I have answered this in the past. You need parallel tunnels for this:
> -----Ursprüngliche Nachricht-----
> Von: Aaron Freeman [mailto:aaronpc at pccreations dot net]
> Gesendet: Freitag, 11. November 2005 22:59
> An: m0n0wall at lists dot m0n0 dot ch
> Betreff: [m0n0wall] Multiple ipsec tunnels
> Is it possible to connect two remote sites that are using
> monowall to a
> single site using monowall through ipsec tunnel? If yes how?
> I tried this with monowall 1.2 with no success. I read that a few
> individuals had trouble with ipsec tunnels after upgraging to
> 1.2, so I
> went back to 1.11 and still can not successfully establish a second
> tunnel. Please help.
> Aaron Freeman
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