Proxy ARP, misconfigured servers, and migrations

June 25, 2014 — Leave a comment

When migrating virtual or physical servers from one data center to another, especially if you are moving from Cisco Catalyst to Nexus switches, it’s helpful to be aware of the concept of Proxy ARP.  Here is a link to a Cisco article that explains Proxy ARP:

http://www.cisco.com/c/en/us/support/docs/ip/dynamic-address-allocation-resolution/13718-5.html.

If Proxy ARP is enabled on a switch/router, it can hide or mask misconfigured default gateways/subnet masks on servers.  A switch/router with this setting enabled can help servers reach devices in other subnets, even if the configured default gateway on a server is incorrect. Once the misconfigured servers are moved to network equipment that has Proxy ARP disabled, the servers will no longer be able to communicate with devices in other subnets.  Proxy ARP is enabled by default on Catalyst switches and disabled by default on Nexus switches.  Make sure to review the Proxy ARP settings in both the originating and destination data center.  If this setting will be disabled at the destination site, run a script to check default gateways and subnet masks on servers before beginning a migration.

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