[MLB-WIRELESS] IP Allocations

Dan Flett conhoolio at hotmail.com
Thu Nov 25 18:00:06 EST 2004

 > Once two areas want to join, they have to establish who between those
> areas
> become the ABR's and create an area 0 between them.
> Once a 3rd area wants to join, again they have to work out who that
> will link to their area 0 which may require some people becoming area
0 to
> make this possible.
> >Hmm but won't this break if you get connected to another area, say
> >8. Doesn't OSPF try and run everything via area 0 to the other
> >

I've done some very brief testing that indicates that Quagga's OSPF
doesn't seem to break when two non-area-0 areas join.  I've been using
"area X range a.b.c.d/20" definition so that ABRs advertise /20 summary
routes for whole areas to other areas.  It seems to work in the absence
of Area 0.  That's not to say that other OSPF implementations will work,
just that Quagga doesn't appear blow up without Area 0.

Whilst it's not looking like happening soon, I think it's good to think
about what we will do when three or more Areas join.  After all, that's
what the whole mission of Melbourne Wireless is.  It may be that a whole
lot of areas connect along their physical borders with no obvious
central point of connection between any of them.  I'd suggest at that
point that we just see what happens with OSPF before defining Area 0.
See if it really does break or not.

If we decide we do need Area 0 I'd suggest allocating IP addresses for
it for backbone connections outside the address ranges for the existing
areas, but still within the supernet.  With no central
point of connection we may have little pockets of Area 0 all over the
place.  At that point we would need to start defining OSPF Virtual links
- OSPF definitely doesn't like Area 0 to be fragmented in little pockets
- all the Area 0 routers have to be physically linked in one area or
virtually linked via other areas.

If that sounds like too much work we could simply find the physical
"centre of gravity" of the connected areas and call it and it's routers
Area 0.

With all this in mind, I think it's important to realise that the best
way to grow the network is to make it easier to access.  Part of this is
making OPSF easier to understand and making building a node easier.  A
generic Quagga/OSPF config file that a budding Melbourne Wireless
node-owner can just 'drop-in' and use straight away is worth
investigating.  Hopefully we can achieve this without making routing
less stable.


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