Tag Archives: Virtualization

Cluster fencing using SNMP fence_ifmib and Cisco switch

Fencing is a vital component in a virtualization cluster; when a cluster member fails it must be inhibited to access shared resources such as network disks or SAN, so that any virtual machine still running on it could be restarted on other members, being sure that no data will be corrupted because of simultaneous access.

Many methods exist to fence failed cluster members, mostly based on powering them off or on disconnecting their network cards; here I would like to show how to use network fencing on a Linux cluster environment (Cman based), using the fence_ifmib against a Cisco managed switch.

The logic behind this mechanism is very simple: once a node has been marked as dead the agent uses the SNMP SET method to tell the managed switch to shut the ports down.

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