In message <[email protected]>, Cutler James
R writes:
> On Feb 5, 2013, at 10:12 PM, Mark Andrews <[email protected]> wrote:
> > prefix: A variable-length field containing an IP address or the
> > prefix of an IP address. An IPv4-mapped address [RFC4291] =
> must
> > be used to represent an IPv4 address as a prefix value. The
> > prefix should be left aligned, big-endian, and zero padded =
> on
> > the right up to the next octet boundary. So the length of =
> this
> > field should be between 0 and 16 bytes
> >=20
> > is ambigious on the encoding of 2002:1234:8734::/64
> >=20
> > is it:
> > 40:20:02:12:34:87:34:00:00:00:00:00:00:00:00:00:00
> > or
> > 40:20:02:12:34:87:34:00:00:00:00:00:00:00:00:00
> > or
> > 40:20:02:12:34:87:34:00:00:00:00:00:00:00:00
> > or
> > 40:20:02:12:34:87:34:00:00:00:00:00:00
> > or
> > 40:20:02:12:34:87:34:00:00:00:00:00
> > or
> > 40:20:02:12:34:87:34:00:00:00:00
> > or
> > 40:20:02:12:34:87:34:00:00:00
> > or
> > 40:20:02:12:34:87:34:00:00
> > or
> > 40:20:02:12:34:87:34:00
> > or
> > 40:20:02:12:34:87:34
> >=20
> > All appear to be legal. It would be cleaner if the
> > floor((prefix-len+7)/8) gave the number of octets in
> > the prefix field.
>
> Mark,
>
> You have me confused here. /64 defines a prefix length of 64 bits, =
> exactly 8 octets. Octet for Octet, 20:02:12:34:87:34:00:00 is =
> unambiguously correct and in accordance with the definition cited. =
> Please explain where the leading 40 originates.
The 40 was the prefix length octet (0x40 == 64). Sorry for not being
clear on that.
The sub-option has a length field which means that you can append
zeros up to the defined maximum (16). As it is a zero padded field
you can also theoretically remove trailing zeros without loss of
information. Nothing in the definition says that you can't do that.
prefix-len: An 8-bit unsigned integer; the number of leading bits in
the prefix that are valid. The value ranges from 0 to 128.
Mark
> James R. Cutler
> [email protected]
>
>
>
>
--
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742 INTERNET: [email protected]
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