[189014] in North American Network Operators' Group
Superfluous advertisement (was: Friday's Random Comment)
daemon@ATHENA.MIT.EDU (Jakob Heitz (jheitz))
Sat Apr 30 15:10:49 2016
X-Original-To: nanog@nanog.org
From: "Jakob Heitz (jheitz)" <jheitz@cisco.com>
To: "nanog@nanog.org" <nanog@nanog.org>
Date: Sat, 30 Apr 2016 19:10:44 +0000
Errors-To: nanog-bounces@nanog.org
A use case for a longer prefix with the same nexthop:
F
/ \
D E
| |
B C
\ /
A
Suppose A is a customer of B and C.
B has a large address space: 10.1.0.0/16.
B allocates a subset to A: 10.1.1.0/24.
B advertises the longer prefix to its backup provider C.
C propagates it to E and then to F.
B MUST advertise both 10.1.0.0/16 and 10.1.1.0/24 to D.
D MUST propagate both of them to F.
Otherwise, if F only receives 10.1.0.0/16 from D, then
F will have the longer match 10.1.1.0/24 to E,
but E is only the backup route.
Thanks,
Jakob.
> -----Original Message-----
> Date: Fri, 29 Apr 2016 08:17:41 -0400
> From: Alain Hebert <ahebert@pubnix.net>
> To: "'NANOG list'" <nanog@nanog.org>
> Subject: Friday's Random Comment - About: Arista and FIB/RIB's
> Message-ID: <00ea292f-e779-25ad-ce89-eae897e9516d@pubnix.net>
> Content-Type: text/plain; charset=3Dutf-8
>=20
> While following that Arista chat... That reminded me of that little
> afternoon project years ago.
>=20
> So I decided to find new hamsters, fire up that VM, refresh the DB's and
> from the view point of a tiny 7206VXR/G1 with 2 T3 peers...
>=20
> The amount of superfluous subnet advertisement drop to ~120k from
> ~166k from the previous snapshot.
>=20
> And this is the distribution by country.
>=20
> country | superfluous
> --------------------+-------------
> United States | 28254
> Brazil | 10012
> China | 7537
> India | 6449
> Russian Federation | 4524
> Korea, Republic of | 4062
> Saudi Arabia | 3297
> Australia | 2989
> Indonesia | 2878
> Hong Kong | 2251
> Thailand | 2093
> Canada | 2019
> Taiwan | 1955
> Ukraine | 1877
> Singapore | 1856
> Bulgaria | 1488
> Argentina | 1436
> Japan | 1403
> Mexico | 1351
> Chile | 1271
>=20
> (Damn Canada, can't break top 10 again).
>=20
> PS: "Superfluous" is a nice way to say that the best path of a
> subnet is the same as his supernet. And yes I'm aware of the Weekly
> Routing Report, I was just curious to see it by country =3DD.
>=20
> -----
> Alain Hebert ahebert@pubnix.net
> PubNIX Inc.
> 50 boul. St-Charles
> P.O. Box 26770 Beaconsfield, Quebec H9W 6G7
> Tel: 514-990-5911 http://www.pubnix.net Fax: 514-990-9443
