Re: [MEXT] Issue #18 ["Home Address Option & ICMP / Binding errors"], part 3 of 3: "Receiving Binding Errors"

[Fabian Mauchle <f1mauchl at hsr.ch>]

-----Ursprüngliche Nachricht-----
Von: mext-bounces at ietf.org [mailto:mext-bounces at ietf.org] Im Auftrag von
Brian Haley
Gesendet: Mittwoch, 27. Mai 2009 05:38
An: Charles E. Perkins
Cc: mext
Betreff: Re: [MEXT] Issue #18 ["Home Address Option & ICMP / Binding
errors"], part 3 of 3: "Receiving Binding Errors"

Hi Charlie,

I might as well comment on all three of these :)

Charles E. Perkins wrote:
> 
> Hello folks,
> 
> Last month, issue #18 showed up without any fanfare on the
> issues tracker list:
>    http://trac.tools.ietf.org/wg/mext/trac/ticket/18
> I'd like to initiate discussion on the points raised as part
> of issue #18.  There are three main points, which can be
> discussed separately.  In this note, I transcribe the
> discussion about the third of the three points.
> 
> =============================================
> 
> Receiving Binding Errors
> 
> In Section 11.3.6. Receiving Binding Error Messages, it is not
> considered that Binding Error Messages can also come from Home
> Agents when acting as a Correspondent Node to its Mobile Nodes
> [see also issue #12]. It is only defined that:
>    "If the mobile node has no upper layer progress information,
>    it MUST remove the (Binding Update List) entry (from the
>    Correspondent Node) and route further communications through
>    the home agent. It MAY also optionally start a return
>    routability procedure (see Section 5.2)."
> 
> If the Correspondent Node is the Home Agent, it is likely that
> there is also no tunnel to route communications through. This
> case may happen if the Home Agent reboots without a persistent
> storage of its Binding Cache.

Will this actually ever happen?  A MN should only ever get a Binding Error
from
it's HA in response to a BU, which might have Status set to 2.  Otherwise,
packets are being sent in the MN-HA tunnel, which doesn't use a HAO, which
is
what Status value 1 is for, which is what Section 11.3.6 is referring to.

> Proposal: If the Binding Error Message was sent by the Home Agent,
> the Mobile Node SHOULD send a Binding Update to the Home Agent
> according to Section 11.7.1.

I *guess* that's ok, depending on how it's inserted in this section, maybe
the
reporter can explain this issue better?

-Brian
------------------------------------------

I will try to:

- Suppose the MN has successfully bound to its HA.
- Now the HA crashes, losing all of its Binding Cache and Tunnel
information. This means that the Tunnel to the MN is now invalid. Any
further packets sent thru the tunnel will be dropped at the HA.
- The MN now starts a direct communication with the HA. (e.g. the user pings
the HA to check if it's alive). As the MN still has a Binding Update List
entry with the corresponding addresses, it will add a HAO to the packet and
send it directly to the HA.
- Upon reception, the HA checks the HAO and will not find a matching Binding
Cache entry and return a Binding Error.
- According to 11.3.6, the MN should now use the Tunnel, which is still
invalid.

Fabian