DHCPv6 and MAC Address inclusion
Simon Hobson
dhcp1 at thehobsons.co.uk
Wed Jan 25 10:05:29 UTC 2012
Ted Lemon wrote:
>>I just don't understand why it was chosen that
>>mac address (read: link layer identifier) was
>>left out of the DHCPv6 packet. What was the
>>reasoning there? What was the harm in
>>including it? Is it not better to have to much
>>information rather than to little?
>
>If you can count on the MAC address being there,
>you can use it as an identifier in a
>non-conforming DHCPv6 implementation. We
>didn't want that, so we couldn't specify it in
>such a way that that would be possible.
I find that a bit strange. Surely the best way to
deal with that is to "name and shame"
non-compliant implementations, rather than deny
everyone something that could be useful "just in
case". Lets face it, there are still plenty of
ways to make a non-compliant implementation -
such as splitting an LL or LLT identifier to
extract the hardware address, something that is
now encouraged by it not being present in the
request packets in it's own field/option.
>I get the sense that you're experiencing a bit
>of fear, uncertainty and doubt about the IPv6
>transition.
I think everyone is !
It's easy to forget that IPv4 used to be as hard
as people are finding IPv6 - at least for those
of us with "a few years" under our belts. I
recall my first contact with IP - this strange
system, with funny numbers, something called a
netmask, and seemingly (in the days before search
engines) no documentation to be found. Back then,
getting online meant a SLIP dialup from a single
machine - putting a network online meant running
a Unix box (or very expensive router) to do the
routing.
The idea of being able to unpack a small plastic
box, put in a username and password, and get a
whole network online in minutes was just science
fiction.
So here we are, in much the same position with
IPv6. Some of the principals are the same (eg
addressing and subnet masks), but a lot is so
very different. A small number of people have
been working on this for some time, the rest of
us are having to start from scratch - and are at
different stages of learning.
So I think it's OK to be confused by it all. I'm
sure it will become clearer as it gets more
widespread and the tools catch up. At the moment,
I think we're still at the stage where people
aren't quite clear what tools are needed, and how
they should work - a bit of chicken and egg;
until adoption is more widespread, it's not clear
what's needed; and until the tools are there,
adoption is a bit harder.
My ISP (Plusnet) is doing a trail of IPv6 to end
users. "It works just fine", but I'm still
struggling with some of the pieces. The ISC
client doesn't support PPP interfaces, and
Wide-DHCP client doesn't appear to support the
scripting ability I *think* I want. So there's an
element of experimenting and adjusting my
requirements to see if I can close that gap.
José Queiroz wrote:
>Hi, sorry if this is a naive view. But, doesn't
>auto-assignment with EUID-64 suffixes attends
>your needs? This way you'll have a fixed IPv6
>address, which haves a strong association with
>the MAC Address, and better, is predictable if
>you know the MAC address of the interfaces.
it will work for some, but it's not a good idea
for public services. Simple example, what if you
want to move a service to a different machine ?
Using EUID-64 addresses means you either have to
change the MAC on the new host to match, or
change the DNS and wait while it propagates -
with a day or 2 of parallel running while caches
expire.
In practice, I suspect we'll start to see a
return to using multiple addresses per
machine/interface - which at one time was the
only way to run multiple web sites on one host.
So there may be some scope for using an EUID-64
address for the machine, and additional addresses
for the service(s) run on it - but that's a whole
new level of management system to sort out. I'm
not looking forward to applying IPv6 at work - I
suffer badly enough with people that won't apply
any logic to IPv4, I hate to think what they'll
do when let loose with (say) 256 networks of 64k
addresses !
--
Simon Hobson
Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.
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