Design Reference

Although you can configure addresses starting with 01.00.5E, which are reserved for IP multicast
address mapping, do not enable IP multicast with streams that match the configured addresses.
This configuration can result in incorrect IP multicast forwarding and incorrect multicast MAC
filtering.
Guidelines for multicast access policies
Use the following guidelines when you configure multicast access policies:
• Use masks to specify a range of hosts. For example, 10.177.10.8 with a mask of
255.255.255.248 matches hosts addresses 10.177.10.8 through 10.177.10.15. The host
subnet address and the host mask must be equal to the host subnet address. An easy way to
determine this is to ensure that the mask has an equal or fewer number of trailing zeros than
the host subnet address. For example, 3.3.0.0/255.255.0.0 and 3.3.0.0/255.255.255.0 are
valid. However, 3.3.0.0/255.0.0.0 is not.
• Apply receive-access policies to all eligible receivers on a segment. Otherwise, one host joining
a group makes that multicast stream available to all.
• Receive access policies are initiated after the switch receives reports with addresses that
match the filter criteria.
• Transmit access policies apply after the switch receives the first packet of a multicast stream.
Multicast access policies can apply to a routed PIM interface if Internet Group Management Protocol
(IGMP) reports the reception of multicast traffic.
The following rules and limitations apply to IGMP access policy parameters when you use them with
IGMP instead of PIM:
• The static member parameter applies to IGMP snooping and PIM on both interconnected links
and edge ports.
• The Static Not Allowed to Join parameter applies to IGMP snooping and PIM on both
interconnected links and edge ports.
• For multicast access control, the denyRx parameter applies to IGMP snooping and PIM. The
DenyTx and DenyBoth parameters apply only to IGMP snooping.
Split-subnet and multicast
The split-subnet issue arises when you divide a subnet into two unconnected sections in a network.
This division results in the production of erroneous routing information about how to reach the hosts
on that subnet. The split-subnet problem applies to all types of traffic, but it has a larger impact on a
PIM-SM network.
To avoid the split-subnet problem in PIM networks, ensure that the RP router is not in a subnet that
can become a split subnet. Also, avoid having receivers on this subnet. Because the RP is an entity
IP multicast network design
132 Network Design Reference for Avaya VSP 4000 Series June 2015
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