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9.2. IP Virtual Server (IPVS)

Red Hat Enterprise Linux 6.5 introduces a new sync message protocol format. This new format is provided to prevent interruptions to business services caused by persistent connections on backup server nodes timing out prematurely, causing inconsistent state in the case of failover to a backup server node.
This new format is not compatible with versions of Red Hat Enterprise Linux 6.4 or earlier, or kernel versions prior to kernel-2.6.32-406.el6. Upgrade backup nodes before upgrading the master node.
To continue using the old format for sync messages, for example if you need to upgrade the master node prior to the backup nodes, set the value of /proc/sys/net/ipv4/vs/sync_version to 0.