3com 5500-SI Manual Do Utilizador

C

HAPTER

 18: M

ULTICAST

 P

ROTOCOL

The forwarding entries in MFC are deleted along with the routing entries in the 
multicast kernel routing table.

Execute 

 command in any view to display the running of the multicast 

configuration, and to verify the effect of the configuration.

Execute 

 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.

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

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

Disable multicast packet 
forwarding debugging

Enable multicast forwarding 
status debugging

Disable multicast forwarding 
status debugging

Enable multicast kernel 
routing debugging

Disable multicast kernel 
routing debugging