WG ACTION: ACCEPT [LL38] Remove vestigial link-local only device text
Erik Guttman <[email protected]> Mon, 05 Jan 2004 20:50:23 +0100
| Newsgroups | gmane.ietf.zeroconf |
|---|---|
| Message-ID | <[email protected]> |
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