Auto-nego or 100-Full

[g.peart]

We have a combination of Dell and Sun servers

at my site and a fierce debate is ongoing as to whether all server switch ports should be set at auto or 100/full. My own preference is auto both ends and fix if that doesn't work.

Does anyone else have an opinon about what's "best" or why they have chosen one method over another.

[Mikhail.Galiulin]

Hi,

I would recommend fixed 100/full-duplex.

Especially for servers.

Check this document for further information:

http://www.cisco.com/warp/public/473/46.html#bk

//Mikhail Galiulin

[glen.grant]

Well I think you are going to get a lot of differing opinions , i would fall in line with you . If you hardcode the ports and then move stuff later you are going to forget they are hardcoded then will have a problem if you stick a user that is set as auto . Generally auto works a lot better than it used to and is adequate ,of course there is always exceptions to that rule , if the switch is only running servers and will never have users on them you could hardcode. It just has to match on both ends , can't be auto on the switch end and hardcode the server nics...

[abhishek_nandavat]

Hi,

Me too would go for the auto settings. I go for the hard-code settings only when things in auto mode arent working out. And things havent been too much wrong with auto! And yeah do remember to keep the settings same on BOTH THE ENDS, that is on the switch and the server.

Hope this helps!

Regards,

AbhisheK

Please rate all helpful posts!!!

[scottmac]

Some of that decision will depend on which switch, which version of IOS, and the client.

There are some combinations that, when the switch is hard coded 100full, and the client is coded for 100full, will generate error messages on the console of the switch (duplex mismatch).

I believe it still works OK, but it cranks out errors ~every minute. If you set the switch to auto/auto, no errors and it works OK.

Even some combinations of Cisco switch to Cisco switch will generate teh same errors (duplex mismatch).

My preference is to hard code static resources, but have, on occasion, had to leave the switch in auto/auto.

My suggestion (now that you know my bias) would be to hard code the switch and resource, and check the console for error messages. If you do't get any, leave it ... if you start seeing duplex mismatch (and you know for a fact there isn't any), then flip it to auto/auto.

There have also been issues in the past between Sun Ethernet NICs and some Cisco switches. If you get a bunch of strange problems on the ports connecting to Sun hosts, verify the incompatibility by trying another switch or swap to a different functioning host port.

Good Luck

Scott

[Edison Ortiz · Accepted solution]

I second your preference. If you want to have some facts in your side, have them read this URL :)

http://www.cisco.com/en/US/products/hw/switches/ps700/products_tech_note09186a00800a7af0.shtml

"Recommended Port Configuration (Autonegotiation or Manual Configuration)

There are many opinions on the subject of autonegotiation. Previously, many engineers advised customers not to use autonegotiation with any switch-connected device. However, improvements in the interoperation of autonegotiation and the maturity of the technology has recently changed the view of using autonegotiation. In addition, performance issues due to duplex mismatches, caused by the manual setting of speed and duplex on only one link partner, have become more common. Because of these recent issues, the use of autonegotiation is regarded as a valid practice."

[g.peart]

Thanks for the input guys but management as decided 100/full, time to reconfigure 300 server ports.

[cajalat]

I realize that you've already made up your mind but let me give you a practical prespective. I manage a network of roughly 17,000 nodes of which roughtly 2000 of them are in a data center (i.e. servers) and the rest are client devices such as desktops, some servers, and various medical equipment. The desktop environment is exclusively auto-negotiated while the server environment was hard-coded on both ends to 100/FULL with some exceptions. We've had more trouble worrying about duplex/speed settings on the 2000 machines while the auto-negotiated client networks have had almost unheard of problems due to negotiation. The problem isn't whether or not setting it one way or another is bad. Like others said, so long as both ends are the same then you generally shouldn't have any problem. The problem stems from people moving devices around or reconfiguring their devices and forgetting to set the port to 100/FULL. On a 2000 node data center environment this happens quite frequenty. The problem is procedural in nature and not really technical. We've recently switch to auto-negotiated across the entire network and we're already reaping the rewards. SysAdmin basically cut one process (i.e. hard-coding the ports) completely out of their procedures which also saved a lot of time in troubleshooting "network problems" if you catch my drift.

So I'm only saying this to advise you to concentrate on process/procedures for how things get provisioned going forward in the DataCenter as this will be the biggest headache for you and having a good process in place will help you.