Инструкции По Установке для 3com S7906E

 

1-7 

Figure 1-4 Network diagram for IGMP proxying 

 

Query from Router A

Report from Router B

Ethernet

Router interface

Host interface

Router B

Router A

Host B

Host A

Host C

Query from Router B

Report from Host

PIM domain

 

 

As shown in 

, two types of interfaces are defined on an IGMP proxy device: 

z 

Upstream interface: Also referred to as the proxy interface. A proxy interface is an interface on 

which IGMP proxying is configured. It is in the direction toward the root of the multicast forwarding 

tree. An upstream interface acts as a host running IGMP; therefore, it is also called host interface.  

z 

Downstream interface: An interface that is running IGMP and not in the direction toward the root of 

the multicast forwarding tree. A downstream interface acts as a router running IGMP; therefore, it is 

also called router interface.  

A device with IGMP proxying configured maintains a group membership database, which storesthe 

group memberships on all the downstream interfaces. Each entry comprises the multicast address, 

filter mode, and source list. Such an entry is a collection of members in the same multicast group on 

each downstream interface.  

A proxy device performs host functions on the upstream interface based on the database. It responds to 

queries according to the information in the database or sends join/leave messages when the database 

changes. On the other hand, the proxy device performs router functions on the downstream interfaces 

by participating in the querier election, sending queries, and maintaining memberships based on the 

reports.  

While IGMP maintains group memberships on a per-interface base, IGMP in a VPN instance handles 

protocol packets based on the VPN instance on the interface. Upon receiving an IGMP packet, the 

router determines the instance to which the message belongs and handles the message within the 

instance. If IGMP running in a VPN instance needs to exchange information with another multicast 

protocol, the router informs the other multicast protocol only within the VPN instance.  

The following documents describe different IGMP versions:  

z 

RFC 1112: Host Extensions for IP Multicasting 

z 

RFC 2236: Internet Group Management Protocol, Version 2 

z 

RFC 3376: Internet Group Management Protocol, Version 3