uplink ports and best practice..autonegotiate or fixed speed

Generally speaking (with the exception of gig for some vendors), you want to set to the same thing on both sides, whether that be auto/auto or 100full/100full, or whatever. Generally speaking, and while I do know of several devices where auto/auto is really required, most of the time it is best to hard code both sides and avoid auto- negotiation. Cisco has gotten a lot better with this in recent years, but you usually can't go wrong with hard-coding both to the setting you want, either 100/full or gig/full.

Here is a link to the best practices:

Thanks for the link and for the information. It looks as though either method will work and that manual configuration is prone to human error. I wonder what they mean by "the maturity of the technology has recently changed the view of autonegotiation.." as of when? The document was updated as of 8/2005 but what does that mean in terms of my 3com superstack 3 3300? My boss has made a big issue over a suggestion by a consultant regarding hard coding Speed & Duplex on Cisco switches connecting to 3com switches and is calling into question my work. Now I'm on the defensive and she wants me to email my config to a Cisco engineer. Note: We have no issue with performance. thanks for your input.

FROM Cisco's website (link you provided) 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 autonegotiation and its use. In addition, performance issues due to duplex mismatches, caused by the manual setting of speed and duplex on only one link partner, are more common. Because of these recent issues, the use of autonegotiation is regarded as a valid practice

3com is the variable that I can't speak to. However, back in the day (I'd say late 90's/early 00's), leaving anything to auto on both sides frequently caused issues. For every box that worked fine, there was one with a NIC from a different vendor that re-acted differently and negotiated incorrectly. The same bet at this time was usually to hard code both sides to the speed/duplex you wanted. This is generally the same approach that most engineers I know take today just because of all of our prior experiences, but gigabit ethernet has pushed auto/ auto as many cards do not have a 1000/full setting.

Additionally, I agree w/ Cisco that things changed what seems to be a few years ago (2004/2005 is probably about right). I now have lots of boxes (probably a good 20%) that are auto on both sides and work great. In fact, some of our NIX boxes require it for some of their NICs depending on NIC function.

To answer your question, I'm not sure what the 'best' is for your 3com equipment, but when in doubt, I always recommend hard-coding. I have had many more problems over the years with auto/auto than the few I have had when there was an issue with hard coding both sides. Just my

2 cents.

This is now a Religious issue mostly : -))

May I recommend reading:- The Duplex Delusion - 2017 - Bod43 (Apologies to Richard Dawkins:-)

As discussed already just use whatever works. Many people hold very strong views on this subject however at the end of the day it is no big deal to figure out if you have a problem or not and to fix it. There is not and never has been a Right Answer to whether to use Auto or not.

I recommend checking the interface counters once a bit of traffic has flowed and if there are no errors then all is OK. I have encountered devices that lied about their duplex setting so I like to check the interface counters. The cisco counters seem reasonably trustworthy.

If you have a mismatch and are getting traffic that highlights the problem the HD end shows Late Collisions and the FD end CRC/Frame errors.

I do know for sure that I have seen 100s of workstations with terrible performance due to poorly managed attempts to use manually set. I have also seen many poeple, while attempting to "fix" poor system performance, check the duplex setting of a port and if not FD set it to FD since it is 'obviously better'. Not even checking the oher end!!!

Whatever you do make sure that both ends are the same : -)

At this point in time I believe setting things to auto is fairly safe. It really depends on how well that feature on the 3coms work.

Performance will be identical If things negotiate properly with auto or are properly static.

I've had issues with packet loss and weird network problems because things were set to 100full and not auto. Wait until you plug a workstation into one of those ports that is hard set in two years and can't figure out why you are getting strange packet loss. It's a problem that unless you have seen it recently you'll burn hours trying to figure out.

My datacenter switches are all auto except to our uplink out of the gateway and things are fine.

Thanks for responding. The help I have received here over the years has been invaluable and I am grateful.

While I don't disagree with any of the comments above, I will repeat that I have NEVER seen uplinks or trunks configured with auto/auto in any of the companies I have worked for (all Global Fortune 100), and in fact, I'm fairly certain that trunks cannot be auto but could be wrong there. In regards to other nodes, I do agree that both solutions are equally viable today and its really a case of trial/ error or following documentation for specific vendors, but I would never leave backbone or distribution network links to negotiation.

I have in the past hard set when possible, on all switch ports used for servers and uplinks, we have any user workstations and servers on separate networks and switches so makes a lot easier.

I have experienced many occasions when running auto on both ends and have heavy traffic from servers or on uplinks, I caused the ports to renegotiate and if there is still heavy traffic during that time can not negotiate correctly seems for the switch to negotiate requires additional processing that under heavy traffic loads gets interrupted or something.

Server folks know to check their interfaces and set appropriately. I do use auto negotiation on copper gig ports for server connectivity but in many cases still hard set links between switches.

I agree that the auto negotiation as gotten a lot better these days and in most cases is probably not needed to hard set. MC

I'm seeing new 3750, sfp gig ports auto having problems with new hp dl360's where the server is pushed to 100 rather than 1000 ... setting it manually on the port and everything works at 1000. Haven't looked for a reason as yet, all cabling is new and its happened on a few new sites recently.