H3C Technologies H3C SecPath F1000-E - Manual (Page 23)

9
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, or
• Setting the minimum time to live (TTL) value required for a multicast packet to be forwarded.
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. An interface configured as a multicast boundary
cannot forward multicast packets (including packets sent from the local device) or receive multicast
packets.
You can configure the minimum TTL required for a multicast packet to be forwarded on all interfaces that
support multicast forwarding. Before being forwarded from an interface, every multicast packet
(including multicast packet from the local device) is subject to a TTL check:
• If the TTL value of the packet (already decremented by 1 on this router) is larger than the minimum
TTL value configured on the interface, the packet will be forwarded.
• If the TTL value of the packet is smaller than or equal to the minimum TTL value configured on the
interface, the packet will be discarded.
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 low 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 protocols 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 the
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