WG ACTION: 1 week continued discussion [LL70] DNAv4 normative or informative?

LL70

This issue will remain open for comment until June 2, 2004.
After that point, if no comments are received, the issue will be
resolved by making DNAv4 normative and leaving the text as it currently
stands.

Bernard suggests the following resolution, which should allow DNAv4 to
remain an informative reference.

Was:
1.9.  When to configure a Link-Local IPv4 address

   Having addresses of multiple different scopes assigned to an
   interface, with no adequate way to determine in what circumstances
   each address should be used, leads to complexity for applications and
   confusion for users.  A host with an address on a link can
   communicate with all other devices on that link, whether those
   devices use Link-Local addresses, or routable addresses.  For these
   reasons, a host SHOULD NOT have both a valid routable address and a
   Link-Local IPv4 address configured on the same interface.


   A routable address is any address that is:

   * a unicast address (see Section 1.2)
   * not a loopback address
   * not contained within the 169.254/16 prefix reserved for Link-Local
      IPv4 addresses

   A "valid routable address" is a routable address that passes the
   reachability test described in section 2 of "Detection of Network
   Attachment (DNA) in IPv4" [DNAv4].

   The assignment and use of a Link-Local IPv4 address on an interface
   is based solely on the state of the interface, and is independent of
   any other protocols such as DHCP.  A host MUST NOT alter its behavior
   and use of other protocols such as DHCP because the host has assigned
   a Link-Local IPv4 address to an interface.

   When an interface has a valid routable address configured on an
   interface, the host SHOULD NOT also assign a Link-Local IPv4 address
   to that interface.

   If a host finds that an interface that was previous configured with a
   Link-Local IPv4 address is now configured with a valid routable
   address, the host MUST always use the routable address when
   initiating new communications, and MUST cease advertising the
   availability of the Link-Local IPv4 address through whatever
   mechanisms that address had been made known to others.  The host
   SHOULD continue to use the Link-Local IPv4 address for communications
   underway when the routable address was configured, and MAY continue
   to accept new communications addressed to the Link-Local IPv4
   address.  Ways in which a valid routable address might be configured
   for the interface include:

   * Manual configuration
   * Address assignment through DHCP
   * Roaming of the host to a network on which a routable address
      assigned to the interface is valid

   If a host finds that an interface that was previously configured with
   a valid routable address no longer has a valid routable address, the
   host MAY identify a usable Link-Local IPv4 address (as described in
   section 2) and assign that address to the interface.  Ways in which a
   valid routable address might no longer be assigned to an interface
   include:

   * Removal of the address from the interface through manual
      configuration
   * Expiration of the lease on the address assigned through DHCP
   * Roaming of the host to a new network on which the address is no
     longer valid.

   Further discussion of the issues in detection of transient failures
   and the use of DHCP in response to network attachment failure is
   provided in "Detection of Network Attachment (DNA) in IPv4". [DNAv4]



Becomes:

1.9.  When to configure an IPv4 Link-Local address

   Having addresses of multiple different scopes assigned to an
   interface, with no adequate way to determine in what circumstances
   each address should be used, leads to complexity for applications and
   confusion for users.  A host with an address on a link can
   communicate with all other devices on that link, whether those
   devices use Link-Local addresses, or routable addresses.  For these
   reasons, a host SHOULD NOT have both a routable address and an IPv4
   Link-Local address configured on the same interface.

   The assignment and use of an IPv4 Link-Local address on an interface
   is based solely on the state of the interface, and is independent of
   any other protocols such as DHCP.  A host MUST NOT alter its behavior
   and use of other protocols such as DHCP because the host has assigned
   an IPv4 Link-Local address to an interface.

   When an interface has a routable address configured on an interface,
   is based solely on the state of the interface, and is independent of
   any other protocols such as DHCP.  A host MUST NOT alter its behavior
   and use of other protocols such as DHCP because the host has assigned
   an IPv4 Link-Local address to an interface.

   When an interface has a routable address configured on an interface,
   the host SHOULD NOT also assign an IPv4 Link-Local address to that
   interface.

   If a host finds that an interface that was previous configured with
   an IPv4 Link-Local address is now configured with a routable address,
   the host MUST use the routable address when initiating new
   communications, and MUST cease advertising the availability of the
   IPv4 Link-Local address through whatever mechanisms that address had
   been made known to others.  The host SHOULD continue to use the IPv4
   Link-Local address for communications underway when the routable
   address was configured, and MAY continue to accept new communications
   addressed to the IPv4 Link-Local address.  Ways in which a routable
   address might be configured for the interface include:

   * Manual configuration
   * Address assignment through DHCP
  * Roaming of the host to a network on which the host has a
        valid routable address

   If a host finds that a routable address is no longer assigned to an
   interface, the host MAY identify a usable IPv4 Link-Local address (as
   described in section 2) and assign that address to the interface.
   Ways in which a routable address might no longer be assigned to an
   interface include:

   * Removal of the address from the interface through manual
      configuration
   * Expiration of the lease on the address assigned through DHCP
   * Roaming of the host to a new network on which the address is no
        longer valid.

   Further discussion of address assignment and the detection of network
   attachment is provided in [DNAv4].

Erik Guttman
ZEROCONF WG Chair