[ALUG] Mostly-OT: Strange ADSL issues

[Mark Rogers]

Wayne Stallwood wrote:
> So it sort of looks like anything that involves data exchange over your
> MTU size fails, which sort of points to a very broken IP stack
> somewhere. 

s/fails/is unreliable/

Ping tests "normally" (ie when things seem OK) show fairly high packet
loss using large packets, say around 10-30% depending on the mood of the
line. When it breaks I get 90-100% loss on large packets. In both cases
I'll usually get 0-5% loss on small packets.

What are correct MTU/MRU/MSS values? I have 1500/1500/1432 at work, but
MSS looks wrong to me. not entirely sure what MSS affects, though.

> But given that you have got this on two different machines,
> with two different connections via two different routers I can't think
> why. Are there any commons between machines, same kernel ? same firewall
> configuration ?
>   

Nothing in common that I can put my finger on. At both ends I have a
LAN, but currently my home LAN is just a Win2k PC and DVD player, plus
the (Linux firmware) router. (I have three of my "home" Linux boxes in
the office. Almost all my tests so far have been on the office line
since that's where I seem to live these days, indeed its where I am now.)

My office LAN has 6-10 Linux boxes of varying flavours, and a similar
number of Win2k/XP machines scattered around. All suffer ADSL loss at
the same time ("looks like the Internet's gone again" is a common phrase
in the office right now). Ping tests I've been running from a RedHat box
and a Win2k box, with no obvious differences in results.

According to http://usertools.plus.net/exchanges/mso.php?id=24202 there
was a BT outage affecting "Peterborough MUX 001 & 002" tail end of
September, and this affected both of my lines (based on searching for
both exchanges at http://usertools.plus.net/exchanges/ and getting
directed to the same faults page). So that gives me some common BT
territory, although whether relevant I don't know.

> I have a larger box of straws somewhere we can try clutching at..bear
> with me while I try to find it :-)
>   

The bear will probably not be interested in the straws!

> Ahh here we go, extra large Tesco Value pack....Can you ping from the
> linux router ? Can you do the ping large packet test from there to
> isolate everything else ?
>   

Can't check from work but will do from home when I get there.  I've just
ordered another Linux firmware router
(http://www.ebuyer.com/UK/product/90976) which I'll plug in at the
office to test with when it arrives on Tuesday (if eBuyer deliver on
time - a small possibility).

-- 
Mark Rogers
More Solutions Ltd :: 0845 45 89 555