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IP Switching on 3500 catalyst

I have a 3500 catalyst that has various PC's running TCP/IP connected on each port. When I try to ping these adresses over my WAN sometimes this works and sometimes this fails. Usually it seem the port has gone to sleep or the ip adddres is no longer in a table on the switch. Is there someway to make this address always available. I want to be able to access the local PC remotely via pc anywhere all the time. Thanks

9 REPLIES

Re: IP Switching on 3500 catalyst

Are you able to ping to the 3500's IP address all the time? If yes, the problem is probably on the PC (it might has gone to sleeping mode or something like that). There is a possibility to use mac-address-table static ... command to enter an entry into the switch MAC table. But it should not be necessary - when PC MAC address expires on 3500 and there is a frame coming with destination address = PC MAC address the frame is flooded to all switch ports.

Community Member

Re: IP Switching on 3500 catalyst

Yes I am always able to ping the 3524xl switch and if I telnet to the switch I can then ping the pc.

Once I do this then I can ping the PC over the WAN link. I was also thinking the PC is going into sleep mode however I have disabled any of these options.

Any other suggestions would be helpful.

Thanks

Community Member

Re: IP Switching on 3500 catalyst

Are you pinging the PCs by their hostname or their IP address? It might be name resolution that is causing your problems.

When you say the ping fails, do you get "request timed out" or "bad IP address" errors?

hope this helps

Re: IP Switching on 3500 catalyst

Are the PCs in the same subnet as the 3524? It seems like some default gateway or ARP proxy or something like that problem to me. Is the route entry in your router static or dynamic? Have you tried ping -t to the PCs? What about traceroute? What is the ping failure exact message?

Community Member

Re: IP Switching on 3500 catalyst

Ia all the ports configured for Portfast?

Community Member

Re: IP Switching on 3500 catalyst

I'm having all of the mentioned symptoms without the WAN link. I have 2 WIN2000 Servers connected to a 3524PWRXL, and they seem to disappear to sometimes. Sometimes I will get a reply on the first ping, and the remaining pings(even using ping -t) will be timed out messages. While ping -t is going on with timed out messages, I can ping the server from the router(which updates the ARP table), and ping -t will start getting replies. Could it be a problem with my 3640 router's ARP cache?

Servers are not going to sleep. I have the same problem whether I ping them by name or by IP. I get "request timed out" messages. The servers are in the same subnet as the 3524. The ARP entry in my router is dynamic, but they are not getting cleared out. In fact, the ARP entries are getting refreshed about every 3-5 minutes. Ping -t does nothing more than a lot of timed out messages. Traceroute is a straight shot in a LAN situation. All of the ports are configured for spantree portfast except my GBIC's.

Community Member

Re: IP Switching on 3500 catalyst

What about the power saving settings of the NIC's used in the PC's. Disable them.

Community Member

Re: IP Switching on 3500 catalyst

What I am finding in my research is that this situation is becomming a big issue with the 3500 series. Its always been a known issue that All switches occasionally have this problem and simply 'shut' ing and 'no shut' ing the interface or unplugging ang plugging the cable back into the interface wil fix the problem.

The problem with my 3524XL switch happens on a daily basis and is very similar to what I have been experiencing lately. I never noticed it because we havn't had to monitor the devices on that network on a daily basis.

Upgrading the IOS will not work or fix the problem is what I have found out in researching this the past 2 weeks.

I manually clear the arp table in my router and that has provided a workaround for me but its getting old, quick!

Community Member

Re: IP Switching on 3500 catalyst

I figured out what my problem was, and here's the low-down: My servers are on the internal network with static NAT translations on my PIX firewall. I had alias commands on my PIX in order for internal hosts to be able to view the server using the same web site that users on the internet are using.

Start a sniffer application and start capturing packets. Clear the arp in your router and on a local PC ("arp -d" and "arp -a" allows you to view your local arp table). Ping the server by name or by IP address...it doesn't matter. With the alias command on my PIX520 running v. 6.1.1, I get two arp replies. I get one from the server with the correct MAC address, and shortly after, I receive a second arp reply with the PIX's MAC address. Remove the alias command, and the only arp reply will be the one from the server itself.

The reason some people see the server sometimes, and others see it all the time has to do with network congestion and latency. If you don't have a PIX, check your DNS server for any misconfigurations. Just a thought.

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