MTU or Fragmentation Problems on 7.0?

[Len Gross]

The following configuration works fine _until_ I make a change in MTU
setting on the link between FreeBSD1 and FreeBSD2

Internet
                                   |
Router                      x.x.x.x
                         192.168.0.1/16
                                   |
FreeBSD #1       192.168.0.202 /16
  6.3                  192.168.1.1/ 24
                                   |
FreeBSD #2        192.168.1.2/24					
  7.0                   192.168.1.5/24
	                  |
FreeBSD #3        192.168.5.2/24
7.0

All connections are Ethernet.

If I change the MTU on 192.168.1.1 to 1450  and the corresponding MTU
on 192.168.1.2 to 1450, then Web Browsing on FreeBSD2 continues to
work, BUT browsing on FreeBSD3  "fails"  (mostly.)

On FreeBSD 3
Ping and nslookup work fine from FreeBSD3
I can get to Google but virtually no other web sites
Using tcpdump there is lots of unusual stuff, some relating to
fragmentation ICMP?

If I put a Web Proxy on FreeBSD 1, everything works fine.

I have tried putting mtu = 1450 using route change on all the routes,
but that didn't help.
When I did this I verified all routes had 1450 mtu via netstat –arW

So I am unsure if this is a FreeBSD bug, a "internet" fragmentation issue or ???
Amongst the strangest things is that FreeBSD 2 is unaffected; Firefox
runs fine there

(There was a thread in October about mtu issues in 7.0 but it didn't
seem to help my problem.)
(I run 1450 MTU to support testing of an experimental protocol., but
all the above is with straight out of the box FreeBSD.)

-- Len