VPN Configuration – IPSec

This VPN configuration use FreeSWAN software. There 2 kinds of FreeSWAN, OpenSWAN and StrongSWAN.

· Download and Install (in this method use RPM Package, but for configuration same with another distro)

· Edit /etc/ipsec.conf file,

version 2.0
config setup
interfaces=%defaultroute
klipsdebug=none
plutodebug=none
nat_traversal=yes

· Add this script into ipsec.conf file
conn vpn-ipsec
authby=secret
pfs=no
left=[IP Client]
right=[IP Interface to Client]
rightsubnet=[subnet]
auto=add
keyingtries=0

*) rightsubnet used to HOST-to-Network connection. If it Host-to-Host you didn’t configure this script.

· Create /etc/ipsec.secrets file to save presharedkey or certificate

: PSK "[password]"
: RSA {
# RSA 2192 bits
# for signatures only, UNSAFE FOR ENCRYPTION
#pubkey=0sAQ......
Modulus: 0xa0........
PublicExponent: 0x03
# everything after this point is secret
PrivateExponent: 0x1a....
}
[Client IP] [Server IP]: PSK "[password]"

· Open the Firewall for UDP port 500 dan PROTO ESP

-A INPUT -i eth0 -p udp --dport 500 -j ACCEPT
-A INPUT -p esp -j ACCEPT