Intermittent IP connectivity

fnbt · ‎03-01-2002

We are in the middle of a project in which we are setting up routing at a site that we have acquired from another company. We have a router at that location and there is currently a router in place that was managed 3rd party for them. All of the clients on their network are set up to use the 3rd party router as their default gateway. Our problem is that when we try and ping a host on their network from our network, we get the first or first two replies and then time out. The next time you try and ping that host you get all timed out responses. We also have hosts that after trying to ping their hosts for a few times will start getting replies every time that they ping for about five minutes and then go back to intermittent again. I have also been told that we might be having some IPX trouble as well, but I don't believe so because I'm seeing the correct SAP table on the router. Anybody got any ideas?

fnbt · ‎03-01-2002

After looking further at this issue I have found that there are one or two hosts on the remote network that I can ping. I believe that the hosts on that network are incorrectly subnetted. Any opinions?

fnbt · ‎03-01-2002

That is not the issue. We are having trouble pinging from router ethernet interface to a computer on their network now.

o.hassairi · ‎03-02-2002

you should check for:

- line quality (errors) make show interface (wan interface)

- line load : may be the line is overused (increase the ping delay or use debug ip icmp to check for ping replies)

- routing table stability: make sure your routes do not change frequently (use show ip route)

mhussein · ‎03-02-2002

Could it be that ICMP is rate-limited on the 3rd party router?

fnbt · ‎03-04-2002

After looking further into this, I have noticed one very interesting fact. If I clear arp on our router I will be able to get to all hosts on the remote network for 2-5 minutes or so. Interface doesn't have an extreme amount of errors, the ip routes seem pretty steady. Not sure where to go from here

jintao99 · ‎03-04-2002

It's more than likely an ARP problem, please check the arp table on your workstation, to see if the MAC for gateway to remote network is pointing to the correct router. I'm guessing somewhere in your network there is misconfigured VLSM, and when the workstation ARP for the gateway to remote network, it gets correct response from the correct router first, but then another ARP response is received from a misconfigured router, and over write the ARP table, the remaining traffic will be mislead to the wrong router.

Hope this will help.

TJ

fnbt · ‎03-06-2002

Kudos to TJ, It was indeed an arp problem from misconfigured VLSM. Looking at a workstation on the remote network we were showing the wrong mac for our routers IP address in the ARP table. Strangely enough we did some scanning and found out that the MAC address for that IP happened to be a printer on the remote network. Very interesting! Thanks for the help.

tvanderwerken · ‎03-04-2002

How many host are we talking about? Almost sounds like a duplicate IP issues. Before you clear arp record the MAC addreses of the host(s) you are trying to get too. Then clear arp and record them again, are they different? Also, is the LAN at the remote site a switched LAN? If so is there any spanning tree issue?

Just a thought.

HTH

Todd