The two primary
functions of the Virtual Private LAN Service (VPLS) control plane are
autodiscovery and signaling. The VPLS BGP Signaling feature enables you to use
BGP as both an autodiscovery and a signaling protocol for VPLS, in accordance
with RFC 4761.
Prior to the VPLS BGP Signaling feature, BGP was used for autodiscovery and Label Distribution Protocol (LDP) for signaling
in accordance with RFC 6074. The VPLS BGP Signaling feature enables you to use BGP as the control plane protocol for both
autodiscovery and signaling in accordance with RFC 4761.
As specified in RFC 4761, internal BGP (iBGP) peers will exchange update messages of the L2VPN AFI/SAFI with L2VPN information
to perform both autodiscovery and signaling. The BGP multiprotocol Network Layer Reachability Information (NLRI) consists
of a Route Distinguisher (RD), VPLS Endpoint ID (VE ID), VE Block Offset (VBO), VE Block Size (VBS), and Label Base (LB).
The figure below shows the format of the NLRI for RFC 4761.
Additional information, such as next-hop, route target (specified for a VPLS instance), and other Layer 2 data are carried
in the BGP extended community attributes. A route target-based import/export mechanism similar to L3VPN is performed by BGP
to filter L2VPN NLRIs of a particular VPLS instance.
Whether you use BGP signaling (RFC 4761) or LDP signaling (RFC 6074) depends on the commands you specify. To enable the VPLS
BGP Signaling feature, use the
autodiscovery bgp signaling bgp command in L2 VFI configuration mode. This command is supported on a per VPLS instance basis.
If a BGP session receives an invalid (that is, not matching the configuration) BGP update advertisement (update or withdraw),
it is ignored.
BGP’s main task in supporting VPLS is route distribution via the L2VPN address family and interactions with L2VPN. Interactions
between BGP and other components remain the same. Basic BGP functionalities like best-path selection, next-hop handling, and
update generation, continue to operate in the same manner with VPLS BGP signaling. BGP RT constraint works seamlessly with
the BGP VPLS Signaling feature.
Virtual Private LAN Service (VPLS) Using BGP for Auto-Discovery and Signaling
Provisioning, Auto-Discovery, and Signaling in Layer 2 Virtual Private Networks (L2VPNs)
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