Subject: [mobile-ip] Question about the I Bit in the Revocation Acknowledgement Messag e

From: "Ahmad Muhanna"<[email-masked]>
Date: Sun, 24 Mar 2002 14:31:35 -0600

Hello all;

I have the following question about the I bit in the Revocation
Acknowledgement Message as mentioned in section 4.3. in the recent I-D
version 02:

"
I              Inform bit.

               Set to '1' by the foreign agent to ask the home agent
               if the mobile node should be informed of the
               revocation.
"

If the Foreign Agent is sending this message to acknowledge receiving a
Revocation Message what does the above text mean?

Thanks for your consideration and help.

Regards;
Ahmad Muhanna

---

From: "Steven M. Glass" <[email-masked]>
Date: Mon, 25 Mar 2002 17:02:43 -0500 (EST)

> Ahmad,

    There's two things that can be going on with the revocation request, and
revocation acknowledge message, and I suppose the above text may need a bit of
clarification in the scenario you're asking about (the answer to your question
is the last half of this explanation).

    In the spirit of the draft (what I was intending to convey):

    If the FA is sending the revocation message, setting the 'I' bit to 1
means it is asking the HA to set the 'I' bit to '1' if it wants the MN to be
informed of the revocation, and to set the 'I' bit ot '0' if it does NOT want
the MN to be informed.

    If the HA sent the revocation request, and sets the 'I' bit to '1' it is
requesting the FA inform the MN.  If the FA does inform the MN, in the
revocation acknowledgement the FA will set the 'I' bit to 1 (so the second
part here is the specific answer to your question), and if the FA does NOT
inform the MN, it sets the 'I' bit to 0.

    Another way to phrase that text would be:

    In the case of the FA revocing the registration, the 'I' bit is set to 1
to request the home agent instruct the FA to whether the MN should be informed
of the revocation.

    Since this functionality is really up to the FA, it 'advertises' it MAY
leave the decision to the HA in the registration phase, that is based on the
'I' bit's setting in the revocation extension.  The key is how this corelates
to what the FA is doing in the revocation request.  Here are all the possibles
(presuming both sides have implied they understand the 'I' bit int the
registration phase):

    H-1. HA revoking registration, requests the MN be informed.  In this case
the HA sends a revocation message to the FA with the 'I' bit set to 1.  If the
FA informs the MN of it's revocation it SHOULD set the 'I' bit to 1 in the
revocation acknowledgement (this is the specific case you asked about).  If
the FA does NOT inform the MN of the revocation, it SHOULD set the 'I' bit to
0.

    H-2. HA revoking registration, requests the MN NOT be informed.  In this
case the HA sends a revocation messasge to the FA with the 'I' bit set to 0. 
If the FA does NOT inform the MN, it SHOULD reply with the 'I' bit set to 0. 
If the FA does inform the MN of the revocation, it SHOULD set the 'I' bit to 1
(these responses by the FA are exactly as above).

    F-1.  FA revoking registration, wants the HA to respond to whether the MN
should be informed, so it sets the 'I' bit to 1.  If the HA wants the MN to be
informed of the revocation, in the revocation acknowledgement, it sets the 'I'
bit to 1, and if it does NOT want the MN informed, it sets the 'I' bit to 0.

    F-2.  FA revoking registration, doesn't care what the HA wants.  In this
case, where the policy in the foreign realm is not request what the HA wants,
the FA SHOULD not imply the choice will be up to the HA in the registration
phase, that is the 'I' bit should be set to 0 in the revocation extension.  In
this way, if the HA recieves a revocation request with the 'I' bit set to 1,
it can infer the MN was informed of the revocation, and that's just the policy
in the foreign realm.  If the policy in the foreign realm is to always NOT
inform the MN of the revocation, the FA conveys this by setting the 'I' bit to
1 in the registration phase (the revocation extension), then setting the 'I'
bit to 0 in the revocation request (implying it has NOT informed the MN).

     I know it seems a bit complex, but (I think) all the functionality is
there, and only uses essentially 2 bits, or 1 bit in each phase.  Does this
make sense? The other solution would be to go to a 'what the agents wants to
be done in the event of a revocation' at the time of registration, but the
nature of policy means that decision should be made at the time of revocation
because the decision on whether to inform the MN is likely to be effected by
why the revocation is happenning, which is why I propose this model. 
Thoughts?  There may be a way to make this cleaner/clearer.

                              Cheers,
                                  Steve

---

From: kleung <[email-masked]>
Date: Mon, 25 Mar 2002 18:39:04 -0800

Steve,

Is there a reason not to inform the MN?

Isn't it better to always inform the MN and let MN decide what to do
with the information?

Not sure if this has already been addressed, so not including WG alias.

Kent

--
     |           |                   Kent Leung
    :|:         :|:                  IOS Development
   :|||:       :|||:                 Voice: 408.526.5030
  :|||||||:   :|||||||:              Email: [email-masked]
.:|||||||||:.:|||||||||:.            URL  : http://wwwin-mobileip:8000
 c i s c o S y s t e m s             "Enabling the mobile wireless age!"