Design Reference

For example, if a receiver is on VLAN 1 on switch S1 and another receiver is on VLAN 2 on
switch S1, traffic can be received from two different paths to the two receivers, which results
in the use of two forwarding records. If the source on switch S2 is on a different VLAN than
VLAN 3, traffic takes a single path to switch S1 where the receivers are located.
Figure 53: IP multicast sources and receivers on interconnected VLANs
6. Avaya recommends the use of Static group-range-to-rendezvous point (RP) mappings in an
SMLT topology as opposed to RP set learning via the Bootstrap Router (BSR) mechanism.
Static RP allows for faster convergence in box failure, reset, and HA failover scenarios;
whereas there are inherent delays in the BSR mechanism as follows:
•
When a router comes back up after a failover or reset, to accept and propagate (*,g) Join
requests from surrounding routers (either PIM Join messages or local IGMP membership
reports) to the RP, a PIM router must determine the address of the RP for each group for
which they desire (*,g) state. The PIM router needs information about the unicast route to
the RP address. The route to the RP address is learned by using a unicast routing
protocol such as OSPF, and the RP address is either statically configured or dynamically
learned using the BSR mechanism.
• When a system comes up after a reset or the standby CP becomes master after an HA
failover, if the RP is not statically configured. It must wait for the BSR to select the RP
from candidate RP routers, and then propagate the RP set hop-by-hop to all PIM routers.
This must be done before a Join message can be processed. If the PIM router receives a
Join message before it learns the RP set, the router drops the Join message and waits for
another Join or Prune message to arrive before it creates the multicast router, and
propagates the Join messages to the RP. The default Join/Prune timer is 60 seconds, and
because of this and the delays inherent in BSR RP-set learning, significant multicast traffic
interruptions can occur. If the RP is statically configured, the only delay is in the unicast
routing table convergence and the arrival of the Join/Prune messages from surrounding
boxes.
IP multicast address range restrictions
IP multicast routers use D class addresses, which range from 224.0.0.0 to 239.255.255.255.
Although you can use subnet masks to configure IP multicast address ranges, the concept of
IP multicast network design
108 Network Design Reference for Avaya VSP 4000 Series January 2015
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