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=utf-8
While following that Arista chat... That reminded me of that little afternoon project years ago.
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...
The amount of superfluous subnet advertisement drop to ~120k from ~166k from the previous snapshot.
And this is the distribution by country.
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
(Damn Canada, can't break top 10 again).
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 =D.
----- 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