Multimedia Traffic Control with IP Multicast (IGMP)

More on IGMP Operation

Number of IP Multicast Addresses Allowed

The total of static multicast filters and IGMP multicast filters (addresses) together can range from 389 to 420, depending on the current max-vlanssetting in the switch. If multiple VLANs are configured, then each filter is counted once per VLAN in which it is used.

Table 12-1. Maximum Allowed Number of Multicast Filters

Max-VLANs

Maximum # of Multicast Filters

Setting

(Static and IGMP Combined)

 

 

1 (the minimum)

420

8 (the default)

413

32 or higher

389

 

 

IGMP Operates With or Without IP Addressing

You can configure IGMP on VLANs that do not have IP addressing. The benefit of IGMP without IP addressing is a reduction in the number of IP addresses you have to use and configure. This can be significant in a network with a large number of VLANs. The limitation on IGMP without IP addressing is that the switch cannot become Querier on any VLANs for which it has no IP address— so the network administrator must ensure that another IGMP device will act as Querier and that an additional IGMP device is available as a backup Querier.

IGMP Function Available With IP Addressing

Available

Operating Differences Without an IP Address

Configured on the VLAN

Without IP

 

 

Addressing?

 

Drop multicast group traffic for which there

Yes

None

have been no join requests from IGMP clients

 

 

connected to ports on the VLAN.

 

 

 

 

 

Forward multicast group traffic to any port on

Yes

None

the VLAN that has received a join request for

 

 

that multicast group.

 

 

 

 

 

Forward join requests (reports) to the Querier.

Yes

None

 

 

 

Configure individual ports in the VLAN to Auto

Yes

None

(the default)/Blocked, or Forward.

 

 

 

 

 

Configure IGMP traffic forwarding to normal or

Yes

None

high-priority forwarding.

 

 

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