Latest questions from the community.
An HPE FlexFabric 5950 48SFP28 8QSFP28 (JH402A) always downgrades an HPE JH419A 100G QSFP28 LC SWDM4 transceiver to 40G and never brings it up at full speed. Why?
A 1000BASE-T copper SFP (Arista SFP-1G-T) in an Arista switch does not link to a device that only rnus 100 Mbit/s, and a 10GBASE-T SFP+ does not fall back to a lower rate either. How does EOS handle speed negotiation for copper SFP modules?
An M290 with the optional two-port fibre module was fitted; can ports A0 and A1 be used as ordinary interfaces, for example for an ISP fibre handoff, and can a 1 Gb SFP be used in them?
What do the port states in the switchshow output of a Brocade Fibre Channel director or switch mean, and which of them point at the transceiver rather than the fabric?
A UCS 6332 fabric interconnect has only 40G QSFP+ ports, but the upstream switches are 10G. How can the FI be uplinked at 10G, and why does the breakout option not appear on some ports?
With auto-negotiation off and 10G configured on sfp1/sfp2 of a CCR1036-12G-4S (RouterOS 6.43.8), MikroTik S+DA0001 and Amphenol DACs still run at 1G and the Cisco side shows no link at 10G. Which part of this link should be checked first?
Cisco troubleshooting document: inserting certain SFPs (for example GLC-SX-MMD or third-party modules) into a Catalyst 3850 C3850-NM sub-module produces %PLATFORMPM-6-MODULEERRDISABLE: The inserted SFP module ... is not supported and %PM-4-ERRDISABLE: gbic-invalid ... putting ... in err-disable…
The poster asked how to test fibre cables from a switch. The guidance covers reading optical levels with show interfaces transceiver / show controllers, comparing TX and RX at both ends, and recognising that a reading of -40, -50 or -80 dBm means no signal is being received. Hardware involved…
A D-Link DES-3200-28 B1 switch logged DDM Port X optic module RX power exceeded the low warning/alarm threshold; the optical level looked abnormally low in the switch although the module measured fine when tested standalone. Hardware involved: D-Link DES-3200-28 B1, DDM-capable SFP. Reported…
Two Jetson Thor devices achieved 100G connectivity directly but with poor speed, and when each was connected to a 100G switch no link formed, although the same optics and cables passed a 100G loopback test against a different switch. The poster wondered whether insufficient speed was breaking…
The poster could not find documentation for the command service unsupported-transceiver and asked what it does and whether there are consequences. It is one of Cisco's hidden commands: without it IOS disables a port when a non-Cisco transceiver is inserted, because the OS reads the vendor field and…
A Huawei S6700 iStack did not form because the optical modules on the dedicated stacking ports 45-48 were of different types; the platform requires identical transceivers on those ports. The four ports 45-48 are the fixed stacking ports, and mixing, for example, an SR module on one and an LR module…
FS Box V2 is a firmware/coding tool kit for optical transceivers and DAC/AOC cables. It reprograms a module's compatibility code so it is accepted by a target switch platform, letting engineers adjust coding in the field or when a switch is upgraded to a version that no longer accepts the old code…
A customer with a 10Gtek ASF-10G-T 10GBASE-T transceiver could not read its EEPROM: ethtool -m ens802f0 returned Cannot get module EEPROM information: Operation not supported. The vendor attributed it to a firmware version mismatch between the NIC and the transceiver. Hardware involved: 10G NIC…
A proposed ixgbe patch would have let X550EM NICs recognise otherwise-unsupported 1G copper SFPs by treating them as 1G SX through a new module parameter, mirroring the existing unsupported-SFP handling. Without the change these NICs simply refuse the copper module, so operators wanting cheap 1G…
