I have an issue, in short I have a server at home with two ports, one 10/100 ethernet management port and an SFP+ port. I cannot connect to the internet using SFP+ port. I am using an external transceiver and have a cat6 cable plugged in from there until my switch. Initially I thought it was a configuration issue related with cisco virl ( which is what i am using the server for) and so I posted my troubleshooting on the respective forum. Towards the end of my troubleshooting and writing my post I thought it would be a good idea to try install windows 7 on the server to see if I could connect to the internet using a different OS.

This also did not work so probably the forum where I posted was not the best choice since its not directly related to VIRL. I would appreciate it if someone could please have a look and point me in the right direction. If further information is required I'm happy to provide it.

My command outputs and troubleshooting can be found in this link below: https://learningnetwork.cisco.com/message/597046

Thank you for your time!

  • Can you quote the relevant parts of your link here? This is in case the external is removed for any reason, other users will lose important context.
    – Burgi
    Dec 22, 2016 at 8:46

2 Answers 2


SFP and SFP+ transceivers do not support autonegotiation of speed and duplex mode.
10000/Full duplex is always assumed. Different speeds on both sides is not supported either (10G to 1G). Speed and duplex mode need to be configured on the switch side. This would be my first check on the switch port used (as a non-Cisco guy I haven't understood how the switch port is configured from the listings you posted on that other forum).

Second, MDI/MDIX is probably not negotiated either. You can check this easily by using a crossover cable. Both capabilities should be documented with the transceiver (which is?).

  • Hi there, Thanks for your time! Basically the Transceiver I have is this one startech.com/Networking-IO/Media-Converters/sfp-https://… and the switch is an unmanaged gigabit switch tp-link.com/us/products/details/cat-42_TL-SG108.html I would expect the switch and transceiver to enforce 1000/Full duplex and to automatically use mdix
    – ttm
    Dec 18, 2016 at 19:24
  • I now see that your port is a SFP+ (10G) and the transceiver is SFP (1G). This might be the source of your problem. I've had SFPs not working in SFP+ ports before. The copper side (SFP to switch) looks OK, both sides support MDI/MDIX and speed auto-nego. Dec 20, 2016 at 10:14
  • It was the wrong transceiver. I checked online and the cost of these things was quite expensive but i fixed the problem by buying a used quanta LB4M switch that came with 2 transceivers for 100eur. I then plugged one into the server and used an LC fibre cable to connect both ends and everything started working
    – ttm
    Mar 13, 2019 at 22:14

Most SFP+ port support auto negotiation, but only some Ethernet GBIC support auto negotiation function, check your GBIC and network card specification. If you need FC connection, you mast use same type & speed SFP transceivers on both sides.

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