[c-nsp] prefixes in AS-Set

[Martin T]

Rob,
why would one like to limit(maximum-prefix) ingress prefixes from IPX?
Doesn't more prefixes mean more choice in terms of routes?
In addition, for example in case of this "peval AS-ACCESSFORALL | sed
's/({//;s/})//;s/, /\n/g' | aggregate -q" example, there are 32
different aggregated prefixes. Now if set maximum-prefix limit value
to 20, which prefixes are accepted? First 20 which are seen by the
router?


Paul, Mark,
in case you set up a prefix filter for an IXP peer, you do the process
I described in the first e-mail and then manually check which
aggregated prefixes you would like to accept and which ones you filter
out using the prefix filter?

Brandon,
thanks for this tool!


regards,
martin

2011/8/3 Brandon Ewing <nicotine at warningg.com>:
> On Wed, Aug 03, 2011 at 08:51:03AM +0300, Martin T wrote:
>>
>> peval AS-ACCESSFORALL | sed 's/({//;s/})//;s/, /\n/g' | aggregate -q
>>
>> This last command would give:
>>
>> $ peval AS-ACCESSFORALL | sed 's/({//;s/})//;s/, /\n/g' | aggregate -q
>> $
>
> Level3 has a nice tool as a result of their automated prefix list generation
> that is available for use:
> whois -h filtergen.level3.net "RIPE::AS-ACCESSFORALL"
>
> So you can avoid all the sed. :)  Check out whois -h filtergen.level3.net
> help for more options -- you can have it output fully formed Cisc-style
> prefix-lists as well.
>
>>
>> So in case XS4ALL announces it's AS-set AS-ACCESSFORALL(it seems to be
>> the only AS-set for company XS4ALL) to ISP-B, the latter would receive
>> all those prefixes above over the established BGP session.
>
> Another nice feature is you can have AS-SETs in AS-SETs.
>
> --
> Brandon Ewing                                        (nicotine at warningg.com)
>