[Openswan Users] NAT-T

Paul Wouters paul at xelerance.com
Mon Mar 27 17:25:45 CEST 2006

On Mon, 27 Mar 2006, Oliver Tomkins wrote:

> It looks exactly the same as when we get a successful connection from a
> non-NAT client.
> > It is most likely an mtu issue. transport mode packets may never get
> > fragmented
> > it the client is behind NAT and udp encapsulation is used.
> >
> I've edited options.l2tpd thus:
> mtu 1710
> mru 1710

That won't work. That size is higher then an ethernet frame!

Our experience has been that setting the ethX mtu to 1472 or 1452, and setting
the mtu/mru in options.l2tpd of 1200 seems to work okay.

> I still don't see any ESP Traffic going to or from the host.  How would I
> prove that UDP encapsulation is actually taking place or is assumed in the
> fact that a connection has been established?

run tcpdump and check for udp 4500 packets.

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