Subject: [netlmm] Proposed text for resolving the multi-homed host issue

From: Basavaraj Patil <[email-masked]>
Date: Sun, 30 Sep 2007 17:31:08 -0500

Hello,

Below is proposed text for resolving the current impasse on the multi-homed
host issue. 

At this time, we do not seem to be making much headway on closing this
issue. We (authors) recognize the issue... But we believe that a complete
solution to the problem needs to be dealt with separately and hence it is
perfectly okay to state that it is out-of-scope of this specification. The
WG can decide to work on the issue as a separate effort.

The proposed text will hopefully be sufficient to close this issue and move
forward. Else we would like to request the chairs to get consensus from the
WG on the proposed text.

"

Sec x.y TBD

   A mobile node which has multiple interfaces may attach to different
   MAGs in a Proxy Mobile IPv6 domain simultaneously. If the mobile node
   is identified by a common MN-ID, the LMA will receive multiple proxy
   Binding Updates from the MAGs to which the mobile node is attached to
   via its multiple interfaces. The LMA cannot differentiate whether the
   Proxy Binding Update from the second MAG is a result of:
   a. the mobile node performing a handoff or
   b. the mobile node attaching via a second interface to another
      MAG in the Proxy Mobile IPv6 domain.

   A host which receives the same prefix from different access routers
   (i.e MAGs) may end up with duplicate addresses being configured on the
   interfaces when IPv6 stateless address auto-configuration is used and
   not based on a unique ID such as an L2 identifier. The behavior of the
   mobile node in such a scenario is unpredictable as it depends on the
   implementation of how duplicate addresses on the interfaces of the
   host are handled. Therefore this  behavior of a multi-homed host
   attaching to a Proxy Mobile IP6 domain via multiple interfaces is
   implementation dependent and out-of-scope for this document.

   As far as this document is concerned, the LMA maintains only a single
   binding cache entry for the mobile node at any given time. This
   binding cache will have the IP address of the MAG that last sent
   a successful Proxy Binding Update as the care-of address. Since the
   mobile node is attached to multiple MAGs, each MAG will keep
   attempting to refresh the binding cache entry in the LMA. This will
   cause the binding cache entry for the mobile node in the LMA to keep
   oscillating between MAGs. This situation becomes recoverable if the
   mobile node turns off one of the interfaces or if the LMA instructs
   one of the MAGs to stop sending proxy BUs for the mobile node.

   In the context of this document, where no changes or enhancements to
   the mobile node are possible, a complete solution for multi-homed
   hosts is considered to be out-of-scope.
"

-Raj

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---

From: Vijay Devarapalli <[email-masked]>
Date: Sun, 30 Sep 2007 17:17:03 -0700

Hi Raj,

Further changes. I don't think a typical host implementation would 
assign the same address to two different interfaces. Here is the new text.

Folks, please comment on the following text.

   A mobile node which has multiple interfaces may attach to different
   MAGs in a Proxy Mobile IPv6 domain simultaneously. If the mobile node
   is identified by a common MN-ID, the LMA will receive multiple proxy
   Binding Updates from the MAGs to which the mobile node is attached to
   via its multiple interfaces. The LMA cannot differentiate whether the
   Proxy Binding Update from a given MAG is a result of the mobile node
   performing a handoff or if the mobile node attaching via a second
   interface to another MAG in the Proxy Mobile IPv6 domain.

   Since the mobile node is attached to the same Proxy Mobile IPv6 domain
   with both interfaces, it may receive the same prefix on both
   interfaces. Typical host implementations do not allow assigning the
   same address to two different interfaces. If the mobile node performs
   IPv6 stateless address auto-configuration using different interface
   identifiers, then it would end up with different addresses from the
   same prefix on the two interfaces. Then it becomes a multi-homed host
   in the Proxy Mobile IPv6 domain.

   As far as this document is concerned, the LMA maintains only a single
   binding cache entry for the mobile node at any given time. This
   binding cache entry will have the IP address of the MAG that last sent
   successful Proxy Binding Update as the care-of address. Since the
   mobile node is attached to multiple MAGs, each MAG will keep
   attempting to refresh the binding cache entry in the LMA. This will
   cause the binding cache entry for the mobile node in the LMA to keep
   oscillating between MAGs. This situation becomes recoverable if the
   mobile node turns of the one of the interfaces or if the LMA instructs
   one of the MAGs to stop sending proxy BUs for the mobile node.

Vijay