Re: Q: is RFC3531 still applicable?

[William Herrin <bill () herrin us>]

On Tue, May 14, 2024 at 1:12 PM Mel Beckman <mel () beckman org> wrote:
> I never could understand the motivation behind RFC3531. Just assign /64s.

Say you have a point of presence (pop) where you serve customers,
allowing each a /56. You assign a /48 to the pop and route the /48 to
the pop rather than routing each /56 individually. Later on you get
more than 256 customers. RFC3531 says you should assign the /48 in
such a way that more often than not you can expand it to /44 without
renumbering instead of assigning another /56 and consuming another
slot in your routing table. The motivation is saving that slot in your
routing table while also avoiding renumbering the subnets already
assigned there.

If you're the customer with the /56, RFC3531 doesn't make much sense.
Your routing table cost is nil and it's desirable to preserve as large
a block in the /56 as possible as long as possible so that you don't
have to ask for more, something the ISP may or may not grant your
class of service.

And of course RFC3531 presumes a hierarchy in your network which is
not necessarily true.

Regards,
Bill Herrin


-- 
William Herrin
bill () herrin us
https://bill.herrin.us/