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

From: Tsirtsis George <[email-masked]>
Date: Thu, 11 Dec 2003 06:26:41 -0500

"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. 

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?

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.

Regards
George

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From: Alexandru Petrescu <[email-masked]>
Date: Fri, 12 Dec 2003 20:48:12 +0100

Tsirtsis George wrote:
> 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.

In case HAx and HAy are on the same link, another possibility might be
for HAx to send an ICMP redirect through the tunnel to MH instructing it
of the better HAy.

> 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.

If HAx sends a compulsory message to MH such as MH is forced to end its
sessions and anchor to HAy, I think there is no need for this compulsory
message.  I think MH has more information about its present location
being closer to HAy (than to HAx) and can take that decision itself, no
need to exchange compulsory messages with HAx.  My oppinion is.

Alex