[j-nsp] Autonegotiation woes with EX-3400

[Benjamin Collet]

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