OISM interworking with MVPN and PIM for MEG or PEG gateways

For EVPN OISM to successfully interwork with MVPN and PIM, it is important to ensure that the MVPN/PIM procedures in the IPVPN network are not modified. In this interworking scenario, two (or more) OISM PEs act as the gateway between the EVPN and the MVPN/PIM network to ensure the OISM procedures are transparent to MVPN/PIM, and vice versa.

SR OS supports the MVPN-to-EVPN Gateway (MEG) and PIM-to-EVPN Gateway (PEG)functions in accordance with draft-ietf-bess-evpn-irb-mcast. Both, Ingress Replication (IR) and mLDP trees are supported on the SBD so that multicast traffic can be received from or transmitted to OISM PEs.

When more than one MEG or PEG is present per EVPN tenant (that is, per SBD), one of the MEG or PEGs acts as the MEG or PEG designated router (DR). The following are the special functions of MEG/PEGs DRs.

The DRs behave as a First Hop Router (FHR) from the MVPN/PIM perspective network and register sources in the OISM domain with the RP in the MVPN/PIM domain.
The DRs behave as Last Hop Router (LHR) from the MVPN/PIM network perspective, and join the shared or source tree. The non-DR PEs remove the SBD R-VPLS interface from the VPRN’s Layer 3 multicast OIF list, which prevents the PEs from sending multicast traffic to the OISM receivers.

The MEG or PEG DR election occurs in each PE attached to the SBD configured as MEG or PEG. Each PE builds a DR candidate list based on the reception of the Inclusive Multicast Ethernet Tag (IMET) routes for the SBD that include the MEG and/or PEG flag. After the evpn-mcast-gateway>dr-activation-timer expires, the PE runs the DR election based on the default algorithm used for EVPN DF election (modulo function of the EVI and number of PEs).

Note: A single DR election is run for MEGs and PEGs of the same SBD. The advertisement of an IMET route with MEG, PEG, or both flags set is controlled by the evpn-mcast-gateway>advertise {mvpn-pim | mvpn-only | pim-only} command.

Note: This section describes the MVPN and PIM procedures for MEG PEs, using MVPN examples. These procedures also apply to PEG PEs, using PIM messages instead of C-MCAST shared or source join routes.

Procedures for sources in MVPN and PIM and receivers in OISM, Procedures for ASM sources in OISM and receivers in MVPN, and Procedures for SSM sources in OISM and receivers in MVPN describe the MVPN and PIM procedures depending on whether the sources and receivers are attached to the OISM or MVPN network.