cisco router VPN setup

The router sets some options by default do a sh run all

Enable ISAKMP
crypto isakmp enable

Phase 1 settings
crypto isakmp policy 5
 encr aes
hash md5
 authentication pre-share
 group 2
crypto isakmp key secretpw address 172.19.140.205

Phase 2

ACL to match traffic
ip access-list extended GBY-VPN
 permit ip 10.55.1.0 0.0.0.255 10.255.1.16 0.0.0.15

Transform set

crypto ipsec transform-set AES-SHA esp-aes esp-sha-hmac

 mode tunnel

Crypto map

crypto map VPN-TUNNEL 1 ipsec-isakmp
 set peer 172.19.140.205
 set transform-set AES-SHA
 match address GBY-VPN

The parts people forget

Apply the crypto map to the outside interface

interface GigabitEthernet1

 crypto map VPN-TUNNEL

Make sure there is a route to other sides public IP

ip route 0.0.0.0 0.0.0.0 172.19.140.1

No NAT may also be required if you have global NAT setup

ip access-list extended NAT_ADDRESSES

5 deny ip 10.55.1.0 0.0.0.255 10.255.0.0 0.0.0.255