[j-nsp] Summarize Global Table

[Pavel Lunin]

> The removal of a large aggregate (say 4/8) and the subsequent required
> addition of all of the subnets under 4/8 could certainly be
> 'interesting' to observe.
> Interesting as well is that 4/8's origin doesn't have to be the flapper,
> just your network (or an intermediate) changing attributes (or exit
> path!) could be enough to induce this problem, no?
Right! This's why it's not bad to play with it around and see whether 
this simple idea really works as expected in real-life.

On one hand 4/8 withdrawal or change should not be worse than installing 
some part of the full table. Very-very roughly, /8 is about 1/200 of the 
full table, which is ~2000 prefixes by now (can be checked but I'm too 
lazy). Not so few but looks acceptable in case a /8 flaps. On the other 
hand, I personally wouldn't try to predict, how often this can happen 
with longer aggregate prefixes for the full table overall, and whether 
it's acceptable. If someone thinks it's obvious — I'd like to hear the 
explanation.