Install guide

IP Multicasting 23
Downstream routers
IGMP snooping learns which ports have routers attached to them, so it can
forward relevant IGMP messages and other IP multicast traffic out those ports.
You can specify the following aspects of this:
■ the kind of packets that indicate to IGMP snooping that a port has a router
downstream
■ which specific ports have routers downstream
Packets that indicate
routers
By default, IGMP snooping identifies router ports by looking for ports that
receive specific multicast packets (such as IGMP queries, PIM messages, OSPF
messages, and RIP messages). You can determine what kinds of packets
indicate a router is downstream, by using the command:
set igmpsnooping routermode={all|default|ip|multicastrouter|
none}
For each option in this command, the following table lists the addresses that
IGMP snooping uses to indicate that a port has a router downstream.
If you specify set igmpsnooping routermode=ip, then you can add and
remove reserved IP multicast addresses to and from the list of router multicast
addresses by using the commands:
add igmpsnooping routeraddress=ipadd-list
delete igmpsnooping routeraddress=ipadd-list
The IP addresses specified must be from 224.0.0.1 to 224.0.0.255.
To display the current mode and list of multicast router addresses, use the
command:
show igmpsnooping routeraddress
This option... means that the port is treated as a multicast router port if
it receives packets from...
all any reserved multicast addresses (224.0.0.1 to 224.0.0.255)
multicastrouter 224.0.0.4 (DVMRP routers)
224.0.0.13 (all PIM routers)
default 224.0.0.1 (IGMP Queries)
224.0.0.2 (all routers on this subnet)
224.0.0.4 (DVMRP routers)
224.0.0.5 (all OSPFIGP routers)
224.0.0.6 (OSPFIGP designated routers)
224.0.0.9 (RIP2 routers)
224.0.0.13 (all PIM routers)
224.0.0.15 (all CBT routers)
ip the current list of addresses, plus addresses specified using the
command add igmpsnooping routeraddress and minus
addresses specified using the command delete igmpsnooping
routeraddress.