> > - If origin makes a ROA only for covering prefix (say /24) then the /28 > announcement would be considered invalid by ROV and (even more likely) > dropped. Also you get more instances of `invalid' announcements, making > adoption of ROVs and ROAs harder. >
AS 10 creates an ROA for X.X.X.X/24 , maxLength 28. This means AS10 can announce any /28 in that /24, and any validator should return valid. (This ignores if the longer than /24s would be accepted by policy or not. ) On Mon, Jan 30, 2023 at 9:19 AM Amir Herzberg <amir.li...@gmail.com> wrote: > Thanks to Lars for this interesting input and results (which I wasn't > familiar with). > > I want to mention another concern with the possible use of hyper-specific > IP prefixes, i.e., longer than /24, which I haven't seen discussed in the > thread (maybe I missed it?). Namely, if you allow say /28 announcements, > then what would be the impact of ROV? Seems this can cause few problems: > > - If origin, say AS 10, makes a ROA for the /28, this would allow an > attacker, e.g., AS 666, to do origin-hijack (announce path 666-10 to the > /28), and attract traffic for the /28 from anybody accepting /28 > announcements (that didn't receive the legit announcement). Plus, of > course, you get more overhead in ROA distribution and validation. > > - If origin makes a ROA only for covering prefix (say /24) then the /28 > announcement would be considered invalid by ROV and (even more likely) > dropped. Also you get more instances of `invalid' announcements, making > adoption of ROVs and ROAs harder. > > Just a thought... Amir > -- > Amir Herzberg > > Comcast professor of Security Innovations, Computer Science and > Engineering, University of Connecticut > Homepage: https://sites.google.com/site/amirherzberg/home > `Applied Introduction to Cryptography' textbook and lectures: > https://sites.google.com/site/amirherzberg/cybersecurity > > > > > On Wed, Jan 25, 2023 at 1:17 PM Lars Prehn <lpr...@mpi-inf.mpg.de> wrote: > >> We performed some high-level analyses on these hyper-specific prefixes >> about a year ago and pushed some insights into a blog post [1] and a paper >> [2]. >> >> While not many ASes redistribute these prefixes, some accept and use them >> for their internal routing (e.g., NTT's IPv4 filtering policy [3]). Rob >> already pointed out that this is often sufficient for many traffic >> engineering tasks. In the remaining scenarios, announcing a covering /24 >> and hyper-specific prefixes may result in some traffic engineering, even if >> the predictability of the routing impact is closer to path prepending than >> usual more-specific announcements. In contrast to John's claim, some >> transit ASes explicitly enabled redistributions of up to /28s for their >> customers upon request (at least, they told us so during interviews). >> >> Accepting and globally redistributing all hyper-specifics increases the >> routing table size by >100K routes (according to what route collectors >> see). There are also about 2-4 de-aggregation events every year in which >> some origin (accidentally) leaks some large number of hyper-specifics to >> its neighbours for a short time. >> >> Best regards, >> Lars >> >> [1] >> https://blog.apnic.net/2022/09/01/measuring-hyper-specific-prefixes-in-the-wild/ >> [2] https://dl.acm.org/doi/pdf/10.1145/3544912.3544916 >> [3] https://www.gin.ntt.net/support-center/policies-procedures/routing/ >> >> >> On 25.01.23 05:12, Forrest Christian (List Account) wrote: >> >> I have two thoughts in relation to this: >> >> 1) It's amazing how many threads end up ending in the (correct) summary >> that making an even minor global change to the way the internet works >> and/or is configured to enable some potentially useful feature isn't likely >> to happen. >> >> 2) I'd really like to be able to tag a BGP announcement with "only use >> this announcement as an absolute last resort" so I don't have to break my >> prefixes in half in those cases where I have a backup path that needs to >> only be used as a last resort. (Today each prefix I have to do this with >> results in 3 prefixes in the table where one would do). >> >> And yes. I know #2 is precluded from actually ever happening because of >> #1. The irony is not lost on me. >> >> >> On Tue, Jan 24, 2023, 7:54 PM John Levine <jo...@iecc.com> wrote: >> >>> It appears that Chris J. Ruschmann <ch...@scsalaska.net> said: >>> >-=-=-=-=-=- >>> >How do you plan on getting rid of all the filters that don’t accept >>> anything less than a /24? >>> > >>> >In all seriousness If I have these, I’d imagine everyone else does too. >>> >>> Right. Since the Internet has no settlements, there is no way to >>> persuade a network of whom you are not a customer to accept your >>> announcements if they don't want to, and even for the largest >>> networks, that is 99% of the other networks in the world. So no, >>> they're not going to accept your /25 no matter how deeply you believe >>> that they should. >>> >>> I'm kind of surprised that we haven't seen pushback against sloppily >>> disaggregated announcements. It is my impression that the route table >>> would be appreciably smaller if a few networks combined adjacent a >>> bunch of /24's into larger blocks. >>> >>> R's, >>> John >>> >>