07-10-2008 07:34 AM - edited 03-03-2019 10:40 PM
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?
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07-10-2008 07:38 AM
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!
07-10-2008 07:38 AM
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!
07-10-2008 07:39 AM
so if the WAN interface receives an address via DHCP I don't need a default route?
07-10-2008 07:43 AM
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.
07-10-2008 07:47 AM
so it is a bad idea to use an interface as my default gateway?
07-10-2008 07:54 AM
Bad for broadcast networks.
You must use ip-address instead of interface.
[Pls RATE if HELPS]
07-10-2008 08:07 AM
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!
07-10-2008 11:40 AM
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
07-11-2008 12:39 PM
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
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