Wireshark-users: Re: [Wireshark-users] Question on InternetPerformanceTroubleshooting

From: "Small, James" <JSmall@xxxxxxxxxxxx>
Date: Fri, 2 Mar 2007 18:41:25 -0500

Hi Sake,

Not an unreasonable suspicion - in fact, when I used:
http://miranda.ctd.anl.gov:7123/
The site suspected a duplex mismatch since my download speed tends to be
less than half of my upload speed.  Many times the upload speed is close
to the advertised rate but I have never been able to get the full
download speed.

Maybe I can double check with the provider on their router - but they
said they already checked everything and the service provider seems
decent.  Still, it's probably worth double checking.

On all my equipment, there are no errors/FCS, drops, out of buffers -
everything is perfect (from an Ethernet stand point anyway).  The newer
stuff is gigabit where the IEEE mandates auto-negotiation in the spec.
The older stuff that's 100 Mbps is hard coded just like you said.

I guess if it were easy there wouldn't be a whole IT profession, eh?
:-)

--Jim

> You probably have checked this already, but I could not resist in
> mentioning it, did you check the duplex settings on the uplink-router,
> the firewall and the switch-ports? If the packet-loss is higher when
> your (local) traffic increases, but your traffic is not maxing out
> your links, it does sound like a local problem and duplex mismatches
> are still source nr.1 in my experience.
> 
> If it is possible, set all speeds and duplex-modes fixed. Having one
> side on fixed and the other side on auto is a sure cause for trouble.
> Having both sides on auto usually works, but does indeed give you
> duplex-mismatches sometimes. If you have a duplex mismatch, you will
> see a lot of FCS/alignment errors on the interface in full-duplex
> mode and a lot of collisions on the interface in half-duplex mode.