Mobile IP with VTUN
This page describes how to set up mobile IP for a mobile host running
RedHat Linux 9 using the VTUN
Mobile IP in the context of this page refers to the ability of a mobile
host to retain the same IP address regardless of its location in the
This has nothing to do with the protocols being developed by the
IETF Mobile IP working group.
On this page, mobile IP is implemented by using a home agent to forward
packets to and from the mobile host. One of the benefits of using mobile
IP is that your TCP connections do not die if your DHCP server gives you a
different IP address, or you move between different networks (such as
wired and wireless).
Note that this setup has only been tested with DHCP-configured interfaces;
it's unknown what other changes may be required (if any) to run mobile IP
over a statically-configured interface.
Here is a picture of the network configuration that the instructions
below try to achieve. You should change all the configuration files
to reflect your own IP addresses.
The dummy0 interface on the mobile host allows the mobile IP
address to be reachable on the mobile host even when the tunnel is down.
There is also a low-precedence default route pointing to the
dummy0 interface which ensures that host unreachable
errors do not happen while the tunnel is being reconfigured.
Here are the steps to set up this mobile IP configuration under RedHat
At this point, you can try bringing down the interfaces on your mobile
host and bringing them back up. The modified dhclient-script
should install a host route for your home agent (server) in the routing
table, and run vtund to set up the tunnel. If vtund
succeeds in setting up the tunnel, it will install a default route going
over the tunnel device.
First, you need to install VTUN
software. You don't need to install the init script on the mobile host
(client), but you do need to install it on the home agent (server).
Download the client VTUN config file and
the server VTUN config file, and install
them on the client and server, respectively, as
/usr/local/etc/vtund.conf. You need to edit both of the
configuration files and change clientname, your-password,
and the mobile IP address, which should be in the same subnet as the home
agent (server). You can leave the other IP address (10.231.11.1) as-is.
If you are running iptables or some other firewall on the home
agent (server), you will need to allow access to TCP and UDP port 5000.
For instance, these commands in /etc/sysconfig/iptables might help:
-A block -p tcp -m tcp --dport 5000 --tcp-flags SYN,RST,ACK SYN -j ACCEPT
-A block -p udp --dport 5000 -j ACCEPT
-A block -p udp --sport 5000 -j ACCEPT
Start the VTUN daemon on the home agent (server), e.g. by running
/etc/init.d/vtund start as root. At this point, you should
be done with the home agent (server) configuration.
Install two scripts on the client machine,
Also, download and install
You need to edit /etc/sysconfig/network-scripts/ifcfg-dummy0
to specify your mobile IP address.
Apply this patch to /sbin/ifup
to prevent an innocuous error message (or download the full
patched version of /sbin/ifup).
Apply this patch to
/sbin/dhclient-script to make DHCP install only a host route
rather than a default route (or download the
full patched version of /sbin/dhclient-script).
You need to edit /sbin/dhclient-script and change
the DEFAULTROUTE variable to the address of your home agent
Lastly, install /sbin/vtun-client.
Edit this file to specify the name of your tunnel (from the
vtund.conf file) and the address of your home agent (server).
If something goes wrong with vtund setting up the tunnel, check
your syslog (e.g. /var/log/messages); vtund is usually
pretty good at logging useful error information there, on both the home
agent (server) and the mobile host (client).
You may want to double-check that your
/etc/sysconfig/network-scripts/ifcfg-XXX files have
PEERDNS set to no; there is no good
reason why you should use the DNS servers supplied by the
DHCP server if your traffic is going through the tunnel.
If you have multiple interfaces up at the same time, it looks like
the Linux routing code will choose the most recently added route.
As a result, your mobile IP traffic will use the most recently