what does it mean when the collision light blinks like crazy?

[SpecialEd]

Recently, at work my internet connection keeps failing. What happens is that the router that connects our DLS to the office freezes. When this happens, I shut the router down and power it back up and the internet works again for a short while before freezing. Well.. i went around the office trying to figure out why this happens and found out that it only freezes when I open internet explorer. I also noticed that the collision light blinks like crazy on my switch. It also continues to blink after my computer has been shut off.
So since then i've shut down my computer and unplugged it from our network and now our internet connection works fine. I was wondering if anyone has experienced a problem like this before. and if so, what can I do about it?

 

[bozo1]

I'd suspect a bad nic, bad cabling between the PC and the switch (could be the jack if you use one, the cross-connect, etc.), or a bad port on the switch.

 

[spidey07]

<< I'd suspect a bad nic, bad cabling between the PC and the switch (could be the jack if you use one, the cross-connect, etc.), or a bad port on the switch. >>


with emphasis on cabling

 

[SpecialEd]

thanks guys. I just remember I switched the Cat 5 cable I was using for a shorter one a few days ago. I'm gonna switch them back to see if that was the culprit.

 

[Poontos]

<<

<< I'd suspect a bad nic, bad cabling between the PC and the switch (could be the jack if you use one, the cross-connect, etc.), or a bad port on the switch. >>


with emphasis on cabling >>


What other factors inhibit more collisions? Or at least, the most common.

 

[spidey07]

collisions are a normal part of half-duplex ethernet. Like when you're using a hub. With a hub you are dealing with a bus topology and only one station on the bus can trasmit at a time - there can be one and only one frame on the wire. A collision happens when one station tries to transmit but hasn't "heard" the frame that is already being transmitted by another station. The frames collide and a special JAM signal is generated on the bus. All stations on the bus then wait a psuedo random amount of time and try to transmit again. High traffic on a hub like 30% utilization or higher will cause excessive collisions to the point that a NIC will have a hard time transmitting a frame because the bus never clears.

Other causes are networks out of spec like disobeying the 5-4-3 rule for ethernet or by having cabling that is out of spec.
Or by having a duplex mismatch one side thinks full the other side thinks half.

Bad nic or bad hub also.

 

[Tallgeese]

<< Other causes are networks out of spec like disobeying the 5-4-3 rule for ethernet >>

I troubleshot a school network like that.
Every day it would go down at almost exactly the same time every morning between 9:30 and 9:35.
Took me about an hour (using a schedule of classes) to run down the problem.

Turns out they had violated the 5-4-3 by cascading one hub too many up in a computer lab that didn't have anyone in it until--you guessed it--9:30.

All came down to tracing connections and mapping the network (using Visio) so we could get an accurate picture of their layout. Also, a case of "too many cooks" swapping cables indiscriminately.

P.S. Even after explaining the rule and giving them the map of their network, they continued to try to stick hubs in all the wrong spots for over a year. At the very least, they started to call me before installing anything so I could check their "design" decisions...heh.

 

[spidey07]

hence the continual frustration with networking.

People just think "Well I just plug it up and it works" I'm with ya tallgeese. You have no idea how many nets I've walked into for an analysis (probably 100 or so) and looked at cabling/hubs/collision lights going crazy.

all the while thinking in the back of my head (sing like disco stew) "walk away not today, disco lady"

 

[ScottMac]

Then there's always the folks that "read something somewhere" about being able to connect a couple ports between the same two switches (hubs) to get a better uplink throughput (on their non-spanning tree switches or just plain hubs).

You know...if you use two half duplex connections, that's like having one full duplex connection< right?

FWIW

Scott

 

[Tallgeese]

Since someone PM'd for clarification, figure I'd share with the whole class...
NOTE: 5-4-3 rule does NOT apply to shared Fast Ethernet networks.

This may explain the 5-4-3 rule better than I can.
Amazingly, NO MENTION of this rule on Practically Networked.