On Saturday 01 Feb 2003 12:53 pm, Ross Slade wrote: > Some background... > > I use a Netcomm modem/router/hub/firewall which runs embedded Linux for my > connection to the internet...on my LAN I have one Mandrake 8.1 box and two > WinME boxes. The Mandrake box is a simple server running Apache, Postfix > and Squid mainly. > > The Netcomm uses port forwarding on ports 80 & 25 (ONLY) to the Mandrake > box. > > As you may have guessed, I have a problem... 8-) > > The problem is this: > > I receive mail and everything else just fine, and I can send small emails > (under about 10-15k) just fine, but cannot send anything larger. If I try > it will start to send then slow gradually until it comes to a grinding halt > and eventually times out. > > As near as I can determine it's related to this: > http://home.uninet.ee/~ragnar/manuals/postfix-19990906-pl02/faq.html#timeou >t s > > My knowledge is very limited, but obviously (?) I need to forward ICMP > messages to the Mandrake box. > > My questions: How? What other ports should be forwarded? > > Thanks... > > -Ross >
This is an interesting problem. The effect you are suffering from is described here http://alive.znep.com/~marcs/mtu/ The ICMP packets I think use the same port number as the data packets, but with a different header, so it is not just a matter of forwarding a different port number. I wonder are you using pppoe (ppp over Ethernet) as your protocol to your ISP? If so then the pppoe overhead could be your problem. The maximum MTU size used with pppoe should be 1480 bytes, but your Ethernet port will have a default MTU size of 1500 bytes. The simplest solution could be to just issue the command ifconfig eth0 mtu 1480 HTH derek -- ---------------------------------- www.jennings.homelinux.net
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