IPSec VPN

Internet Protocol Security (IPsec) is a Protocol suite for securing Internet Protocol (IP) communications by authenticating and encrypting each IP packet of a communication session. IPsec also includes protocols for establishing mutual authentication between agents at the beginning of the session and negotiation of cryptography keys to be used during the session.

IPsec is an end-to-end security scheme operating in the internet Layer  of the internet Protocol Suite. It can be used in protecting data flows between a pair of hosts (host-to-host), between a pair of security gateways (network-to-network), or between a security gateway and a host (network-to-host).

Cisco Router to Cisco Router Configuration:

R2 Router Configuration:

R2#write terminal Building configuration... Current configuration : 1412 bytes ! version 12.3 service timestamps debug datetime msec service timestamps log datetime msec no service password-encryption ! hostname R2 ! boot-start-marker boot-end-marker ! ! no aaa new-model ! resource policy ! clock timezone EST 0 ip subnet-zero no ip domain lookup ! ! crypto isakmp policy 10 authentication pre-share ! crypto isakmp key ciscokey address 200.1.1.1 ! ! crypto ipsec transform-set myset esp-3des esp-md5-hmac ! crypto map myvpn 10 ipsec-isakmp set peer 200.1.1.1 set transform-set myset !--- Include the private-network-to-private-network traffic !--- in the encryption process: match address 101 ! ! ! interface Ethernet0/0 ip address 172.16.1.1 255.255.255.0 ip nat inside ip virtual-reassembly ! interface Ethernet1/0 ip address 100.1.1.1 255.255.255.0 ip nat outside ip virtual-reassembly crypto map myvpn ! ip classless ip route 0.0.0.0 0.0.0.0 100.1.1.254 ! ip http server no ip http secure-server ! !--- Except the private network from the NAT process: ip nat inside source list 175 interface Ethernet1/0 overload ! !--- Include the private-network-to-private-network traffic !--- in the encryption process: access-list 101 permit ip 172.16.1.0 0.0.0.255 10.1.1.0 0.0.0.255 !--- Except the private network from the NAT process: access-list 175 deny ip 172.16.1.0 0.0.0.255 10.1.1.0 0.0.0.255 access-list 175 permit ip 172.16.1.0 0.0.0.255 any ! ! ! control-plane ! ! line con 0 exec-timeout 0 0 line aux 0 line vty 0 4 login ! end R3 Router Configuration: R3#write terminal Building configuration... Current configuration : 1630 bytes ! version 12.3 service timestamps debug datetime msec service timestamps log datetime msec no service password-encryption ! hostname R3 ! boot-start-marker boot-end-marker ! ! no aaa new-model ! resource policy ! clock timezone EST 0 ip subnet-zero no ip domain lookup ! crypto isakmp policy 10 authentication pre-share crypto isakmp key ciscokey address 100.1.1.1 ! ! crypto ipsec transform-set myset esp-3des esp-md5-hmac ! crypto map myvpn 10 ipsec-isakmp set peer 100.1.1.1 set transform-set myset !--- Include the private-network-to-private-network traffic !--- in the encryption process: match address 101 ! ! ! interface Ethernet0/0 ip address 10.1.1.1 255.255.255.0 ip nat inside ip virtual-reassembly ! interface Ethernet1/0 ip address 200.1.1.1 255.255.255.0 ip nat outside ip virtual-reassembly crypto map myvpn ! ! ip classless ip route 0.0.0.0 0.0.0.0 200.1.1.254 ! no ip http server no ip http secure-server ! !--- Except the private network from the NAT process: ip nat inside source list 122 interface Ethernet1/0 overload !--- Except the static-NAT traffic from the NAT process if destined !--- over the encrypted tunnel: ip nat inside source static 10.1.1.3 200.1.1.25 route-map nonat ! access-list 101 permit ip 10.1.1.0 0.0.0.255 172.16.1.0 0.0.0.255 !--- Except the private network from the NAT process: access-list 122 deny ip 10.1.1.0 0.0.0.255 172.16.1.0 0.0.0.255 access-list 122 permit ip 10.1.1.0 0.0.0.255 any !--- Except the static-NAT traffic from the NAT process if destined !--- over the encrypted tunnel: access-list 150 deny ip host 10.1.1.3 172.16.1.0 0.0.0.255 access-list 150 permit ip host 10.1.1.3 any ! route-map nonat permit 10 match ip address 150 ! ! ! control-plane ! ! line con 0 exec-timeout 0 0 line aux 0 line vty 0 4 login ! end