Subject: [NSIS] [Fwd: Mobility Issue: Routing state HA->MN]

From: Roland Bless <[email-masked]>
Date: Tue, 30 Sep 2008 14:41:08 +0200

Hi,

I'm forwarding this mail from Max since it didn't get through somehow.
I apologize if its a duplicate in the end...

Subject: Mobility Issue: Routing state HA->MN
From: Max Laier <[email-masked]>
To: "[email-masked]" <[email-masked]>
Cc: Roland Bless <[email-masked]>
Date: Tue, 30 Sep 2008 02:58:03 +0200

Hello,

while implementing mobility aware QoS signaling as per "nsis-applicability-
mobility-signaling" I came across another issue.  This concerns MIP6 tunnel 
mode with co-located Care-of-Address, sender-initiated signaling with CN as 
sender.

The proposed QoS-Signaling looks like this:

  CN (Sender)  HA (Tentry)  Tnode    MN(CoA)    MN(HoA) (Receiver)
       |          |          |          |          |
       | RESERVE  |          |          |          |
       +--------->|          |          |          |
       |          |RESERVE-t |          |          |
       |          +=========>|          |          |
       |          |          |RESERVE-t |          |
       |          |          +=========>|          |
       |          |          |RESPONSE-t|          |
       |          |RESPONSE-t|<=========+          |
       |          |<=========+          |          |
       |          |          |          |          |
       |         (*)         |          |          |
       |          |          |          |          |
       |          |           RESERVE              |
       |          +.------------------------------>|
       |          |           RESPONSE             |
       |          |<-------------------------------+
       | RESPONSE |          |          |          |
       |<---------+          |          |          |
       |          |          |          |          |

At the time denoted by the (*) the HA needs to establish routing state with 
the MN at its HoA by sending a GIST-Query.  The HA uses the signalling source 
address (S=1) in the IP-header [which we currently have to as the existing 
MIP6 implementation refuses to send otherwise, but this is a general problem 
as the HA may use the signalling source anyhow].  The problem with this is 
that the HA has an active MIP6-binding with the MN and will send this message 
in route-optimization mode instead of tunnel mode.  Thus, the first 
intermediate Tnode will intercept the message and try to establish routing 
state of its own.  This results in a GIST-Query back to the HA (since the 
Tnode has likely no MIP6-binding with the MN) and we are in a loop.

The only indication that the Tnode should not intercept the Query is the 
mobility routing header in the IP6-header.

How should this be addressed?  There are a couple of alternatives, neither of 
which seem to be quite "the right thing":

  1) Extend the interception rules to consider the presence of a routing 
header as encapsulation.

  2) Prevent the HA from using "S=1"-mode. (This can't currently be 
implemented due to a ?bug? in existing MIP6 code).

  3) Some local hack to MIP6 to force the packet into tunnel mode.  This would 
be in line with the requirement that "the Query mimics the actual data flow as 
closely as possible", but is difficult to implement and is certainly not in 
the spirit of MIP6.

Any ideas?

-- 
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