Installation guide

If you do not specify a multicast address in the cluster configuration file, the Red Hat High Availability

Add-On software creates one based on the cluster ID. It generates the lower 16 bits of the address

and appends them to the upper portion of the address according to whether the IP protocol is IPv4 or

IPv6:

For IPv4 — The address formed is 239.192. plus the lower 16 bits generated by Red Hat High

Availability Add-On software.

For IPv6 — The address formed is FF15:: plus the lower 16 bits generated by Red Hat High

Availability Add-On software.

Note

The cluster ID is a unique identifier that cman generates for each cluster. To view the cluster

ID, run the cman_to o l status command on a cluster node.

You can manually specify a multicast address in the cluster configuration file with the following

command:

ccs -h host --setmulticast multicastaddress

Note that this command resets all other properties that you can set with the --setmulti cast option

to their default values, as described in Section 5.1.5, “ Commands that Overwrite Previous Settings” .

If you specify a multicast address, you should use the 239.192.x.x series (or FF15:: for IPv6) that

cman uses. Otherwise, using a multicast address outside that range may cause unpredictable

results. For example, using 224.0.0.x (which is " All hosts on the network") may not be routed

correctly, or even routed at all by some hardware.

If you specify or modify a multicast address, you must restart the cluster for this to take effect. For

information on starting and stopping a cluster with the ccs command, refer to Section 6.2, “ Starting

and Stopping a Cluster” .

Note

If you specify a multicast address, make sure that you check the configuration of routers that

cluster packets pass through. Some routers may take a long time to learn addresses, seriously

impacting cluster performance.

To remove a multicast address from a configuration file, use the --setmul ti cast option of the ccs

but do not specify a multicast address:

ccs -h host --setmulticast

5.14 .3. Configuring a T wo-Node Clust er

If you are configuring a two-node cluster, you can execute the following command to allow a single

node to maintain quorum (for example, if one node fails):

ccs -h host --setcman two_node=1 expected_votes=1

Red Hat Ent erprise Linux 6 Clust er Administ rat ion