Weird Solaris stuff

[Michael Smith <mj...@cursci.co.uk>]

I've just been spending most of today trying to work out why it is that
a few people scattered about on the net can't connect to our web server
(though they don't seem to have the problem with anybody else). I've
tried different operating systems and different web servers; the problem
appears with solaris 2.5 (with TCP patches) but not with linux or IRIX. 
It appears with both apache and Netscape servers (relief).

I managed to get a log-on to an affected machine, to do some remote
requests.  While the server thinks it completes the transaction
successfully, the client can only grab very small files.  I found that I
can get a file 365 bytes long but not 366 bytes long (in this case I
just get a Connection closed error).  This is reproducable.  I've got
some TCP traces via the sun "snoop" program, which is a bit over my head
but the size of the big data packet goes up from 590 to 591 bytes.

Has anybody else had a similar experience, or any idea what might be
going on?

Thanks for any help

Michael Smith

Re: Weird Solaris stuff

[Cliff Skolnick <cl...@steam.com>]

Sounds like something with the dynamic path MTU might be not working.   
As a test, reduce the MTU on the ethernet interface on the solaris box to 
something small like 256 and see if things work.

If it works with a small MTU, then you need to find out why ICMP
TYPE=unreachable, CODE=must fragment packets are not making it back to 
your solaris box.  Most likely it is a firewall problem, so you might 
want to get anyone involved with filtering involved.  I've also see brain 
dead routers do this, they just *don't* send the ICMP packet and drop the 
data :(

There is an ndd variable that you can tweek to turn of path mtu 
detection, but it escapes me right now and I don't have easy access to a 
solaris box at the moment.  But it would be better to find the offending 
router or firewall and fix it.


Hope this helps,
Cliff

On Tue, 22 Oct 1996, Michael Smith wrote:

> I've just been spending most of today trying to work out why it is that
> a few people scattered about on the net can't connect to our web server
> (though they don't seem to have the problem with anybody else). I've
> tried different operating systems and different web servers; the problem
> appears with solaris 2.5 (with TCP patches) but not with linux or IRIX. 
> It appears with both apache and Netscape servers (relief).
> 
> I managed to get a log-on to an affected machine, to do some remote
> requests.  While the server thinks it completes the transaction
> successfully, the client can only grab very small files.  I found that I
> can get a file 365 bytes long but not 366 bytes long (in this case I
> just get a Connection closed error).  This is reproducable.  I've got
> some TCP traces via the sun "snoop" program, which is a bit over my head
> but the size of the big data packet goes up from 590 to 591 bytes.
> 
> Has anybody else had a similar experience, or any idea what might be
> going on?
> 
> Thanks for any help
> 
> Michael Smith
> 

Cliff Skolnick    N1DPH   | Remember you are unique, just like everyone else.
cliff@steam.com           |
PGP key via finger        | - insert cool quote here -