Cisco Support Community
Community Member

Proxy ARP issue

Hi Sir,

I'm troubleshooting an issue.

An FTP server is connected to a router with proxy ARP disabled. Local hosts can FTP to this server, but remote hosts fail to FTP. However, remote hosts able to ping to the FTP server. I've verified that no ACLs are configured on routers' interfaces along the IP path that deny FTP traffic.

Is there a possibility that disabling proxy ARP causes the problem? If the same remote host can ping to the server but can't FTP, this already isolated network layer and lower layers issue, and disabling proxy ARP should not be the cause of the problem.

It is unknown how the server is configured, whether it's pointing gateway to the router or it relies on proxy ARP. If it uses proxy ARP, pings from remote hosts should fail by right. Any thoughts?

Please advise if you've seen a similar scenario.

Thank you.


Lim TS


Re: Proxy ARP issue

Proxy ARP allows the router to respond to an ARP request (if a valid route is present)for a host that is not on the connected network where the ARP broadcast is heard. If the subnet mask and default gateway is correctly configured on the FTP server proxy ARP is not a factor. The server will only ARP to discover the MAC addresses of other hosts on the same subnet or the router interface on the subnet.

With your symptom I would want to be sure you don't have a duplicate IP address. The fact that local hosts are able to FTP suggests a whole duplicate subnet. Unplug your server and try the remote ping.

If that isn't your problem it is time to put a network analyzer (ethereal or Sniffer) on the server.

Please rate helpful posts.

CreatePlease to create content