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

[Brian Haley <brian.haley at hp.com>]

Fabian Mauchle wrote:
> -----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.

But wouldn't the BUL entry show that it's communicating with its HA, so it would
use the tunnel?  There wouldn't be a HAO inserted in that case.  How will it
attempt this direct communication?

If the MN somehow disables mobility and removes it's home binding, then it won't
be inserting a HAO, just using basic IPv6.

> - 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.

If the MN knows the tunnel is invalid, it should update it's binding at the HA.

-Brian