Path MTU Problem

[Sergey]

> Is it possible that you have PF or IPFW filter rules in place 
> that drop ICMP?  Just because tcpdump shows you the frame 
> arrived at your system, does not mean that it was "seen" by 
> the kernel.

No, it's virgin clean install, without any packet filtering enabled

> > here comes icmp frag packets. strange what sometimes 
> tcpdump complains 
> > about tcp header in icmp packet and sometimes not
> 
> The reason for this complaint is that frag_needed packets 
> return a portion of the original IP frame back to the sender, 
> but the number of bytes is not sufficient to see the entire 
> TCP header.  However, there is enough to see the src/dest 
> IP's and src/dest port numbers, as tcpdump shows you.  But 
> tcpdump cannot decode past the end of the returned frame, so 
> it shows an error.

I c