Frequently need to clear ARP in order to access internet

jcowser · ‎03-25-2013

We have installed an ASA5512 behind a Comcast cable modem. Users are able to browse to the internet for 5-10 minutes before their sessions hang. Clearing of ARP, "clear arp" re-enables the ability to access the internet, but only for 5-10 minutes.

I tried disconnecting the LAN side and only running a single laptop through the ASA but the behavior is the same.

Any thoughts on what I might check?

Thanks,

Jerry

Jouni Forss · ‎03-25-2013

Hi,

Last time I have faced this issue at work has been related to missconfigured ISP side. It has happened both at my home connection (good thing I work at the ISP ) and one customer connection.

In those occasions also the only thing from the users side correcting this situation was to "clear arp" which would then result the ASA to automatically generate ARP request for the gateway address which would then again somehow re-enable connectivity for a short perioid of time. (or atleast that is what to me seemed to correct the situation)

Before I cleared the ARP I could only see broadcast traffic in a capture directly at the ASA interface. As soon as the "clear arp" was issued all unicast traffic started to work.

My home connection problem was related to a situation where I had changed my home connection (ADSL) to use a public subnet staticly rather than a DHCP IP address. They had also forgotten to remove some DHCP related settings on the DSLAM side which caused the problem.

If this is a new installation I would ask the ISP to check what the problem could be and/or monitor the situation while it happens and is corrected. If it happens so often it shouldnt be problem to catch.

- Jouni