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Setup OpenConnect VPN Server for Cisco AnyConnect on Ubuntu 14.04 x64

Published on: Tue, Mar 10, 2015 at 1:11 pm EST

OpenConnect server, also known as ocserv, is a VPN server that communicates over SSL. By design, its goal is to become a secure, lightweight, and fast VPN server. OpenConnect server uses the OpenConnect SSL VPN protocol. At the time of writing, it also has experimental compatibility with clients that use the AnyConnect SSL VPN protocol.

This article will show you how to install and setup ocserv on Ubuntu 14.04 x64.

Installing ocserv

Since Ubuntu 14.04 does not ship with ocserv, we will have to download the source code and compile it. The latest stable version of ocserv is 0.9.2.

Download ocserv from the official site.

wget ftp://ftp.infradead.org/pub/ocserv/ocserv-0.9.2.tar.xz
tar -xf ocserv-0.9.2.tar.xz
cd ocserv-0.9.2

Next, install the compile dependencies.

apt-get install build-essential pkg-config libgnutls28-dev libwrap0-dev libpam0g-dev libseccomp-dev libreadline-dev libnl-route-3-dev

Compile and install ocserv.

./configure
make
make install

Configuring ocserv

A sample config file is placed under the directory ocser-0.9.2/doc. We will use this file as a template. At first, we have to make our own CA cert and server cert.

cd ~
apt-get install gnutls-bin
mkdir certificates
cd certificates

We create a CA template file (ca.tmpl) with the content similar to the following. You can set your own "cn" and "organization".

cn = "VPN CA" 
organization = "Big Corp" 
serial = 1 
expiration_days = 3650
ca 
signing_key 
cert_signing_key 
crl_signing_key 

Then, generate a CA key and CA cert.

certtool --generate-privkey --outfile ca-key.pem
certtool --generate-self-signed --load-privkey ca-key.pem --template ca.tmpl --outfile ca-cert.pem

Next, create a local server certificate template file (server.tmpl) with the the content below. Please pay attention to the "cn" field, it must match the DNS name or IP address of your server.

cn = "you domain name or ip"
organization = "MyCompany" 
expiration_days = 3650 
signing_key 
encryption_key
tls_www_server

Then, generate the server key and certificate.

certtool --generate-privkey --outfile server-key.pem
certtool --generate-certificate --load-privkey server-key.pem --load-ca-certificate ca-cert.pem --load-ca-privkey ca-key.pem --template server.tmpl --outfile server-cert.pem

Copy the key, certificate, and config file to the ocserv config directory.

mkdir /etc/ocserv
cp server-cert.pem server-key.pem /etc/ocserv
cd ~/ocserv-0.9.2/doc
cp sample.config /etc/ocserv/config
cd /etc/ocserv

Edit the config file under /etc/ocserv. Uncomment or modify the fields described below.

auth = "plain[/etc/ocserv/ocpasswd]"

try-mtu-discovery = true

server-cert = /etc/ocserv/server-cert.pem
server-key = /etc/ocserv/server-key.pem

dns = 8.8.8.8

# comment out all route fields
#route = 10.10.10.0/255.255.255.0
#route = 192.168.0.0/255.255.0.0
#route = fef4:db8:1000:1001::/64
#no-route = 192.168.5.0/255.255.255.0

cisco-client-compat = true

Generate a user that will be used to login to ocserv.

ocpasswd -c /etc/ocserv/ocpasswd username

Enable NAT.

iptables -t nat -A POSTROUTING -j MASQUERADE

Enable IPv4 forwarding. Edit the file /etc/sysctl.conf.

net.ipv4.ip_forward=1

Apply this modification.

sysctl -p /etc/sysctl.conf

Start ocserv and connect using Cisco AnyConnect

First, start ocserv.

ocserv -c /etc/ocserv/config

Then, install Cisco AnyConnect on any of your devices, such as iPhone, iPad, or an Android device. Since we used a self-signed server key and certificate, we have to uncheck the option which prevents insecure servers. This option is located in the settings of AnyConnect. At this point, we can setup a new connection with the domain name or IP address of our ocserv and the username/password that we created.

Connect and enjoy!

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