Re: [dhcwg] WG consensus action: ACCEPT LL34 better transition to routable from v4LL using DHCP

Mika Liljeberg wrote:
> On Tue, 2003-09-30 at 20:11, Erik Guttman wrote:
> 
>>I do agree with you.  The DHCP client should not be broken or effected
>>by IPv4LL.  The host stack which uses both will of course be more
>>complex than one which does not.
> 
> 
> Are you saying it is ok to run the DHCP and v4LL state machines
> independently of each other? I just want to be absolutely clear on this.

The DHCP client state machine is not effected by IPv4LL state machine.
The IPv4LL state machine *is* effected by the DHCP client state machine.

Note that according to section 1.7:

    Where a Link-Local IPv4 address has been configured on an interface,
    and a routable address is later configured on the same interface, 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.

This means that the DHCP state machine has succeeded in configuring
an interface, it has implications for the IPv4 link-local interface.

We do not have a diagram of a state machine for IPv4LL, but perhaps
that would be very useful.  I think it would look something like
this:

      Interface is active and has no <---------------------+
      IPv4 address configured                              |
              |                                            |
              v    interface has IPv4 addr configured?     |
      +-->  INIT ---------------------------------------> EXIT
      |       | 2.2          1.7                         ^  ^
      |       v    <-------------------+                 |  |
      |     SELECT <---+               |                 |  |
      |       | 2.1    | ARP with      |                 |  |
      |       v        | claimed       |                 |  |
      |     CLAIM      | address     ADAGIO              |  |
      |       ^ | 2.2.1| received      ^                 |  |
      | 2.2.1 | v    --+               |2.2.1            |  |
      |   CLAIM-WAIT ------------------+                 |  |
      |       | 2.2.1 -----------------------------------+  |
  2.5 |       v        interface has IPv4 addr configured?  | 

    DOUBT  ANNOUNCE          1.7                            | 

      ^|      | 2.4                                         |
      |+->      v      interface has IPv4 addr configured?  |
      +-- CONFIGURED ------------------------------> DEPRECATED
      2.5  ^     | 2.5       1.7
conflict! |     |
           +-----+
            defend

   State       Behavior
   ==========  =============================================
   INIT        Host has no configured IPv4 address on an
               interface.  INIT waits before entering SELECT
               state.  If INIT detects it has been configured
               during this time, INIT goes to EXIT state.  See
               Section 2.2.

   SELECT      Select a suitable address.  See Section 2.1.  The
               only possible transition is to CLAIM state.

               A special case of SELECT is where the host has
               woken up and previously had a link-local address
               configured.  In this case, the previously configured
               is selected.  See Section 2.2.

   CLAIM       Send a probe as per Section 2.2.

   CLAIM-WAIT  Wait for any ARP messages with the claimed
               address originating from a different sender.

               If interface is configured during this wait
               period enter EXIT state, do not configure an
               IPv4 LL address.  See Section 1.7.

               If an ARP message indicates that the selected
               address is in use, and this is the first through
               nineth retry, enter SELECT state.  If this is
               the tenth or more retry, enter ADAGIO state.
               See Section 2.2.1.

               If no ARP message is detected as the result of
               the probe after the wait duration ends, and this
               is the first or second try, return to CLAIM state.
               If this is the third try, enter the CONFIGURED
               state.  See Section 2.2.1.

   ADDAGIO     Wait at least a minute then enter SELECT state.

   ANNOUNCE    Send ARP announcements the enter CONFIGURED
               state.

   CONFIGURED  The link-local address has been configured for
               the interface and is now usable.  The host must
               respond to three events.

               If a claim is detected, respond with a defending
               ARP.  Stay in CONFIGURED state.

               If an ARP with a conflicting assignment of the
               configured address is detected, defense may be
               undertaken once (enter the state of DOUBT) or
               go directly to INIT state, surrendering the
               configured address.

   DOUBT       If an ARP with a source address is detecting
               which conflicts with the configured address
               during 10 seconds, proceed to INIT state.
               See Section 2.5.

               Otherwise, the conflicting use of the address
               has been defended against.  Return to the
               CONFIGURED state.  See Section 2.5.

   DEPRECATED  This state is entered when a link-local address
               has been autoconfigured for an interface, then
               subsequently the interface receives a configured
               address (as from DHCP).  In this state, new
               connections are established with the configured
               address and the link-local address is not advertised.
               Eventually, one SHOULD transition to EXIT state.
               See Section 1.7.

   EXIT        Cease using the IPv4 link-local address, do not
               attempt to configure another such address unless
               an interface exists for which there is no IPv4
               link-local address configured.



I hope that this makes it clear:  In each case where there is
a transition marked "interface has IPv4 addr configured? 1.7"
this could be caused by the DHCP state machine entering BOUND
state.  It is also possible to transition from EXIT to INIT
in the case where a configured address is no longer available.
We do not enter into a full discussion of this transition in
this specification.  It is considered in more detail in
http://www.ietf.org/internet-drafts/draft-ietf-dhc-dna-ipv4-02.txt

Erik