Route aggregation w/o AS-Sets

Christopher Morrow morrowc.lists at
Tue Apr 14 19:20:16 UTC 2020

On Tue, Apr 14, 2020 at 3:02 PM Lars Prehn <lprehn at> wrote:
> Thanks for all the answers! I think I have one more detail I'd like to know.
> Lets say you own X/22. You have delegated X/23 to your customer, keeping the other /23 for yourself. For some reason, your customer also owns and announced (to you) all remaining IPs necessary to complete X/21.

(most of this is covered in petach's note actually... his 3 rules look
like they cover your cases)

Ideally if you have authorization to announce the /22 you do that.
If your customer announces the /23 good for them, you can choose to
hide this (if you don't think they have other paths where that /23
will be seen), you'd hide it through a bunch of different means, but
perhaps simplest is tag customer routes which are part of your
aggregates with a community and filter that community on exit to other

> Do you announce the aggregate X/21 (including addresses not associated with you), the aggregate X/22 (only address belonging to you), or the more specific route X/23 (including only addresses delegated from you to your customer)?

You don't have authorization to announce the /21 (given your scenario
above) so please don't do that. That will make all manner of other
people made at you :(

I think your choices in your scenario are:
  1) announce the covering /22 only (use community example to filter
the customer's /23)
  2) announce the covering /22 and the customer originated /23

you should never announce a prefix for which you do not have
authorization to announce... this way leads to route hijacks.

> Best regards,
> Lars
> On 14.04.20 06:07, Christopher Morrow wrote:
> Don't user as-sets step one.
> Rpki does not understand how to express an as-sets' authorization.
> Why do you want to do this?
> On Mon, Apr 13, 2020, 13:34 Lars Prehn <lprehn at> wrote:
>> Hi everyone,
>> how exactly do you aggregate routes? When do you add the AS_SET
>> attribute, when do you omit it? How does the latter interplay with RPKI?
>> Best regards,
>> Lars

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