This chapter introduces the “Tenant Routed Multicast” (TRM) solution
in BGP EVPN VXLAN fabric. TRM relies on standard-based BGP IPv4 MVPN Address-Family
[RFC 6513] and [RFC 6514]. Figure 19-1 illustrates the basic idea of TRM
operation. (1) Leaf switches establish a Multicast tunnel per tenant, which they
are using for forwarding tenant-specific Intra/Inter-VN Multicast traffic. (2)
When Leaf -101 starts receiving Multicast flow from host Cafe to group
239.77.77.77, it updates its tenant specific MRIB table and generates an MVPN
route-type 5 “Source Active Auto-Discovery
(SA A-D)” route, where the MP-REACH-NLRI carries information about
Source-Specific group (S, G). This route-type is used for discovering if there
are any Multicast receivers behind remote leafs. When Leaf-102 receives the BGP
Update message, it imports information into the BGP table. (3) Next, host Bebe
sends an IGMP join message. (5) Leaf-102 updates its MRIB and then it generates
the MVPN route-type 7 “Source-Tree Join” route. By doing this,
it informs the source that it has local receivers for Multicast group
239.77.77.77. Leaf-101 installs the route into BGP table and updates its MRIB
by adding the NVE interface into group-specific OIL. Then it starts forwarding
Multicast flow received from host Cafe to the core over Source-Specific Multicast
delivery tree which is actually tunneled over tenant-specific Multicast tunnel.
In other words, the destination IP address in outer IP header use Multicast
tunnel-group address 238.101.102.103 and the source IP address is taken from
interface NVE1. By doing this, the actual tenant-specific Inter-VNI Multicast
flows are totally transparent to the Spine switch.
This chapter starts by explaining how
Multicast tunnels used for Intra-VN (L2), and Inter-VN (L3) are established and
how MRIB is constructed. Then it introduces the configuration required for
TRM. The last two-section discusses BGP MVPN Control Plane operation and
Multicast data forwarding Data Plane operation.
Figure-19-1: Tenant Routed Multicast (TRM) Topology.
The rest 35 pages can be read from my VXLAN book "VXLAN-A Practical guide to VXLAN" published in Leanpub.com
