Concept Guide

When the querier receives a leave message from a host, it sends a group-specic query to the subnet. If no response is received, it sends
another. The amount of time that the querier waits to receive a response to the initial query before sending a second one is the last
member query interval (LMQI). The switch waits one LMQI after the second query before removing the group from the state table.
• Adjust the period between queries.
INTERFACE mode
ip igmp query-interval
• Adjust the time period between queries used to discover IPv6 multicast groups.
Interface mode
ipv6 mld query-interval
• Adjust the maximum response time.
INTERFACE mode
ip igmp query-max-resp-time
• Adjust the maximum amount of time that the querier waits, for an IPv6 query response, before taking further action.
Interface mode
ipv6 mld query-max-response-time
• Adjust the last member query interval.
INTERFACE mode
ip igmp last-member-query-interval
• Adjust the amount of time the querier waits, for the initial query response, before sending the next IPv6 query.
Interface mode
ipv6 mld last-member-query-interval
Preventing a Host from Joining a Group
You can prevent a host from joining a particular group by blocking specic IGMP reports using an extended access list containing the
permissible source-group pairs.
NOTE
: For rules in IGMP access lists, source is the multicast source, not the source of the IGMP packet. For IGMPv2, use the
keyword any for source (as shown in the following example) because the IGMPv2 hosts do not know in advance who the source
is for the group in which they are interested.
To apply the access list, use the following command.
• Apply the access list.
INTERFACE mode
ip igmp access-group access-list-name
Dell EMC Networking OS Behavior: Do not enter the ip igmp access-group command before creating the access-list. If you do,
after entering your rst deny rule, the Dell EMC Networking OS clears the multicast routing table and re-learns all groups, even those not
covered by the rules in the access-list, because there is an implicit deny all rule at the end of all access-lists. Therefore, conguring an
IGMP join request lter in this order might result in data loss. If you must enter the ip igmp access-group command before creating
the access-list, prevent the Dell EMC Networking OS from clearing the routing table by entering a
permit any rule with a high sequence
number before you enter any other rules.
In the following example, virtual local area network (VLAN) 400 is congured with an access list to permit only IGMP reports for group
239.0.0.1. Though Receiver 2 sends a membership report for groups 239.0.0.1 and 239.0.0.2, a multicast routing table entry is created only
for group 239.0.0.1. VLAN 300 has no access list limiting Receiver 1, so both IGMP reports are accepted and two corresponding entries are
created in the routing table.
Internet Group Management Protocol (IGMP)
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