dhcpcd-discuss

RFC 3633 Page 9 (Section 10)...

In a message sent by a requesting router to a delegating router, the
values in the fields can be used to indicate the requesting router's
preference for those values.  The requesting router may send a value
of zero to indicate no preference.  ==> A requesting router may set the
IPv6 prefix field to zero and a given value in the prefix-length
field to indicate a preference for the size of the prefix to be
delegated. <<== (emphasis added.)


So the ability to fill in an OPTION_IAPREFIX to have a prefix of all 
zeros and a length of XX -- e.g. the ip 6 address "::/60" -- is what 
lets the client request his preferred delegated prefix length.

This doesn't seem possible with the current client.



-- Rob.



-------- Original Message --------
Subject: IA_PD and prefix length _requests_ ??
Date: Fri, 20 Jun 2014 16:50:15 -0700
From: Robert White <rwhite@xxxxxxxxx>
To: dhcpcd-discuss@xxxxxxxxxxxx

Howdy,

So Comcast will give out three kinds of addresses. If you do an ia_na
you'll get a ::/128 address. If you do an ia_pd you'll get a ::64
address by default. And ...

If you do an ia_pd and "ask for one" (electronically) you'll get a ::/60
with four bits for your internal subnets. [I know /60 is the magic
number but I don't know if you can get other values between /60 and /64.]

I can not figure out how to "ask for one" using dhcpcd. Apparently
"wide-dhcp" (or some name like that) will format a request with the
necessary preferred prefix length because of being able to set an
sla_len or something.

I see some syntactic definitions for IAPREFIX but, if it _is_ in-place
and functional, I can't figure out how to make one and attach it to the
ia_pd.


I would have _expected_ some syntax like:

ia_pd 7/4 int0 int1 # not currently valid syntax

or

ia_pd 7 int0/1/1 int1/2/3 # currently valid syntax

to "shave off" the largest prefix supplied (e.g. four (4) in example 1,
or three(3) in example two) from the request so that the request would
go out for a prefix with the shaved value (e.g. ::/60 in example one, or
::/61 in example two) such that the sum of the request length and the
largest specified prefix is 64.

ALTERNATELY... adding an (optional) explicit term with the actual
desired prefix length might be better.

ia_pd ::/48 (rest of syntax here)

--- So am I missing something or is the feature nonexistent?

-- Rob White.