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One bad NIC on LAN brings it to a crawl?

B

BadThad

Lifer
I have a 6 PC LAN in my house. Last night, 3 of the PC's on the LAN had REALLY slow, start/stop access to the internet. Transferring files from the web would start fast, then drop to almost nothing, then freeze, then go really slow. To make a long story short...I pulled the cable from one of the PC's on the lan and everything cleared up.

My LAN is a Cisco 675 Router, connected to a 10/100 switch to which all the PC's are plugged into.

I didn't have time to look at that PC yet, but how the hell can one PC cause so much grief? This machine has ZAPro, it's LOCKED from the internet and the IP is released....yet it was causing issues with my internet traffic.

I'm confused!
 
Try turning the auto negotiation off, and then change it to 100 full duplex, i'm assuming that is what the network is running at. If this doesn't work, spend $5 and replace the NIC. this is possible to bring a network down. if the router and the NIC are fighting back and forth with auto negotiation, it will drop the network for other users.
 
Ah...interesting. Yes, this is a 100 Mb/s lan. The prob is this NIC is actually integrated into my nForce2 mobo. 🙁 Where do I find the setting for auto negotiation? ....device mgr?
 
I don't have any hands on experience with the NForce2's NIC's. But I hear about a lot of problems with those. You might want to disable that one, and get a cheap PCI one from a nearby computer store.
 
Originally posted by: foshizzle
I don't have any hands on experience with the NForce2's NIC's. But I hear about a lot of problems with those. You might want to disable that one, and get a cheap PCI one from a nearby computer store.
Click to expand...

I have lot's of nic's laying around....I'll just toss one in tonight, thanks.

How can something like this problem effect a large network of like 500 PC's?
 
Very easy, one NIC streaming has been known to bring large networks to their knees, especially if they're not properly partitioned.
 
a single NIC can make ALOT of noise if it wants to.


it can totally flood the network with random noise and prevent any others form using it.
 
Thanks everyone.

I finally had time to investigate. There was no unusual running processes on the machine and everything looked fine. I rebooted it and the problem went away. This machine is a dedicated distributed computing cruncher who's IP is always released and ZA Pro is locked...it gets NO other use at all. The only time I unlock ZA is to obtain an IP and transmit data (about 3 min/day), then it's released and locked. It's running Win2k Pro with no service packs, no windows updates applied nor antivirus....really nothing installed on it except the SETI@Home CLI client. That's all this PC does. It's been working fine for 4 months now....this has me stumped. My LAN has been running for about 5 years now and I've never encounted anything like this.

Anymore ideas?
 
Originally posted by: gunrunnerjohn
It could just be a defective NIC. I've had NICs die and lock up the whole subnet they're on.
Click to expand...

That's exactly what the problem was, as bizzare as it seems because it was my main PC. Today it went flaky, I could connect to my backbone provider but not my ISP nor the web. I tossed the old NIC and put a new one...everythings like it should be now. Note: My main PC has all service packs, security patches, AV and ZA Pro, just to please martind1....hehehehehe.

Thanks for the help everyone! 🙂
 
A flaky NIC can cause all sorts of nasty stuff: one of the nastier ones being a simple broadcast storm. You've got an excellent router though, but your switch probably has zero features for controlling such a beast - at best, it is probably only a simple repeater. A good switch will detect this and automatically disable the port (either from a flood of errors, (runts, discards, etc) or broadcast storm as what it sounds may be happening). Are ALL the lights on your switch/hub continually lit? Can you check the multicast/non-unicast traffic on every NIC while it's happening?

Do you have any other NICs in that machine that are connected simulatenously?
 
One possibility that it could be that happened to me today -

Internet access was up and down (t-1 into a netgear router/firewall) and sometimes the router stopped responding. Pings were 1300 ms to the router or other clients. At first I thought the router was dying or the t-1 router was sending it something funky that was causing traffic. Firewall logs showed a lot of traffic flagged as a "smurf" attack, but it was all internal. Finally figured it out.

6 of the 15 computers had the nachi worm. They weren't doing anything malicious to the computers, but were sending out crazy traffic on the LAN. As I treated each one the network got faster and faster and then the router started responding.

Just to doublecheck, you might want to run stinger on all the pc's. Yeah, I had a good firewall going too. I think a laptop physically left the office, got infected and came back in.
 
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