BGP-based auto-discovery (AD) is performed by using a multicast VPN address family. Any PE router that attaches to an MVPN must issue a BGP update message containing an NLRI in this address family, along with a specific set of attributes.
The PE router uses route targets to specify MVPN route import and export. The route target may be the same as the one used for the corresponding unicast VPN, or it may be different. The PE router can specify separate import route targets for sender sites and receiver sites for a specific MVPN.
The route distinguisher (RD) that is used for the corresponding unicast VPN can also be used for the MVPN.
When BGP AD is enabled, PIM peering on the I-PMSI is disabled, so no PIM hellos are sent on the I-PMSI. C-tree to P-tunnel bindings are also discovered using BGP S-PMSI AD routes, instead of PIM join TLVs.
For example, if AD is disabled, the c-mcast-signaling bgp command fails and the following error message displays:
C-multicast signaling in BGP requires auto-discovery to be enabled
AD is enabled by default on the 7210 SAS-R6 and 7210 SAS-R12.
If c-mcast-signaling is set to bgp, the no auto-discovery command fails and the following error message displays:
C-multicast signaling in BGP requires auto-discovery to be enabled
When c-mcast-signaling is set to bgp, S-PMSI AD is always enabled (configuration is ignored).