CBS350 SFP-10G-LR link only comes up when the TX fiber is inserted before RX; faulty transceiver pair

Question

While rolling out single-mode fiber between Cisco CBS350-8MGP-2X switches (firmware 3.4.0.17) with SFP-10G-LR modules, the poster hit strange behaviour: the link only comes up if the duplex LC connector is split and the TX fiber is inserted first, then the RX fiber. Inserting the joined LC connector, or inserting RX before TX, leaves the link down, and after a reboot of either switch the link does not return until the same ritual is repeated. The modules were alwyas visible in the switch's transceiver information; only the data link failed. The poster aksed whether anyone had seen this and what could cause it.

Hardware: Cisco CBS350-8MGP-2X
Transceivers: SFP-10G-LR
Form factor: SFP+

Symptoms / messages:

10G LR link only comes up when TX is inserted before RX
link does not re-establish after a switch reboot
transceivers detected but data link stays down

optictech · Accepted Answer

Couldn't reproduce the problem in the lab, so I swapped the lab optics with the field pair - and the field link immediately worked as expected. So one or both of the original SFP-10G-LR modules are defective, even though they were always detected; it just behaves like a negotiation failure. Testing the bad pair individually is next.

lambdapilot72 · Answer

I doubt SFP-10G-LR is actually listed for the CBS350 in the Cisco TMG compatibility matrix. The matrix is the authoritative source here.

fiberwolf · Answer

Here's a guide on displaying transceiver details on Cisco SMB switches, in case it helps.

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