Igmp And Pim-Sm Interaction - Avaya 8800 Planning And Engineering, Network Design

Multicast network design
Figure 104: IGMP interaction with DVMRP
Switch C is not configured with any multicast ports (that is, is a nonmulticast router, or mrouter). If
switch A is the querier, it becomes the mrouter (multicast router port) port for C. The receiver cannot
receive data from source S because C does not forward data on the link between C and B.
You can surmount this problem by using one of the following methods:
• Configure ports P1 and P2 as mrouter ports on the IGMP Snoop VLAN.
• Configure switches A, B, and C to run Multicast Router Discovery (MRDISC) on their common
VLANs.
MRDISC allows the Layer 2 switch to dynamically learn the location of switches A and B and thus,
add them as mrouter ports. If you connect switches A and B together, no specific configuration is
required because the issue does not arise. It also does not occur when DVMRP uses the same
switch as the querier and forwarder, for example, when IGMPv2 is used.

IGMP and PIM-SM interaction

This section describes a possible problem that can arise when IGMP Snoop and PIM-SM interact. In
this example, switches A and B run PIM-SM, and switch C runs IGMP Snoop. A and B interconnect
with VLAN 1, and C connects A and B with VLAN 2.
If a receiver (R) is placed in VLAN 2 on switch C, it does not receive data. PIM chooses the router
with the higher IP address as the Designated Router (DR), whereas IGMP chooses the router with
the lower IP address as the querier. Thus, if B becomes the DR, A becomes the querier on VLAN 2.
IGMP reports are forwarded only to A on the mrouter port P1. A does not create a leaf because
reports are received on the interface towards the DR.
June 2016 Planning and Engineering — Network Design
Comments on this document? infodev@avaya.com
220