Collisions on Network

Unanswered Question
Dec 7th, 2007

Hi everyone, can anyone help me with this problem.Last weekend our internet connection started running very slowly.

Between the B.T router and our network is a 2950 switch. This switch is showning excessive single and multi collisions. Can anyone point me in the right direction as to finding out what is causing this?


I have this problem too.
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scarboroughbc Fri, 12/07/2007 - 03:02

Hi Jon

I checked the router port on the 2950, its set to 10Mb/half, confirmed this is as it should be with B.T.

I have changed all the CAT5e cables and swapped out the switch.

I have attached a vsd file of our setup.

The switch 'OUR NETWORK' shows no collisions.

Port 1 on 'Dirty Switch' shows the following -

single col 2254, multi-col 1067

Port 5 show no errors

Port 13 shows 193 single-col, 41 multi-col and 500 late.

B.T have changed the Cisco2600 internet router just in case.


Jon Marshall Fri, 12/07/2007 - 03:06


Can you attach the vsd. Actually could you save as a jpeg and then attach as i don't have visio on the laptop i'm working on at the moment.

Be aware that if a port is set to 10half then you will get collisions, you can't avoid them. Is there any reason why BT cannot set their 2600 router port to be 10full and you do the same on your switch ?


scarboroughbc Fri, 12/07/2007 - 03:34

Hi Jon

I was told by the B.T engineer that it had to be 10Mb/half.

I have asked them again if it can be set to 100/full.

The link has been working for a number of years, the collisions only started last weekend.

I have attached the diagram as a .bmp file.


Jon Marshall Fri, 12/07/2007 - 03:43


1) The collision on the port that connects your firewall to the "dirty switch". Can you check the duplex and speed settings on both the 2950 port and the firewall.

2) The collisions on the port that connects to BT router. When you say the collisions only started last weekend then i don't see how BT can be saying it should be 10half unless they have made a recent change. If that is their standard (and we use BT and i'm not aware of it) then i would expect you have to been seeing collisions on this link ever since you put it in because as i said before collisions are a natural thing on a non-full duplex connection.

If you haven't already, have a look at the "excessive collisions" bit of of the doc i sent a link to.

Also if you have only just started seeing collisions can you ask BT why you never used to get them if their router interface has always been set to 10half.


scarboroughbc Fri, 12/07/2007 - 03:52


Thanks for that, I will check with B.T.

I have a meeting at 12:00 and then have to go to a remote site to install a new server.

I may not get a chance to look at this again today.


scarboroughbc Tue, 12/11/2007 - 06:07


After much testing it turned out to be a server problem.

Thats for your assistance.



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