IPSec between Linux and the NetScreen

VPNs are a fine thing, especially if you are not at home and you need to access your beloved network. I am using VPN connections since I have implemented them at my Pfsense using openvpn.

Since I got my NetScreen/Juniper SSG5 here, I cannot use Openvpn anymore - So I was forced to dig into IPSec stuff. My laptop will be the roadwarrior connecting to my home. That’s why I have to do it the DialUp way, which doesn’t really include a modem. DialUp connections are connections, initiated by the client.

Our environment:

• Netscreen: 1.2.3.4
• Roadwarrioir: 172.16.1.2
• Private Network: 192.168.10.0/24

• User: myuser
• IKE ID: user@host.com
• Group: dialupusers
• Preshared Key: secret

Users & Groups

set user "myuser" ike-id u-fqdn "user@host.com" share-limit 1 set user "myuser" type ike set user "myuser" "enable" set user-group "dialupusers" user "myuser"

Auto-IKE VPN and Policy

set ike gateway "dialupvpn" dialup "dialupusers" Aggr outgoing-interface "ethernet0/0" preshare "secret" proposal "pre-g2-3des-sha" set ike gateway "dialupvpn" nat-traversal set ike gateway "dialupvpn" udp-checksum set vpn "dialupvpn" gateway "dialupvpn" no-replay tunnel idletime 0 proposal "g2-esp-3des-sha" set address "Trust" "192.168.10.0/24" 192.168.10.0 255.255.255.0 set policy top from "Untrust" to "Trust" "Dial-Up VPN" "192.168.10.0/24" "ANY" Tunnel vpn "dialupvpn" log

Believe it or not, but that’s all folks - nothing more to do on the NetScreen except for ‘save’ and ‘quit’ for signing off. Our next stop is the linux box, having the ipsec tools already installed. The Gentoo Package would be net-firewall/ipsec-tools.

Regarding the kernel, please make sure, the following options are available - either as a module or compiled into:

• PF_KEY sockets (CONFIG_NET_KEY)
• AH transformation (CONFIG_INET_AH)
• ESP transformation (CONFIG_INET_ESP)
• IPCOMP transformation (CONFIG_INET_IPCOMP)
• DES, SHA1, (etc) from Crypto API

Our pre-shared key (PSK) used in the NetScreen config has to be filled into /etc/racoon/psk.txt to be assigned to a vpn connection. /etc/racoon/psk.txt:

# ipv4/ipv6 adresses
1.2.3.4        abc123

Regarding target hosts we’d like to connect to, they have to be defined in the racoon.conf file… /etc/racoon/racoon.conf:

# Pre-shared key
path pre_shared_key "/etc/racoon/psk.txt";
Remote host
remote 1.2.3.4
{
exchange_mode aggressive;
my_identifier user_fqdn “user@host.com”;
proposal {
encryption_algorithm 3des;
hash_algorithm sha1;
authentication_method pre_shared_key;
dh_group modp1024;
}
}
A sample sainfo section
Create one for each subnet you want to access, etc.
sainfo address 172.16.1.2 any address 192.168.10.0/24 any
{
pfs_group modp1024;
encryption_algorithm 3des;
authentication_algorithm hmac_sha1;
compression_algorithm deflate;
}

… which are used in the ipsec.conf to tell the kernel where to send the packets to. /etc/ipsec.conf:

#!/usr/sbin/setkey -f
flush;
spdflush;
outbound
spdadd 192.168.2.0/24 192.168.10.0/24 any
-P out ipsec esp/tunnel/172.16.1.2-1.2.3.4/require;
inbound
spdadd 192.168.10.0/24 192.168.2.0/24 any
-P in ipsec esp/tunnel/1.2.3.4-172.16.1.2/require;

Now save the config files and start the connection. But don’t be shocked if it doesn’t work at the first packet - that’s a common ‘problem’ as authentication has to be done first. But if 15 seconds or more have passed without success, it’s time to have a look at the logfiles.