CBS350 SFP-10G-LR link only comes up when the TX fiber is inserted before RX; faulty transceiver pair
2
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 always visible in the switch's transceiver information; only the data link failed. The poster asked 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
Comments 3
Accepted (posted by the poster): the problem could not be reproduced in the lab, so the lab optics were swapped with the field pair and the field link immediately worked as expected; one or both of the original SFP-10G-LR modules are defective even though they were always detected, behaving like a negotiation failure. Testing the bad pair individually was the next step.
A respondent doubted that SFP-10G-LR is listed for the CBS350 in the Cisco TMG compatibility matrix; the poster pointed to the entry (and the COPI page at copi.cisco.com), while the respondent maintained that the matrix is the authoritative source.
A respondent shared a guide on displaying transceiver details on Cisco SMB switches, which the poster had already been using to monitor the modules.