Network Slowdown

Hi!

Ehh...

I got few computers that when them are connected to local network(DHCP Router) then whole network slows down to zero. I did simple reinstall of whole windows (xp) that was on those boxes and it helped.
But I still have one quisetion how is it possible? I mean what is it depends on?
I have not found any issues in the logbook and hardware configuration looks ok for me.
All of them have had spy-vir problems but one of them was reinstalled(not by me in the begining) and have had problem left.
And one of them have had some hadware problems(cable was not good), but modem connection was working good.

In my network based on windows boxes, one linux server(samba) and one windows server(file server). All are connected to the router throug switches. Can it be some conflicts with them and "damaged" computers?

could be caused by alot of things. Malware is a huge concern, lots of broadcasts/outbound connections because of them would casue a slowdown. P2P programs are a big issue also. Malfunctioning NICs could cause a problem, faulty switch/router, misconfigured network settings, etc...

What type of cable are you using and what is the configuration of the network and the topology of it? How many routers/switchs etc?(i know you said the two servers are connected to a router via a switch, what about the clients?)

Are there different subnets?

How many clients in total?

When you say the network slowed to zero do you mean that absolutley no traffic is being transmitted? Did you try a ping?

If you try to be as discriptive as possible about your hardware config software config it will be easier to discover if it is a harware fault, configuratoin fault or a software fault. It may also be possible to give you a few tips on speeding your network up.

Install and run something like Ethereal and see what traffic is going over the wire.

If computer have that kind of malware that overloading network, can then proxy or firewall stop overloading?
[comp dmg][LAN] (proxy/firewall) [LAN][ROUTER] [freedom]

The Problem Could be within your Servers. The servers could be acepting incoming Ping's. This is also known as a DOS. Does you Server run a Firewall? Have you taken a peek at your LAN And WAN routing tables? This Could be a problem as well. If your NIC Cards are not working Properly this could also cause the problem. Check to make shure they are all working. Check your network to see if all users are following you rules, Sometimes Users that are File sharing and using Mesangers will cause this. I think your problem is within your hardware. So inspect each Machine to make certian that this is not your problem. Good luck with you Project. :)

About 5 computers include servers.
Standard CAT5
All configuratin getting from just one standard "home" router.
So nothing is diffirent.

Yes ping being slower and slower then stops all.
Sometimes it tooks about 5 to 40 sec to get slowdown, when bad computer is connected.

ehh, i see that it very difficult.
When I will get one more like this I may be will send more info here, but what to look at?
.....
t.ex. I can write what kind of spyvir was found on that kind of computers.
----
I using as standard avast and clamscan.

Thank you Mr. FreeZ3
I almost forgot about DDos attacks.
Ehh, I think now that if routers 192.168.x.1
being attacked so whole network may go down.

Am I right about that?

you would be incredibly stupid to blame this on a DDoS attack rather than checking the million other things that are internal. but in theory if somone attacked your only point to the internet then you COULD lose internet connnectivity.

you should check into a ton of other things (like your firewall/router logs) before jumping to any conclusions.

How about doing a network sniff to see what's travelling on the network itself?