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Innovation: Multicast over MCT

by pmoyer on ‎02-15-2013 08:18 AM (46 Views)

I’d like to continue a previous discussion about Brocades Multi-Chassis Trunking (MCT) technology. Please see the earlier blog: MCT with VPLS. The MCT w/VPLS capability was part of NetIron Software Release 5.3. In NetIron Software Release 5.4, we added a powerful enhancement to provide Multicast over MCT.

A diagram of this capability is shown below. In the diagram, there are two MLXe routers who are MCT peers. They have multicast receivers downstream and multicast sources upstream.

pim_mct_base.jpg

The diagram shows that the MCT Cluster Client Edge Ports (CCEPs) now have the ability to support the Internet Group Management Protocol (IGMP) and the Protocol Independent Multicast (PIM) protocol. As you recall, the CCEPs are the MCT customer facing edge ports. The diagram shows multiple host receivers behind two layer-2 switches, who are the MCT clients, and the host receivers are sending IGMP join requests toward the network. IGMP is used by hosts to establish and manage their multicast group membership.  The MCT client layer-2 switches are directly connected to the CCEPs of the MCT cluster. Each layer-2 switch is doing standard link aggregation (LAG) to connect to both of the MLXe routers. As with all MCT configurations, the client layer-2 switches are unaware that they are connected to two MLXe routers; this is the active/active redundancy that MCT provides.

Both of the MCT peers will receive IGMP join requests and will subsequently send PIM joins toward the multicast Rendezvous Point (RP) or multicast source, depending on whether PIM-SM (*, G) or PIM-SSM (S, G) is being used. So, PIM runs on the network facing interfaces of the MCT peers, including the Inter-Chassis Link (ICL). The MCT ICL is also used to synchronize the IGMP membership state between the MCT peers. The result is that both of the MCT peers will install the correct multicast membership state. The diagram shows a few of the scenarios that are possible; where sources can be somewhere inside the IP network or directly attached to either MLXe router. However, the sources and receivers can actually be reversed such that sources are behind the MCT client layer-2 switches and the host receivers are either somewhere in the IP network or directly attached to either MLXe router.  All variations are supported.

A hashing algorithm determines if the active multicast outgoing interface (OIF) is a local CCEP interface or the ICL. As shown in the diagram below, multicast traffic can arrive on both MLXe routers from the source but the MLXe with the local forwarding state is the only one that forwards traffic to the host receiver.

pim_mct_forward.jpg

Since both MCT peers are properly synchronized, forwarding is performed as expected on the multicast shortest-path tree.

Some of the benefits of this compelling enhancement are:

  • Redundancy – Active/Active redundancy for multicast traffic with a sub-second failover capability
  • Load Sharing – Multicast traffic can be load shared between MCT peers allowing optimal link utilization
  • Fast Convergence – There is no need to rebuild the multicast distribution tree if a CCEP is down

As an example of a possible failure scenario; If CCEP2 fails, the MCT peers will remain synchronized such that the redundant MCT peer immediately takes over as the active forwarding device.

pim_mct_forward_failure.jpg

So, you can see that this is a very powerful feature as it provides for an active/active redundancy capability while maintaining the optimal multicast forwarding tree under failure scenarios. This is no easy feat!

Continue to stay tuned to this page for additional NetIron enhancements, as Brocade continues to lead the industry in innovation!