To what extent is negotiation speed indicative of network performance?

[rubberduck]

If I see a connection that has been negotiated as gigabit is that good evidence that I will get close to gigabit speeds? Conversely, can you have gigabit negotiated speed but real world performance is much worse (assuming it is not a device at fault)?

 

[Caged]

It's the speed at which your device will communicate with the device at the other end of the cable, nothing more. The negotiated rate means nothing in terms of the wider network performance.

It seems like you're close to asking a question but trying to skip a couple of steps and looking at the wrong thing - what's the actual issue?

 

[Semple]

As above, both devices could easily negotiate at 1gbps but many other factors could prevent transfer rates getting anywhere near that.

In fact, isn't negotiated link speeds more used for capping bandwidth links? i.e. if you don't want transfer to go about 0.5gbps, then you set it accordingly.

 

[the-evaluator]

In fact, isn't negotiated link speeds more used for capping bandwidth links? i.e. if you don't want transfer to go about 0.5gbps, then you set it accordingly.

It's one way of doing it but physical link speed isn't the best way of doing it for a number of reasons. First one that springs to mind is you're limited to speeds that an interface can run at. So say you have a 1Gbps link but you want 200Mbps maximum throughout, you can't control that with the physical link speed as you won't get a network card to link at 200Mbps.

 

[Avalon]

Context is everything. My MacBook connects to a switch at gigabit, if the device on the other end is 100Mbit, you aren't going to get faster than that. Same with WAN side for anything remote - you are only ever as fast as the slowest part of the link.