vpn isakmpd ipsec, one side with only one interface

[Wesley M.]

o;?Hi, 

I was using ipsec vpn between 2 OpenBSD Gateway. It worked very
well.

Here : 

---rl0---[fwA]---rl1--------(internet)---------sis1---[fwB
with ftpd]---sis0--- 

Now we remove ftp services from fwB and put it on an
other machine fwC with an internet connection (only one network card). is
it possible to keep a vpn online from fwA and fwC, and so computersA can
reach again ftp using vpn (provided by fwC). Perhaps i need to use vether
on fwC so briged pf ?

Here the old ipsec.conf from fwB:
ike esp from
172.17.2.0/24 to 192.168.0.0/24 peer ip_fwA 
 main auth hmac-sha1 enc
aes-256 group modp1024 
 quick auth hmac-sha1 enc aes-256 group modp1024 

psk "demopassword"

My idea on fwC : 

add verther0 with : "inet
172.17.2.21 255.255.255.0" 

Need help ;-) 

Thank you very much. 

Wesley.