nanog mailing list archives
Re: Route aggregation w/o AS-Sets
From: Matthew Petach <mpetach () netflight com>
Date: Tue, 14 Apr 2020 02:32:37 -0700
On Mon, Apr 13, 2020 at 10:35 AM Lars Prehn <lprehn () mpi-inf mpg de> 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
I generally would use the atomic-aggregate knob to generate aggregate routes for blocks I controlled, when the downstream ASN information was not necessary to propagate outside my network (usually cases where I had multiple internal ASNs, but all connectivity funneled though a single upstream pathway.) If you have discrete downstream ASNs with potentially different external pathways, you shouldn't be generating aggregate routes that cover them; that's just bad routing 101. Thus, my rules for aggregation always came down to: 1) is there more than one external/upstream pathway for the ASN and prefix? If so, don't aggregate. 2) is redundant, reliable connectivity between all the external gateway routers that would be announcing the aggregate? If not, don't generate a covering aggregate. 3) If there's only a single upstream pathway through you for the ASN and prefix, and that won't be changing any time soon (eg, you have a collection of downstream datacenter with their own ASNs and prefixes, but they all route through a common backbone), then use the atomic-aggregate option to suppress the more specific AS_PATH information, and simply announce the space as a single aggregate coming from your backbone ASN. That way, there's no confusion with RPKI and AS_SETS; all you're ever announcing are simple AS_PATHs for a given prefix. Best of luck! Matt
Current thread:
- Route aggregation w/o AS-Sets Lars Prehn (Apr 13)
- Re: Route aggregation w/o AS-Sets Christopher Morrow (Apr 13)
- Re: Route aggregation w/o AS-Sets Lars Prehn (Apr 15)
- Re: Route aggregation w/o AS-Sets Christopher Morrow (Apr 14)
- RE: Route aggregation w/o AS-Sets Deepak Jain (Apr 15)
- Re: Route aggregation w/o AS-Sets Lars Prehn (Apr 15)
- Re: Route aggregation w/o AS-Sets Alejandro Acosta (Apr 13)
- Re: Route aggregation w/o AS-Sets Warren Kumari (Apr 14)
- Re: Route aggregation w/o AS-Sets Matthew Petach (Apr 14)
- <Possible follow-ups>
- RE: Route aggregation w/o AS-Sets Jakob Heitz (jheitz) via NANOG (Apr 15)
- Re: Route aggregation w/o AS-Sets Matthew Petach (Apr 15)
- RE: Route aggregation w/o AS-Sets Jakob Heitz (jheitz) via NANOG (Apr 15)
- Re: Route aggregation w/o AS-Sets Matthew Petach (Apr 15)
- Re: Route aggregation w/o AS-Sets Christopher Morrow (Apr 13)