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:
>>> 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?
> -------------------------------------------
> 
> According to Section 10.4.2 the HA acts as a correspondent node when
> directly communicating with the MN. I suppose the opposite (MN sending
> directly to HA) should also apply. Also the conditions for Route
> Optimization (sending packets directly to the correspondent node, which is
> the HA in this case) on p.109 are true for the HA BUL entry. Or is there a
> rule I have overseen?

Yes, I almost forgot about that paragraph in Section 10.4.2, direct
communication between the MN and HA doesn't seem to be explained in the same
manner, it's kind-of just inferred from Section 11.1.

> -------------------------------------------
> 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
> -------------------------------------------
> 
> IF it knows. I'm not sure if the MN will recognize that the other tunnel
> endpoint has failed.

I would guess that no forward progress is being made would be the way?

Either way, I didn't have any problem inserting this text, I was just curious
about the details.  Section 10.4.2 provides the reason.

Thanks,

-Brian