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326 CHAPTER 18: MULTICAST PROTOCOL
The forwarding entries in MFC are deleted along with the routing entries in the
multicast kernel routing table.
Displaying and
Debugging Common
Multicast Configuration
Execute display command in any view to display the running of the multicast
configuration, and to verify the effect of the configuration.
Execute
debugging command in User View to debug multicast.
There are three types of multicast routing tables: individual multicast routing tables of
each multicast routing protocol; a multicast kernel routing table integrating the
routing information of those individual routing tables; and a multicast forwarding
table in conformity with the kernel routing table and in charge of the multicast packet
forwarding.
Multicast forwarding table is mainly used in debugging. Generally, users can obtain
required information by viewing the multicast kernel routing table.
Internet Group
Management Protocol
(IGMP)
IGMP is a protocol in the TCP/IP suite, responsible for management of IP multicast
members. It is used to establish and maintain multicast membership among IP hosts
and their directly connected neighboring routers. IGMP excludes transmitting and
maintenance of membership information among multicast routers, which are
completed by multicast routing protocols. All hosts participating in multicast must
implement IGMP.
Hosts participating in IP multicast can join and leave a multicast group at any time.
The number of members of a multicast group can be any integer and their location
can be anywhere. A multicast router does not need and cannot keep the membership
of all hosts. It only uses IGMP to learn whether receivers (that is, group members) of a
multicast group are present on the subnet connected to each interface. A host only
needs to keep the multicast groups it has joined.
Table 327 Displaying and debugging Common Multicast Configuration
Operation Command
Display the multicast routing
table
display multicast routing-table [ group-address
[ mask { mask | mask_length } ] | source_address
[ mask { mask | mask_length } ] |
incoming-interface { interface-type
interface_number | register } ]*
Display the multicast
forwarding table
display multicast forwarding-table [
group_address [ mask { mask | mask_length } ] |
source_address [ mask { mask | mask_length } ] |
incoming-interface { nterface-type
interface_number | register } ]*
Enable multicast packet
forwarding debugging
debugging multicast forwarding
Disable multicast packet
forwarding debugging
undo debugging multicast forwarding
Enable multicast forwarding
status debugging
debugging multicast status-forwarding
Disable multicast forwarding
status debugging
undo debugging multicast status-forwarding
Enable multicast kernel
routing debugging
debugging multicast kernel-routing
Disable multicast kernel
routing debugging
undo debugging multicast kernel-routing