02-26-2007 02:20 AM - edited 03-05-2019 02:34 PM
Hello,
I have a Cisco router trying to communicate to a remote host on the Internet through our gateway Router. Both routers are on the same subnet. We kept having intermittent communication issues. During our troubleshooting, we noticed that the ARP table entry for the gateway router on the internal router kept showing it as "INCOMPLETE".
The only thing that would fix it would be performing a "CLEAR ARP" on the router.
Why would there be ARP issues between Routers on the same subnet? Is there a setting on the router that I need to verify/change on the interface of router ? Anyone else ever have this problem?
Regards,
Mujeeb
02-26-2007 04:10 AM
Can you post the interface configuration of both your router. Is your ip proxy-arp disabled on the interface?
Cheers
Hoogen
02-26-2007 09:47 PM
Hello Hoogen,
Below is the interface conf of both routers.
Gateway Router Fast ethernet:
no ip redirects
no ip proxy-arp
ip accounting output-packets
ip route-cache same-interface
ip route-cache policy
no ip mroute-cache
full-duplex
no cdp enable
Requesting Router:
no ip unreachables
ip directed-broadcast
ip load-sharing per-packet
ip route-cache same-interface
no ip mroute-cache
duplex full
Regards,
Mujeeb
02-26-2007 10:43 PM
For some reason the ARP-sending router doesn't receive a reply.
You could run a 'debug arp' on the router(s) to verify ARP-requests are received and/or replies are transmitted.
HTH
Rolf
02-26-2007 10:59 PM
Hi Mujeeb
Are you using default route point to Gateway Router?
If yes
What is next-hop's type which you use?
1. Next-hop IP address
ip route 0.0.0.0 0.0.0.0 a.b.c.d
2. Connected interface
ip route 0.0.0.0 0.0.0.0 fastEthernet x/x
If you use 2 then you can change to 1 for test?
Or Can you enable proxy arp on gateway's interface( Fastethernet)?
Please test and let us know
HTH
02-27-2007 02:32 AM
Mujeeb please enable your ip proxy-arp on the gateway router fast ethernet.
HTH
Hoogen
Do rate if this helps :)
02-27-2007 03:02 AM
Dear Hoogen,
I want to ask a question before enabling proxy-arp that what would happen if I set arp time-out value to zero. Will it work for me ?
and one more question is that Proxy-arp is a mechanism in which a device sends its MAC address on behalf of someone else ip address. A router which is working as gateway to Internet should have proxy-arp enabled or not ? why network peoples recommends that proxy-arp should be disabled on core routers ?
Regards,
Mujeeb
02-27-2007 03:30 AM
Making arp timeout as zero is not a good practice.
This link should help you out why we need proxy-arp. http://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186a0080094adb.shtml
Cheers
Hoogen
02-28-2007 03:57 AM
Hello,
I removed the arp timeout 0 command from interface and after that I tried another thing that I put down static ARP entries on both routers for each other ip addresses which is working fine for us.
Now the same issue is occuring with secondary ip addresses. Gateway Router is unable to get mac address for secondary ip address of Internal Router , I know problem will be solved if I put down static ARP entry for secondary ip address but the question I want to ask that what is the cause of this behaviour and problem is at Gateway router or at Internal Router as we have been using same routers since long.
Note: I have attached a file to show ARP entries.
Regards,
Mujeeb
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