Huawei S6730-H24X6C uplink will not link a 40G QSFP+ DAC to a QNAP LAN-40G2SF-MLX card
Small office rack: there is a 40G card in the file server and a switch with spare uplink ports, so instead of buying another box I tried to hang the server straight off the switch. Both ends see the cable, the link never comes up.
- Huawei S6730-H24X6C, QSFP28 uplink ports
- QNAP LAN-40G2SF-MLX in the server, which is a rebadged ConnectX-3 Pro with 40G QSFP+ ports
- ACC761-10000S direct attach cable between the two
The switch reads the cable and shows its transceiver information, the card sees a cable as well, and the port is down on both sides:
# ethtool ens2
Settings for ens2:
Speed: Unknown!
Duplex: Unknown! (255)
Link detected: noWhat I have already checked:
- looped the same cable between two ports of the switch itself, it comes up straight away, so the cable is not dead
- tried to set the speed by hand and to toggle auto-negotiation on the uplink port, and the CLI does not offer either on these ports
- reseated both ends and moved to the other uplink port, no difference
The port defaults to 100GE and I cannot find any way to make it accept a 40G cable. Is that a hard limitation of these uplinks, or is there a mode I have not found yet?
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Comments 3
The cable is fine and so is the card. Those uplinks come up as 100GE, and a port sitting in 100GE mode does not fall back for a 40G QSFP+ cable. It is not a negotiation you can influence, it is the port type.
The obvious-looking command is a dead end.
undo assign port-speed 100GEis what gets suggested in most threads, and the box answers that it is an unrecognised command on the 100GE ports, which is where people give up and start suspecting the cable. The form that actually applies is the port type, from system-view:Then reboot, the conversion only takes effect after the restart. After that the QSFP28 uplinks come up as 40GE and a 40G card links normally. Check the result with:
Two things to be aware of.
allmeans all: every 100GE uplink on the chassis becomes 40GE, so if you have or expect a real 100G link on that switch, do not put the server there. And schedule the reboot, there is no way to flip a single port live.A QSFP+ caable in a QSFP28 cage is normally a non-event, same cage and same four lanes at a lower per-lane rate, so the ACC761-10000S is not where I would look. What does
display device port-speed configurationshow you on that box? On these Huawei uplinks the rate is a device-level property of the port group rather than something you configure on the interface, which is exactly why the port offers you no speed or autoneg options. Post that ouutput, and also say whether any of the other uplinks are in use, because whatever you end up changing there is unlikely to affect just one port.That was it.
undo assign port-type 100ge allfrom system-view, reboot, and the port came up with the QNAP card at 40G on the first attempt. Neither the cable nor the ConnectX-3 Pro needed anything done to it. Giving up 100GE on the uplinks stings slightly, but there is nothing in this rack that will run at 100G any time soon, so it is a fair trade.