Subject: [MEXT] Use of simultaneous home and foreign interfaces

From: RYUJI WAKIKAWA <[email-masked]>
Date: Wed, 26 Dec 2007 16:11:35 +0900

Hi all,

This is the proposed text for MCoA.

thanks,
ryuji

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When a mobile node returns home with other interfaces active attached
to foreign link, it MUST decide one of following operations:

1. it returns home and de-registers all the bindings
2. it returns home and shutdown the interface attached to the home link.
   The binding of the old CoA bound to that interface MUST be deleted
   from one of active interface attached to the foreign link.
3. it returns home and continue using all the interfaces attached to
   both foreign and home links.

In order to achieve the scenario3, the home agent MUST intercept all
the packets meant for the mobile node and would decide whether to send
the traffic directly to the home address on the link or tunnel to the
CoA that the mobile node has registered at the home agent. The home
agent would make this decision based on the type of packet/flow.  The
delicate part would be to create a neighbor cache entry for the mobile
node so that the home agent can deliver the packet on-link. The home
agent would need to know the L2 address of the interface with which
the mobile node is attached to the home link.  In order to create the
neighbor cache entry for the mobile node, following operations are
required.

The mobile node sends a de-registration binding update to the home
agent from the interface attached to the home link. In the Binding
Update, the BID sub-option must be stored for the BID assigned to the
interface. The H (Home/Foreign IFs active) flag MUST be set in the BID
sub-option. When the H flag is appeared, the home agent learns that
the mobile node continue using interfaces attached to both foreign and
home links. If H flag is unset, the home agent deletes either all the
bindings or the binding corresponding to the BID (i.e. scenario 1 or
2).

When the home agent sends the Binding Acknowledgment, it MUST stores
one of two new status values in the BID sub-option depending on home
agent configuration at the home link. The new values are:

TBD-A (under 128): NDP is permitted for HoA at home link
TBD-B (under 128): NDP is prohibited for HoA at home link

When the home agent is solo router at the home link, it can intercept
all the packets by IP routing without proxy NDP. It stops proxy ND for
the requested HoA and reply the TBD-A value to the mobile node. The
neighbor cache entry for the mobile node is created by NDP operation
(i.e. NS/NA exchange). On the other hand, if it is not solo router, it
MUST continue defending HoA by proxy NDP to capture all the mobile
node's traffic. The home agent, then, returns TBD-B value in the BID
sub-option. The home agent also requires to learn the mobile node's
layer2 address (i.e. MAC address) during this binding de-registration.
I can keep the learned layer2 address as the neighbor cache entry for
the mobile node so that it can construct the Ethernet header for the
packets meant for the mobile node and forwards them directly to the
mobile node's interface attached to the home link.

According to [RFC3775], the mobile node MUST NOT assigns the HoA to
the interface attached to the home link and MUST NOT attempt NDP
operations for the HoA. It MUST NOT send and reply to Neighbor
Solicitation for the HoA. The HoA must be tentative address at this
moment until it receives Binding Acknowledgment with success status
value.

When it receives the binding acknowledgment and BID sub-option, it
MUST assign HoA at the interface attached to the home link according to
the status field of the BID. If the value is TBD-A, it can start
defending HoA by NDP as a regular IPv6 operation and let the HoA as
valid IPv6 address. The home agent can create neighbor cache entry for
the mobile node by NS and NA exchange as the regular IPv6.

If the home agent receives the TBD-B, it MUST NOT defends its HoA at
the home link by ND. When the mobile node sends packets from the
interface attached to the home link, it MUST learn the layer2 address
(i.e. MAC address) of the next hope (i.e. default router, it can be
home agent) during the binding de-registration and construct the
packet including Ethernet header with the learned home agent's layer2
address.

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