3Com CoreBuilder 2500, User Manual

Page: 69 / 244

Multicast Interfaces 5-5
Multicast Interfaces
This section describes the characteristics of the CoreBuilder 2500
multicast interface.
DVMRP Metric Value The DVMRP metric value determines the cost of a multicast interface.
A higher cost results in a slower link. The default value is 1 .
Time-To-Live (TTL)
Threshold
The TTL threshold determines whether the interface forwards multicast
packets to other switches and routers in the subnetwork. If the interface
TTL is greater than the packet TTL, then the interface does not forward
the packet. The default value of
1 means that the interface forwards
most packets.
Rate Limit The rate limit determines how many multicast packets can travel over the
interface per second. The CoreBuilder 2500 system drops multicast traffic
that travels faster than this rate. The default value of
0 means that no
rate limit is in effect. A lower rate limit results in fewer multicast packets
traveling over the interface.
Multicast Tunnels
Multicast tunnels logically connect two multicast routers through one or
more unicast routers. The multicast router at the local endpoint of the
tunnel puts multicast packets in a format that unicast routers can
interpret and forward. The multicast router at the receiving endpoint
reformats the packets into their multicast format. Tunnels are virtual links
through the unicast IP network.
Multicast tunnels have characteristics similar to those of a multicast
interface: a DVMRP metric value, a TTL threshold, and a rate limit. When
you define a multicast tunnel, you also specify the destination address of
the multicast router at the tunnel’s remote endpoint.