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Community Member

switch-collissions

I am having a network based on cisco 2900 and cisco 1900 switches and hubs.

My network performance is very slow.

2900 is the backbone switch and cisco 1900 switches are connected to 2900 switch. i am having 6 hubs which are connected to 1900 switches. All servers are connected directly to switches only. But Ihave observed that some packets are missed between two servers which are connected to the same 1900 switch.

When i see the port statistics on the 1900 switch i see some collissions and multiple collissions.

why should collissions observed on the port which is directly connected to a system.

collissions can be seen on a port which is connected to the hub.

please help me in understanding the operation of a switch.

my email id is gdp@tc4hq.cmcltd.com

4 REPLIES
Community Member

Re: switch-collissions

The most likely reason for the collisions in my opinion is due to a large amount of broadcasts due probably to Traffic flowing from your users to the servers and then to the Internet. Also, check the protocols you are using. Remove all protocols that are not necessary to your network. Too many and/or unnecessary protocols can result in a large amount of network traffic, i.e. IPX/SPX and Netbeui are chatty and broadcast oriented.

Unfortunately, it doesn't seem that you have any VLANS set up (your equipment list does not support VLANS). Esentially, it seems your network has one large Broadcast domain (switches do not block broadcasts). You may want to look into upgrading your switches so you can implement VLANS, which will give you smaller broadcast domains.

Anyway, Hope this helps. Good luck.

Community Member

Re: switch-collissions

If your servers are configured with auto 10/100mbps NIC, I have always found that it is best to fix the port speed on the NIC and on the switchport, in addition fix the communication to Full Duplex for servers (depending on the switch either 10 or 100 Mpbs full duplex). Auto Negotiations do not always work well! I would recommend to put servers 100Mbps full duplex on the 2900.

Also if you are working in a NT/windows environment and you find that people are experiencing login problems (not finding domain, etc) that portfast should be configured on switchports connected to host (do not put portfast on trunk ports)

more info on http://www.cisco.com/warp/public/473/12.html

I like using a tool like Fluke Network Inspector which can really visualise your key devices and pin point your problems.

Hope this helps,

Good Luck,

(yoshinobu_kawahara@hotmail.com)

Community Member

Re: switch-collissions

Hi,

Thanks for ur reply...

i had removed from all pcs the ipx/spx protocol.

i had configured a wins server also to reduce the broad cast traffic.

and i found out one server which is generating heavy network traffic brtoad cast and removed it from the network. Still i am seeing lot of collissions on ports of the switch. Can collissions occur in a port which is directly connected to a pc or server.

i think collissions may occur on ports which are connected to hubs.

Can u send meany tool as a mail to me...

thanks once again for replying to my problem.

g d prasad

Community Member

Re: switch-collissions

Check, that those ports uses Full Duplex mode (the network cards on the servers connected to those ports should use Full Duplex as well). The collisions might occur because in case of Half Duplex the switch port and network card uses the same pair to send and receive - it looks like you use hub with only 2 ports - so, you may have some collisions, especially with heavy traffic. In case of Full Duplex different pairs used to send and to receive - no collisions...

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