I'm setting up a development machine which runs Ubuntu 12.04 and KVM for virtualization. I have a guest running Ubuntu 12.04 which can be accessed from the host via its IP address which is assigned by libvirt. The guest can also access the internet, no problem there.

However, now I want to setup PPTP so I can connect to the host (from my workstation running Windows 7) and directly access guests without relying on SSH port forwarding.

I can connect from my W7-machine to the host (PPTP), but I cannot access any virtual machines (which are accessable from the host directly).

Relevant configuration files

cat /etc/network/interfaces

auto lo
iface lo inet loopback

# device: eth0
auto  eth0
iface eth0 inet static
  address   x.x.x.x
  broadcast x.x.x.x
  netmask   x.x.x.x
  gateway   x.x.x.x

# default route to access subnet
up route add -net x.x.x.x netmask x.x.x.x gw x.x.x.x eth0

virsh net-edit default

<network>
  <name>default</name>
  <uuid>xxxxxxxx-72ce-3c20-af0f-d3a010f1bef0</uuid>
  <forward mode='nat'/>
  <bridge name='virbr0' stp='on' delay='0' />
  <mac address='52:54:00:xx:xx:xx'/>
  <ip address='192.168.122.1' netmask='255.255.255.0'>
    <dhcp>
      <range start='192.168.122.2' end='192.168.122.254' />
      <host mac='52:54:00:yy:yy:yy' name='web1' ip='192.168.122.11' />
    </dhcp>
  </ip>
</network>

cat /etc/pptpd.conf (commented lines removed)

# TAG: option
#   Specifies the location of the PPP options file.
#   By default PPP looks in '/etc/ppp/options'
#
option /etc/ppp/pptpd-options

# TAG: logwtmp
#   Use wtmp(5) to record client connections and disconnections.
#
logwtmp

#(Recommended)
localip 192.168.122.1
remoteip 192.168.122.234-238,192.168.122.245

cat /etc/ppp/chap-secrets*

# Secrets for authentication using CHAP
# client    server  secret          IP addresses
xxxxx       *       yyyyyyyyyy              192.168.122.100

I get the correct IP address when connecting my W7-machine, but when I try to ping the virtual machine at 192.168.122.11 I get

Reply from 192.168.122.1: Destination port unreachable.

It's probably something trivial I'm missing but I can't for the life of me figure out what it is. So I'm turning to you, serverfault.