Configure a separate network for a VMware lab

A new VMware lab was needed: it should be completely separated by production network and, in the same time, should be accessible by remote workstations. This time a VPN approach was used: lab_diagram A Linux server provides connectivity to lab networks ( Each client can reach the lab networks using a VPN (PPTP) connection terminating on the Linux gateway. Everything inside the lab networks cannot see outside world: the Linux gateway acts as a firewall too.

Using this approach routing of corporate network has not been modified.

Configuring Linux networking

The Linux server uses eth0 to reach the corporate network ( and eth1 to reach the lab (

# cat /etc/sysconfig/network-scripts/ifcfg-eth1

The gateway will be used to route all lab networks, summarized in

# cat /etc/sysconfig/network-scripts/route-eth1 via

Be sure that Linux gateway can route traffic:

# cat /etc/sysctl.conf | grep ip_forward
net.ipv4.ip_forward = 1
# sysctl -p

Installing and configuring PPTP daemon

There are many VPN tunnels available, but the most simple and ready to use is PPTP, provided on Linux by PopTop. PopTop repository and install both ppp and ppptpd packages:

# rpm -Uvh pptpd-1.4.0-1.rhel5.i386.rpm ppp-2.4.4-14.1.rhel5.rpm

In our example, clients will use ip address range:

# cat /etc/pptpd.conf
option /etc/ppp/options.pptpd

The mppe encryption is not supported on some distributions; because it’s a VPN connection through a corporate network used for test purposes, encryption can be disabled:

# cat /etc/ppp/options.pptpd | grep mppe

Then create required user(s):

# /etc/ppp/chap-secrets
# Secrets for authentication using CHAP
# client        server  secret                  IP addresses
user            pptpd   password                *

Finally start PPTP daemon:

# service pptpd start
# chkconfig pptpd on

Configure the Linux firewall

Lab networks cannot be reach the outside world, except for DHCP and TFTP services:

# iptables -A INPUT -s -d -i eth1 -j ACCEPT
# iptables -A INPUT -i eth1 -p udp -m udp --dport 69 -j ACCEPT
# iptables -A INPUT -i eth1 -p udp -m udp --dport 68 -j ACCEPT
# iptables -A INPUT -i eth3 -j REJECT --reject-with icmp-port-unreachable
# iptables -A INPUT -i eth3 -j DROP

The REJECT keywords will prevent timeout when requests start from inside the lab.

If lab must connect to outside networks, NAT (MASQUERADE) is required:

# iptables -A POSTROUTING -o bond0 -j MASQUERADE
# iptables -A FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT
# iptables -A FORWARD -d -i eth3 -p udp -m udp --dport 8080 -j ACCEPT
# iptables -A FORWARD -i eth3 -j REJECT --reject-with icmp-port-unreachable
# iptables -A FORWARD -i eth3 -j DROP

Configuring a Windows client

The configuration is very simple:

  1. add a new VPN connection, use PPTP as VPN type with no cryptography;
  2. configure the IP address of the Linux gateway (;
  3. use the account previously configured (admin:)
  4. be sure “Use default gateway on remote network” is unchecked (under Advanced TCP/IP settings configuration);
  5. be sure “Disable class based route addition” is unchecked.

After connecting the client should be able to reach the network because of the route is installed:

C:\Windows\system32>route print | find ""     11