Subject: Re: 169.254/16 IP addresses

From: "Mike Borella" <[email-masked]>
Date: Fri, 14 Apr 2000 08:24:46 -0500

People may be NATing linklocal addresses very soon or already.  The problem
is that quite a few large customers use private space for their networks, but
want customized equipment that can be just dropped in (i.e. a small subnet
of logically distinct hosts and routers) and work with no IP configuration.
The solution is the linklocal space, with a NAT to the outside world.  Choosing
any
other address space would cause major grief.

-Mike

Richard Johnson <[email-masked]> on 04/14/2000 04:15:47 AM

Sent by:  Richard Johnson <[email-masked]>

To:   Mark Thompson <[email-masked]>
cc:   [email-masked] (Mike Borella/MW/US/3Com)
Subject:  Re: 169.254/16 IP addresses

Mark Thompson writes:
 > I think the idea is that link-local addresses are used to communicate
 > *only* with devices on the local link, and that global addresses (or,
 > IYL, NATable addresses from Net10 etc.) are used for the "I want to
 > route to the outside world" cases.
 >
 > Actually, the draft does imply that IPv4 link-local autoconf is used to
 > "hunt" DHCP servers that appear after the local host comes up (Section
 > 4, "Ongoing checks for a DHCP server"). The idea is that your device
 > gets a link-local address when no globally-routable one (or NATed one)
 > is discovered, and then runs with it up until a DHCP server (or NAT gw)
 > becomes available.

Unless there's some more recent version of the draft than what I've
seen, there's no mention of NAT in the draft at all.  It says:

    Addresses allocated by this mechanism MUST NOT be routed by any net-
    work device.  The addresses are designed to be link local addresses.
    Link local address are to be, by definition, restricted to the local
    network segment.  Allocation of link-local addresses in an IPv6 net-
    work is described in [IPv6SAC].

It's quite obvious why one would not want these addresses routed, but
there are very good reasons why someone may want to NAT these
addresses and there's no mention of whether NATing them is looked upon
as "good" or "bad".  I see no reason why it should be mandated that
NATing these addresses shouldn't be done.  I would bet that regardless
of what any document says, someone will end up allowing an option of
NATing these addresses anyway simply because some customer will demand
it.

 > If you know by *specification* that the link-local addresses are only ever
 > going to be seen by local devices, and that routers by *specification*
 > MUST NOT route/munge/forward packets destined to those addresses, I can
 > see cases where you can make certain assumptions about the communication
 > (topological location, security, etc. etc.) that you can't otherwise.

I think the strongest reason here would probably be security, but even
that somewhat fails when one starts thinking of wireless networks.
Sounds like a false sense of security to me.

/raj

---

From: Daniel Senie <[email-masked]>
Date: Fri, 14 Apr 2000 09:26:59 -0400

> other address space would cause major grief.

What method is being used in these cases for discovering the NAT box? I
can think of a few ways to do it, but am curious what products are doing
this, and which mechanism(s) are used for the discovery.

-- 
-----------------------------------------------------------------
Daniel Senie                                        [email-masked]
Amaranth Networks Inc.                    http://www.amaranth.com