ROV concern for hyper-specific prefixes (renamed from `Re: Smaller than a /24 for BGP?')

Mon Jan 30 14:39:09 UTC 2023

>
> - 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.lists at 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 <lprehn at 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 <johnl at iecc.com> wrote:
>>
>>> It appears that Chris J. Ruschmann <chris at 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
>>>
>>
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