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Re: IPv6 RA vs DHCPv6 - The chosen one?
From: Ray Soucy <rps () maine edu>
Date: Fri, 23 Dec 2011 15:33:13 -0500

On Fri, Dec 23, 2011 at 3:06 PM, Tomas Podermanski <tpoder () cis vutbr cz> wrote:
Can you be more specific? I can not imagine situation where SLAAC could
solves a problem that DHCP would not.

SLAAC is the magic that makes the link-local scope work.  I think
having a link-local scope is a good thing, so I think I'll keep SLAAC.
 Now that I'm keeping SLAAC, I think I might as well make it an option
for global unicast addressing.

DHCPv6, especially on a large scale, does have a cost.  A small
network doesn't need much of a server, but for a large network the
amount of requests can be high.  DHCP is also something that isn't
trivial to distribute across systems to avoid a single point of
failure, there is an entire discussion on the design issues of making
a salable DHCP solution, especially if you want more than a generic
open pool.  I'd say being able to use SLAAC and avoid that complexity
is something worth while.

RA is much more responsive than DHCP was.  When an IPv6 router goes
away, hosts can release global addresses for that prefix and fail over
gracefully, rather than depending on stale configuration data and
blindly sending packets.  In the future, we'll likely see RA leveraged
to provide better availability than we've seen with IPv4.

Then there is the entire issue of someone misconfiguring a DHCP server
and having to run around rebooting systems to get them to drop the
bogus information (or wait for leases to expire, typically several
hours).  At least with RA + DHCPv6 you can recover from this in a
reasonable amount of time.

There are other special case considerations; extensions like privacy
addressing kind of become not so private if everything is being logged
by a DHCPv6 server.  It's legitimate that you might want a network
where the anonymity of users is provided.  Especially as we continue
to see increased requirements for log retention by governments.

-- 
Ray Soucy

Epic Communications Specialist

Phone: +1 (207) 561-3526

Networkmaine, a Unit of the University of Maine System
http://www.networkmaine.net/


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