3Com S7902E, Руководство по настройке

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1-10
Configuring a Multicast Forwarding Range
Multicast packets do not travel without a boundary in a network. The multicast data corresponding to
each multicast group must be transmitted within a definite scope. Presently, you can define a multicast
forwarding range by specifying boundary interfaces, which form a closed multicast forwarding area.
You can configure a forwarding boundary specific to a particular multicast group on all interfaces that
support multicast forwarding. A multicast forwarding boundary sets the boundary condition for the
multicast groups in the specified range. If the destination address of a multicast packet matches the set
boundary condition, the packet will not be forwarded. Once a multicast boundary is configured on an
interface, this interface can no longer forward multicast packets (including packets sent from the local
device) or receive multicast packets.
Follow these steps to configure a multicast forwarding range:
To do... Use the command... Remarks
Enter system view system-view —
Enter interface view
interface interface-type
interface-number
—
Configure a multicast
forwarding boundary
multicast boundary
group-address
{ mask |
mask-length }
Required
No forwarding boundary by
default
Configuring the Multicast Forwarding Table Size
The router maintains the corresponding forwarding entry for each multicast packet it receives.
Excessive multicast routing entries, however, can exhaust the router’s memory and thus result in lower
router performance. You can set a limit on the number of entries in the multicast forwarding table based
on the actual networking situation and the performance requirements. If the configured maximum
number of multicast forwarding table entries is smaller than the current value, the forwarding entries in
excess will not be immediately deleted; instead they will be deleted by the multicast routing protocol
running on the router. The router will no longer add new multicast forwarding entries until the number of
existing multicast forwarding entries comes down below the configured value.
When forwarding multicast traffic, the router replicates a copy of the multicast traffic for each
downstream node and forwards the traffic, and thus each of these downstream nodes forms a branch of
the multicast distribution tree. You can configure the maximum number of downstream nodes (namely,
the maximum number of outgoing interfaces) for a single entry in the multicast forwarding table to
lessen burden on the router for replicating multicast traffic. If the configured maximum number of
downstream nodes for a single multicast forwarding entry is smaller than the current number, the
downstream nodes in excess will not be deleted immediately; instead they must be deleted by the
multicast routing protocol. The router will no longer add new multicast forwarding entries for newly
added downstream nodes until the number of existing downstream nodes comes down below the
configured value.