enable
configure terminal
no ip domain-lookup
service password-encryption
hostname R4
enable secret class
line console 0
password cisco
login
logging synchronous
exit
line vty 0 4
password cisco
login
exit
banner motd #Unauthorized access prohibited#
ip dhcp pool VLAN_C_POOL
network 192.168.3.0 255.255.255.0
default-router 192.168.3.1 
ip dhcp pool VLAN_D_POOL
network 192.168.4.0 255.255.255.0
default-router 192.168.4.1 
ip dhcp excluded-address 192.168.3.1
ip dhcp excluded-address 192.168.4.1
interface g0/1
ip address 10.0.20.3 255.255.255.248
no shutdown
exit
interface g0/0
ip address 203.0.113.26 255.255.255.252
no shutdown
exit
ip route 0.0.0.0 0.0.0.0 203.0.113.25
interface Tunnel0
ip address 172.16.12.2 255.255.255.252
tunnel source 203.0.113.26  
tunnel destination 203.0.113.17
no shutdown
exit
router ospf 1
network 172.16.20.3 0.0.0.7 area 0 
network 172.16.12.0 0.0.0.3 area 0
end
copy running-config startup-config