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The new information model required changes to the BGP usage of the NLRI for VPLS. The
extended MH NLRI for Multi-Homed VPLS is compared with the BGP AD and BGP VPLS
NLRIs in Figure 81.
Figure 81: BGP MH-NLRI for VPLS Multi-Homing
The BGP VPLS NLRI described in RFC 4761 is used to carry a two (2) byte site-ID that identifies
the MH Site. The last seven (7) bytes of the BGP VPLS NLRI used to instantiate the pseudowire
are not used for BGP-MH and are ZEROed out. This NLRI format translates into the following
processing path in the receiving VPLS PE:
• BGP VPLS PE: no Label information means there is no need to setup up a BGP
pseudowire
• BGP AD for LDP VPLS: length =17 indicates a BGP VPLS NLRI that does not require
any pseudowire LDP Signaling.
The processing procedures described in this section start from the above identification of the BGP
Update as not destined for pseudowire signaling.
The RD ensures the NLRIs associated with a certain site-id on different PEs are seen as different
by any of the intermediate BGP nodes (RRs) on the path between the multi-homed PEs. In other
words, different RDs must be used on the MH PEs every time an RR or an ASBR is involved to
guarantee the MH NLRIs reach the PEs involved in VPLS MH.
The L2-Info extended community from RFC 4761 is used in the BGP update for MH NLRI to
initiate a MAC flush for blackhole avoidance to indicate the operational and admin status for the
MH Site or the DF election status.
After the pseudowire infrastructure between VSIs is built using either RFC 4762 (LDP VPLS) or
RFC 4761 (BGP VPLS) procedures or a mix of pseudowire Signaling procedure, on activation of
a multi- homed site, an election algorithm must be run on the local and remote PEs to determine
which site will be the designated forwarder (DF). The end result is that all the related MH sites in
a VPLS will be placed in standby except for the site selected as DF. Alcatel-Lucent BGP-based
multi-homing solution uses the DF election procedure described in the IETF working group
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