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Here you can see two company locations are interconnected through public internet using cisco router R1 and R2 ( the perimeter routers). I am configuring IPsec VPN (secure VPN ) between these sites . The protected networks are 192.168.1.0/24 and 192.168.100.0/24 . Ie interested traffic is generated between these private networks. Means only traffic between these private networks are encrypted.

Router R1 configurations

Phase 1 configuration

a) ISAKMP Policy configurations

#crypto isakmp policy 10

#encyption 3des

#hash Md5

#group 2

#authentication pre-share

b) Pre-shared authentication key

#Crypto isakmp key cisco123 address 10.1.2.3

c) Define interesting traffic

#access-list 100 permit ip 192.168.1.0 0.0.0.255 192.168.100.0 0.0.0.255

Phase 2 configurations

d) Ipsec parameters

#crypto ipsec transform-set WAN_SET esp-3des esp-md5-hmac

e) Define crypto map

#crypto map WAN_MAP 1 ipsec-isakmp

#set peer 10.1.2.3

#match address 100

#set transform-set WAN_SET

f) Applay this map to interface

#int s0

#crypto map WAN_MAP

Router R2 configurations