Network Virtualization using Extreme Fabric Connect

Network Virtualization Using Extreme Fabric Connect
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Figure 46 IP Multicast Over L3 VSN that Comprises L2 VSNs
A more common requirement is for the L2 VSN segment to be allowed to perform IP multicast routing to
any other BEB in the L3 domain (L3 VSN or IP Shortcuts) as well as efficient snooping within the L2 VSN
segment. This is possible but requires, on the L2 BEB, configuration of an IP interface on which SPB
Multicast is enabled. This IP interface is thus exclusively used for VRF awareness and the ability perform
SPB Multicast rather than being used as a gateway for IP unicast traffic.
Caution
If the L2 BEB must participate in L3 VSN domain SPB multicast, then the platform used
needs to be L3 VSN capable. That is, it needs to be a VOSS VSP platform.
An ERS platform can only be used as an L2 BEB and be activated for SPB multicast in an
L3 domain if IP Shortcuts are being used.
Tip
If the L2 BEBs in the example topology depicted in Figure 46 were DVR leaf nodes, then it
would be sufficient to SPB multicast enable the DVR IP interface on the DVR controller
and automatically IP multicast routing will be performed across the L3 domain as well as
snooped within the L2 VSN domain.
One common misconception when trying to understand SPB multicast is to assume that IP multicast traffic
must follow the same path as IP unicast traffic, as is the case with traditional IP multicast routing such as
PIM. In the example illustrated in Figure 46, if IP multicast was activated across the entire L3 VSN domain
(including the L2 VSN), then the middle L3 BEB will IP forward all unicast traffic between the top and
bottom IP subnets. Yet from an IP multicast perspective, that same L3 BEB will not perform any BEB
function for IP multicast traffic being forwarded between the same IP subnets (and indeed does not even
need to be SPB multicast enabled). That is because SPB multicast is entirely performed by the ingress and
egress BEBs alone by leveraging SPB I-SID delivery trees. If the core node happens to be on the shortest