BGP Auto-Discovery for LDP VPLS
Page 286 7210 SAS M Services Guide
BGP Auto-Discovery for LDP VPLS
BGP Auto Discovery (BGP AD) for LDP VPLS is a framework for automatically discovering the
endpoints of a Layer 2 VPN offering an operational model similar to that of an IP VPN. This
model allows carriers to leverage existing network elements and functions, including but not
limited to, route reflectors and BGP policies to control the VPLS topology.
BGP AD is an excellent complement to an already established and well deployed Layer 2 VPN
signaling mechanism target LDP providing one touch provisioning for LDP VPLS where all the
related PEs are discovered automatically. The service provider may make use of existing BGP
policies to regulate the exchanges between PEs in the same, or in different, autonomous system
(AS) domains. The addition of BGP AD procedures does not require carriers to uproot their
existing VPLS deployments and to change the signaling protocol.
BGP AD Overview
The BGP protocol establishes neighbor relationships between configured peers. An open message
is sent after the completion of the three-way TCP handshake. This open message contains
information about the BGP peer sending the message. This message contains Autonomous System
Number (ASN), BGP version, timer information and operational parameters, including
capabilities. The capabilities of a peer are exchanged using two numerical values: the Address
Family Identifier (AFI) and Subsequent Address Family Identifier (SAFI). These numbers are
allocated by the Internet Assigned Numbers Authority (IANA). BGP AD uses AFI 65 (L2VPN)
and SAFI 25 (BGP VPLS).
Information Model
Following is the establishment of the peer relationship, the discovery process begins as soon as a
new VPLS service instance is provisioned on the PE.
Two VPLS identifiers are used to indicate the VPLS membership and the individual VPLS
instance:
• VPLS-ID — Membership information, unique network wide identifier; same value
assigned for all VPLS switch instances (VSIs) belonging to the same VPLS; encodable
and carried as a BGP extended community in one of the following formats:
→ A two-octet AS specific extended community
→ An IPv4 address specific extended community
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