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No Data being passed on 3550 Switch Ports


We recently replaced our 3-Com Hub\Switches with Cisco 3550 series switches and are having problems with some Users not being able to transfer any Data.

Details are

1. The link light comes up and Port State shows connected but user can't pass any data.

When we connected the same user to a port on 3-Com, it works fine.

We are suspecting that the Cable length might be > 100m, however i do't understand that why 3-Com will work ?

The Users are using IBM ThinkPads, when we connect the problematic port to a Network Printer (HP), then the printer works. So it definitely point towards some signal strength issues.

Can it be a problem with IBM ThinkPads or the Switch ? I am tempted to think, its Cisco as 3-Com works fine.


Re: No Data being passed on 3550 Switch Ports

May be a Spanning Tree Protocol issue. A lot of the older 3Com switches were set to STP disabled when they shipped from the factory, you had to turn it on. That meant you could plug in a workstation and the switchport would go right to forwarding traffic. Only recently (last 2 or 3 years or so) did they start shipping with STP enabled, and I think Spanning Tree FastPort enabled on 10/100 connections. (FastPort is their version of Cisco's PortFast.)

Cisco seems to always enable STP by default in their switches. This could result in a 30-50 second delay when link is initiated; if computer boots fast and uses DHCP, maybe the computer's not getting an IP address and defaulting to something that's not going to route on your network. May also explain why your HP network-attached printer works: it probably has a static IP address.

Try enabling "spanning-tree portfast" on each of the Cisco switches' ports where computers are having problems. This jump-starts the switch port to forwarding when link is first established.

If that doesn't fix it, another possibility is the drivers on the computers' network adapters may not be autonegotiating speed and/or duplex correctly. Check to make sure you have the latest ones.

Hope this helps.

Community Member

Re: No Data being passed on 3550 Switch Ports

Well We took care of the Spanning Tree issue already and that still didn't help.

Even when we gave the PC static IP and Port was in forwarding State, it still wouldn't work.

We are going to check the Cable using a Cable Tester and try to find any issues.

Though even if we found any issues (e.g. over length etc) it is still surprising that 3-Com works..!

Re: No Data being passed on 3550 Switch Ports


It might also be a NIC compatibility problem.

Have you tried to connect an IBM ThinkPad to C3550 via a short cable?

If it works OK, I'd consider cable length problem, if not, I'd think about NIC compatibility (see



Community Member

Re: No Data being passed on 3550 Switch Ports


Think Pads does work at all other locations, where cable length is definitely under 70-80m.

So this maybe a cable length issue.

Regards \\ Naman

Community Member

Re: No Data being passed on 3550 Switch Ports

For each interface you might want to do this:

interface FastEthernet0/2

no ip address

duplex half

speed 10

no snmp trap link-status

spanning-tree portfast

Also make sure IP helper is turned on

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