[WLANware] DHCP servers and Subnets in Wireless Mesh Networks [Mesh Architecture]

[Juergen Neumann]

Hi Naman,

> I am Naman Muley. I am involved with building a wireless community mesh
> network in India. 

That's great! What kind of community network are you planning to deploy?
To what degree do you want to include the community in building the
network?

> I wanted to understand the options for deploying DHCP
> servers in wireless mesh networks. I wanted your opinions as the freifunk
> community is highly active and experienced with mesh deployments.

Yes. We are building distributed networks. We are also distributing the
ownership of the network. So that the people own their own and maintain
their routers. The DHCP servers are comletely decentralized.

> I understand that mesh nodes are all layer 3 routers. Generally, in a wired
> network, we have one single DHCP server for the whole network and DHCP
> relay agents at various routers down the heirarchy.

That does not sound like a distributed network, but rather like a top
down aproach. If you want a centralized service like a single DHCP
server, you should focus on batman-advanced. This is a layer 2 aproach
which is ideal for such an infrastructure.

> 1. Should a wireless mesh network big enough to cover a campus (for
> starters) have one huge subnet or multiple subnets

This highly depends on your social model. If you are planning a top-down
network network design, then you should go for one big subnet. But if
you are planning for a buttom-up distributed peer-to-peer network, then
you should think of multible subnets.

> 2. A central DHCP vs multiple DHCP's assigning addresses from different
> subnets?

See 1.

> 3. If we do have multiple subnets, how is the mobility affected? I mean,
> because once you get an IP address from a subnet, you get a default gateway
> in that subnet also. Once you move out of the range of that subnet's
> router(s), how do hosts maintain connectivity?

I your end-users are able to run the mesh-software (OLSR or batman) on
their devices, then this is no problem, because they can choose a fixed
gateway with both applications. If they are just "stupid" dhcp clients,
then once again batman-adavanced as a layer 2 protocol would be the
reasonable choice. 

> 4. In case we use IP handoff for the above problems, I'd be very greateful
> if you could point me to the implementations for the same.

See 3.

> 5. How do you do it in Freifunk? If you have some ip registry links or
> architecture links, I'd really really appreciate it!

We are running quite chaotic networks. Our focus is not so much on
seamless handover, but to provide maximum freedom and resposibily to
every single individual node-owner. We want to run distributed networks
to the maximum degree that is possible. Some things will not work in
these kinds of networks, such as seamless handover to dhcp clients. But
that is not our main focus. We just want to be as decentralized as
possible. 

> Thank you so much for all the efforts! I appreciate any help from the
> community!

What exactly are you planning? Are you heading for a infrastructure you
are planning for the community, or do you want to include the community
in setting up and building this infrastructure?

Greets from Berlin!

JuergeN