[personal profile] gdt

I can't beleive I have to write this in 2016, more that twenty years after the bug in the DEC "Tulip" ethernet controller chip which created this mess.

There are only two ethernet speed and autonegotiation settings you should configure on a switch port or host:

1.

Auto negotiation = on

2.

Auto negotiation = off
Speed = 10Mbps
Duplex = half

These are the only two settings which work when the partner interface is set to autonegotiation = on.

If you are considering other settings then buy new hardware. It will work out cheaper.

That is all.

But...

Oh, so you know what you are doing. You know that explicitly setting a speed or duplex implicitly disables autonegotiation and therefore you need to explicitly set the partner interface's speed and duplex as well.

But if you know all that then you also know the world is not a perfect place. Equipment breaks. Operating systems get reinstalled. And you've left a landmine there, waiting for an opportunity...

A goal of modern network and systems administration is to push down the cost of overhead. That means being ruthless with exceptions which store away trouble for the future.

Auto negotiation

Date: 2016-04-17 02:02 (UTC)
From: [identity profile] edm.livejournal.com
At this point I'd say if you can't configure autonegotiation = on, you should probably just buy new gear. It's less painful that way.

But I do agree that 10/half is the least bad option if you find you really can't replace the ancient "can't autonegotiate to save its life" thing (eg, because they stopped making it). (And probably next round of switch upgrades it doesn't work at all -- I've seen multiple 10G switches with no 10M support...)

Ewen

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Glen Turner

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