[MLB-WIRELESS] Route Aggregation and IP Allocation

[Dan Flett]

Returning to the issue of Route Aggregation and IP Allocation - I believe 
there is a way to allocate IP addresses in a Metropolitan-Area-Network like 
ours that has a hope of working - and that is to scrap the existing system 
allow the existing (and future) network clusters to apply for large slices 
of the overall metropolitan supernet, and then allow the clusters to slice 
their allocation into smaller networks.

This is a "bottom-up" approach - the overall 10.10.0.0/16 supernet that 
Melbourne Wireless uses should remain unallocated until a cluster applies 
for a slice.  It could then be allocated a /23 or /24, which the cluster 
would then, under it's own local administration, slice into /28s for local 
nodes.

Currently we have taken a "top-down" approach to IP allocation.  We have 
sliced Melbourne into 11 geographic regions based on expected areas of 
internal connectivity.  The regions have had /20 supernets assigned to them 
from Melbourne Wirleless's 10.10.0.0/16.  Some of these regions are very 
large - RGSouthern and RGPeninsula for example, and have more than one 
network cluster within their geographic borders.  The nodes within the 
Region Group have had /28 subnets assigned to them without regard as to 
which cluster they are in within that Region.  Each cluster usually only has 
one or two uplinks providing extra-cluster connectivity, but because there 
are multiple clusters sharing subnets from the same /20 allocation pool, it 
is impossible to aggregate the routes on a per-cluster basis.  The 
"bottom-up" approach solves this problem.

In our existing network, which the clusters the way they are, we would 
simply allow existing network clusters to work out for themselves that they 
are a cluster, and where the borders should be drawn.  The node-owners in 
that cluster could then give themselves a name.  Council or suburb names 
would be a good idea.  The cluster centred around Vaskos' Node BHH could be 
called Coburg.net.  The cluster that my node (GMR) is in could be called 
Glen-Eira.net.  Just some ideas...  I don't think it would be a problem 
using suburb names - there are plenty of businesses and community groups 
that use suburb or council names and I don't think they need the permsission 
of their Local Council to do so.

Unfortunately, implementing this idea would involve everyone having to give 
up their IP addresses and us all starting over again.  Of course this would 
cause massive upheaval and may kill the network that we have built so far.  
So I don't suggest that we should jump into doing something like this 
lightly.  Perhaps someone can suggest a way of migrating to such a system 
over time.

Anyway, something to think about and discuss.  This is basically a similar 
problem to the problem the Internet itself had in the early 90's.  The 
result was the invention of Classless-Inter-Domain-Routing (CIDR), which 
made IP address allocation more efficient.  While we aren't running out of 
IP space, we are having problems aggregating our routes.  We have the 
benefit of hindsight and can hopefully deal with the problem without too 
much pain.

Here's a link that explains CIDR:
http://public.pacbell.net/dedicated/cidr.html

Cheers,

Dan



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