[AusNOG] Unadvertised large IPv4 allocations in the APNIC region

Julien Goodwin ausnog at studio442.com.au
Thu Oct 21 23:16:09 EST 2010

Just a little experiment, but hopefully of some interest to people here.

The full post is on livejournal, but the first few paragraphs are below.


A few days ago I wondered how many of the large (/16 through /9)[1][2]
IPv4 allocations were laying unused.

Armed with a copy of the APNIC whois data (An old one from the end of
March this year) that I had lying around on my laptop, and a fresh dump
of BGP routes from one of my border routers[3] (Monday night) I set to work.

>From the whois DB I extracted 2,666 allocations, but as I've done no
hand-verification there could be justified reasons for some of the
unused routes. In at least one case it appears the blocks may since have
been handed back, although given the size of the block in question (it's
the /9 that's unannounced) I'd have expected at least some noise on one
of the ops or RIR lists. Given the age of the DB any new allocations are
most likely announced by now removing one source of error.

Then I simply matched my list of known allocations against the BGP
tables looking for *any* route of that prefix, or longer (Valid source
of error here if multiple contiguous blocks announced as a supernet, we
often do this at work with a few of our /23's that were originally
allocated as a pair of /24's). There's another issue that as *any* route
is enough for me even a single /24 is enough for me to consider an
entire /9 "in use".

Overall the allocations are very highly advertised, with only 13.5% of
allocations unadvertised completely (on the public Internet, it's
impossible to know how many may actually be in use behind NAT's).
Converted into individual address that drops to 7.8%, much better then
the Internet as a whole which sees roughly 38%[4] of allocations
unadvertised. My numbers are so good for two reasons, first the
aforementioned use of a single route (potentially a /24) to be enough
for even a /9; second, as these blocks are larger they're far more
likely to be assigned to people more serious about their networks, and
even if they went out of business their network was likely sold as an asset.

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