New Extreme 5420M-24 fibre uplink transmits but never receives: the two ends were forced to different speeds
Replacing an old Dell switch with an Extreme 5420M-24, the same SFP module that had worked in the Dell would not bring the network up: the uplink port was active with rising TX counters but RX stayed at zero, no DHCP address, no ping to the firewall, and a new SFP+ module behaved the same. Ethernet mode had been enabled with disable stacking-support.
- Hardware: Extreme 5420M-24, Extreme X440, Dell switch, Extreme 5520
- Transceivers: 1G SFP, SFP+ module
- Form factor: SFP, SFP+
Symptoms / messages:
TX counters rise, RX stays zero
no DHCP over uplink
Comments 1
Swap optics between both ends, check VLANs, and verify speed/duplex on both sides; a reader added that some optics vendors deliberately lock modules to specific switch brands.