keeping the routing table in check: step 1

Edward B. DREGER eddy+public+spam at
Thu Feb 16 03:48:24 UTC 2006

Hopefully this thread will be quick and less convoluted.  Rather than 
simply alluding to "one prefix per ASN", I'd like to detail an 
allocation scheme that works toward that.

Find the largest contiguous block.  Split in half.  Round to appropriate 
boundary.  Assign.  Space at the end of the block is reserved for 

Ignoring special subnets for simplicity:

0/x, 128/x,
64/x, 192/x,
32/x, 96/x, 160/x, 224/x,
16/x, 48/x, 80/x, 112/x, 144/x, 176/x, 208/x

assuming all grow at equal rates.  96/x ends up growing quickly?  No 
problem.  Skip 112/x for the time being.

In short, allocate IP space logarithmically.  Start with /1 alignment, 
proceed to /2, then /3, and so on.  Keep the array as sparse as possible 
so an assignment can be extended without hitting, say, a stride 4 

Perhaps RIRs should look at filesystems for some hints.  Imagine a 
filesystem that's 30% full yet has as much fragmentation as IPv4 space. 
Something is wrong.

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