This article is adapted from https://www.v2ex.com/t/180070 and http://hjc.im/shi-yong-strongswanda-jian-ipsecikev2-vpn/. The major difference is ShadowVPN is replaced by StrongSwan IPsec VPN in this article.
Readiness Check
- Upgrade your staging/production environment to the latest version. Make sure all security patches are installed.
- Make sure you have packages libpam0g-dev libssl-dev make gcc installed.
Building StrongSwan
Download the latest version here: http://download.strongswan.org/strongswan.tar.gz
Unarchive it, and configure using the following params:
./configure --enable-eap-identity --enable-eap-md5
--enable-eap-mschapv2 --enable-eap-tls --enable-eap-ttls --enable-eap-peap
--enable-eap-tnc --enable-eap-dynamic --enable-eap-radius --enable-xauth-eap
--enable-xauth-pam --enable-dhcp --enable-openssl --enable-addrblock --enable-unity
--enable-certexpire --enable-radattr --enable-tools --enable-openssl --disable-gmp --enable-kernel-libipsec
We have to specify routing table’s priority on client server(not IPsec Access Server) since we wants to specify routing table manually: –with-routing-table-prio=32800. Also, TAP/TUN device is enabled instead of StrongSwan’s own kernel module. It will simplify the configuration later.
Then make and install it.
Configure IPsec Access Server
Just a reminder, if you have any issues about IP range, please refer to the demo topology graph. The image is unavailable right now for some reason. I’ll fix it ASAP.
Go to /usr/local/etc. Edit ipsec.secrets:
: PSK "<IPsec PRE SHARED KEY, PLEASE REMEMBER TO REPLACE IT WITH YOU OWN KEY>"
s2s : XAUTH "<ANY PASSWORD YOU WANT, PLEASE REMEMBER TO REPLACE IT WITH YOU OWN PASSWORD>"
Go to /usr/local/etc. Edit ipsec.conf:
config setup
uniqueids=never
conn s2sbj1_xauth_psk
keyexchange=ikev1
left=%defaultroute
leftauth=psk
leftsubnet=0.0.0.0/0
right=%any
rightauth=psk
rightauth2=xauth
rightsourceip=100.11.2.0/24
auto=add
Go to /usr/local/etc. Edit strongswan.conf:
charon {
load_modular = yes
duplicheck.enable = no
compress = yes
plugins {
include strongswan.d/charon/*.conf
}
# In China, please consider about replacing 8.8.8.8/8.8.4.4 to 114.114.114.114. They do offer correct DNS query results outside mainland China, as long as you have configured the Chinese routing exception for it(route to non-mainland China outbound server)
dns1 = 8.8.8.8
dns2 = 8.8.4.4
nbns1 = 8.8.8.8
nbns2 = 8.8.4.4
}
include strongswan.d/*.conf
Turn on IPv4 forwarding in sysctl.conf.
Edit iptables. The following configuration is for Ubuntu 14.04 LTS. For other Linux distro, check out its documentation.
iptables -A FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -A FORWARD -s 100.11.0.0/24 -j ACCEPT
iptables -A FORWARD -s 100.11.1.0/24 -j ACCEPT
iptables -A FORWARD -s 100.11.2.0/24 -j ACCEPT
iptables -A INPUT -i eth0 -p esp -j ACCEPT
iptables -A INPUT -i eth0 -p udp --dport 500 -j ACCEPT
iptables -A INPUT -i eth0 -p tcp --dport 500 -j ACCEPT
iptables -A INPUT -i eth0 -p udp --dport 4500 -j ACCEPT
iptables -A INPUT -i eth0 -p udp --dport 1701 -j ACCEPT
iptables -A INPUT -i eth0 -p tcp --dport 1723 -j ACCEPT
iptables -A FORWARD -j REJECT
iptables -t nat -A POSTROUTING -s 100.11.0.0/24 -o eth0 -j MASQUERADE
iptables -t nat -A POSTROUTING -s 100.11.1.0/24 -o eth0 -j MASQUERADE
iptables -t nat -A POSTROUTING -s 100.11.2.0/24 -o eth0 -j MASQUERADE
Save it
iptables-save > /etc/iptables.rules
cat > /etc/network/if-up.d/iptables<<EOF
#!/bin/sh
iptables-restore < /etc/iptables.rules
EOF
chmod +x /etc/network/if-up.d/iptables
Configure IPsec client
Suppose you have the correct StrongSwan with TAP/TUN and routing table priority installed.
Go to /usr/local/etc, edit ipsec.secrets, just put what you have in the previous step.
Go to /usr/local/etc, edit ipsec.conf:
config setup
uniqueids=never
strictcrlpolicy=no
conn s2sbj1
keyexchange=ikev1
ikelifetime=1440m
keylife=120m
# Enable this will cause authentication failure
aggressive=no
ike=aes-sha2-modp2048
esp=ase-sha2
xauth=client
left=<eth0's IP address>
# Ask your server
leftsourceip=%config
leftauth=psk
leftauth2=xauth
rightauth=psk
rightauth2=xauth
right=<Your IPsec VPN Server's public IP address>
# For Microsoft Azure and other service providers who use SNAT, specify that to prevent IKE_SA failure
rightid=%any
xauth_identity=s2s
auto=add
rightsubnet=0.0.0.0/0
Establish Connection
On your IPsec VPN server, type sudo ipsec start .
On your client server, type:
sudo ipsec start
sudo ipsec up s2sbj1
It should get connected shortly. Go to ifconfig and you should find a new network adapter called ipsec0.
Configure rule-based routing
Create a new routing table.
user@ibntwkstgepbj1:~$ sudo vim /etc/iproute2/rt_tables
200 bj1s2s
:q
user@ibntwkstgepbj1:~$
Get the routing configuration in table 220 (IPsec table).
user@ibntwkstgepdm1:~$ sudo ip route list table 220
default dev ipsec0 proto static src 100.11.2.1
42.159.66.233 via 10.0.0.1 dev eth0 proto static src 10.0.0.4
Specify the default route for this table (copy it from 220):
user@ibntwkstgepdm1:~$ sudo ip route add default dev ipsec0 proto static src 100.11.2.1 table bj1s2s
(You don’t have to copy the second line I guess, but I added that)
Add IP rules.
user@ibntwkstgepdm1:~$ ip rule add from <IP Range> table bj1s2s
Refresh routing table.
user@ibntwkstgepdm1~$ ip route flush cache
Compose a shell script if you want to compelte that automatically for every reconnection.
Conclusion
We implemented a simple line optimization using rule-based routing in this example. For application-based service, you are all set and ready to go. For VPN access services, configuration for iptables is needed in order to tag data packets and route them correctly. Check out this article for more details.
I didn’t offer a auto routing script in this example. I strongly recommend you to write it since it saves your time by configuring routing table automatically.
For multiple IPsec connections and routings, just specify the source IP, which is 100.11.2.1 and 100.21.2.1 in routing tables. They use the same adapter.
AnyConnect client refused to use smartcard
