Design Reference

Multicast MAC filtering
Certain network applications, such as the Microsoft Network Load Balancing solution, require
multiple hosts to share a multicast MAC address. Instead of flooding all ports in the VLAN with
this multicast traffic, you can use Multicast MAC filtering to forward traffic to a configured subset
of the ports in the VLAN. This multicast MAC address is not an IP multicast MAC address.
At a minimum, map the multicast MAC address to a set of ports within the VLAN. In addition,
if traffic is routed on the local Virtual Services Platform 4000, you must configure an Address
Resolution Protocol (ARP) entry to map the shared unicast IP address to the shared multicast
MAC address. You must configure an ARP entry because the hosts can also share a virtual
IP address, and packets addressed to the virtual IP address need to reach each host.
Avaya recommends that you limit the number of such configured multicast MAC addresses to
a maximum of 100. This number is related to the maximum number of possible VLANs you
can configure because for every multicast MAC filter that you configure the maximum number
of configurable VLANs reduces by one. Similarly, configuring large numbers of VLANs reduces
the maximum number of configurable multicast MAC filters downwards from 100.
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 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.
IP multicast network design
114 Network Design Reference for Avaya VSP 4000 February 2014
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