Best Practices for OOB Clusters with IGMP Snooping

The following are best practices for out-of-band (OOB) clusters if Internet Group Management Protocol (IGMP) snooping is enabled in the cluster.

Clustering relies on the IGMP protocol to discover peer nodes and to communicate with them. Switches often have IGMP snooping enabled by default, which will filter IGMP packets from ports that do not have periodic IGMP membership reports. This can cause IGMP packet drops in out-of-band clusters.

Refer to About IGMP Snooping in a Cluster for more information. Also refer to the following best practices:

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allow Internet Group Management Protocol (IGMP) traffic by using an IP filter chain. Refer to Allow IGMP Traffic.

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enable an IGMP querier. Refer to Enable an IGMP Querier.

These best practices result in the following:

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hostnames being properly displayed in CLI commands that display cluster information such as show cluster global brief

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nodes joining clusters faster, especially nodes that are not capable of becoming a leader, such as GigaVUE TA Series nodes

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no multiple leaders being created in an out-of-band cluster. This can occur when a node that is capable of becoming a leader is not able to see the current leader and hence elects itself as a leader.

About IGMP Snooping in a Cluster

IGMP snooping is a networking feature that monitors IGMP membership reports received from different ports on a networking switch and learns the ports to which multicast groups belong. When a port stops sending membership reports about a multicast group, the switch will stop forwarding the group’s traffic to the port.

An IGMP querier is a router (or switch) feature that periodically queries the network for multicast group interests. If a node on the network belongs to a certain multicast group, it responds to the queries, the router then records or refreshes its record of the node’s interest in the traffic for the group, and the router forwards traffic to the network towards the node. The switches on the network with IGMP snooping enabled also learn from the responses and maintain their records about the nodes’ interests in groups and forward traffic accordingly.

Hostnames are detected using Multicast Domain Name System (mDNS) packets, which are in multicast group 224.0.0.251.

An IP filter is a chain of rules for the treatment of packets. Refer to the “Using IP Filter Chains for Security” section in the GigaVUE-OS CLI Reference Guide.

Allow IGMP Traffic

If IP filtering is enabled (and IGMP snooping is enabled):

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Verify that IGMP traffic is allowed.

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For example, issue the following CLI commands:

(config) # ip filter chain INPUT rule append tail target ACCEPT dup-delete protocol igmp

(config) # ipv6 filter chain INPUT rule append tail target ACCEPT dup-delete protocol igmpv6

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Verify that mDNS traffic is allowed.

If IGMP snooping is disabled, you do not need to allow IGMP traffic. However, you must allow UDP multicast traffic that targets 224.0.0.251. For example, issue the following CLI command:

(config) # ip filter chain INPUT rule append tail target ACCEPT dup-delete dest-addr 224.0.0.251 /32

where:

dest-addr specifies the multicast group

Enable an IGMP Querier

If IGMP snooping is enabled:

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Check if there is an IGMP querier on the cluster network. The querier periodically sends queries that trigger the nodes in the cluster to send IGMP membership reports. For example, use a sniffer tool to verify if there is an IGMP querier on the network, such as Wireshark.

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IGMP snooping and IGMP snooping querier settings vary by networking switch. Refer to the respective documentation for how to configure them on your device.

When IGMP traffic is allowed and an IGMP querier is enabled in the network, the switches in the network will be refreshed through the IGMP membership reports.