Network Virtualization using Extreme Fabric Connect

Network Virtualization Using Extreme Fabric Connect
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Tip
In a design where the source is SMLT connected to two ingress BEBs, both BEBs forming
the SMLT cluster will IS-IS announce availability of the IP multicast stream.
In the absence of receivers, the SPB Fabric does not set up any multicast tree and the ingress BEB silently
discards the multicast packets it receives from the source.
On the receiver side, the protocol used for registering receivers is still IGMP, which is automatically enabled
on the BEB VSN segments where SPB IP multicast was activated. On these segments the IP Multicast
enabled BEB will become the IGMP querier.
Tip
In the Extreme Networks implementation, IGMP versions 1 to 3 are supported. By default,
IGMP version 2 is used. By using IGMPv3, it is possible to support Source-Specific IP
Multicast over SPB.
Tip
External IGMP queriers and hence external IP multicast routers, should not exist on Fabric
Connect access segments enabled for IP multicast. Otherwise a single IGMP querier will be
elected and Fabric Connect multicast may not work as expected.
Note
The main benefit of using IGMP version 3 is that receivers can register for source-specific
groups (i.e., instead of just requesting to join Multicast stream 239.0.0.10 as IGMP v2 would
do, IGMP v3 could ask to join only the Multicast stream 239.0.0.10 sent from source with IP
172.16.10.100), which is more secure in the sense that it becomes harder to try and spoof a
multicast stream using a different source IP address. IGMP version 3 was defined to allow
these source-specific joins so that it could be used in conjunction with Source-Specific PIM
(PIM-SSM), which was an attempt to simplify PIM-SM by removing the Rendezvous Point
(RP) functionality.
While this did somewhat simplify PIM, on the other hand, source-specific multicast
burdens the application on the receivers with a required prior knowledge of the source IP
of the desired multicast streams.
When an IGMP join is received, an entry is added to the IGMP membership table. The IS-IS LSDB is then
checked by the BEB to see whether or not a matching IP multicast stream exists somewhere in the Ethernet
Fabric. If a match is found, constrained to the same VSN (i.e., the IGMP receiver is on the same VSN as the
source of the stream), the BEB will update its I-SID TLV. This will indicate that it wishes to be added to the
multicast I-SID tree for the corresponding IP multicast stream rooted at the BEB where the source of the
stream is located. If no multicast tree was yet set up, it is now set up. If a multicast tree was already in place,
a new branch is added to it.
Tip
The time to set up the SPB multicast tree is in the order of 100 milliseconds, which in the
case of video distribution or video surveillance allows the applications to rapidly flick
across the available channels without the typical latency observed on traditional PIM IP
Multicast deployments. This should be combined with the use of IGMP immediate leave
feature.