I am connected to the IPv6 world via a gif tunnel with mtu 1280. This
seems to be the default since I didn't set it myself.

I have problems to reach ftp.netbsd.org from the router:

$ ftp ftp.netbsd.org
Trying 2001:4f8:4:b:2e0:81ff:fe21:6563...
Connected to ftp.netbsd.org.
220 ftp.netbsd.org FTP server (NetBSD-ftpd 20020615) ready.
Name (ftp.netbsd.org:rhialto): ftp
331 Guest login ok, type your name as password.
Password:
230-

421 Service not available, remote server timed out. Connection closed
ftp: Login failed.

The same from any other machine in my internal network. However, if on
one of those I set the mtu to 1200 (royally below 1280) then it works
fine:

$ ftp ftp.netbsd.org
Trying 2001:4f8:4:b:2e0:81ff:fe21:6563...
Connected to ftp.netbsd.org.
220 ftp.netbsd.org FTP server (NetBSD-ftpd 20020615) ready.
Name (ftp.netbsd.org:rhialto): ftp
331 Guest login ok, type your name as password.
Password:
230-
    The NetBSD Project FTP Server located in Redwood City, CA, USA 
    100 Mbps connectivity courtesy of                      ,        ,
    The Internet Software Consortium          WELCOME!    /(        )`

...etc, a big welcome message.

This makes me think our IPv6 stack might have a problem detecting when
it needs to send smaller packets (path MTU detection).

I can't set the MTU on my tunnel any lower - and setting it higher does
not help.

Any ideas?
-Olaf.
-- 
___ Olaf 'Rhialto' Seibert - rhialto@       -- Woe betide the one who feels
\X/ polderland.nl  -- remorse without sin - Tom Poes, "Het boze oog", 4444.