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Auto Negotiation Advertise doubt

Posted: Wed Sep 11, 2019 9:46 pm
by Zock
Hello everyone, i was troubleshooting some problems with the speed negotiation of some SFPs, besides that, i just would like to know what the Auto Negotiation Advertise actually does.

On the Wiki it just says: "When enabled, the interface "advertises" its maximum capabilities to achieve the best connection possible."

As i was testing some SFPs i can tell it doesnt matter which check boxes i click, it only matters if the Auto Negotiation checkbox is checked or not.

I can check or uncheck all of the checkbox and it will negotiate the same speed, it doesnt matter so my question is why are there the checkbox?

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Thanks!

Re: Auto Negotiation Advertise doubt

Posted: Thu Sep 12, 2019 9:04 am
by tablefulfads
I am not much clear about the checkbox. Wanna know about this?

Re: Auto Negotiation Advertise doubt

Posted: Wed Oct 02, 2019 7:52 pm
by Zock
I am not much clear about the checkbox. Wanna know about this?
Of course.

Re: Auto Negotiation Advertise doubt

Posted: Wed Oct 02, 2019 9:46 pm
by laxmimikrotik
when you are enabling auto it means the speed of the port will be adjust by the both devices which are connected with each other .so there will not be any problem if you will click on every check box..you can advertise but the availability speed of both devices will take over..!!

Re: Auto Negotiation Advertise doubt

Posted: Wed Oct 02, 2019 10:06 pm
by Zacharias
It's very simple.. if you don't want the router to decide the best speed it can achieve, uncheck auto negotiate and manually select the 1 speed you want the router to use...
For example,
If you select auto negotiate and advertise 1G and 10G, the router will select the best it can achieve.. lets say 10G..
However if you don't select auto negotiate and advertise 1G only then the router will use that speed...
If you select manually a non supported speed it wont negotiate at all...
But, if you dont select auto and advertise all speeds then yes, again it will choose the best it can...

Re: Auto Negotiation Advertise doubt

Posted: Thu Oct 03, 2019 7:43 am
by Amm0
99.999% time you should leave them all selected, and auto-negotiate enabled. It just works.

The only cases I can think of where this would this need to change:
  • the cable has some intermitted interference/issue that cause a lower speed to be selected sometimes - when that happens you could have a few dropped packets as it switches. e.g. you might want to uncheck a higher speed that didn't always work.
  • if the other end NIC/switch has some bug where auto-negotiate fails – recall some model of NIC years ago had some issue that were the vendor told me to turn off auto-negotiate and set the speed, which fixed the issue
  • you really want a hard failure (link drop) if a lower speed were to be selected – e.g. if your application needs 1000Gb network link, and if it went to 100Gb, you'd rather have it use a redundant line or what not than use the lower speed.

Re: Auto Negotiation Advertise doubt

Posted: Thu Oct 03, 2019 9:34 am
by Guntis
For SFP/SFP+ cages, highest rate supported by the module will be chosen. Setting speed to 1Gbps and disabling auto-negotiation is needed when you use SFP modules in SFP+ cages, or if you use SFP+ modules in SFP cages.

That being said there are modules that support auto-negotiation, such as S-Rj01 and S+Rj10, which will link up to rate that connected device advertises. It's worth while to keep in mind that auto-negotiation capabilities need to be supported by the module and not all 1000Base-T, 10GBase-T modules support all rates, some modules only support one or two given rates, for example 1Gbps and 10Gbps.

Also, Auto-Negotiation is mandatory for 1000Base-T, meaning that setting speed manually to 1Gbps and disabling AN, will result in no link on Ethernet interface.