Long HTTP connection delays in LAN

[Matthew Seaman]

Reinis Ivanovs wrote:
> Hello,
> 
> I have a strange HTTP connectivity problem in my LAN. There is a
> FreeBSD 7.1 system that runs the httpd, a Vista system that I use to
> connect to it, and a Tomato 1.23 WRT54GL router between them. It often
> occurs that I can ping the FreeBSD system just fine, but HTTP
> connections get "stuck" for minutes on end. After they become
> "unstuck", everything works normally for a while, and then the problem
> might come back. I know the httpd is running fine during those times
> because there are no delays connecting locally or from outside the
> LAN. It seems I also get similar delays when I try to connect to the
> router's web administration panel. There are so many variables that
> I'm not sure whether the problem lies with FreeBSD or something else.
> I'm hoping somebody with more networking experience could give me some
> hints about where to look, because I'm seriously stuck.

This sounds suspiciously like MTU problems.  ie. one of those machines
is occasionally sending packets too big for the other side to cope with
*and* PathMTU discovery is not working.

However, I can't see why that should be an issue with two machines and a
router all directly connected via ethernet: the standard MTU of 1500 bytes
is almost certainly correct in that case.

MTU problems usually occur when you tunnel one protocol through another
(which includes such things as IPSec) or when you convert from ethernet
to some other wire protocol, such as PPP.  In any case, there should be
an automatic mechanism to enable the MTU to be adjusted dynamically --
firewalling out all ICMP traffic (which is the not the latest bit of 
bogus security lore but merely the most intractable and stupid) will
lead to effects like that.

	Cheers,

	Matthew

-- 
Dr Matthew J Seaman MA, D.Phil.                   7 Priory Courtyard
                                                  Flat 3
PGP: http://www.infracaninophile.co.uk/pgpkey     Ramsgate
                                                  Kent, CT11 9PW

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 259 bytes
Desc: OpenPGP digital signature
Url : http://lists.freebsd.org/pipermail/freebsd-questions/attachments/20090426/3aa8ef92/signature.pgp