BGP FLEX
draft-bgp-flex-00

Internet Engineering Task Force                          ZB. ZOUNDI, Ed.
Internet-Draft                                          12 February 2026
Intended status: Informational                                          
Expires: 16 August 2026

                                BGP FLEX
                           draft-bgp-flex-00

Abstract

   The Border Gateway Protocol (BGP) is a very important protocol in the
   Internet to exchange routing information between network domains.
   BGP populates the routing table with valid routes, sometimes the
   routes populated by BGP are not the best choices specially when a ISP
   provides IP Transit service to an other ISP, and the two ISP are
   peering at an Internet Exchange Point.

   Let us assume that ISP A provides IP Transit to ISP B, and the two
   are peering at an Internet Exchange Point.
   The return traffic from Internet to ISP B via ISP A will be routed
   over the Internet Exchange Point instead of the IP Transit link
   between the two ISP, because of BGP Local preference which has
   usually a higher value on Internet Exchange links.
   This will lead to an issue because the return traffic IP Transit
   service is now passing over the Internet Exchange link.

   An other issue faced in Internet Exchange Point, is the sub-optimal
   routing caused by the advertisment of the most specific routes over
   Internet by ISP.
   Let us assume that ISP A wants to advertise most specific routes to
   Internet for traffic Engineering, the peers of ISP A at the Internet
   Exchange Point could also receive the most specific routes over
   Internet .
   This will mean that traffic from the peers of ISP A towards ISP A
   will now go through Internet because of most specific routes which is
   not suppposed to be the case.

   To solve that ISP A will have to send the same specific routes over
   the Internet Exchange Point which will increase complexity.
   This document provides aletrnative solutions that can be used to
   solve the above problems

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Acronyms  . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  BGP Flex  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  BGP Flex Concepts . . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  BGP Local Source IP (BLSI)  . . . . . . . . . . . . . . .   4
     4.2.  BGP Remote Source IP (BRSI) . . . . . . . . . . . . . . .   4
     4.3.  BGP Remote Peer IP (BRPI) . . . . . . . . . . . . . . . .   4
     4.4.  Source IP Router Advertiser (SIRA)  . . . . . . . . . . .   4
   5.  Routing mode in BGP Flex  . . . . . . . . . . . . . . . . . .   5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

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1.  Introduction

   In the past years BGP has been operating by relying on the same route
   table for Internet Exchange and Internet prefixes.
   As explained above there are issues caused by this BGP behaviour.

   To solve these issues, we would like to propose protocol based on BGP
   called BGP Flex.  BGP Flex will create two different routing tables
   like VRF concepts.
   One route table will be populated with prefixes received over
   Internet Exchange links and the other one with prefixes received over
   Internet.  The decision to use a particular route table will depend
   on some criterias that will be discussed in this document.

2.  Terminology

2.1.  Acronyms

   1.  IX : Internet Exchange

   2.  IXP : Internet Exchange Point

   3.  BLSI : BGP Local Source IP

   4.  BRSI : BGP Remote Source IP

   5.  SIRA : Source IP Router Advertiser

   6.  BRPI : BGP Remote Peer IP

   7.  CISP : Customer ISP refers the ISP buying service from an other
       ISP

   8.  SISP : Seller ISP refers to the ISP selling service to customer
       ISP

3.  BGP Flex

   As explained in the introduction, the routing issues mentionned there
   can be solved by BGP Flex.
   BGP Flex is an extension of BGP that will create a dedicated IX route
   table different from the default routing table.
   When BGP will advertise the routes over the IX, these routes will be
   marked as IX routes on the receiving router and will be inserted into
   the IX route table.
   The decision to choose a particular routing table will depend on the
   classification of the packet.
   This has been explained in the section 5 of this document.

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   The fact that IX route table is separated from Internet route table
   will solve routing issues and the sub-optimal routing described in
   abstract section, because each route table is independant of the
   other.

   In the next section, we will define the key concepts of BGP Flex

4.  BGP Flex Concepts

4.1.  BGP Local Source IP (BLSI)

   The BLSI refer to the public IP owned by the ISP.
   These IP are important as they determine how the packet will be
   routed, the ISP should explicitily define the BLSI on at least one
   router.

4.2.  BGP Remote Source IP (BRSI)

   In some situations the ISP announces other ISP public IP over the
   IXP, in this situation, the main ISP needs to declare the other ISP
   block as BGP Remote Source IP (BRSI).
   This will make a difference between ISP own blocks and other ISP
   public IP.
   There are two ways to define the BRSI as stated below :

   1.  Static mode defined locally on the router from the SISP side

   2.  Dynamic mode by receiving via the IP routes from CISP via BGP

   In the static mode, the BRSI are mapped to CISP BGP ASN.
   In the dynamic mode, when the SISP receives the routes from CISP, the
   SISP will flag the received routes as BRSI and maps the routes with
   CISP BGP ASN.

4.3.  BGP Remote Peer IP (BRPI)

   These are the IP received from other peers at the IXP.

4.4.  Source IP Router Advertiser (SIRA)

   Up to now, we have seen how to define the BLSI and BRSI, but what if
   they more routers in ISP core backbone ?
   This is where the Source IP Router Advertiser (SIRA) plays a role,
   the BLSI and BRSI will be configured on the SIRA which will advertise
   the BLSI and BRSI to other routers in the ISP core backbone.
   It is advisable to define at least two nodes as SIRA for redundancy
   purpose.

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   BGP will be extended to support the advertisement of BLSI and BRSI.
   Note that routes received by SIRA are not used for routing, they are
   only used to identify the BLSI and BRSI required by BGP Flex for
   routing.

5.  Routing mode in BGP Flex

   In this section, we will discuss how to classify a packet received by
   a router.
   For BGP Flex to know how to route the packets, BGP needs to classify
   the packets.
   There are two main categories : IX packets and Internet packets.
   The IX packets refer to the IP packet with source IP from BLSI, BRSI
   or BRPI described in the BGP Flex concepts section.
   Any other packets will be treated as Internet packets.
   If the packet is classified as IX then IX route table will be checked
   first, if there is a match the packet is forwarded using the IX
   routing table otherwise the packet will be routed based on the
   Internet table .
   If the packet is not classified as IX then the packet will be routed
   based on the Internet route table, in this case only the Internet
   routing table is checked.

   To summarize if the packet is classified as IX packet, the routes
   tables will be checked following an order (IX routing table first,
   then Internet rouing table).
   If the packet is not IX packet it is an Internet packet, in this case
   only Internet routing table is used.

6.  IANA Considerations

   BGP Flex supports both IPv4 and IPV6, it will require two SAFI

   1.  specific SAFI to identify the Network Layer Reachability
       Information (NLRI) exchanged via IX

   2.  specific SAFI to identify the BLSI and BRSI advertised by SIRA

7.  Security Considerations

   BGP Flex is an extension of BGP, so all security considerations for
   BGP can be applied.
   It also advisable to apply all best practices at an Internet Exchange
   Point

8.  References

8.1.  Normative References

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   [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>.

Author's Address

   ZOUNDI Bonaventure (editor)
   Abidjan
   Côte d'Ivoire
   Phone: +2250586757570
   Email: zoundibona@yahoo.fr

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