[Gllug] hello, and a NAT problem

[Richard Cohen]

On Sun, 7 Mar 2004, lists wrote:

> Hello, Im Julian, Ive just upgraded to London & Linux. I hope that this is
> an appropriate place to air my dumb questions...

Yes, it is.  Welcome :-)

> PROBLEM with NAT
>
> This is what I have done to try get this mandrake 9.2 (2.4.22) to share a
> dsl connection across the wireless lan:
> # echo "1" > /proc/sys/net/ipv4/ip_forward
> # iptables -t nat -A POSTROUTING -o ppp0 -j MASQUERADE
>
> Now, most services work: I can do dns lookups on tiscali's dns from the
> clients, I can fetch an email from a pop3 server from the clients, I can
> ping, traceroute etc. But /most/ of the web times out (I can do google
> searches and open some other near, fast sites that I have definitely not
> been to before). On some sites, I can open some pages, but not others. And
> if I a client has more than one pop3 message waiting, the mail client times
> out.
>
> I don't know how to start with this one -- can anyone point me in the right
> direction?

This sounds to me a little like an MTU problem - like you have two networks
connected back-to-back, a different MTU on each, and when one tries to send
a packet which is too big for the other, things stop working.  That would
mean that small web pages - like google, say, and single mails which don't
generate a large stream of data, all work fine, but larger things don't.

I could be talking nonsense, but I have seen this sort of thing before...

ifconfig should tell you what the MTU is on the relevent interfaces.

> thanks for your time,
>
> Julian

Cheers
Richard
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