So, as periodically happens to me, what started as an idle curiosity
turned into an experiment. I took a look at a RIB snapshot from
Friday, from one of the RouteViews collectors, to see how common it is
that a block gets advertised by two different ASes, as a whole block
by one, and as a set of smaller blocks by the other.
It turns out there's a non-trivial amount out there -- 490 blocks
broken up, adding 1,815 prefixes announced, accounting for 19,623 RIB
entries. More details below; let me know if you're interested in even
more. Seems kind of interesting, as a form of deaggregation that
doesn't show up in things like the CIDR report (since it's not within
a single AS).
(Standard caveats apply: This is a quick pass, not controlled for
things like two ASes belonging to the same entity.)
--Richard
Total number of deaggregated prefixes: 490
Total additional prefixes advertised: 1815
Total additional RIB entries: 19623 (0.5% out of 3530845 total entries)
Total addresses affected: 78863360 (roughly 1,203 /16s)
Extremal points:
1. Largest deaggregated block: 17.0.0.0/8, advertised by AS7018
(AT&T), deaggregated into two /9s by AS714 (Apple Engineering)
2. Most fractured block: 58.140.0.0/14, advertised by AS3786 (LG
DACOM, KR), deaggregated into 69 prefixes (ranging from /17 to /24) by
AS10036 (C&M Communication, KR).
Distribution of the number of additional prefixes:
Prefixes Count
2 343
3 13
4 80
5 5
6 1
7 4
8 17
9 5
10 1
11 1
14 1
15 1
16 6
17 1
20 2
32 7
34 1
69 1
Distribution of prefix lengths deaggregated:
Len Count
8 1
11 1
12 3
13 9
14 17
15 22
16 47
17 25
18 29
19 65
20 52
21 56
22 69
23 92
24 2
Distribution of the number of addresses affected:
Addresses Count
512 2
1024 92
2048 69
4096 56
8192 52
16384 65
32768 29
65536 25
131072 47
262144 22
524288 17
1048576 9
2097152 3
4194304 1
33554432 1
