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question about no ip proxy-arp command

I found that my arp table is very big and it consume about 3% CPU of my 1721. Will "no ip proxy-arp" command decrease my arp table? What did "ip proxy-arp" do? I know it is enabled by default, if I turn it off, will it be affect my Internet and Intranet connection? Any idea will be appreciated. Thanks!

Router Info: Cisco 1721, 96M RAM, WIC-2T(nat inside, f0 also), WIC-1Enet (nat outside).

2 REPLIES
Bronze

Re: question about no ip proxy-arp command

One of the disadvantages to having proxy arp enabled is an increased amount of ARP traffic. Take a look through this url on proxy ARP for a better understanding of what this command does:

http://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186a0080094adb.shtml

Also check your route statements, if you have a default route pointing to a broadcast interface (ip route 0.0.0.0 0.0.0.0 ethernet 0) this will increase your arp table, if possible, change the route statement to use a next hop address.

Bronze

Re: question about no ip proxy-arp command

If the 1721's ARP table is very large, it's probably because another device is doing proxy-arp for the 1721 rather than the 1721 itself doing proxy-arp. As mentioned above, static routes (especially static default routes) pointing to Ethernet interfaces rather than specific next-hop addresses are a common cause of this. A router with such a route has to ARP for every destination that uses the default route; a device with proxy-arp enabled then responds to all of these ARP requests with its MAC address so that it can forward the packets appropriately.

So, it's probably a problem with the 1721's routing table. I'd suggest fixing it, since proxy-arp essentially allows broken networks to function as if they're not broken, which is generally bad.

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