         belong to different local domains (no confederation of ASes
         exists).  The validation procedure will fail because the
         topology is non-congruent across domains.

7.  IANA Considerations

   This memo includes no request to IANA.

6.

8.  Security Considerations

   No new security issues are introduced by relaxing the validation
   procedure for IBGP iBGP learned flow specifications. Flow Specifications.  With this proposal,
   the security characteristics of BGP flow specifications Flow Specifications remain
   equivalent to the existing security properties of BGP unicast
   routing.  Traffic flow specifications Flow Specifications learned from IBGP iBGP peers are
   trusted, hence, it is not required to validate that the originator of
   an intra-domain traffic flow specification Flow Specification matches the originator of
   the best-match unicast route for the flow destination prefix.
   Conversely, this proposal continues to enforce the validation
   procedure for EBGP eBGP learned traffic flow specifications. Flow Specifications.  In this way,
   the security properties of [RFC5575bis] are maintained such that an
   EBGP
   eBGP peer cannot cause a denial-of-service attack by advertising an
   inter-domain flow specification Flow Specification for a destination prefix that it does
   not provide reachability information for.

7.

9.  Acknowledgements

   The authors would like to thank Han Nguyen for his direction on this
   work as well as Waqas Alam, Keyur Patel, Robert Raszuk, Eric Rosen
   and Shyam Sethuram for their review comments.

8.

10.  Normative References

   [I-D.ietf-idr-rfc5575bis]
              Hares, S., Loibl, C., Raszuk, R., McPherson, D., and M.
              Bacher, "Dissemination of Flow Specification Rules",
              draft-ietf-idr-rfc5575bis-14 (work in progress), April
              2019.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271,
              DOI 10.17487/RFC4271, January 2006,
              <https://www.rfc-editor.org/info/rfc4271>.

   [RFC4456]  Bates, T., Chen, E., and R. Chandra, "BGP Route
              Reflection: An Alternative to Full Mesh Internal BGP
              (IBGP)", RFC 4456, DOI 10.17487/RFC4456, April 2006,
              <https://www.rfc-editor.org/info/rfc4456>.

   [RFC5065]  Traina, P., McPherson, D., and J. Scudder, "Autonomous
              System Confederations for BGP", RFC 5065,
              DOI 10.17487/RFC5065, August 2007,
              <https://www.rfc-editor.org/info/rfc5065>.

   [RFC6793]  Vohra, Q. and E. Chen, "BGP Support for Four-Octet
              Autonomous System (AS) Number Space", RFC 6793,
              DOI 10.17487/RFC6793, December 2012,
              <https://www.rfc-editor.org/info/rfc6793>.

Authors' Addresses
   James Uttaro
   AT&T
   200 S. Laurel Ave
   Middletown, NJ  07748
   USA

   Email: ju1738@att.com

   Juan Alcaide
   Cisco
   7100 Kit Creek Road
   Research Triangle Park, NC  27709
   USA

   Email: jalcaide@cisco.com

   Clarence Filsfils
   Cisco

   Email: cf@cisco.com

   David Smith
   Cisco
   111 Wood Ave South
   Iselin, NJ  08830
   USA

   Email: djsmith@cisco.com

   Pradosh Mohapatra
   Sproute Networks

   Email: mpradosh@yahoo.com