Transparent Mobile IP update

Simon Chudley sly at
Fri Mar 28 06:22:25 EST 2003


Just a quick update on the transparent mobile IP software that has
been discussed in a recent thread, (WDS links & P2P mode posted by
Mike Saywell). We think it may be of interest to anybody looking
at a lightweight (client wise) solution to mobility across multiple
subnets. At least it seems to solve some of the problems we came
across :-)

In brief, the mobile network consists of a series of correspondent
nodes (CNs), a single mobile location register (MLR) and lots of
dumb mobile clients. Essentially, each CN runs on the border gateway
between mobility-equipped cells (i.e. on a machine doing routing
with an access point attached.

As Mike mentioned, new clients are detected in a cell, and assigned
a /30 network (single cell subnet), which they will keep through
that 'mobile session' (in fact they can keep/reserve this allocation
forever, enabling static-ish IPs for mobile hosts wherever they may
be located at a given time in the network).

They can then migrate between cells, being detected by new CNs
(various methods to do this, plan to directly hook this into HostAP
in the near future for speedy handovers), upon which the network
will 'mutate' to serve that host (i.e. tunnels established to parent
CN, destruction of tunnels to the CN they just migrated from etc.)

Main point being that the client is just any IPv4 device, it need
not even know it is mobile; hence no client software. The only thing
the client knows is that their gateway's MAC address appears to
change occasionally :-) The MLR sits there being 'the all knowing
entity', updating as hosts migrate and providing information such
as IP allocations in cells etc. So, this is a great resource for
assessing network load/usage/seeing if your mates are bound to the
same access point and such other useful things!

A few niceties: transactional (distributed two phase commit) handovers
between cells (won't leave network in inconsistent state, hopefully!),
integrated DHCP sever (eventually), pretty nippy handovers (should
be lots quicker once HostAP integration is in), support for different
types of tunnels (could have CNs negotiating to use a compressed
tunnel for example), IP allocation at MLR, so you can use an external
admin app to control/visualise the entire network (got a prototype
client to do this with pretty graphics ;)

As Mike said, it should be up on Sourceforge over the next week,
just ironing it out a bit and doing a quick howto before it goes
public, and will mail to this list when done. Stability wise, it's
getting there. Basically, we plan to run it in a test state on a
few embedded PCs on top of a couple of buildings soon, but it is a
bit bare on the docs/nice interface kinda things.

Hopefully this kind of approach fits into some of the deployment
plans of people on this list, and I hope it will be of use to some
groups. HostAP integration is the next step!

In the mean time, questions welcomed, either by email or IRC, see



Southampton Open Wireless Network

More information about the HostAP mailing list