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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. You can define a multicast forwarding
range by:
•
Specifying boundary interfaces, which form a closed multicast forwarding area.
•
Setting the minimum 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. After you configure an interface as a multicast
boundary, the interface can no longer forward multicast packets (including packets sent from the local
device), nor receive multicast packets.
You can also 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) undergoes a TTL check:
•
If the TTL value of the packet (already decremented by 1 on this router) is larger than or equal to the
minimum TTL value configured on the interface, the packet will be forwarded.
•
If the TTL value of the packet is smaller than the minimum TTL value configured on the interface, the
packet will be discarded.
To configure a multicast forwarding range:
Step Command
Remarks
1.
Enter system view.
system-view
N/A
2.
Enter interface view.
interface
interface-type
interface-number
N/A
3.
Configure a multicast
forwarding range.
•
Configure a multicast
forwarding boundary:
multicast boundary
group-address
{
mask
|
mask-length
}
•
Configure the minimum packet
TTL required for a multicast
packet to be forwarded:
multicast minimum-ttl
ttl-value
Use either method.
•
By default, no forwarding
boundary is configured.
•
By default, the TTL value is 1.
Configuring the multicast forwarding table size
The router maintains the corresponding forwarding entry for each multicast packet that it receives.
However, excessive multicast routing entries can exhaust the router's memory and cause lower
performance.
You can set the maximum number of entries in the multicast forwarding table according to the networking
situation and the performance requirements. If the configured upper limit is smaller than the number of
existing entries in the multicast forwarding table, the entries in excess are not deleted immediately. The
multicast routing protocol that runs on the router will delete them. The router will no longer add new
multicast forwarding entries until the number of existing multicast forwarding entries decreases below the
upper limit.
