[lpi-discuss] IPv6 in exam LPI ?

Bryan J. Smith b.j.smith at ieee.org
Wed Aug 17 14:23:24 EDT 2005

"Bryan J. Smith" <b.j.smith at ieee.org> wrote:
> and there is 3 bits near the front header that designates
> its the local LAN.

Sorry, I mixed concepts (and mega-oversimplified there).

The first 3-bits are pretty key in IPv6 designation.

The first 3-nibbles (nibble=4-bits -> 12-bits) are almost an
absolute indicator of the type of subnet.

FE8 indicates IPv6** LINKLOCAL, and it's what you'll see on
_any_ IPv6 node, period.  This is also known as the FE80::/64
network.  It's equivalent in the IPv4 world is the 169.254/16
network, although unlike IPv4 nodes that might drop their
169.254/16 assignment when they get their address from DHCP,
a IPv6 node _always_ has its IPv6 LINKLOCAL address.  In
fact, a IPv6 DHCP typically only assigns another IPv6 network
(top 64-bits) and the lower 64-bits (based on the 48-bit
address) stays the same.

It's this basic IPv6 identification that I think needs to go
in the next rev of any exam.  Whenever IPv4 is discussed,
there needs to be at least the mention of IPv6 -- even if
we're just teaching people to disable it with ifconfig.

-- Bryan

**NOTE:  If you haven't heard by now, IPv6 uses 128-bit of
16-bit x 8 double-words.  E.g., FE80::0200:ABCD:EF12:3456 is
a local LAN IPv6 address with a MAC address of
AB:CD:EF:12:34:56.  The IPv6 nomenclature allows for "::" to
shorten/abbreviate one or more double-words that are 0000 --
such as typical in the LINKLOCAL (which is FE80::/64).

Bryan J. Smith                | Sent from Yahoo Mail
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