why would all ports blink at the same time? 1

[TiggerDaKat]

I have Cnet, Linksys, Dlink, as well as 3Com switches at many locations. Many of them have the same issue. All ports blink at the same time. I thought the purpose of a switch was to intelligently route traffic to it's destination only and not broadcast to all ports. I understand that there is broadcast traffic that occurs, but this is a constant thing. Any ideas what I should do or look for? Would this be a cause of a slow network, which users have been complaining about frequently?
Thanks in advance everyone.

Eric

 

[TimRegester]

Broadcast is the answer. I have often seen networks where the complaint was all switch ports blinking. Network analysis proved it was broadcast traffic causing it.

The switches are behaving properly.

I would get a network protocol analysis off a selection of ports. This will reveal the extent of the broadcast traffic and this combined with switch stats and maths should reveal whether this may be contributing to a slow network as well as point at a solution.

 

[TiggerDaKat]

Thanks very much for the info. Would you have any recommendations on where I can learn how to troubleshoot this better? We're pretty much a "two-man-show" and can't afford the expensive software and hardware for troubleshooting. Again, thanks for your help.

Eric

 

[TimRegester]

Pure network analysis can be done using ethereal which is available for free from

http://www.ethereal.com.

If you have managed switches and a unix OR NT box then MRTG from

http://people.ee.ethz.ch/~oetiker/webtools/mrtg/

will help though an understanding of SNMP will be necessary.

If you have up to date 3Com kit then network supervisor will help immensely this will flag any errors again if the switches are managed. but should help faultfind the network and is available free for a sixty day trial.

As for training, this is a long haul, I would suggest the book switched Lans by John J Roese McGraw Hill ISBN 0-070053413-6 has an excellent guide to troubleshooting though the book itself is a good intro it is a little dated.

For general switch info "The Switch Book" by Rich Seifert published by Wiley is almost the bible.

Understanding ethernet protocol analysis involves understanding the ethernet frame, how switching works the IP protocol stack etc.

http://www.protocols.com

will help here but there are many books on the subject and many courses. None of the Cisco courses are useful if you have a 3Com network apart from learning the basics. Other training providers and the N+ exam will help. The 3Com university has a basic network course that once signed up for is free and a good starter. There are other useful modules there as well.

I hope this helps.