This post outlines how to set up a site-to-site VPN on a Cisco router. Both sides need to match crypto iskamp policy and transform set.
crypto isakmp policy 1
encr 3des
hash md5
authentication pre-share
group 2
crypto isakmp key SecureComputing! address xxx.xxx.xxx.xxx
!
!
crypto ipsec transform-set MYVPN esp-3des esp-md5-hmac
!
crypto map MYVPN 10 ipsec-isakmp
set peer xxxx.xxxx.xxxx.xxxx
set transform-set MYVPN
match address 110access-list 110 remark MYVPN TO REMOTEVPN
access-list 110 permit ip 192.168.1.0 0.0.0.255 192.168.2.0 0.0.0.255 (Where 192.168.2.0 is the remote network your trying to get to.)interface atm1.0
crypto map MYVPN
access-list 111 deny ip 192.168.1.0 0.0.0.255 192.168.2.0 0.0.0.255 (This denys NAT)
access-list 111 permit ip 192.168.1.0 anyip nat inside source list 111 interface atm0.1 overload