3Com 4007, Implementation Manual, Page: 439 / 684

Key Guidelines for Implementation 439
6 View the various displays, routing table and cache to see how the module
is processing IP multicast traffic.
See “Viewing the DVMRP Routing Table” and “Viewing the DVMRP
Cache” later in this chapter.
7 Use the traceroute option for troubleshooting or to determine the traffic
paths.
See “Using IP Multicast Traceroute” later in this chapter.
Impact of Multicast
Limits
As described in Chapter 9, you can use the
bridge port
multicastLimit
option to set per-port multicast limits. This
optional
feature can prevent segments of your network from being adversely
affected by multicast or broadcast storms. If network users have trouble
receiving IP multicast application traffic, verify that bridge ports are not
configured with a bridge port multicast limit that is too low.
Impact of IEEE 802.1Q
on Multicasts
Multicasting in 802.1Q VLAN tagging environments may have
performance implications for a Multilayer Switching Module. Specifically,
if you have multiple VLANs associated with a single port, the module is
forced to replicate multicast packets to each VLAN that has multicast
group members, even if the path to reach the members is the same
physical link. To achieve wirespeed multicast performance, 3Com
recommends that you configure only one VLAN per port. Contact your
3Com representative about network design options.
Protocol
Interoperability
Routing protocols other than DVMRP exist to support IP multicast
functions. Interoperability issues between these routing protocols mean
that you should plan your routing infrastructure carefully. Contact your
3Com representative for more information.