Subject: [Mipshop] Question on HMIPv6 tunneling

From: Mikko Hautala <[email-masked]>
Date: Thu, 28 Jul 2005 11:32:37 +0300

Hi,

I'm a student at the Helsinki University of Technology, working with my 
Master's Thesis.
I have a dilemma on how HMIPv6 is working, and I thought this mailing 
list could be a right place to ask
for advice.

My question is simple (although it has two parts):

On the draft it is said that a bi-directional tunnel is formed beetween 
the MN and MAP and all packets sent
by the MN are tunneled to the MAP (section 6.1 of the HMIPv6 draft).

i) Does this mean, that when MN is communicating to CN through HA using 
reverse tunneling
(one option in 6.1.1 of the HMIPv6 draft), there are actually three IPv6 
headers needed when
MN sends packets to CN ?

Like:

 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  Dest: MAP    Source: LCoA    |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  Dest: HA     Source: RCoA    |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  Dest: CN     Source: HA      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  Layer 4-> headers            |
 .				 .

ii) What about when MAP intercepts packets tunneled from HA to RCoA, 
that already contain
two IPv6 headers - does MAP first decapsulate the packet before 
encapsulating and tunneling
it to the MN's LCoA ? (in my opinion this isn't directly stated in the 
section 6.2 HMIPv6 draft)

Regards,
Mikko Hautala
Helsinki University of Technology
[email-masked]

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---

From: Theo Pagtzis <[email-masked]>
Date: Thu, 28 Jul 2005 10:58:38 +0100

Hi Mikko,

without looking at the details of the protocol headers, I would say that

when the MN communicates with the CN through HA, the communication is 
transparent, ie. the CN is not aware of any tunneling or HA 
interventions. In this light what you put down as

|   . . .                       |

would not be a sensible thing to do, since it is the MN that the CN is 
communicating with (remember that as Reverse tunneling specifies, IP in 
IP is assumed unless stated otherwise).

So let's put down a simple example:

The CN communicates with the MN. Thus we have:

|  Source CN    |    Dest MN    |

The HA applies the functions HA->intercept->tunnel. There we have

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Source HA    |    Dest RCoA  |  (assume that RCoA is the MAP address)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Source CN    |    Dest MN    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Now when the MAP receives the packet it should de-tunnel the packet 
(i.e. remove the outer header), and then attach its own. So the MAP 
functions are MAP->de-tunnel->re-tunnel

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Source RCoA  |    Dest LCoA  |  (fwd path of the bi-dir tunnel)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Source CN    |    Dest MN    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The MN would simply detunnel this to

|  Source CN    |    Dest MN    |

Now (symmetrically) on the return path we should have:

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Source LCoA  |    Dest RCoA  |  (return path of the bi-dir tunnel)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Source MN    |    Dest CN    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

the MAP de-tunnels this and re-tunnels to

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Source RCoA  |    Dest HA    |  (return path of the bi-dir tunnel)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Source MN    |    Dest CN    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

the HA de-tunnels this and then simply dispatches the packet with no 
further intervention.

|  Source MN    |    Dest CN    |

The above are to say that tunneling is not effected end-to-end with 
between the MN/CN. So to aid the implementor the spec should really 
differentiate between

1) A tunnel CHAIN
2) A NESTED tunnel.

IMHO HMIPv6 should effect a tunnel CHAIN. In principle the MAP does not 
'intercept' packets destined to the MN since the RCoA destination would 
be really the MAP address. Instead there the MAP router (i) de-tunnels 
the packet and (ii) sees the home address option and then decides which 
LCoA tunnel to use to send the packet to the MN (i.e. re-tunnels).

Also if we accept that the MAP is a localised instantiation (see LMM 
requirements) of the HA then the MN should really NOT deal directly with 
its home agent. The MAP should be responsible for this. This would give 
us also perfect MN location privacy at the local domain, controlled by 
the MAP, etc..etc.

Hessam of course could verify this, but I would also agree that it would 
be nice if the next HMIPv6 spec revision, could make this clearer, 
perhaps by adding in the above example.

regs
theo

-- 
Theodoros Pagtzis
Nets & Mobile Systems Group
UCL-CS