Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Announcements

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. And see here for current known issues.

New Member

speed/duplex settings

Hi,

Can experts here guide on two queries below..

01: I know only speed mismatch causes the connection lose.. but if two ends are configured at auto/auto and I just set duplex at one end as "full" (speed remains auto/auto).. will this cause connection lose ??

02: Is it require to change the speed first and than duplex.. ??
      If I change the duplex first, will it cause the connection lose ??

4 REPLIES
New Member

01. It wont cause the

01. It wont cause the connection to be lost but with WAN connections i have seen performance degradation such as packet loss on my next-hop IP.

02. Duplex will not cause the connection to be lost

 

You can run both commands quickly in few seconds. It is up to you which order you choose for duplex and speed but both needs to be synced and same at both end for optimal performance. Good Luck.

Super Bronze

DisclaimerThe Author of this

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

#1 If one side is configured auto duplex and the other side full duplex, the connection will normally still pass traffic but very slowly due to the errors caused by the duplex mismatch (the auto side will set itself to half duplex).

 

#2 I believe some equipement wants one setting set before the other, and other equipment doesn't care.  I recall changing the duplex setting may cause the interface to bounce.

 

PS:

If you equipment works with auto/auto, use it, that's current best practice (for the 21th century wink).

New Member

Helo friends,Thanks for

Helo friends,

Thanks for helping .. Your inputs are really helpful..

I would like to share my experience when I did this activity.. Just to mention, this was changed on WAN Ethernet links termination as RJ45 connection on CE router..

01: Initially the supplier and CE router was set on auto/auto..  I check on CE, the interface was negotiating on 100M/half duplex..  I just changed the duplex on CE .. and I got disconnected.. to me I should not be since duplex mismatch doesn't cause lose of connection.. so my end was speed auto, duplex full and supplier is auto/auto.. this looks still perfect.. and should not cause any disconnection.. but it happened..

02: When I asked my colleagues here, they said  yes.. speed should be changed first before duplex.. I have not read it anywhere but practical implmentation can be different.. so couldn't understand the logic of first changing the speed.

I got to reboot the router to get the connection back.. and worst of my bad luck, it was a Data Center router... sad

New Member

1:  Duplex mismatch causes

1:  Duplex mismatch causes one side to be half duplex, the other to be full.  You'll see late collisions on the half-duplex side if the full-duplex side transmits when the half-duplex side thinks it's in the clear.  The full-duplex side may see input errors during times of collision, but the collision counters won't increment since collision detection is turned off.

2:  Changing duplex will not cause a bounce.  However, changing speed will.  It will be momentary, but it will be there.  If you have a routing relationship on the link, expect it to bounce.

4683
Views
0
Helpful
4
Replies
CreatePlease login to create content