noproxyarp issues

Unanswered Question
Aug 13th, 2008

so it would seem on ASAs running 7.x....proxyarp is enabled by default and I have run into multiple instances where not disabling it causes problems with connectivity between two hosts connected to the same switch as one another on one side of the ASA (i think its always the outside but im not sure)

What is the ASA trying to do with this feature enabled by default and what is it actually doing that is causing these problems when its not disabled?

I have this problem too.
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robertson.michael Wed, 08/13/2008 - 11:30

Hi Chris,

When an ASA is configured for proxy ARP, it will respond to ARP requests on behalf of a host for a global address in its configuration, even though it does not technically own that IP address. In other words, if the ASA sees an ARP request for an IP address that is a configured global address, it will respond with its own interface MAC address on behalf of the host it is protecting. As for why this would cause problems for you, we would need to know a bit more about what situations you have had trouble with this.

Here is a link to the command reference for 'sysopt noproxyarp', which also gives a pretty good explanation of what proxy ARP is:

http://www.cisco.com/en/US/docs/security/asa/asa80/command/reference/s8.html#wp1377599

Hope that helps.

-Mike

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