question about DUPLEX MODE

['chris']

hi

the first device (ADSL router) is FULL DUPLEX 10 MB/s
how to setup the second device (100MB switch) ?
FULL DUPLEX or AUTO ?

and what happens if both are on AUTO ?

kind regards
chris

[Bill Costigan · Accepted solution]

If you are sure the first device the running full duplex 10MB/s then the switch port should also be set 10FD.

If only one side is set for auto, the auto negotiation may not work and the side set for auto may default to half duplex. You'll then have one side at 10FD and the other at 10HD and you'll get lots of errors.

['chris']

thanks !

that means the best solution is to setup both sites: router and switch to AUTO Negotiation ?

[Bill Costigan]

I would then check to see what it is really running at from both sides. Just to make sure one side or the other doesn't have a problem with AUTO setting.

[Les Ligetfalvy]

It has always been my preference to hard code fixed links, that is links that are not subject to change by someone other than me, especially when using a mix of products like Cisco, Nortel, etc. and especially when they are trunk or uplinks.

['chris']

but both: router and switch support AUTO Negotiation, that for sure
and why not to setup both devices on AUTO Negotiation ?

If they both are on AUTO, I should not have
any collisions or errors, isn't it ?
the same should be if I hard-code fixed links,
I mean to set both on FULL DUPLEX.

[Bjorn Tore Paulen]

Auto and Auto does not necessarily mean that equipment negotiate correctly. There is actually no explicit standard regarding Auto negotiatiion. If you get FCS errors etc it seems that Auto-Auto is not working. And Ohm's law states that FullDuplex-Auto never will work. You then will get FDx-HDx. For a 100Mbit link that has FDx-HDx typically will give 2-3Mbps(!)

The best setting towards an Auto port is either Auto or 100Hdx.

['chris']

thanks for all answers !

@Bjorn
do you mean if AUTO on both sites doesn't work correctly, to try one device on AUTO and other one on HALF DUPLEX ?

[Les Ligetfalvy]

I would always try hard coding 100/full on both sides. I have seen where auto would work one time but then on a reboot it would not. Leave auto/auto for end-user connections where the capabilty is not always known.