Friday, February 1, 2008

Think about switching

While working on the bench I was asked to help troubleshoot a problem at a client side. Some users could work with their computer and not print and vice versa.

I received documentation and the name & phone of the contactperson I was to meet the next morning. The next day I started investigating the problem. After checking the network, reading some more documentation and making a few calls I found the solution to the problem: port roles. The Cisco Catalyst Express has the option to give a role to a port depending on the device that is connected. So you have roles like server, workstation, router, etc.

In this case the port role was server. The behaviour of this port role is that it will only allow traffice for one IP number. If on the other end of the port there is a hub that connects several devices problems start. With several devices requesting IP addresses via DHCP, only the first request is approved by the port role. The other DHCP requests are ignored. Setting the port role to other solved this problem.

What I have learned from this, is that taking a five minute look at the default settings could have avoided this problem. Since there were no servers connected to this switch the port role was not correct and you don't have to be Cisco Certified to figure that one out.

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