netdev - [iproute2] Rightmost part IPv6 address masking?

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Message-ID: <20220805030929.613f7bc7@nvm>
Date:   Fri, 5 Aug 2022 03:09:29 +0500
From:   Roman Mamedov <rm@...anrm.net>
To:     netdev@...r.kernel.org
Subject: [iproute2] Rightmost part IPv6 address masking?

Hello,

ip6tables supports the little-known format to mask the rightmost part of an
IPv6 address:

# ip6tables -A FORWARD -d ::a:b:c:d/::ffff:ffff:ffff:ffff -j ACCEPT

would match any IP which ends with the specified sequence, i.e.:
*:*:*:*:a:b:c:d. This is really useful in cases where the ISP provides a
dynamic IPv6 prefix, or there are prefixes from multiple ISPs in a LAN.

However in iproute2 there is no such support for "ip rule": 

# ip -6 rule add from ::a:b:c:d/::ffff:ffff:ffff:ffff lookup main
Error: inet6 prefix is expected rather than "::a:b:c:d/::ffff:ffff:ffff:ffff".

I suppose the iproute2 developers might be reading this, so could you please
consider adding support for masks like these? Aside from that, would you
reckon there's a limitation which would prevent this kind of masks from
working on the kernels-side?

Or maybe anyone can suggest the proper way to specify this for "ip rule" which
is supported currently?

Thanks

-- 
With respect,
Roman