[sdnog] Common problem in sudan | Duplex mismatch

Bernd Spiess bernd.spiess at de-cix.net
Tue Jan 27 23:11:24 SAST 2015

Hi Scott 

good point ... in general there is no magic - the problem is quite standard on 100 MBit interfaces when you don´t
define if you connect auto to auto or manual to manual - if you try to mix auto negotiate with manual duplex you
have for sure this problem.

the check of duplex errors should be part of each link check after turnup - and as things are changing you should
also periodically check your interfaces on switches and routers ...

last: if you have performance problems - as you said: you can in many cases bet on a duplex problem in your network...
... and this is also one of the reasons why your switches should be in all cases manageable...

PS: keep up that great work - quite a perfect mailing list with very good discussions :-)


Bernd Spiess
Manager Peering Service
DE-CIX Management GmbH | Lindleystrasse 12 | 60314 Frankfurt am Main | Germany 

-----Ursprüngliche Nachricht-----
Von: sdnog-bounces at sdnog.sd [mailto:sdnog-bounces at sdnog.sd] Im Auftrag von Scott Weeks
Gesendet: Dienstag, 27. Jänner 2015 21:35
An: sdnog at sdnog.sd
Betreff: Re: [sdnog] Common problem in sudan | Duplex mismatch

--- tariq198487 at hotmail.com wrote:

The most common problem I face when I check the links status in every network here in sudan that some links are *half* duplex. 

   Why? May be there is compatablity issue between Huawei and cisco. 

   What is the impact? Huge packet loss and very slow browsing experience. 

   How to solve it? I do not know, I just try randomly all posible settings in both routers cisco & Huawei till it get resolved. 

For discussion:
 Do you have this problem in your network? Or have you faced it before.  Please help if you know the right settings for both routers.

Note: I am serious every network I checked it has this problem.

I have seen this on our network.  For example, I have seen 
100Mbps half-duplex be auto-negotiated between two devices
from different manufacturers.  I go in and hard code them 
when I find them.  I use a script to look through the nightly
backups (I get the output from various commands as well as
the configs) to find them.

In cisco's routers:

conf t

int f1/0/1
speed 100
duplex full

wr mem


Sdnog mailing list
Sdnog at sdnog.sd

Sdnog mailing list
Sdnog at sdnog.sd

More information about the sdnog mailing list