[c-nsp] Route Aggregation and Deaggregation

[Tony]

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 <nsp-list at pollok.net>
>To: Tony <td_miles at yahoo.com> 
>Cc: Jennifer Pruett <jennypruett88 at gmail.com>; "cisco-nsp at puck.nether.net" <cisco-nsp at puck.nether.net> 
>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 <jennypruett88 at gmail.com>
>>> To: cisco-nsp at puck.nether.net
>>> 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
>
>
>