Splitting network cable

[alex]

Hi all,

Do you know how to use split cables with Cisco switch?

We have a few network cables that are split at the patch panel onto two ports.

Two pairs of wires are configured to send/receive data on pins 1-2-3-6 on both ports.

From patch panel regular CAT5 cable goes to a switch.

When we had CAT5 cable connected to HP Procurve this spit cable configuration worked fine for us. PCs were able to connect to the network and so on.

When we switched the cable from patch panel to go to Cisco 4507 we are not longer able to connect to the network.

If we connect a non-split cable to the same port on Cisco switch, connection is established just fine.

It looks like Cisco equipment does not handle split cables in the same way as others, even so pins 4-5-7-8 should not be in use.

Of course splitting cables is not an ideal solution, but have anyone ran into the same issue with Cisco switches?

Is there a special tweak at the switch/port level to support split cables?

Thanks,

Alex

[Peter Paluch · Accepted solution]

Alex,

I am sorry to disappoint you but I believe there is no quick solution for this situation. Aside from deactivating the PoE on the port (just for security purposes) and setting the port statically to 10 Mbit operation (because higher speeds are going to suffer greatly from the interference between individual wire pairs in the split cable), I don't think there is anything more you could do, apart from correcting the cabling and using full (non-split) cable runs.

All Ethernet equipment is certified and warranted to work if used with appropriate physical cabling that fulfills certain criteria, and for LAN switches like the 4500 series, it is expected that the cabling satisfies the Cat5e criteria or higher. No vendor is going to put any hidden commands into his product just to force it to work on a substandard cabling - simply because a vendor cannot (and does not want to) warrant its products to work under non-standard (thus varying and unpredictable) conditions. The twisted-pair cabling is already being stretched to its very limits when using it for data transmission in Ethernet.

Best regards,

Peter

[alex]

Disabling PoE did the trick.

[Lars Persson · Accepted solution]

Hi

If you are running gigabit ethernet you need all 4 pairs. Only 10/100 can run on 2 pair.

regs Lars

[alex]

We are running in Auto mode. So after disabling PoE we got 100mb link. 1 gig would be nice to have, but as you said all 4 pairs must be available.