On 2014-04-16 17:55 , Fredy Kuenzler wrote:
Am 16.04.2014 13:08, schrieb Jeroen Massar:
More specifics are evil and give weird routing in various locations.
Not always. When Init7 started to propagate more specifics to it's four /19 and /18, about 2gig of inbound traffic switched from transit links to peering links. This is real money and IMHO a valid reason to propagate selectivly more specific prefixes (i.E. two /20 for one /19).
While you are absolutely right that it is good for traffic engineering (how the heck could I disagree with that? :)
When some other entity (especially a transit for other networks) filters those prefixes out, the results will vary.
The evil part is in the hidden problem it creates; not even the routing pollution (See also previous response...)
Massiv deaggregation however is indeed evil, and there are just too many networks out there which do it unconsciously in a very stupid way.
Init7 is filtering away more than 10000 more specific prefixes from transit. To explain this a bit further I'd like to point to a presentation I gave a while ago during NANOG 54.
https://www.nanog.org/meetings/nanog54/presentations/Monday/Kuenzler.pdf
I always liked: http://www.swinog.ch/meetings/swinog7/BGP_filtering-swinog.ppt
Always good to see what dogfood gets eaten... :)
Greets, Jeroen