Subject: WG ACTION: ACCEPT [LL38] Remove vestigial link-local only device text

From: Erik Guttman <[email-masked]>
Date: Mon, 05 Jan 2004 20:50:23 +0100

Change Section 2.8 from

2.8.  Link-Local Packets are Local

    The non-forwarding rule means that hosts may assume that all
    169.254/16 destination addresses are "on-link" and directly
    reachable.  The 169.254/16 address prefix MUST NOT be subnetted.
    This specification utilizes ARP-based address collision detection,
    which functions by broadcasting on the local subnet. Since such
    broadcasts are not forwarded, were subnetting to be allowed then
    address conflicts could remain undetected.

    The non-forwarding rule is important because it is expected that
    Link-Local-only devices will often be simple devices of the kind that
    currently use X10 [X10], USB [USB] or FireWire [1394].

    The designers of these devices currently assume that they will
    communicate only with other local devices, and this allows them to
    produce cost-effective devices by implementing a degree of security
    appropriate for that expected environment.  Any network gateway
    device that blindly forwards the contents of Link-Local IPv4 packets
    off the local link (or onto the local link) exposes simple Link-
    Local-only devices to a much greater degree of risk than their
    designers may have planned for.

    This does not mean that Link-Local devices are forbidden from any
    communication outside the local link.  IP hosts that implement both
    Link-Local and conventional routable IPv4 addresses may still use
    their routable addresses without restriction as they do today.

    Simple devices that implement only a Link-Local IPv4 address may also
    communicate with hosts outside the local link, provided that such
    communication is mediated through a device capable of enforcing
    appropriate security controls.  For example, a home heating
    thermostat that implements only a Link-Local IPv4 address could be
    controlled from a remote Web browser, by having an intermediary on
    the local network which accepts incoming HTTP connections, uses
    appropriate cryptographic methods to verify the authority of the
    remote user, and then uses Link-Local IPv4 packets to communicate
    with the thermostat to get status and issue commands.

    It should be understood that this mediated communication is not
    mandatory; it is an option afforded to designers of extremely simple
    devices.  Any designer of a device desiring unmediated communication
    outside the local link need only implement today's conventional IP
    host software (e.g. a DHCP client) in order to enjoy the same degree
    of global addressability available to other conventional IPv4 hosts.
    Such networked devices should of course implement a degree of
    security appropriate to being connected to a global public network.

To:

2.8.  Link-Local Packets are Local

    The non-forwarding rule means that hosts may assume that all
    169.254/16 destination addresses are "on-link" and directly
    reachable.  The 169.254/16 address prefix MUST NOT be subnetted.
    This specification utilizes ARP-based address collision detection,
    which functions by broadcasting on the local subnet. Since such
    broadcasts are not forwarded, were subnetting to be allowed then
    address conflicts could remain undetected.

    This does not mean that Link-Local devices are forbidden from any
    communication outside the local link.  IP hosts that implement both
    Link-Local and conventional routable IPv4 addresses may still use
    their routable addresses without restriction as they do today.

Please see: http://www.merit.edu/mail.archives/zeroconf/msg00003.html
And: http://www.drizzle.org/~aboba/ZEROCONF/ll38.html

Regards,

Erik

---

From: John Schnizlein <[email-masked]>
Date: Mon, 05 Jan 2004 15:06:25 -0500

Removal of the vestigial text is welcome. Please consider removing 
the second paragraph also because it seems to imply that a host could 
"implement both Link-Local and conventional routable IPv4 addresses",
although we have a rough consensus that a host with a "conventional"
address should not use a Link-Local address.

That a host could implement these different addressing modes only
under different circumstances, which you presumably meant, is just
a little too subtle an interpretation for a reader who has not
been through the protracted discussion.

John

At 02:50 PM 1/5/2004, Erik Guttman wrote:
>...