Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Community Member

ARP table includes all public addresses visited

I have an 831 running Version 12.4(19b) IOS. For some reason the ARP table includes every single address visited, whether it is on the LAN or through a VPN or on the internet. I believe this is slowing the performance of the router and might even be causing routing issues. The router hangs for a few seconds whenever I clear the ARP table. I've attached the config and a sample of the ARP table. Why would the router include all those non-LAN addresses in the ARP table?

1 ACCEPTED SOLUTION

Accepted Solutions
Hall of Fame Super Gold

Re: ARP table includes all public addresses visited

Because of that in your config:

ip route 0.0.0.0 0.0.0.0 Ethernet1

Configure "no ip route ..." for the command above. You have already a default route because the interface is using dhcp.

Please rate post if it helps!

8 REPLIES
Hall of Fame Super Gold

Re: ARP table includes all public addresses visited

Because of that in your config:

ip route 0.0.0.0 0.0.0.0 Ethernet1

Configure "no ip route ..." for the command above. You have already a default route because the interface is using dhcp.

Please rate post if it helps!

Community Member

Re: ARP table includes all public addresses visited

so if the WAN interface receives an address via DHCP I don't need a default route?

Re: ARP table includes all public addresses visited

DHCP server will send you a default gateway.

ip route 0.0.0.0 0.0.0.0 Fastethernet0/0

In this case, the router generates an ARP request for each IP address that is not reachable through more specific routes, which practically means that the router generates an ARP request for almost every address on the Internet.

Community Member

Re: ARP table includes all public addresses visited

so it is a bad idea to use an interface as my default gateway?

Re: ARP table includes all public addresses visited

Bad for broadcast networks.

You must use ip-address instead of interface.

[Pls RATE if HELPS]

Hall of Fame Super Gold

Re: ARP table includes all public addresses visited

It's a bad idea, but since it works anyway, most people doesn't realize the ARP havoc until looking into the router like you did.

Thanks for the appreciation and good luck!

Hall of Fame Super Gold

Re: ARP table includes all public addresses visited

Just a small clarification: it is not good to point a static route (especially a static default route) to an interface if the interface is a broadcast type interface which uses ARP. But if the interface is a point to point link (such as HDLC, PPP, or point to point Frame Relay) then it is not bad at all. In fact it is fairly good for the static route to point at point to point interfaces.

HTH

Rick

Hall of Fame Super Silver

Re: ARP table includes all public addresses visited

Hello Paolo,

there is another reason to avoid using this type of static route over a broadcast network: the trick works until someone disables the proxy-arp on the other router's interface.

I saw this on a production network some years ago.

Best Regards

Giuseppe

569
Views
10
Helpful
8
Replies
CreatePlease to create content