BIER MVPN uses MP-BGP as an overlay to signal MVPN. It uses RFC 6514 the same way P2MP RSVP-TE.
BIER MVPN introduces a new tunnel type of BIER (0x0B).
BIER PMSI replaces PIM, mLDP, and RSVP-TE P2MP in the core. There is no PMSI per (C-S, C-G), PMSI is used to reach all PE nodes interested in the C-Flow.
The VC label represents the VRF. Within the VRF, the payload IP header (C-S,C-G) finds the OIF based on PIM, IGP, and MLD states.
When a root PE (BFIR) receives a multicast packet and determines that the packet needs to be forwarded to the appropriate BFERs, the source PE encapsulates the multicast packet in a BIER header as described in BIER encapsulation. The root PE adds the appropriate VC label advertised by MP-BGP and PTA and forwards it to the BIER domain.
Figure: BIER MVPN packet format shows the BIER MVPN packet format.
The original packet has a VC label identifying the VRF added first, then the packet (MPLS payload) is forwarded using BIER PMSI by adding a BIER header identifying the BFERs and BIER label learned using IGP from the next-hop router, as described in BIER forwarding. Finally, when the packet arrives on the BFER, the BIER label is stripped, the BIFT is used to identify whether the packet needs to be handled by a corresponding VRF (because the bit in the header corresponds to the BFER BFR-ID). The BFER strips the BIER header, uses the VC label to identify the VRF instance, strips the VC label, and forwards the packet according to the legacy multicast protocols configured on the SAPs of the MVPN (for example, PIM, IGMP, and MLD OIFs).
SR OS supports BIER as I-PMSI and S-PMSI. By default, all (C-S, C-G) are forwarded using I-PMSI. If a throughput threshold is configured in MVPN and that threshold is surpassed by a (C-S, C-G), then the traffic for that stream is switched from I-PMSI to S-PMSI. BIER uses standard NG-MVPN signaling for S-PMSI and uses leaf AD routes from the leaf PEs to set up S-PMSI to the corresponding leaf that is interested in a specific (C-S, C-G).
The BIER MVPN configuration is as follows.
*A:Dut-A>config>service>vprn>mvpn# info
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auto-discovery default
c-mcast-signaling bgp
umh-selection hash-based
provider-tunnel
inclusive
bier
sub-domain 0
no shutdown
exit
exit
selective
bier
sub-domain 0
no shutdown
exit
data-threshold 224.0.0.0/4 1
exit
exit
vrf-target unicast
exit
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*A:Dut-A>config>service>vprn>mvpn#