Re: [MEXT] Comments on draft-ietf-mext-binding-revocation-02

["Stupar, Patrick" <[e-mail]>]

Hi Ahmad,

Please see answers inline

Best Regards,

Patrick

> -----Original Message-----
> From: Ahmad Muhanna [mailto:[e-mail]]
> Sent: Friday, December 12, 2008 2:34 AM
> To: Stupar, Patrick
> Cc: [e-mail]
> Subject: RE: Comments on draft-ietf-mext-binding-revocation-02
> 
> Hi Patrick,
> Thanks for your review. Please see responses inline.
> 
> Regards,
> Ahmad
> 
> 
> > -----Original Message-----
> > From: Stupar, Patrick [mailto:[e-mail]]
> > Sent: Wednesday, December 10, 2008 7:19 PM
> > To: Muhanna, Ahmad (RICH1:2H10)
> > Cc: [e-mail]
> > Subject: Comments on draft-ietf-mext-binding-revocation-02
> >
> > Hi Ahmad,
> >
> > I have reviewed binding revocation draft and have the
> > following comments/questions.
> >
> > - In MIPv6, Binding Update and Binding Ack have two different
> > MH type values. Why isn't the same approach taken for BRI and
> > BRA and only one value is used?
> 
> [Ahmad]
> This was discussed on the mailing list for a long time and agreed that
> using one MH type will help in preserving the MH type space. I believe
> the "Heartbeat Mechanism for PMIPv6" is a wg doc in Netlmm and use one
> MH type for the Request and Response. On the other hand, do see an
> issue
> or problem in having a single MH type for both messages?

[Patrick] If the WG is worried about MH type space then I am fine with
the proposed message format.

> 
> >
> > - BRI has a revocation trigger field which is used for two
> > main usages.
> > One is the provisioning of the reason why the revocation was
> > sent (e.g.
> > inter-MAG handoff) and the other is related to specific
> > binding revocation procedures (e.g. IPV4 HoA Binding only,
> > Per-Peer Policy). I think it would be cleaner if the two
> > concepts remain separated in the messages, for instance
> > defining additional flags for Per-peer policy or
> > IPv4 HoA Binding only.
> 
> [Ahmad]
> I see what you are saying. However, as you said, the Revocation
Trigger
> field is defined to give the reason which caused the revoking node to
> send the BRI message. Thus far, I believe all of the defined values
are
> inline with that definition or reasoning. For example: When the LMA
> sets
> the R. Trigger value to "IPv4 HoA Binding Only" it means that the
> reason
> behind sending this BRI message is to revoke the IPv4 HoA address in
> the
> case that the MN is assigned two proxy HoA(v4 & v6) for the same pCoA.
> I
> do not see this as a policy decision, because it is no difference from
> the MAG sending a BRI with R. Trigger value is set to for example,
> "Access Network Session Termination"
> 
> As for the R. Trigger value of "Per-Peer Policy", This is only
> restricted to Global Revocation when the (G) bit is set. I still
> believe
> that "Per-Peer policy" also indicate the reason that allowed the LMA
to
> send this Global BRI. Do you have a different name for this R. Trigger
> value that would fit better?
> 

[Patrick]IMHO "IPv4 HoA Binding Only" is not the reason that triggered
the BRI, it's the action that the MN is requested to perform. Anyhow, my
concerns were not related to the list of reasons in the revocation
trigger, but to the fact that some values of the field imply some
actions and other values don't. My suggestion is that the actions are
taken by MN and HA based on flags (e.g. Global Revocation) and not on
the revocation trigger. Only the case of "IPv4 HoA Binding Only" lacks
of a proper flag.  


> >
> > - In the draft you refer to MAG identity, where is this term
> > defined? I wasn't able to find it in RFC 5213.
> 
> [Ahmad]
> Actually, under section 4.1. "Peer Authorization Database (PAD)
Example
> Entries", you can find the MAG-ID is defined there as mag_identity_1.
> It
> is the same concept here. However, I agree that we do not have a
> mobility option which is specific for carrying MAG-ID but the draft is
> using the MN-ID in a very specific scenario. How the LMA would check
if
> this MAG is authorized for Global revocation is out of scope.
> 

[Patrick] what I meant here is that in section 2 of RFC5213 there is the
definition of MN identity and that I would expect something similar for
the MAG in BRI draft. For MN identity, RFC5213 claims that MAC address
or NAI can be used. Are there similar guidelines for MAG identity?  


