Lucent Technologies P550 - Manual (Page 142)

Configuring IP Routing (Layer 3)
7-16 Cajun P550/P220 Switch Operation Guide
In addition, IP multicasting distributes information to multicast groups in two specific
ways:
❒ Multicast Forwarding - allows a switch to forward multicast traffic from the local
router to group members on directly attached subnetworks. If a multicast packet is
forwarded to multiple interfaces on one VLAN, only one Forwarding Entry is added
on the VLAN for the packet. One copy of the packet is sent to the VLAN.
❒ Multicast Routing - allows a switch to deliver multicast traffic between
neighboring routers and across the network.
For example, the switch could use Internet Group Membership Protocol (IGMP) Only to
forward multicast traffic to locally attached subnetworks. However, if the multicast traffic
in question is needed to be sent to a neighboring router, the switch could use DVMRP to
send the information between routers. Since IGMP is a required protocol for any
multicast routing protocol (for example, DVMRP), it is automatically enabled when you
enable DVMRP.
Note: You must globally enable IP multicast routing in order to successfully
configure IGMP or DVMRP. Refer to “Configuring IP Global Routing”, earlier
in this chapter, for instructions on enabling IP multicast routing.
Configuring IGMP
IGMP enables hosts to inform routers when they join or leave groups. Routers
periodically query hosts (query interval) for the groups in which the hosts are members.
When there is more than one router in a broadcast domain (subnet), one of the routers
becomes the designated querier. Only the designated router queries the hosts.
Both IGMP Version 1.0 and IGMP Version 2.0 are supported. After selecting the specific
IGMP version for an interface, you can manually configure the Version 1.0 querier. The
selection of the querier for Version 2.0 is dynamic but can be overridden.
Enabling the IGMP Global Configuration
To enable IGMP global configuration:
1. In the IP Configuration section of the Web Agent window, click Global
Configuration. The IP Global Configuration dialog box opens.
2. From the IP Multicast Forwarding pull-down menu, select Enable. This enables
IP multicast globally.
3. In the IGMP Configuration section of the Web Agent window, click Global
Configuration. The IGMP Global Configuration dialog box opens.
4. From the IGMP pull-down menu, select Enable.