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206.0.0.0/8 and /19s

  • From: Sean Doran
  • Date: Sat Sep 23 18:26:17 1995

After much discussion with many different people,
including some at registries, I have modified our
filter-list to accept /19s in the 206.0.0.0/8 block.

The change will take effect upon the next clearing of
exterior BGP sessions with our various neighbours.

Note that there will be no further relaxtion of
the /19 limit, and that the principal reasoning
behind the change from /18 to /19 for this block
is as follows:

	-- a miscommunication between me and various
	   registries several months ago which led
	   to registries and perhaps some providers
	   handing out some /19s that they honesty
	   expected would pass through the filters;
	   the fact that they did, to some extent,
	   due to the minor implementation glitch
	   on this side, exacerbated the problem.

	-- several people have aggregated long prefixes
	   into /19s (thank you) and find that they
	   cannot reasonably do further aggregation
	   to /18s due to various allocation policies.


This change increases the number of prefixes AS1239 will
route towards by 129, all of which are /19s, and many of
which can and should be aggregated into even shorter
prefixes.  

Note that this will not help anyone who is announcing
anything longer than a 19-bit prefix in the 206.0.0.0/8
range, nor anyone who is expecting to be able to
announce /19s in 207.0.0.0/8 - 239.0.0.0/8.

At this time, I don't intend to have AS1239 routers accept
/19s in those blocks from its external peers, nor do
I expect to increase the maximum length of the prefixes
accepted from 206.0.0.0/8 beyond that which registries
were allocating as part of their slow-start scheme
with the expectation that /19s probably were short 
enough that they would stay routable everywhere.

	Sean.
- --
Sean Doran <smd@sprint.net>