Multicast in a network verification

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By default, PowerHA® SystemMirror® uses unicast communications for heartbeat. For cluster communication, you can optionally select to configure a multicast address or have CAA automatically select the multicast address if your network is configured to support multicast communication. If you choose to use multicast communication, do not attempt to create a cluster until you verify that multicast packets can be sent successfully across all nodes that are part of the cluster.

To test end-to-end multicast communication for all nodes used to create the cluster on your network, run the mping command to send and receive packets between nodes.

If you are running PowerHA SystemMirror 7.1.1, or later, you cannot create a cluster if the mping command fails. If the mping command fails, your network is not set up correctly for multicast communication. If so, review the documentation for your switches and routers to enable multicast communication.

You can run the mping command with a specific multicast address; otherwise, the command uses a default multicast address. You must use the multicast addresses that are used for creating the cluster as input for the mping command.
Note: The mping command uses the interface that has the default route. To use the mping command to test multicast communication on a different interface that does not have the default route, you must temporarily add a static route with the required interface to the multicast IP address.

The following example shows a success case and a failure case for the mping command, where node A is the receiver and node B is the sender.

Success case:
Receiver

root@nodeA:/# mping -r -R -c 5
mping version 1.1
Listening on 227.1.1.1/4098:

Replying to mping from 9.3.207.195 (nodeB.aus.stglabs.ibm.com) bytes=32 seqno=0 ttl=1
Replying to mping from 9.3.207.195 (nodeB.aus.stglabs.ibm.com) bytes=32 seqno=1 ttl=1
Replying to mping from 9.3.207.195 (nodeB.aus.stglabs.ibm.com) bytes=32 seqno=2 ttl=1
Replying to mping from 9.3.207.195 (nodeB.aus.stglabs.ibm.com) bytes=32 seqno=3 ttl=1
Replying to mping from 9.3.207.195 (nodeB.aus.stglabs.ibm.com) bytes=32 seqno=4 ttl=1

Sender

root@nodeB:/# mping -R -s -c 5
mping version 1.1
mpinging 227.1.1.1/4098 with ttl=1:

32 bytes from 9.3.207.190 (nodeA.aus.stglabs.ibm.com) seqno=0 ttl=1 time=0.985 ms
32 bytes from 9.3.207.190 (nodeA.aus.stglabs.ibm.com) seqno=1 ttl=1 time=0.958 ms
32 bytes from 9.3.207.190 (nodeA.aus.stglabs.ibm.com) seqno=2 ttl=1 time=0.998 ms
32 bytes from 9.3.207.190 (nodeA.aus.stglabs.ibm.com) seqno=3 ttl=1 time=0.863 ms
32 bytes from 9.3.207.190 (nodeA.aus.stglabs.ibm.com) seqno=4 ttl=1 time=0.903 ms

--- 227.1.1.1 mping statistics ---
5 packets transmitted, 5 packets received, 0% packet loss
round-trip min/avg/max = 0.863/0.941/0.998 ms
Failure case:
Receiver

root@nodeA:/# mping -r -R -c 5 -6
mping version 1.1
Listening on ff05::7F01:0101/4098:

Replying to mping from fe80::18ae:19ff:fe72:1a15 bytes=48 seqno=0 ttl=1
Replying to mping from fe80::18ae:19ff:fe72:1a15 bytes=48 seqno=1 ttl=1
Replying to mping from fe80::18ae:19ff:fe72:1a15 bytes=48 seqno=2 ttl=1
Replying to mping from fe80::18ae:19ff:fe72:1a15 bytes=48 seqno=3 ttl=1
Replying to mping from fe80::18ae:19ff:fe72:1a15 bytes=48 seqno=4 ttl=1

Sender

root@nodeB:/# mping -R -s -c 5 -6
mping version 1.1
mpinging ff05::7F01:0101/4098 with ttl=1:


--- ff05::7F01:0101 mping statistics ---
5 packets transmitted, 0 packets received, 100% packet loss
round-trip min/avg/max = 0.000/0.000/0.000 ms
Note: To verify a result, you must check the sender side of the mping command only. Also, note the percentage of packet loss. To verify whether multicast is working on a network, you must perform the mping tests with both nodes tested as both the sender and receiver. Typically, the non-verbose output provides you the necessary information. However, if you choose to use the -v flag with the mping command, a good knowledge about the internals of the program is necessary, without which the verbose output can be misunderstood. You can also check the return code from the sender side of the mping command. If an error occurs, the sender side returns 255. Upon success, it returns 0.

Cluster Aware AIX (CAA) selects a default multicast address if you do not specify a multicast address when you create the cluster. The default multicast address is created by combining the logical OR of the value (228.0.0.0) with the low 24 bits of the IP address of the node. For example, if the IP address is 9.3.199.45, then the default multicast address would be 228.3.199.45.

The Internet Protocol version 6 (IPv6) addresses are supported by PowerHA SystemMirror 7.1.2, or later. When IPv6 addresses are configured in the cluster, Cluster Aware AIX (CAA) activates heartbeating for the IPv6 addresses with an IPv6 multicast address. You must verify that the IPv6 connections in your environment can communicate with multicast addresses.

To verify that IPv6 multicast communications are configured correctly in your environment, you can run the mping command with the -6 option. When you run the mping command, it verifies the IPv6 multicast communications with the default IPv6 multicast address. To specify a specific IPv6 multicast address, run the mping command with the -a option and specify an IPv6 multicast address. You do not need to specify the -6 option when using the -a option. The mping command automatically determines the family of the address passed with the -a option.