Cisco Nexus and 10GbE Autonegotiation not supported?

[michaelbs]

Hi,

I'm currently reading through the Interfaces Config Guide for Nexus 5600 NX-OS 7.x and have found the following statement:

Autonegotiation configuration is not applicable on 10-Gigabit Ethernet ports. When autonegotiation is
configured on a 10-Gigabit port the following error message is displayed:
ERROR: Ethernet1/40: Configuration does not match the port capability

Is it true that autonegotiation is not supported for 10GbE Interfaces on Cisco Nexus? I thought autonegotation was supported by 10GbE?! So would it be best practice so set a fixed speed on all Interfaces (servers, other switches) connected to the 10GbE ports on the Nexus switches?

Thanks,
Michael

[Reza Sharifi · Accepted solution]

Hi,

That is correct.  The 10Gig ports do not auto-negotiate. Yes, it is best practice to hard set the switch ports and the servers at 10Gig.

HTH

[michaelbs]

Hello Reza,

thank you very much for the clarification!

Best Regards,
Michael

[michaelbs]

Hi Reza,

an additional question: Do you know whether this is true for all types of 10GbE ports or only 10-GBASE-T? The Nexus 5600 documentation is not consistent here, with stating "10-Gigabit Ethernet ports" in once sentence and "10GBASE-T" in another.

And what I can see too - all my SFP 10G ports are configured with auto-duplex, so I guess only the auto-negotiation of speed is not supported?

Best Regards
Michael

[Bilal Nawaz]

Hello Michael,

I think there is common confusion here between the 10GbE and 10-GBASE-T.

10Gb Ethernet can run over 10-GBASE-T (twisted pair copper) and 10-GBASE-SR (fibre). [these are just examples]

You can't have 10Gb as half duplex, there is no auto-negotiation of 10Gb. To my recollection the N5K's as well as 4500X and other platforms, they pick up which type of SFP you have and speed is according to the SFP you put in.

hth

Bilal

[michaelbs]

Hi Bilal,

thanks. Yes, I know that 10GbE can run over both media types, the problem here is that the documentation starts with stating that auto negotiation is not supported for 10GbE in beneral but later references only 10-GBASE-T, so I was not sure what is true - whether auto-negotiation only not works with copper or with all ports.

But I guess then it is true for all 10GbE ports, no matter what media-type. It's somewhat stange however, since I have read that auto-negotiation is generally supported for 10GbE (according to Wikipedia, at least). Maybe only Cisco doesn't supported auto-negotiation for 10GbE.

Thank you again,
Michael

[itman0001]

Hi man!  is not only cisco 10GB port not supported auto nogetiation, all the 10GB port cannot supported auto nogetiation. This is technical standard.

[richmaxw]

No. Ten gigabit twisted-pair (10GBASE-T) ports have to support auto-negotiation. It is part of the standard:

• https://ieee802.org/3/10GBT/public/jan04/lynskey_1_0104.pdf
• https://www.ieee802.org/3/an/public/jul04/lynskey_2_0704.pdf
• http://noahdavids.org/self_published/gigabit-AN.html

You cannot turn auto-negotiation off. You can, however set the speed. Setting the speed simply tells the port what speed to advertise to the connected device. It does not disable auto-negotiation.