>> I don't get how path information is lost in this draft. The AS Path is >> not altered in any advertisement, so it's not like aggregation, where >> you replace a series of AS' with a single AS, or anything like that. > > Hi Russ, > > 10.1.0.0/16 AS path 12 5 4 2 > 10.1.1.0/24 AS path 12 1 > > The 12->1 path, 1 being a completely different origin AS than the > covering route's origin from 2, is lost when 10.1.1.0/24 is aggregated > into 10.1.0.0/16.
No more than if the longer prefix were filtered for any other reason --such as if the provider is originating the shorter prefix, and decides to filter the longer prefix for whatever local policy reason. The only way to see this as "losing AS Path information," is to see the filtering of any possible route, including routes lost because they aren't the best path, as "losing AS Path information." >>> - But even if they do share a common origin AS, if you have an internal AS >>> partition, things may be unhappy if the more specific provided you >>> forwarding coverage and it got suppressed. >> >> AS partitions are already handled in the draft as written. If the two >> routers with overlapping prefixes aren't reachable through iBGP (no >> matter what their AS numbers might happen to me), then the mechanism >> won't suppress the longer prefix. > > Suppose an Internet-connected network consists of site A and site B. > 10.1.1.0/24 is advertised from and used by site A while 10.1.2.0/24 is > advertised from and used by site site B. Both sites advertise > 10.1.0.0/16. Sites A and B are connected to each other, so if site A > receives a packet for 10.1.2.1, it will forward it to site B. > > If site B should lose its internet connection, packets for 10.1.2.1 > will follow the covering route via site A and still reach site B. > Regardless of aggregation. This has always been true of any form of aggregation --this draft doesn't introduce any new risk in this area. When you aggregate at any level, ever, you always introduce the risk of suboptimal routes and/or routing black holes. Does this mean all routes advertised into the DFZ should be /24's, or host routes? :-) Russ _______________________________________________ GROW mailing list [email protected] https://www.ietf.org/mailman/listinfo/grow
