Approach to allocating netblocks

Frank Bulk frnkblk at
Wed Jan 14 16:30:18 UTC 2009

I see what you're saying, but what if the customer whom you assigned the
0/30 to wants a larger block...rather than making them renumber (which in
the case of a small customer, is a very painful experience because of all
the DNS and router/firewall reconfiguration issues that they don't normally
deal with and therefore cause their service provider (us) and their
consultant a lot of grief), I would want to give them 0/29.  But if the 4/30
is already assigned to someone else, I'm stuck.

But perhaps the BCP is to make the customer renumber, in which case I'm
making things more complicated than they need to be.


-----Original Message-----
From: Dave Israel [mailto:davei at] 
Sent: Wednesday, January 14, 2009 10:17 AM
To: frnkblk at
Cc: NANOG list
Subject: Re: Approach to allocating netblocks

If most of your allocations are small, and you don't plan on growing
them very often, you'll probably do better with starting at the ends and
working your way inward.For example,. for /30s, allocate 0/30,  then
4/30,  248/30, and 252/30 before moving in to 8/30, 12/30, 240/30, and
244/30.  That way you're preserving larger netblocks for as long as
possible before breaking them up.

Frank Bulk wrote:
> For the first time we have our own ARIN-assigned netblocks that we can now
> split out and divide to our customers.
> What's the best approach to handing out /30's, /29's, etc. that is
> as possible but allows for customers to expand their allocation to a
> neighboring block?
> I was thinking of having one /24 for each block size, and then do the
> and conquer approach by allocating the first /30, for example, as 0 and
> then next two at 64 and 192, etc.  Once there's only one /30 free between
> each allocation, I would start using another /24.  Of course, that would
> mean 50% (or less) utilization.
> Ideas?
> Frank

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