maximum ipv4 bgp prefix length of /24 ?

Wed Oct 11 18:29:13 UTC 2023

> On Oct 10, 2023, at 22:44, Willy Manga <mangawilly at gmail.com> wrote:
> 
> 
> 
> > On 11/10/2023 03:52, Delong.com wrote:
>> 
>>> On Oct 10, 2023, at 13:36, Matthew Petach <mpetach at netflight.com> wrote:
>>> [...]
>>> Owen,
>>> 
>>> RPKI only addresses accidental hijackings.
>>> It does not help prevent intentional hijackings.
>> OK, but at least they can help limit the extent of required desegregation in combat unless I misunderstand the whole MAXPREFIXLEN option.
> 
> Actually, RFC 9319 do recommend to "avoid using the maxLength attribute in ROAs except in some specific cases". But I recognise that this RFC is not yet implemented everywhere.

It’s a BCP, and may be worthy of reconsideration.

The justification in section 1.0 paragraph 3 of that basically points out exactly what I said people _SHOULD_ be doing _IF_ they use max prefix and have failed to do in “84% were vulnerable…”.

> 
> 
>>> 
>>> RPKI only asserts that a specific ASN must originate a prefix.  It does nothing to validate the authenticity of the origination.
>> Nope… It ALSO asserts (or can assert) an attribute of “Maximum allowed prefix length”.
>> E.g. if I have a ROA for AS65500 to originate 2001:db8::/32 with a “Maximum Length” attribute of /36, then any advertisement (even originated by 65500) that is longer than /36 should be considered invalid.
> 
> Yes, but in that scenario any advertisements between /32 and /36 from that prefix originated by AS65500 are *valid* . That's why "ROAs should be as precise as possible, meaning they should match prefixes as announced in BGP" [1]

You completely ignored my statement of the need for appropriate AS-0 ROAs to block those.

Owen