Strange network issue

steve.barr · ‎10-04-2008

I don't know exactly how to describe my problem, but I'm hoping someone may be able to give me some suggestions on what to try.

Our school district has 8 buildings, 2 connected via T-1 circuits, 3 connected by our private gb fiber, and 3 connected via 10mb Embarq MetroEthernet. The three buildings on the Embarq fiber are configured identically and have the same equipment. (Cisco 3524/3550 switches and a 2621 router for SRST.)

Last week, one buildings had trouble connecting to the Internet. Local network traffic to the Novell servers and printers was OK. The strange thing is their Cisco IP phones work perfectly. They have not had a problem with the phones. The voice vlan is 96, the data vlan is 32 and the mgmt vlan is 252. (Each buildings phones, data and mgmt are on different vlans)

At the high school, the vlan interfaces are present on a Cisco 3640 router. I can ping devices on both ends of the fiber. I have deleted and re-created the vlan 32 interface and no change.

I have tried swapping switches at the remote site, and swapping the router at the high school. Nothing resolves the problem. The problem appears to lie at the high school in the switch stack or router, but I don't know how to pin-point the problem.

Tomorrow I am planning to configure a spare switch and connect just the problem building to the router and see what happens.

Are there statistics in the switches and/or router that will help find the problem?

I'm pulling my hair out on this one. All of the network support people I have talked to at my ISP have no ideas.

If you have any suggestion, I'm all ears.

Thanks!

Steve Barr

Madison Local Schools

kneber · ‎10-04-2008

Can you ping/get to other networks outside local sub-net?

Have you checked routing tables?

1. On VLAN32's gateway: check that the routing table contains the default route, and that nexit hop is what you expect it to be.

2. On other routers: check that VLAN32's IP address is present, and that next hop is what you expect it to be.

steve.barr · ‎10-05-2008

Yes, we can pin and telnet to other subnets.

The routing tables appear correct. I will check again today.

The strange thing is that some traffic on vlan32 works. I can ping other devices all around the network, I can access some https websites at the ISP, but I can't access my web server.

Steve

milan.kulik · ‎10-05-2008

Hi,

as "I can access some https websites at the ISP, but I can't access my web server.", are you able to Ping your web server by the IP address?

If yes, it looks like a DNS problem within your VLAN 32.

If not, try traceroute to the web server as see what's the last hop repyling.

BR,

Milan

steve.barr · ‎10-10-2008

Sorry I haven't been back to the forums before today. I've been searching and playing catch-up.

Monday, around noon, the network started working normally again. When I left for lunch it was still down, and it was up after lunch.

I still have no concrete idea what caused (or fixed) the problem.

I could ping and traceroute to my web server, but I could not access it via a browser. I though about a DNS issue, but I couldn't access the web server by IP either.

I'm glad it's back working, I just wich I could determine what caused the problem.

Thanks to all who offered suggestions.

Steve