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FTOS Configuration Guide for the C-Series - Force10 Networks

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Adjusting <strong>the</strong> IGMP Querier Timeout Value<br />

If <strong>the</strong>re is more than one multicast router on a subnet, only one is elected to be <strong>the</strong> querier, which is <strong>the</strong><br />

router that sends queries to <strong>the</strong> subnet.<br />

1. Routers send queries to <strong>the</strong> all multicast systems address, 224.0.0.1. Initally, all routers send queries.<br />

2. When a router receives a query it compares <strong>the</strong> IP address of <strong>the</strong> interface on which it was received<br />

with <strong>the</strong> source IP address given in <strong>the</strong> query. If <strong>the</strong> receiving router IP address is greater than <strong>the</strong><br />

source address given in <strong>the</strong> query, <strong>the</strong> router stops sending queries. By this method, <strong>the</strong> router with <strong>the</strong><br />

lowest IP address on <strong>the</strong> subnet is elected querier and continues to send queries.<br />

3. If a specified amount of time elapses during which o<strong>the</strong>r routers on <strong>the</strong> subnet do not receive a query,<br />

those routers assume that <strong>the</strong> querier is down, and a new querier is elected.<br />

The amount of time that elapses be<strong>for</strong>e routers on a subnet assume that <strong>the</strong> querier is down is <strong>the</strong> O<strong>the</strong>r<br />

Querier Present Interval. Adjust this value using <strong>the</strong> command ip igmp querier-timeout from<br />

INTERFACE mode.<br />

Configuring a Static IGMP Group<br />

Configure a static IGMP group using <strong>the</strong> command ip igmp static-group. Multicast traffic <strong>for</strong> static<br />

groups is always <strong>for</strong>warded to <strong>the</strong> subnet even if <strong>the</strong>re are no members in <strong>the</strong> group.<br />

View <strong>the</strong> static groups using <strong>the</strong> command show ip igmp groups from EXEC Privilege mode. Static<br />

groups have an expiration value of Never and a Last Reporter value of CLI, as shown in Figure 416.<br />

Configuring an IGMP Join Filter<br />

Block IGMP reports from hosts, on a per-interface basis based on a group address and source address<br />

specified in an access list.using <strong>the</strong> command ip igmp access-group access-list-name from INTERFACE<br />

mode.<br />

<strong>FTOS</strong> Behavior: Do not enter <strong>the</strong> command ip igmp access-group be<strong>for</strong>e creating <strong>the</strong> access-list. If<br />

you do, upon entering your first deny rule, <strong>FTOS</strong> clears multicast routing table and re-learns all groups,<br />

even those not covered by <strong>the</strong> rules in <strong>the</strong> access-list, because <strong>the</strong>re is an implicit deny all rule at <strong>the</strong><br />

end of all access-lists. There<strong>for</strong>e, configuring an IGMP join request filter in this order might result in<br />

data loss. If you must enter <strong>the</strong> command ip igmp access-group be<strong>for</strong>e creating <strong>the</strong> access-list,<br />

prevent <strong>FTOS</strong> from clearing <strong>the</strong> routing table by entering a permit any rule with high sequence number<br />

be<strong>for</strong>e you enter any o<strong>the</strong>r rules.<br />

<strong>FTOS</strong> <strong>Configuration</strong> <strong>Guide</strong>, version 7.7.1.0 591

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