ignore max length as an argument of roa_check

[Job Snijders]

On Wed, Mar 31, 2021 at 04:34:12AM +0200, Ondrej Zajicek wrote:
> So my point/idea is that if this case is valid, then using RPKI-style
> checking for BLACKHOLE is broken idea anyway, 

Yes, the design pattern of using ROAs for blackholing appears
problematic. Mangling ROAs and then using the resulting deteriorated
information to 'approve blackholes' appears to defeat the purpose of
RPKI ROAs. ROAs exist to help increase network reachability :)

> and perhaops we should instead focus on implementing (IMHO) proper
> checking for BLACKHOLE routes, similar to one for flowspec validation:
> 
>   BLACKHOLE route received from A is valid if i have (RPKI-valid)
>   regular route from A for network N covering the BLACKHOLE route
>   and (optionally) such route is best route for network N.

+1

The above appears a worthwhile direction, more elegant than overriding a
cryptographically signed attestation on the expected prefix length.
'ignore max length' appears to me as a dangerous button. I support
Pier's suggestion to remove this config knob because of the risk of
unintended consequences.

In the below slide deck I've outlined some suggestions to make
activation of blackhole requests dependent on 'normal routing', and in
doing so - any and all work to improve 'normal routing security' will
also improve 'blackholing routing'.

http://iepg.org/2019-03-24-ietf104/blackholing_reconsidered_ietf104_snijders.pdf

Kind regards,

Job