Basic configuration question

[kylehughes]

This question is more for our upper IT management, so please be nice since it is a very basic / stupid question.

We currently have 7 Cisco 3524-XL switches (10-12+ yrs old) which are 10/100.  We purchased a handful of Cisco 3750X switches to replace them going with the whole stackwise and redundant power supplies.  Our current configuration on the old 3524 switches is that they have hardset all the ports on them to 100MB/FULL since devices would auto-neg to 100/Half.

Since we're going from 10/100 to 10/100/1000 switches, I want things to auto-neg as I have heard in the past and experienced that things work better when it auto-neg to gigabit.  My upper management is afraid since the old switches wouldn't auto-neg correctly that we should hard set all the ports on the new switches, which would be a nightmare since some ports would be hard set to 100/FULL others to 1000/FULL, etc..  We've tested just about all of our devices at auto with the switches and they've all auto-neg to the correct speed.

In short, is Auto-Negotiation the way to go with the newer switches or is it still better practice to hard set your ports?

Thanks

[Mike Bailey · Accepted solution]

There are two schools of thought to this.

There are those who like myself have worked in the IT industry for a long time and can recall the early days of auto-negotiation where different vendor devices wouldn't auto-negotiate together due to different standards and as a result tend to like to hard-code things where possible to avoid auto-negotiation issues.

There are also those who swear that auto-negotiation is the way to go as most devices should auto-negotiate nowadays and its more likely that hard-set ports will cause issues due to auto-neg devices connecting.

My personal preference is where a port is permanently assigned to a fixed device (Server, Router, Switch etc) then I always fix both ends to 100/FULL or 1000/FULL depending on the media type.

However any port facing a device that will change (e.g. PC's, laptops etc) I always ensure is auto-negotiate.

Have only had a couple of issues with the above approach where:

1) Human error means the fixed ports don't match

2) Some client devices won't auto-negotiate

[kylehughes]

Thanks for your response Mike.  I'm in about the same mindset as you where if you have a few devices that are always that way to hard-set but to leave PC's, Terminals, Printers, etc... to auto.

Thanks again for your input.

[Leo Laohoo]

I have >3 years experience with "auto" negotiation with the 2900/3500XL and I can tell you frankly that the word "auto" in auto negotiation, in regards to 2900XL/3500XL, is a falacy.  Auto negotiation with the "next generation" of switches (such as the 2940/2950/2955, 2970 and 3550) have improved auto negotiation capability.

I mean it's OK when you are talking about computers with, say, Pentium 100 NIC blocks.  But with 3-year old computers?  There's a very big chance the computer's NIC and the 3500 are incompatible.

I have a controversial case where my client bought 5K brand new computers with Intel Pro/1000 MT (CSCec00968).  In some cases, the switch would go NUTS!  As in the interface would flap like a yo-yo on crack.  (I was seeing log errors like "interfce BLAH flapping XX times in one minute" or something).  The only way to stabilize the interface was to hard code the speed and duplex of the PC.  Take note that the bug is for a PoE version of the 3500XL but I can assure you that it's not.

Old computers?  They are fine and worked well with "auto" negotiation.

Nowadays, auto negotiation has "matured" quiet a bit.  Tell your management to sleep soundly.  The new generation of NIC cards and 3750X will play very, very nice.