Are Crossover Cables supported for Red Hat High Availability cluster interconnect?

Environment

• Red Hat Enterprise Linux (RHEL) with the High Availability Add-On
• Red Hat High Availability Cluster with 2 nodes
• 2 cluster nodes that are connected with a crossover cable that is used for internal cluster communication (ie. cable directly from one node to the other without passing through a network switch or direct copper IB connection without switches).

Issue

• Does Red Hat support the use of crossover cables for the cluster heartbeat network in a two node cluster?
• Does Red Hat support the use of direct copper IB connection (without switches)?

Resolution

Red Hat does not support use of a crossover cable for cluster communication. A crossover cable can be used for testing, however limitations listed below should be understood and a crossover cable should not be used in production environments.

Root Cause

• Crossover cable cannot be supported for cluster message traffic due to the method of handling a link down event on the cluster interconnect interface.
• When the cluster interconnect link fails on one cluster node, both nodes will report a link down event because there is no signal coming from the other end of the crossover cable.
• This can cause confusion in the cluster as the link goes up and down with fence events and server reboots.
• When one node goes down or starts up, there is link up/down activity on the other node; this is precisely what leads to the support limitations that we have in place around crossover cables. On a proper switched network you should not see one cluster node's link status affecting other cluster nodes..
• Please refer to Red Hat Enterprise Linux Cluster, High Availability, and GFS Deployment Best Practices for more information about supported and unsupported cluster configurations.

Diagnostic Steps

This article applies if:

• You have a 2 node Red Hat Enterprise Linux cluster
• You wish to connect both nodes via a crossover cable without passing through a switch or hub, or you wish to know if this configuration is supported.

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