Linux

Ask something
Discussion Locked

Auto Negotiation doesn't work

0 helpful
6 replies

by cpfeiffe 1 view

Closed to new repliesThis discussion is closed. It stays readable, but it takes no new replies.
I think we can all agree that auto negotiation doesn't always work. Sometimes you'll reset the switch or server and both sides will come up 100FD and sometimes they won't. In most cases one side will come up 100HD. This is typical of auto-sense, but I've seen it over and over with auto-negotiate too. I need a document from a reliable source (Cisco, Nortel, IEEE, etc.) that describes this behavior. I haven't had any luck finding one so I would appreciate it if anyone can point me to one.

6 replies

by ann777

The last paragraph here:
http://www.sgi.com/peripherals/networking/gbe_faq.html

Most engineers know that the best option is to set 100 full duplex on both ends and force negotiation in that manner. I'm not sure that
this is "written" aside from known/experienced. Yes, auto negotiation is flaky at times; I've seen it too.

The last paragraph here says the same:
http://vegan.net/lb/archive/01-2001/0130.html

It's best to say "ensure both ends of the link are set the same way"; thismeans auto both ends is fine (though most engineers will always set full both ends on connections not involving hosts) . Autonegotiate only really fails if one end is hard coded full or half duplex. And every time I've had autonegotiate mis-negotiate a link "by itself", it's been because of a unidirectional link (dud copper) or a dodgy bit of Cat5 (dud copper :).

by greybeard770

Hard code those settings if you can depend on the equipment not changing. If you move connections from a switch (capable of full duplex) to a hub (half duplex only) you create problems. The situation you have is that data transfer gets to snail speed when one end is full duplex and the other is half duplex, even at high megabits per second rates.

by cpfeiffe

In response to the second answer - I fully agree that it should be forced when possible. AN just doesn't always work. We are bringing a case to networking to have them force every switch port to 100FD instead of auto and really would like to find some vendor documentation or a vendor's answer to an online question stating that AN doesn't always work. It would just help our case.

This discussion is closed to new replies.