Re: [gentoo-user] Slow local network - how to debug?

[Mick <michaelkintzios@gmail.com>]

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On Friday 22 Feb 2013 08:04:38 Helmut Jarausch wrote:
> Hi,
> 
> I have no experiences in debugging a slow network.
> 
> At home, I have a router which is connected to my telephone line via
> VDSL2.
> I have 2 PCs one of which is connected by an ethernet cable (i.e.
> wired) while the other
> one uses a wireless connection which is specified as 56 Mbit/s.
> 
> When  copying data from one machine to the other one I see varying
> speeds from only 0.5 Mbits/s up to
> more than 20 Mbits/s. I have no idea why it is so slow some times.
> There are no other wireless devices nearby.

Where do you see these transfer speeds?  On the wired machine, or on the 
wireless machine?

What do you use to check the transfer speed?

Do the speeds go up when you used a Cat5e cable at full duplex?

Have you scanned for access points to be absolutely sure that there are no 
other wireless devices, or APs?

Do you use encryption?

What frequency and channel are you on and have you tried to change 
channel/frequency?  (some domestic devices like cordless phones, wireless 
earphones, bluetooth, microwaves, perimeter sensors, etc. can cause co-channel 
and adjacent channel interference and/or force sharing of the bandwidth).

Are both machines and the router's LAN on the same MTU?


> What tools and techniques can I use to debug this situation?
> 
> Many thanks for a hint,

First use ifconfig to see how many dropped packets you get on both machines.  
Then use iwconfig, or cat /proc/net/wireless on the PC running the wireless to 
see how many discarded packets you get, fragmentation, etc. as well as nwid 
packets from different networks on the same frequency.

Then check with e.g. iptraf-ng what network connections are running, their 
rate(s) and if any of these should not be there.

The router stats may also be revealing in this respect, as well as dropped 
packets on the WiFi.

I hope the above will give something to work with, others may have better 
ideas and more specialised tools for troubleshooting this.

PS.  I haven't mentioned spectrum analysers to keep this thread within the 
realm of quick fixes, but if you do have EM interference and the source of it 
is obscure, you may need more professional equipment to nail this problem.
-- 
Regards,
Mick

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