unusual cable sequence

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 Question by Ben Potts posted 01 Apr 2004
 unusual cable sequence
I ran into a unique wiring for a cable, and am curious if anyone can tell me what it is. We have a straight through cable running from a cisco router to a cisco switch. Before it gets to the switch the previous tech put an extender onto his original cable that has all of the color pairs next to each other, and the pins at the switch are the same. We need to add a hub or switch in between the two, but we cannot get it to work. Everytime we plug a straight cable from the router to our new hub/switch, we get a link light on both and activity. However we can't get a link light for the existing switch when we plug that cable into our new hub/switch. Any ideas or explanations for the strange wiring would be appreciated.
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 Answer by Dmitri Abaimov posted 01 Apr 2004
Dear Ben,

Although it is difficult to visualize the extender ("all color pairs next to each other, and the pins at the switch are the same"), I would suggest that, if straight-through patch cable does not work, then you need just an Ethernet crossover cable. It is pretty common to require a crossover between a router and older switches. The new one most likely has auto-sensing and switches to crossover mode by itself. You can check the pinout here: http://www.cabling-design.com/references/pinouts/10-100base_t_crossover.shtml. You can crimp it yourself; however, as with any patch cord, we always recommend to purchase a factory-made one due to performance and reliability concerns. On that page you'll find links to the online sources for cross-over cables.

Sincerely,
Dmitri Abaimov, RCDD

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