Extreme Networks ExtremeWare XOS 11.0, Справочник по командам

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ExtremeWare XOS 11.0 Command Reference Guide 877
18
IP Multicast Commands
IP multicast routing is a function that allows a single IP host to send a packet to a group of IP hosts.
This group of hosts can include devices that reside on or outside the local network, or within or across a
routing domain.
IP multicast routing consists of the following functions:
• A router that can forward IP multicast packets
• A router-to-router multicast protocol [for example, Distance Vector Multicast Routing Protocol
(DVMRP) or Protocol Independent Multicast (PIM)]
• A method for the IP host to communicate its multicast group membership to a router [for example,
Internet Group Management Protocol (IGMP)]
NOTE
You must configure IP unicast routing before you configure IP multicast routing.
IGMP is a protocol used by an IP host to register its IP multicast group membership with a router.
Periodically, the router queries the multicast group to see if the group is still in use. If the group is still
active, a single IP host responds to the query, and group registration is maintained.
IGMP is enabled by default on the switch. However, the switch can be configured to disable the
generation of period IGMP query packets. IGMP should be enabled when the switch is configured to
perform IP unicast or IP multicast routing.
Protocol Independent Multicast (PIM) is a multicast routing protocol with no inherent route exchange
mechanism. The switch supports dense mode and sparse mode operation. You can configure dense
mode or sparse mode on a per-interface basis. After they are enabled, some interfaces can run dense
mode, while others run sparse mode.
PIM Dense Mode
Protocol Independent Multicast-Dense Mode (PIM-DM) is a multicast routing protocol that is similar to
DVMRP. PIM-DM routers perform reverse path forwarding (RPF). However, instead of exchanging its
own unicast route tables for the RPF lookup, PIM-DM uses the existing unicast route table for the RPF
check. As a result, PIM-DM requires less system memory.