Subject: RE: [Mip4] WG adoption call on draft-kulkarni-mobileip-dynamic-as signment-02.txt

From: Kent Leung <[email-masked]>
Date: Thu, 11 Dec 2003 15:40:22 -0800

At 06:26 AM 12/11/2003 -0500, Tsirtsis George wrote:

>  "I support the adoption of this document as a workgroup document"
>
>
>A little bit more thought should be put into redirection from one assigned
>HA to another. This is the case where a MN is registered with HAx and
>potentially has active sessions based on the assigned HoAx. Based on section
>4.2.2, HAx may for example detect that the MN is moving too far away from
>HAx and closer to HAy. HAx can then reject the next RREQ from the MN with a
>REDIRECTED-HA-ADDRESS Extension pointing to HAy. According to the current
>text the MN has now no choice but dropping HoAx (and all its associated
>sessions) to register with HAy which should provide HoAy. This will cause
>sessions to drop for the benefit of optimizing routing...not ideal IMO.

Right.  The assumption is that the MN is intelligent enough to decide 
exactly when
to re-anchor with a new HA (such as in idle state).  While MN has an active
session, it needs to maintain HoAx by setting the HA Address field to HAx
and not AZOA.

>One way to avoid this is to introduce a flag that specifies the redirection
>as optional or compulsory. If it is optional the MN should be able to stay
>with HAx for a while longer (e.g.: until current sessions stop and MN is
>idle). This may also require the REDIRECTED-HA-ADDRESS Extension (with
>flag=optional) to be attached to positive RREP rather than rejections. If,
>however, flag=compulsory (due to policy or other reasons) then the MN will
>have to register with HAy immediately per current draft and
>REDIRECTED-HA-ADDRESS Extensions will be attached to a reject RREP.
>
>Thoughts?

Redirection is optional or compulsory based on the HA address field being 
set to
HAx or AZOA.  If MN wants to stay with HAx until the active session
terminates, then the HA address field is set to HAx.  If MN don't care which HA
is being used, and want optimal routing, then AZOA should be used in RRQ.

Does this satisfy your needs?

>Finally, I think the draft would benefit from some clarification about how
>dynamic/static HoA allocation is affected by HA redirection. When HA
>redirection is used for load balancing (i.e.: all HAs are likely to be able
>to handle all HoA prefixes) MNs with static HoAs may be redirect. This can
>not be done if the HA redirection is used to provide a local HA to the MN in
>which case the assigned HAs are not likely to support all the HoA prefixes.

Right, we should add more content on this topic.  My take on this is that for
RRQs with static HoAs, the HoA field provides indication to the entity that's
doing redirection to reach the proper HA (one that has the HoA subnet).

Kent

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From: Tsirtsis George <[email-masked]>
Date: Fri, 12 Dec 2003 14:31:21 -0500

inline

-----Original Message-----
From: Pete McCann [mailto:[email-masked]]
Sent: Friday, December 12, 2003 6:56 PM
To: Tsirtsis George
Cc: 'Alpesh'; 'Kent Leung'; Henrik Levkowetz; [email-masked]
Subject: RE: [Mip4] WG adoption call on
draft-kulkarni-mobileip-dynamic-assignment-02.txt

George, I'm sure you didn't mean that exactly. :)

GT> just joking :-)

Anyway, I wonder why the HA is in a good position to do a redirect to
a "more local" HA, especially because the two HAs are by definition
not local to each other and are likely to be in different
administrative domains.

GT> Whether the HAs are in same or different administrative domains is a
matter of deployment. In my day job I am dealing with wide area Mobile IP
deployments and as such it is very possible that clusters of HAs are serving
different geographical areas under the same administrative domain.

Instead, it seems like the MN could implement some policy for shifting
its HA, based on information about the domain to which it is connected
(FA NAI?) and the existence of any local sessions.  Note that "local
sessions" may include low-traffic TCP connections (terminal shells)
which it may be difficult or impossible for the HA to detect.

GT> Thus I think redirection should most of the time be optional/

When no local sessions exist, the MN could request the assignment of a
new HA based on the existing draft.  It could even leave its existing
registration in place for a period of time if it wanted to overlap the
two registrations.

GT> Well, my point is that it might not be possible for the mobile to know
that it would be a good idea to redirect. Anyway, I am trying to make a
logical point in this case but I do not see this as a major requirement in
the real world at least as far as I can see. To make that clear, in the part
of the real world that I am dealing with the mobile is in a position to know
when it is time to choose another HA and thus to optimize its routing. 

GT> As an engineer, however, I see that in the general case it might be the
case that the HA knows the topology better than the mobile. Generally
speaking operators do not like end points to know a lot about the topology
of the network (and NAIs are not always advertised by FAs and are not
available when CCoAs are used). The HA, however, IS part of the topology so
an operator may configure such info in the HAs. 

GT> Anyway, I am not going to defend this idea for too much longer :-)

George