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One Administrative Domain using BGP

Document Type Active Internet-Draft (individual)
Authors Jim Uttaro , Avinash Lingala , Keyur Patel , Dhananjaya Rao , Bin Wen , Alvaro Retana , Srihari R. Sangli , Prodosh Mohapatra
Last updated 2023-03-13
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Inter-Domain Routing                                           J. Uttaro
Internet-Draft                                                A. Lingala
Intended status: Standards Track                                    AT&T
Expires: 11 September 2023                                      K. Patel
                                                            Arrcus, Inc.
                                                                  D. Rao
                                                           Cisco Systems
                                                                  B. Wen
                                                               A. Retana
                                            Futurewei Technologies, Inc.
                                                               S. Sangli
                                                        Juniper Networks
                                                            P. Mohapatra
                                                        Sproute Networks
                                                           10 March 2023

                  One Administrative Domain using BGP


   This document defines a new External BGP (EBGP) peering type known as
   EBGP-OAD.  EBGP-OAD peering is used between two EBGP peers that
   belong to One Administrative Domain (OAD).

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

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   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 11 September 2023.

Copyright Notice

   Copyright (c) 2023 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Discussion  . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Operation . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Next Hop Handling . . . . . . . . . . . . . . . . . . . .   4
     3.2.  MULTI_EXIT_DISC (MED) Handling  . . . . . . . . . . . . .   4
     3.3.  Route Reflection  . . . . . . . . . . . . . . . . . . . .   4
   4.  Deployment and Operational Considerations . . . . . . . . . .   4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   At each EBGP boundary, BGP path attributes are modified as per
   standard BGP rules [RFC4271].  This includes prepending the AS_PATH
   attribute with the autonomous-system number of the BGP speaker and
   stripping any IBGP-only attributes.

   Some networks span more than one autonomous system and require more
   flexibility in the propagation of path attributes.  These networks
   are said to belong to One Administrative Domain (OAD).  It is
   desirable to carry IBGP-only attributes across EBGP peering when the
   peers belong to OAD.  This document defines a new EBGP peering type
   known as EBGP-OAD.  EBGP-OAD peering is used between two EBGP peers
   that belong to OAD.  This document also defines rules for route
   announcement and processing for EBGP-OAD peers.

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1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Discussion

   Networks have traditionally been demarcated by an autonomous system/
   BGP border which correlates to an administrative boundary.  This
   paradigm no longer serves the needs of network designers or customers
   due to the decoupling of IGP from BGP, BGP-free core in the underlay
   (e.g. using BGP labeled unicast [RFC8277]), the use of BGP to
   facilitate multiple service overlays (e.g., L2VPN, L3VPN, etc.)
   spanning multiple regions and AS domains, and the instantiation of
   customer sites on multiple content service providers (CSPs).

   For example, sites in a BGP/MPLS VPN [RFC4364] may be distributed
   across different AS domains.  In some cases, the administrator of the
   VPN may prefer that some attributes are propagated to all their sites
   to influence the BGP decision process.  An example could be
   LOCAL_PREF which is ignored if received on an EBGP session [RFC4271].

3.  Operation

   [RFC4271] defines two types of BGP peerings used during a BGP
   protocol session.  As part of the extensions defined in this
   document, the EBGP peering is divided into two types:

   1.  EBGP as defined in [RFC4271].

   2.  EBGP-OAD as defined below.

   The EBGP-OAD session is a BGP connection between two external peers
   in different Autonomous Systems that belong to OAD.  In general, the
   EBGP-OAD speakers follow the EBGP route advertisement, route
   processing, path attribute announcement and processing rules as
   defined in [RFC4271].  However, EBGP-OAD speakers are also allowed to
   announce and receive any IBGP-only or non-transitive attributes that
   were restricted to remain within an Autonomous System [RFC4271].

   Unless explicitly specified, all path attributes MAY be advertised
   over an EBGP-OAD session.  The reception of any path attribute over
   an EBGP-OAD session MUST NOT result in an error, unless it is
   malformed.  Received path attributes SHOULD NOT be ignored by the
   receiver, unless directed to by local policy.

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   Unless explicitly specified, the current processes for the
   advertisement of path attributes remains unchanged when advertised
   through an EBGP-OAD peering.  The process for EBGP advertisement MUST
   take priority over the process for IBGP advertisement.  For example,
   the AS_PATH attribute is modified as specified in Section 5.1.2 of
   [RFC4271], bullet b ("BGP speaker advertises the route to an external

   An EBGP-OAD speaker MUST support four-octet AS numbers and avertize
   the "support for four-octet AS number capability" [RFC6793] .

   The following sections describe modifications to route advertisements
   and path attribute announcements that are specific to the EBGP-OAD

3.1.  Next Hop Handling

   It is reasonable for EBGP-OAD peers to share a common Interior
   Gateway Protocol (IGP).  In such a case, NEXT_HOP attribute and the
   Next Hop in the MP_REACH_NLRI attribute [RFC4760] MAY be left

3.2.  MULTI_EXIT_DISC (MED) Handling

   The determination of the neighboring AS for the purpose of BGP Route
   Selection [RFC4271] MAY also consider the ASN of the EBGP-OAD peer.
   If so, all the peers in the receiving ASN MUST be configured to use
   the same criteria.

