Cisco switch and auto-negotiate speed

Posted on 2005-04-14
Medium Priority
Last Modified: 2012-08-14
I've heard from someone that there is and has been an issue with Cisco switches and Microsoft operating systems that causes massive slowdowns when the switches are set for ato-negotiate on speeds.  They claim that if you set all the ports on your switch to 100 full rather than auto that you will increase speeds as much as double.  I asked them to show me with some tests to prove with with a couple ports before we do this across the board but I tend to think that if this ever was an issue that it would be resolved by now.  They said it really had a lot to do with 2 or 3 switches linked together but if a site had 2-3 switches in place, moving everything to 100 full would greatly increase speeds.

Can anyone confirm this or it is just a myth?  I'm looking forward to doing our own tests but wanted to check with others as well.
Question by:Eagle6990
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Assisted Solution

neteducation earned 75 total points
ID: 13786593
from personal experience I can tell you that certain cisco switches (or let's rather say certain IOS-Releases) have problems autonegotiating with quite some common network cards. However if they have problems then no communication at all is possible. Then, of course you have to switch. Apart of this I did nt see any increase/decrease in speed when autonegotiating/not autonegotiating

Expert Comment

ID: 13786652

At my place of buisness we use cisco switches and 2 different network cards.  We use Intel and 3com.  As a thought we switched the switches to hardcode at 100 full.  We then set the computers to 100 full.  To our surprise it didn't help.  In fact it made it slower.  We decided to switch it back to autonegotiate and the whole network sped up.  My opinion would be to stay on autonegotiate.

Hope this helps.
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Expert Comment

ID: 13786969
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Expert Comment

ID: 13787265
My rule of thumb:
if a switch port is going to connect to a server, hardcode both ends to the highest possiblity; full-100, etc; if a port is going to connect to a PC/Wordstation, leave it as auto; for uplink or trunk between, always hardcode both ends as well.
LVL 17

Author Comment

ID: 13787392
But why?  Do you have any history or proof of why you do that?

No disrespect but I could say my rule of thumb is to hardcode every other port except port 13 on a switch but without a good reason, I don't see the point.  Especially when I can go into Windows and see that my link is working at 100.

Assisted Solution

Promethyl earned 75 total points
ID: 13787851
>I've heard from someone that there is and has been an issue with Cisco switches and Microsoft operating systems that causes massive slowdowns when the switches are set for ato-negotiate on speeds.  

It has been my experience the slowdown (besides bad IOS code) is when you don't match them.

When you use neg. or ethernet@wirespeed, and the other device is set to 100/FULL, it causes packet loss, errors, et al.
If you're going to do it, match them. Either do all or none. There are instances where having negotiation is a good thing ... EMI anyone?  But generically, I like 100/FULL. Just no one understands it.
For the price of equipment these days, however, get gigabit on everything you can. The cards are cheap, the switches are getting reasonable...

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Expert Comment

ID: 13788134
Negotiation has proven to be a problem in my experience.  This problem is not limited to Microsoft OSs. The problem with negotation stems from the fact that each vendor implements duplex negotiation differently.  Even when interconnecting two Cisco products, duplex negotiation issues may arrise.  Hard coding however is not the only answer.  By hard coding both sides (asuming that the setting takes and that the displayed speed/duplex in the OS is the setting you chose) you eliminate the possibility that one side missdetects duplex. Just because Windows tells you the network card is set to 100 Full does not mean that it is (I do however trust the fact that my switch is hard coded to 100 full).  The true way to test this is to take a larger sample of workstations/servers with a variety of network chipsets (taking a Dell/Compaq/HP server may not be sufficient as all may use the same network chipset) and pass a large file and compare transfer times (the specs of the machine should not influence throughput).  This problem of duplex is more prevalent in my experience with 3COM network cards, Intel chipsets do appear to fare better.   A far bigger problem arrises when one negotiates both speeds and duplex (try plugging a printer that only supports 10/Half into a switch that is set for auto).  Cisco themselves has flipflopped from time to time as to which method is king (hardcode or auto)

Expert Comment

ID: 13790575
we fix speeds on servers, we had many proofs, it looks as if the speed is negotiated once, then during heavy load (backups etc.) since there is a flood of packets, one side decides to try and negotiate the speed again, because there were excessive errors on the interface, for example. Cisco is not limited to that, 3com is as well, at least in my experience...

This occurences could be monitored from the switch, as interface resets... (cisco terminology)

I guess that negotiation is not the best of things one could have on the card which is under heavy load at any point in time. You should use any FD combination, iether 10 or 100Mbps, as in this way you can get the maximum out of that. FOr desktops, it is not practical to do that, as there will always be a machine which does not have this set, and occasionally gives you headaches, since you have to troubleshoot a lot...


Expert Comment

ID: 13790808
Maybe breaking up broadcast domains and setting up proper VLANS would be a way to help this as well, at least from Vladan's example. If you experience similiar trouble, this might be a way out.
LVL 11

Expert Comment

ID: 13795622
SPEED auto is simple and reliable.

DUPLEX auto is hairy and often unreliable.  Which wouldn't be so bad except that half does collision detection and full has to rely on timeouts to detect collisions....

AND I've seen some specific cases where auto makes a working 100/full connection, but explicit 100/full passes only a trickle.  So try auto speed/full duplex first, but if it's REALLY SLOW then try auto/auto.


Expert Comment

ID: 13796828
If this switch is going to be running this switch at the access layer of your network you might want to consider running CATOS and not IOS. CATOS from my experiences preforms much better when it comes to end devices such as comptuers, printers ect.

You are asking for some proof... This is going to be a bit hard to get because Cisco is not going to admit to troubles with there product. They always try and make the problem out to be CPE/YOUR NIC having the problem.

Where I currently work we have over 10000 ports connected to 6500 series switches running CATOS and we have only a handful that needed to be hard coded. The ones that are hard coded are running obscure OS with old hardware.

LVL 17

Author Comment

ID: 13797286
We have not had any problems with anything acting funny or having trouble connecting.  I was just told that we could increase performance but as far as I know, everything is running just fine how it is.  It sounds like I only need to hardcode it if I'm having an issue and since I'm not, I don't see the advantage of going through every switch and setting that unless I need it.

Accepted Solution

ender78 earned 225 total points
ID: 13798382
I have to disagree that the switch software has anything to do with auto-negotiation success.  Certain devices are more problematic than others and you need to figure out which ones will have to be hardcoded.

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