Re: Duplex negotiation over 100Base fibre

[Jared Mauch <jared () puck nether net>]

> On Feb 29, 2016, at 11:07 AM, Jason Lixfeld <jason+nanog () lixfeld ca> wrote:
>
> Hello,
>
> My understanding is that for 1G and 10G optical networks, there is no concept of half-duplex mode, but I’m unclear 
> about half duplex in the 100M optical world.  Specifically, if I connect two 100Base-LX (or BX) transceivers 
> together, is there a requirement for the controller(s on either side) to select between full or half duplex, either 
> by static configuration, or auto-negotiation?


I can say even at 1G speeds, the fiber is just the medium, the underlying data stream can still be half-duplex or 
require autonegotation or the lack of it. I recall many years ago having to adjust settings for GSR <-> Foundry 
negotiation and how it would vary depending on the device, so if you changed from GSR -> 6500/7600, you may have to 
make changes to maintain link.

Having a standard device/switch/config will help you here.

Most media converters I’ve seen have a switch on the side that lets you set if it should advertise autonegotation, take 
the super-cheap MC220L as an example, it has a switch for this purpose.

After many years of hard coding things to gig/full, i’ve started to see the autonegotation work much better and require 
less custom coding of the config.  This doesn’t stop someone from plugging in really-old stuff, and we still see people 
connecting at 10/half or 10/full when I really wonder what they are connecting.

- Jared