3.3.  Route Reflection

   BGP Route Reflection [RFC4456] is an alternative to full-mesh IBGP.
   The ORIGINATOR_ID and CLUSTER_LIST attributes MUST NOT be advertised
   over an EBGP-OAD session.  If received, the procedures in [RFC7606]

4.  Deployment and Operational Considerations

   For the EBGP-OAD session to operate as expected, both BGP speakers
   MUST be configured with the same session type.  If only one BGP
   speaker is configured that way, and the other uses an EBGP session,
   the result is that some path attributes may be ignored and others
   will be discarded, but the BGP session will remain operational.

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   The default BGP peering type for a session that is across autonomous
   systems SHOULD be EBGP.  BGP implementation SHOULD provide a
   configuration-time option to enable the EBGP-OAD session type.  If
   the session type is changed once the BGP connection has been
   established, the BGP speaker MUST readvertise its entire Adj-RIB-Out
   to its peer.  Requesting a route refresh [RFC7313] is RECOMMENDED.

   The requirement that Import and Export Policies exist [RFC8212]
   SHOULD be disabled if both peers are configured with the EBGP-OAD
   session type.

   If multiple peerings exist between two autonomous systems that belong
   to OAD, all SHOULD be configured consistently.  Improper
   configuration may result in inconsistent or unexpected forwarding.
   The inconsistent use of EBGP-OAD sessions is out of scope of this

   BGP Confederations [RFC5065] provide similar behavior, on a session
   by session basis, as what is specified in this document.  The use of
   confederations with an EBGP-OAD peering is out of scope of this

   The consideration of the ASN of the EBGP-OAD peer to determine the
   neighboring AS for MED comparison Section 3.2 may result in the
   creation persistent route oscillations, similar to the Type II Churn
   described in [RFC3345].  [RFC7964] provides solutions and
   recommendations to address this issue.

5.  IANA Considerations

   This memo includes no request to IANA.

6.  Security Considerations

   This extension to BGP does not change the underlying security issues
   inherent in the existing BGP protocol, such as those described in
   [RFC4271] and [RFC4272].

   This document defines a new BGP session type which combines the path
   attribute propagation rules for EBGP and IBGP peering.  Any existing
   security considerations related to existing path attributes apply to
   the new EBGP-OAD session type.

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   By combining the path attribute propagation rules, IBGP information
   may now be propagated to another autonomous system.  However, it is
   expected that the new session type will only be enabled when peering
   with a router that also belongs to OAD.  If misconfigured, the impact
   is minimal due to the fact that both [RFC4271] and [RFC7606] define
   mechanisms to deal with unexpected path attributes.

7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [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,

   [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,

   [RFC5065]  Traina, P., McPherson, D., and J. Scudder, "Autonomous
              System Confederations for BGP", RFC 5065,
              DOI 10.17487/RFC5065, August 2007,

   [RFC6793]  Vohra, Q. and E. Chen, "BGP Support for Four-Octet
              Autonomous System (AS) Number Space", RFC 6793,
              DOI 10.17487/RFC6793, December 2012,

   [RFC7313]  Patel, K., Chen, E., and B. Venkatachalapathy, "Enhanced
              Route Refresh Capability for BGP-4", RFC 7313,
              DOI 10.17487/RFC7313, July 2014,

   [RFC7606]  Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K.
              Patel, "Revised Error Handling for BGP UPDATE Messages",
              RFC 7606, DOI 10.17487/RFC7606, August 2015,

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   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.

   [RFC8212]  Mauch, J., Snijders, J., and G. Hankins, "Default External
              BGP (EBGP) Route Propagation Behavior without Policies",
              RFC 8212, DOI 10.17487/RFC8212, July 2017,

7.2.  Informative References

   [RFC3345]  McPherson, D., Gill, V., Walton, D., and A. Retana,
              "Border Gateway Protocol (BGP) Persistent Route
              Oscillation Condition", RFC 3345, DOI 10.17487/RFC3345,
              August 2002, <>.

   [RFC4272]  Murphy, S., "BGP Security Vulnerabilities Analysis",
              RFC 4272, DOI 10.17487/RFC4272, January 2006,

   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
              Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
              2006, <>.

   [RFC4760]  Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
              "Multiprotocol Extensions for BGP-4", RFC 4760,
              DOI 10.17487/RFC4760, January 2007,

   [RFC7964]  Walton, D., Retana, A., Chen, E., and J. Scudder,
              "Solutions for BGP Persistent Route Oscillation",
              RFC 7964, DOI 10.17487/RFC7964, September 2016,

   [RFC8277]  Rosen, E., "Using BGP to Bind MPLS Labels to Address
              Prefixes", RFC 8277, DOI 10.17487/RFC8277, October 2017,



Authors' Addresses

   Jim Uttaro

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   Avinash Lingala

   Keyur Patel
   Arrcus, Inc.

   Dhananjaya Rao
   Cisco Systems

   Bin Wen

   Alvaro Retana
   Futurewei Technologies, Inc.

   Srihari Sangli
   Juniper Networks

   Pradosh Mohapatra
   Sproute Networks

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