VPN configuration

What is?

Configuration

For this example image you have two autonomous system’s running EIGRP ()

Setting up GRE Tunnel

Setting up GRE Tunnel

router(config)# interface tunnel 0
router(config-if)# ip address [ip address] [subnet mask]
router(config-if)# tunnel source g0/1
router(config-if)# tunnel destination [Device 2 edge interface]
router(config-if)# exit
router(config)# access-list 101 permit gre host [device ip] host [destination ip]

After this advertise the gre tunnel in your routing protocol. This could be RIP, OSPF, BGP or EIGRP.

Repeat these two steps for each device then test connectivity between them

Setting up VPN

router(config)# crypto isakmp enable
router(config)# crypto isakmp policy 1
router(config)# authentication pre-share
router(config)# encryption des
router(config)# hash md5
router(config)# group 1
router(config)# lifetime
router(config)# exit
router(config)# crypto isakmp key [pre-shared key] address [ip of network]
router(config)# crypto ipsec transform-set [transform set name] esp-3des esp-sha-hmac
router(config)# crypto map [crypto map name] 1 ipsec-isakmp
router(config)# match address [access list number]
router(config)# set peer [ip of external network edge router]
router(config)# set transform-set [transfrom set name]
router(config)# set pfs group2
router(config)# set security-association lifetime seconds 44000
router(config)# exit

Testing

show crypto isakmp sa
show crypto ipsec sa