Network Professionals - need help!

[Longy]

Ok I've got a really annoying network problem!

Please find attached a basic layout of the network to help you picture the scene.

Problem:

The network has been running fine for months but all of a sudden I seem to be getting a fault with the internet connection on just one subnet (subnet B).

The internet will work fine and all of a sudden it will just stop working (as in won't load internet pages or stream radio). I then have to disable the network connection on the windows box (the NIC that connects to Router A) and enable it and everything works again fine for maybe hours or even a day or two but the problem will raise its head again.

Router A and Router B can access the internet fine no problem and stayed connected indefinably.

I've changed the network lead and updated the drivers for the NIC but it still seems to do it!

Heres the strange thing:

Went the internet goes down from subnet B I can log into Router A from subnet B and ping Router A from subnet B no problem but I can't ping www.google.com although router A can ping google.

Thoughts?

If the NIC was faulty I shouldn't beable to connect to router A surely?

Why can I ping Router A and not the internet unless I disable the network connection and enable it again?

any help would be great!

 

[rich[182]]

Out of curiosity, are you using static ip addresses or dhcp, and if dhcp which router(s) is/are issuing dhcp, if static what you using for default gateway, if you've 2 different routers issuing dhcp what are the dhcp lease expiry times also

As for physical connectivity, are you using forced speed & duplex or auto-auto, would recommend full duplex 100Mb if routers have fastethernet as opposed to ethernet (i assume NIC on server will support 100Mb)

Some NICs / interfaces can have auto-negotiation issues that have resulted in similar problems, especially if both devices are auto-auto, sometimes get dropouts where both devices can't negotiate and the unplugging/plugging forces reconnection

http://searchnetworking.techtarget.com/tip/0,289483,sid7_gci1212464,00.html
Id use 100Mb-Full both ends if supported rather than 10Mb-half to auto-auto or even auto-auto to auto-auto

 

[Longy]

Router A is static ip based

Router B is using the onboard DHCP on the subnet side and Router C is windows server DHCP on the subnet side static on the otherside. Using default lease times. Both subnets are completely different and don't see each other.

Yes i'm using full duplex 100mb. The windows server box has 2 x NIC's for routing purposes. The subnet side NIC doesn't have any such problems.

I have noticed the other NIC on the server uses resource allocations such as TOE but i've tried tweaking them but of no effect.