MPD and fragmentation

[Mihai Tanasescu]

Hello,


With help from another FreeBSD user on this list I was able to set up an 
MPD pptp server to allow windows machines to connect to it.

Unfortunately now I've stumbled upon some strange behaviors.

First of all I'm getting icmp losses even if I use a test LAN to make a 
tunnel to the local FBSD machine, but these don't seem to affect my 
transfer rate when trying to get a large file via HTTP from the same 
machine.

What bothers me most is that some sites (like msn.com, microsoft.com, 
etc) don't seem to be loading.
What I first thought about was the mss problem and so I discovered the 
following:

22:54:36.633254 IP (tos 0x0, ttl  64, id 14254, offset 0, flags [DF], 
proto: ICMP (1), length: 56) FBSD-IP > 207.68.183.32: ICMP FBSD-IP 
unreachable - need to frag (mtu 1336), length 36

In my config file I have:
set iface mtu 1500
set link mtu 1440
set iface enable tcpmssfix

My full config is posted here:
http://pastebin.com/m66a3c05f
My system:
FreeBSD 6.1-RELEASE-p17
MPD 4.1

I played a bit with the above mentioned values with no luck unfortunately.
I'm still wondering (don't know if I'm right) if a too large packet 
comes from 207.68.183.32 why doesn't it get fragmented upon being sent 
via ng0 -> pptp1 and instead of this happening my machine sends an ICMP 
unreachable back.
Also I have pf running on that machine with a NAT rule for traffic not 
destined to the local network (but after several experiments with that 
nothing changed in regard to the problem I have).

I'm banging my head against the wall as I don't know what else to try 
anymore.

Can someone help me out ?