Cisco interface fully rejects Ethernet cable with bad 4-5 pair

[Mzt834]

A single Ethernet cat5e connects two Cisco CBS 350 8-port switches, which recently replaced two SG-350 10-port switches.

It's very tough to pull cable there and the Ethernet line has no continuity on wires 4 & 5 (used a cable tester, not Cisco's copper test).

One of the Cisco switches refuses to link at all with that Ethernet line -- no link light and shows down status (same with SG-350 and CBS 350) and can't use the Cisco GUI copper test feature because it doesn't show anything in the interface.

The previous IT crew worked around this (with the SG-350) by installing a small unmanaged NetGear switch to act like a bridge. The bad ethernet cable plugs into the unmanaged NetGear, which doesn't care that 4-5 are dead, and an Ethernet patch cable connects the unmanaged switch to the Cisco at 100Mbps in the same interface (I think gi10). So gi10 is ok with the line from the unmanaged switch but refuses to ackknowledge at all the cat5e w/missing 4-5.

The cheap unmanaged switch doesn't care that the cat5 has a bad pair (4-5) and operates at 100Mbps.

QUESTION: is there a setting in the Cisco CBS 350 that would make that interface work with that semi-bad Ethernet cable, albeit at 100Mbps?

Then I could remove the goofy unmanaged switch, which has nothing else it in.

[marce1000]

  ... is there a setting in the Cisco CBS 350 that would make that interface work with that semi-bad Ethernet cable, albeit at 100Mbps?

                                  - Would it simply not be better to use fully working Ethernet cables ?

 M.

[Mzt834]

Of course.

The previous IT company opened walls and ceiling for the line.

The owner doesn’t want to do that again to pull another line.

Thanks for the sage insight instead of answering the question.

[Leo Laohoo]

The question is not "can it be done".  The right question is "WHERE" are the broken pairs.  Are they at the ends or are they in the middle.  If they are at the ends then, duh, re-terminate it. 

Cheap-ass "TDR" will only say if there is a broken pair or not.  Reliable ones will be able to determine where the faulty pairs are. 

[Mzt834]

Thanks. The previous IT company said the broken pair is mid cable. They worked hard to get it to work, including reterminating the line. They came up with the workaround. I called the guy who did it.

I asked the owner to reconsider running a line.

It’s amazing to me that the unmanaged cheap switch can just switch down to 100Mbps but the Cisco refuses to deal with it. Rhetorically, why not? Maybe 4-5 aren’t totally dead but shorting and that’s why the more sophisticated Cisco says no way while the dumb netgear treats it as just a missing pair.

[Leo Laohoo · Accepted solution]

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@Mzt834 wrote:
It’s amazing to me that the unmanaged cheap switch can just switch down to 100Mbps but the Cisco refuses to deal with it.

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Oh the Cisco switch can as long as it is not running a buggy code.  In this case, it is.  
Ok, so here is a workaround, terminate the RJ45 to only Pairs A & B.  Do that and it will work.

[Mzt834]

THANKS