compaq loopback cables ?

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- tg
  
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posted
15 years ago

Wed, Oct 22, 2008 9:46 PM

I recently bought a cisco module NM-16ESW (16 port switch) and when it arrived all the sockets had little 2 inch cables sticking out of them. These cables were sealed at the end and some were labelled: Compaq PN 317463-001 SPARE

317465-001 ID 10036233 REV. C I saw on google they are called 'Compaq loopback cables' and I saw several places that advertised them for sale but I don't know what they're for. does anyone know what the function of these is? thanks for any advice.

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- Doug McIntyre
  
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posted
15 years ago

Wed, Oct 22, 2008 10:14 PM

Guess they wanted to get rid of them.. :)

I don't find them all that useful, but they just loop the transmits back out to the receives for the port, so you can test that everything looks good on the port and comes up and tests out for the switch.

Ie. make one here.

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Much like a T1 loopback connector which will loop the T1 transmit back to receive so you can test the wire and find faults, you can test each port with the ethernet loopback plugged in.

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- Bod43
  
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posted
15 years ago

Wed, Oct 22, 2008 10:23 PM

Without researching the exact devices it seems likely that they are Ethernet loopback plugs.

I have not read these but the GOOGLE heading seems to suggest that they will be of interest.

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"Use Loopback Testing for Fast Ethernet and Gigabit Ethernet Interfaces"

They will bring the port UP if it is enabled.

Any packets sent out will be sent back in.

If STP is enabled then of course the ports will transition to STP blocking state. Unless of course portfast is enabled and a broadcast storm overwhelms the CPU first.