Subject: LL2 modified

From: Erik Guttman <[email-masked]>
Date: Tue, 11 Feb 2003 15:05:38 +0100 (CET)

LL2 now contains suggested text (from Robert Elz)

Description of Issue  Explicit Additional Mechanism to disable v4LL

Submitter Name  Erik Guttman    

Submitter Email Address [email-masked]    

Date first submitted  6 Feb 2002    

Reference

http://www.merit.edu/mail.archives/zeroconf/2003-01/msg00459.html
Security considerations with the proposal:
http://www.merit.edu/mail.archives/zeroconf/2003-01/msg00473.html

Comment Type ['T'echnical | 'E'ditorial] T 

Priority ['S' Must fix | '1' Should fix | '2' May fix ] S 

Section Not in document presently.

Rationale/Explanation of issue: 

The specification should be modified to define or require some
additional mechanism to disable IPv4 LL autoconfiguration. This
mechanism would be mandatory to implement and cause all hosts using IPv4
LL to stop doing so. Lengthy description of problem: ... the desire to
have a way to disable LL addresses isn't so that the network manager can
make sure that no-one can use the net without their permission, or
similar, that's ludicrous, the node(s) could just configure themselves
with network 10 addresses, or 192.168, or anything else (including
addresses from the block that are designated for use on the net in
question). 

The reason is because the net manager knows what will, and won't work
properly on their net, and can provide advice to the nodes as to what
they should do in order to work well in the local environment. What is
requested is RFC 2563 or some derivative. 

Requested Change: 

1.3 Alternate Configuration Mechanisms

As explained in the previous section (1.2), the link-local addresses
assigned by this protocol are intended for small ad-hoc networks.
However, it is very rare for a system to be constructed that can
only ever be connected to such networks. When connected to a
properly managed network, nodes should operate correctly for that
network.

To allow for this, all nodes that implement this protocol MUST also
provide some mechanism to allow for routable addresses to be configured.
That mechanism MAY use the DHCP protocol [RFC2131] in appropriate cases,
but other means, such as manual configuration, are also adequate.

Many nodes using this protocol, on large networks, can cause excessive
traffic as explained in the previous section (1.2). For this reason,
and others, it can be necessary to disable use of link-local addresses
in some situations where they are not required. The configuration
mechanism provided MUST provide a mechanism to disable the assignment
of link local addresses on an interface. Where that configuration
mechanism uses DHCP, the node MUST implement the DHCP option to disable
stateless auto-configuration in IPv4 clients [RFC2563].

---

From: Keith Moore <[email-masked]>
Date: Tue, 11 Feb 2003 09:54:09 -0500

oppose this as written.  manual configuration capability is not sufficient to
relieve a host of the need to try DHCP before configuring an LL address. 
nor is it sufficient to leave the mechanism by which a host obtains a routable
address unspecified.
here's how I'd modify it:

a host that attempts to automatically configure an address MUST implement
DHCP, and MAY implement LL.  If the host implements LL it MUST give preference
to DHCP.

(but we need to work this out in more detail)

a host MAY (SHOULD?) permit manual configuration of addresses to override any
DHCP or LL address assignment.  a host MAY be manually configurable to
allocate an LL address even if it has obtained a routable address by other
means.