Problems connecting Cisco router to 3Com hub

[moetech]

I have multiple remote sites that have cisco 1720's that the fast ethernet interface is plugged into a 3com 10mb hub. This doesn't happen everday, not even every week, but it has been happening sporadically. I will get a call saying one of the remote sites can not connect to the main server. When I look at the router everything is up and looking good, but when I try to ping one of the pc's behind the router no reply. Pinging from a pc to the routers ethernet interface...no reply. While this is happening there is a still a link light on both the router and 3com hub. What fixes this is I shut down the ethernet interface and then bring it back up and everything is fine again. I have also set the speed on the interface to 10 and that seemed to help, but not 100%

Has anyone else had a problem connecting 3com hubs to cisco routers? I am going to suggest my client purchase some cisco switches, but that is going to be pretty costly because they have about 20 sites and I need to be positive about the problem being with the 3com hubs.

Thanks for any help on this!

-Matt

 

[rburke]

There might be a problem with auto-negotiate between the router and the hub. The router can handle full-duplex, but a hub can only handle half-duplex. If you were using a switch, then it creates seprate collision domains and can operate at full-duplex because it doesn't have to worry about collisions from other equipment sending signals(assuming there are only 2 end devices attached to one segment of ethernet).
So I would recommend trying to set the ethernet interface to half-duplex, since auto-negoriation can cause problems at times, similar to what you are describing.

burke

 

[moetech]

Burke, thanks for the reply!

I did change the speed fron auto to 10 on the ethernet interface. This has helped, but it did not fix it totally.

 

[rburke]

Well, I would suggest getting some kind of switch instead of using hubs. Really in any kind of working environment switches will want to be used instead of hubs, even if it is a 10Mb switch. I would try getting a cheap 10Mb switch, you can pick up 3Com ones on Ebay for less than $50, and see if that helps. Or if you were going to upgrade to Cisco switches, then the 2900-XL-EN series would work great, although a bit pricey($1000). But that series of switches has reached its End of Sale period, so there is only a limited time to get them(from Cisco, Eay will always have them). Sorry I couldn't give you a more exact answer, but i think upgrading to a switch will at least help the problem if not solve it. Let us know what happens, or if you have anymore questions.

burke

 

[moetech]

Thanks, Going to switches is what I am thinking also. But, it will definitely be a cost thing. These remote sites are small and they need probably 16 ports. The decision is not up to me, but I am going to recommend going to al cisco equipment. Thanks for your help!