> >
> >
> > Some other comments related to specific sections:
> >
> > - page 21: in the first section after the bullet list, there
> > is the following sentence:
> > "As described in Section 7.3, the LMA SHOULD retransmit this BRI to
> >    the MAG before deleting the mobile node IP tunnel to the mobile
> >    access gateway until it receives a matching Binding Revocation
> >    Acknowledgement or the BRIMaxRetransmitNumber is reached. "
> > But this doesn't always apply, e.g. in case of inter-mag
> > handoffs. What am I missing?
> 
> [Ahmad]
> Yes, I see what you are saying here. It seems that the text needs some
> tweaking.
> Do you have any suggestion?
[Patrick] How about referring to the BCE?
Proposed text:
"As described in Section 7.3, the LMA SHOULD retransmit this BRI to
the MAG before deleting BCE until it receives a matching Binding
Revocation
Acknowledgement or the BRIMaxRetransmitNumber is reached. " 
Though I am not sure this text is helpful as it is already captured
later in the draft.


> 
> >
> > - why is the A bit setting mandatory in case of IPv4 HoA
> > binding only revocation?
> 
> [Ahmad]
> May be if you tell me why not, we could change it?

[Patrick] I have nothing against it. But that "MUST" implies that a BRI
with the "IPv4 HoA Binding Only" value in the revocation trigger field
and A bit not set is not properly formatted. What does the MAG do in
this case?

> 
> >
> > - section 10.1.1:
> > "BRI MUST be formatted as in Section 6.1 and if the (P) bit is set,
> >       the mobile access gateway must validate that the
> > impacted binding
> >       have the proxy binding flag set."
> > MAG is not supposed to have any proxy binding flag or is it?
> > How can it validate this flag?
> 
> [Ahmad]
> Good catch. There is another incident below it too.
> What about the following text for both bullets:
> "
>    o  BRI MUST be formatted as in Section 6.1 and the (P) bit is set.
> 
>    o  If the Global (G) bit is set and the Revocation Trigger field is
>       set to "Per-Peer policy", the mobile access gateway identify all
>       bindings that are registered at the LMA and hosted at the MAG.
>       This Binding Revocation Indication does not include any other
>       mobility options. In this case, the MAG MUST send a BRA with the
>       appropriate status code to the LMA.
> "
> 

[Patrick] fine with me, thanks

> >
> >
> > -section 11.1
> > " If the Acknowledgement (A) bit is set in the Binding Revocation
> >       Indication and the MN has the BCE in registered state,
> > the mobile
> >       node MUST send a Binding Revocation Acknowledgement."
> >
> > MN has no BCE, it has a binding update list.
> [Ahmad]
> Right. Thx. What about the following:
> 
>    o  If the Acknowledgement (A) bit is set in the Binding Revocation
>       Indication and the MN has a Binding Update List entry for the
> source
>       of the BRI message, the mobile node MUST send a Binding
> Revocation
> 
>       Acknowledgement. However, in all other cases when the (A) bit is
> set
>       in the BRI, the mobile node SHOULD send a Binding Revocation
> Acknowledgement.
>       In all cases, the mobile node MUST follow Section 11.2 when send
>       a BRA using the appropriate status code.
> 
[Patrick] I would perform the check based on the HoA and CoA contained
in the BRI. 
Proposed text:

   o  If the Acknowledgement (A) bit is set in the Binding Revocation
      Indication and the MN has a Binding Update List entry for the Care
of address and the Home Address
      Contained in the BRI message, the mobile node MUST send a Binding
Revocation

      Acknowledgement. However, in all other cases when the (A) bit is
set 
      in the BRI, the mobile node SHOULD send a Binding Revocation
Acknowledgement.  
      In all cases, the mobile node MUST follow Section 11.2 when send 
      a BRA using the appropriate status code.


> >
> > -section 11.1
> > "If the Revocation Trigger field value is "Administrative Reason",
> >       the mobile node MUST NOT try to re-register with the home
agent
> >       before contacting its home operator."
> >
> > I don't think that BRI specs have to mandate the MN to
> > contact the home operator, the text at the end of section
> > 11.1 is enough IMO.
> >
> [Ahmad]
> I see your point, It seems a very strong requirement and for a well
> behaved MN implementation, it may not be a problem to remove the whole
> bullet. However, for a non-well behaved MN, it may be necessary to
keep
> something. What about if we demote MUST NOT to SHOULD NOT. Would that
> work?
> 
> 
[Patrick] I was not worried about the "MUST" or "SHOULD", but by the
fact that IMO the action to be taken after receiving a BRI with that
value in the trigger field is implementation dependant as already
described later in the draft

> NEW TEXT:
>    o  If the Revocation Trigger field value is "Administrative
Reason",
>       the mobile node SHOULD NOT try to re-register with the home
agent
>       before contacting its home operator.
> 
> TEXT at end of 11.1 that Patrick is referring to:
> 
>    The Revocation Trigger field value in the received Binding
> Revocation
>    Indication could be used by the mobile node to define what action
> the
>    mobile node could do to be able to register again and receive its
IP
>    mobility service, e.g. contacting its home operator.
> 
> > I have some typos and editorial corrections as well, I will
> > send them off-list.
> 
> [Ahmad]
> Please send them. Thanks for your review and good comments!
> 
> >
> > Regards,
> >
> > Patrick
> >
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