I would hope that IF ($deity forbid) you needed to pull a single /24 out of a /19 then it would be done in a way to create the smallest number of resulting prefixes, eg:
/19 = /20 + /21 + /22 + 2x /24 Which would result in "only" 4 extra prefixes being announced than a single /19. regards, Tony. >________________________________ > From: Sascha Pollok <[email protected]> >To: Tony <[email protected]> >Cc: Jennifer Pruett <[email protected]>; "[email protected]" ><[email protected]> >Sent: Thursday, 19 July 2012 4:05 PM >Subject: Re: [c-nsp] Route Aggregation and Deaggregation > >Hi Jen, > >+1 for Tony. I would just like to make clear: please do NOT deaggregate >the /19. You can advertise a more-specific /24 to ISP3 OR advertise >the more-specific /24 to all three ISPs. But please do *not* deaggregate >the /19 into 32x /24. > >Good luck >Sascha > >On Wed, 18 Jul 2012, Tony wrote: > >> Hi Jen, >> >> You can do that. All of your traffic for the /24 will come to you via ISP3 >> as this is a more specific match than the /19 it is part of. If you drop >> your link to ISP3, then your /24 traffic will then be received via one of >> the /19's you advertise to ISP1 & ISP2. >> >> If this is your intention, then go for it. No need to also advertise the /24 >> to ISP1 & ISP2 unless you want some of the traffic for that /24 to come >> inbound on those links. >> >> >> >> regards, >> Tony. >> >> >> >> >>> ________________________________ >>> From: Jennifer Pruett <[email protected]> >>> To: [email protected] >>> Sent: Thursday, 19 July 2012 3:28 PM >>> Subject: [c-nsp] Route Aggregation and Deaggregation >>> >>> Good day! >>> >>> Question for any BGP guru's; we have a couple of ASR routers as our border >>> routers which are advertising a few /19's. The question is not directly >>> related to the ASR hardware, but the >>> process and best practice of aggregating PI assigned space. If we advertise >>> our /19's via ISP1 and ISP2 and then introduce ISP3 and only advertise a >>> /24 from one >>> of the /19's, do we have to deaggregate the /19 that the /24 was pulled out >>> of to accommodate the /24 that we would advertise via ISP3? What are the >>> ramifications of >>> such actions? >>> >>> Thanks for your time >>> Jen > > > _______________________________________________ cisco-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
