Cross-Over cable helps

Cisco to Cisco normally means problem free in networking world, right? Not all the time…

Some say in Cisco world, if there is a setting with auto option, then you auto do not use that option. I follow the “rule” most of the time.

2 Cisco mid-range switches connected together with a CAT5 cable and one end was initially configured for full duplex 100mbps and the other end is auto negotiation. I then found the auto end was only running as half duplex 100mbps. So I thought I need to hardcode the value to match the other to improve the link performance. After the speed and duplex setting, I typed in “shut” (interface light went dark), then “no shut” (interface light stayed dark)… Ran the commands again, same thing… Bad cable? …

Long story short, the “Bad Cable” was a straight-through cable and it does not work on 10/100 link between 2 switches!!! (here is a animation that shows why) If I used a gigbit interface on either end, I would not have the issue OR if I remember the basic to use cross-over cable between 10/100 interfaces to connect switches, I would not have issue either.

As of 2012, most of the business class switches are Gigbit capable or 10 Gigbit capable switches. Those high speed interfaces are not only faster and they also help you do other stuffs. People now start to forget what was required in old days and do not even have cross-over cables anymore…

BTW, avoid entering data-center at 4:30 PM Friday if you can 🙂


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