3Com CoreBuilder 3500, Implementation Manual, Page: 349 / 592

Configuring IGMP Options 349
Configuring IGMP
Options
You can enable or disable IGMP snooping and querying functions, set the
interface time-to-live (TTL) threshold, and obtain summary and detail
displays of IGMP-related information.
Querying and
Snooping Modes
Your system divides IGMP functions into two modes:
■
Querying — Allows an IP multicast routing interface to function as
the querier if so elected.
■
Snooping — Allows the system to forward multicast packets only to
the appropriate ports within its routing or bridging interfaces.
Important
Considerations
■
Both modes are enabled as the factory default . These settings apply to
the entire system. You cannot enable or disable snooping or querying
on specific interfaces.
■
3Com recommends that you keep both modes enabled at all times.
They add little processing overhead to the system.
Configuring DVMRP
Interfaces
DVMRP is the protocol used to develop source-rooted spanning trees
between routers in the network. You can enable or disable DVMRP on
individual routing interfaces.
Important
Considerations
■
The default setting for DVMRP on each new interface is
disabled
.
■
If DVMRP is disabled, the interface cannot participate in forming IP
multicast spanning trees. If the Internet Group Management Protocol
(IGMP) is enabled, the system can still forward IP multicast traffic.
■
Enabling DVMRP causes the system to assign default values of
1
for
both the TTL threshold and metric on the interface. You can modify
these values at any time.
■
A TTL threshold value of
1
means the interface forwards all IP
multicast packets except those which have expired (packet TTL is 0).
Before you change the TTL threshold value, consider the relative
location of the system in the network and your networking objectives.