Subject: Re: [Mip6] Non-tunnelled Echo Req MN to HA

From: RYUJI WAKIKAWA <[email-masked]>
Date: Thu, 4 Jan 2007 13:06:00 +0900

Hi Alex,

On 2006/12/29, at 21:10, Alexandru Petrescu wrote:

> Francis Dupont wrote:
>> In your previous mail you wrote:
>>> I'm trying to clarify the following ping scenario: MN sends an ICMP
>>>  Echo Request to its HA, as a non-tunnelled packet.  Src: CoA, Dst:
>>>  HA@ and DO: HoA.
>>> Remark this is a non-tunnelled packet.
>> => in fact it is the standard way to send a direct packet from MN  
>> to HA (as the HA is a common CN for direct traffic).
>
> Yes, it is the standard way to communicate between MN and HA.  I'm not
> sure though what is meant by 'HA is a common CN' in usual discussion.
> This is something we've discussed separately (eg does HA send a  
> BRR, as
> a CN would) and there was no conclusive decision.  This is something
> needed very often in implementation.  For example let's say I  
> embark in
> implementing an HA.  Should I make it send BRRs or not.

Yes, you should if HA needs to communicate with MNs whose home prefix  
is other than the HA's one.
HA always be HA only for own MNs, and can be correspondent node for  
other MNs.
This is very clear from 3775.

Of course, you can skip implementation of BRR if your HA never  
communicates with other MRs.

ryuji

> This pinging HA question also reflects a need for clarification.
>
>>> Should the HA simply send back ICMP echo replies to the CoA?  Or  
>>> should the HA be bothered by the HoA in DO and send back the echo  
>>> reply _only_ if the corresponding binding cache entry (HoA-CoA)  
>>> exists, and otherwise send a Binding Error to MN?
>> => none of them: the HA ICMP engine should send replies to the MN HoA
>>  and the MIPv6 code should add a type 2 RH through the registered CoA
>>  (which can be the same of a different address).
>
> Ok.
>
>>> I'm tempted to say that HA should ignore the HoA in DO and just
>>> reply back to MN.  MN and HA should still act as simple hosts and
>>> ping each other non-tunnelled.
>> => if you want that you must avoid the DO, usually it is done by  
>> forcing the source address to the CoA.
>
> Errr... I understand the principle: don't put DO in Echo Req and thus
> the Echo Reply won't have an RH.  (the src address _is_ the CoA).  But
> the ping program is not capable to optionally add DO or not.
>
>> Merry Christmas!
>
> Thanks !  Et Bonnes Fetes !
>
> Alex
>
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---

From: Alexandru Petrescu <[email-masked]>
Date: Mon, 08 Jan 2007 16:44:25 +0100

RYUJI WAKIKAWA wrote:
>>>> I'm trying to clarify the following ping scenario: MN sends an 
>>>> ICMP Echo Request to its HA, as a non-tunnelled packet.  Src: 
>>>> CoA, Dst: HA@ and DO: HoA. Remark this is a non-tunnelled 
>>>> packet.
>> Yes, it is the standard way to communicate between MN and HA.  I'm 
>> not sure though what is meant by 'HA is a common CN' in usual 
>> discussion. This is something we've discussed separately (eg does 
>> HA send a BRR, as a CN would) and there was no conclusive decision.
>>  This is something needed very often in implementation.  For
>> example let's say I embark in implementing an HA.  Should I make it
>> send BRRs or not.
> 
>  is other than the HA's one. HA always be HA only for own MNs, and
> can be correspondent node for other MNs. This is very clear from
> 3775.

What's clear in 3775 is that CN sends BRR, not HA.

It is good for HA to send BRR to its MNs (that do have same home
prefix), because a renewing BU to HA (one that is sent right before the
BC entry expires) can get lost; at that point the HA can send a BRR to
its MN before deleting the BC entry.

This is not specified in 3775.

> communicates with other MRs.

Ok, but I think it makes sense for an HA that is not CN to anybody to
send BRR to its own MNs.

Alex