[j-nsp] Autonegotiation woes with EX-3400

[Norman Elton]

Benjamin,

Your note made me realize there are multiple levels of autonegotiation
that I had no idea even existed. I see a wikipedia spiral in my
future!

Thanks for the recap.

Norman

On Sun, May 10, 2020 at 9:55 AM Benjamin Collet <juniper-nsp at clt.tf> wrote:
>
> Hi,
>
> On Tue, May 05, 2020 at 08:42:20PM +0200, Gert Doering wrote:
> > > We've long standardized on running autonegotiation, everywhere. Do
> > > others actually disable autonegotiation on "managed" connections,
> > > where you're configuring both ends of the link?
> >
> > Devices or Carriers disabling autoneg are a major PITA and need to
> > rot in hell.  It's a mandatory part of the standard and should be
> > treated as such.
> >
> > (So, no, we never disable autoneg unless talking to something stupid)
>
> Actually it's only mandatory on 1000Base-TX.
>
> The thing is that auto-negotiation on 1000Base-X includes link fault
> signaling, which is great... and not a mandatory part of the 1000Base-X
> standard, albeit often implemented.
>
> It is not an issue as long as the remote party implements
> auto-negotiation on 1000Base-X (which is optional) and link fault
> signaling (which is an optional part of auto-negotiation) and doesn't
> use an SGMII-based transceiver as they don't support link fault signaling
> (I don't know about RGMII-based transceivers but I wouldn't bet on them
> having the management interface for it).
>
> In the unlikely (right?) event that the aforementioned conditions are
> not met, for the link to go up, one solution is to disable
> auto-negotiation entirely. Another one is to play with the
> `auto-negotiation remote-fault` knob if you're using a MX/ACX device
> (good luck understanding the documentation on that one).
>
> I am not advocating for disabling auto-neg (and link fault signaling) on
> 1G fibre links, on the contrary, but there are good and valid reasons to
> do so.
>
> Benjamin
> --
> Benjamin Collet
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