Cisco IE 4000, Software Configuration Manual

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Configuring IGMP Snooping and MVR
Restrictions for IGMP Snooping and MVR
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You can set the maximum number of IGMP groups that a Layer 2 interface can join by using the ip igmp max-groups
interface configuration command. Use the no form of this command to set the maximum back to the default, which
is no limit. This restriction can be applied to Layer 2 ports only—you cannot set a maximum number of IGMP groups
on routed ports or SVIs. You also can use this command on a logical EtherChannel interface but cannot use it on
ports that belong to an EtherChannel port group.
Information About IGMP Snooping and MVR
This chapter describes how to configure Internet Group Management Protocol (IGMP) snooping on the switch, including
an application of local IGMP snooping, Multicast VLAN Registration (MVR). It also includes procedures for controlling
multicast group membership by using IGMP filtering and procedures for configuring the IGMP throttling action.
Note: For IP Version 6 (IPv6) traffic, Multicast Listener Discovery (MLD) snooping performs the same function as IGMP
snooping for IPv4 traffic.
Note: You can either manage IP multicast group addresses through features such as IGMP snooping and MVR, or you
can use static IP addresses.
IGMP Snooping
Layer 2 switches can use IGMP snooping to constrain the flooding of multicast traffic by dynamically configuring Layer 2
interfaces so that multicast traffic is forwarded to only those interfaces associated with IP multicast devices. As the name
implies, IGMP snooping requires the LAN switch to snoop on the IGMP transmissions between the host and the router
and to keep track of multicast groups and member ports. When the switch receives an IGMP report from a host for a
particular multicast group, the switch adds the host port number to the forwarding table entry; when it receives an IGMP
Leave Group message from a host, it removes the host port from the table entry. It also periodically deletes entries if it
does not receive IGMP membership reports from the multicast clients.
Note: For more information on IP multicast and IGMP, see RFC 1112 and RFC 2236.
The multicast router sends out periodic general queries to all VLANs. All hosts interested in this multicast traffic send join
requests and are added to the forwarding table entry. The switch creates one entry per VLAN in the IGMP snooping IP
multicast forwarding table for each group from which it receives an IGMP join request.
The switch supports IP multicast group-based bridging, rather than MAC-addressed based groups. With multicast MAC
address-based groups, if an IP address being configured translates (aliases) to a previously configured MAC address or
to any reserved multicast MAC addresses (in the range 224.0.0.xxx), the command fails. Because the switch uses IP
multicast groups, there are no address aliasing issues.
The IP multicast groups learned through IGMP snooping are dynamic. However, you can statically configure multicast
groups by using the
ip igmp snooping vlan vlan-id static ip_address interface interface-id global configuration
command. If you specify group membership for a multicast group address statically, your setting supersedes any
automatic manipulation by IGMP snooping. Multicast group membership lists can consist of both user-defined and IGMP
snooping-learned settings.