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"Auto" Sensing Switch Ports

Level 12

I just finished troubleshooting an issue where the link between a small workgroup switch and the switch upstream in the LDF kept going down. The workgroup switch was setup amongst a small group (10) of users and they'd basically reboot the switch when the issue occurred.

Manually setting the speed and duplex states on both switches resolved the issue. So, I've gotta ask doesn't this seem a little ridiculous to you? I mean, after all these years we're still having to manually configure these settings to maintain reliability on the switches? Seems pretty freak'in crazy to me...

Are you guys experiencing similar problems or was this an isolated case? I'm not hands-on with the gear as often as I used to be and would like your perspectives...

Flame on...


Level 13

i hard code all my ports

now Cisco is telling me I should use auto auto port config


only auto auto  enables auto auto mdx, ie straight or cross cables can be use and the switch will determine which one you have

with hard coded, you must use the right cable type

to bad there is a command to turn on auto mdx

Level 15

I haven't had to hard code a port in over 5 years.  Auto sense works for linux, windows, etc. for me.  Sure the issue might have been with the smaller switch.  I have had issues with non-managed switches not communicating well with upstream cisco switches.

Level 20

I had once incident in the last few years where auto sensing didn't work, but by and large auto seems to work these days

Level 17

Generally speaking you should hard set full/100 and for 1Gb interfaces, leave it as auto.

This post is back from 2007.

Level 16

I agree Superfly. Pretty basi unless there is a compelling reason not to.

Level 15

I see that you must update the firmware of this device and it does not work you susbtitui for cisco. (Never fail)

Level 17

Auto works in most cases - it usually depends on the end device.... so yeah, every now and again there may be an Old SMB Cisco node that gets finicky. 

Level 18

I hate it when they auto negotiate down...and down...and down.

Level 17

I prefer to Error Disable, at least is attempts to come back on its own.

Level 17

I guess it just means it doesn't work?

Level 19

This problem still happens sometimes but luckily most times both sides can be auto/auto.  The duplex mismatch add on to Orion has helped some too.  Now it's part of NPM I think.

Level 21

It's 2016, and this old thread still bears reviewing.  Auto negotiation of port speed and duplex has been a standard for twenty years, and has been reliable as long as vendors write NIC drivers that comply with the standards.

Yet I continually see present-day equipment coming with requirements for hard coded switch port speed and duplex.

Worse, they want static IP addresses, manually assigned DNS entries, and workstations MUST be installed on the subnet as their server because they are not Layer-3-aware--they don't have places in their network settings for subnet mask entries and gateway settings.

When will we ever learn?

Level 12

i love orionSmiley Happy