Subject: Re: [MEXT] [mext] #11: De-registration when returning home[VijayDevarapalli <[email-masked]>]

From: "Vijay Devarapalli" <[email-masked]>
Date: Wed, 9 Jul 2008 15:05:54 -0400

Rajeev,

> 1. HA to stop proxying. Of course the Dereg-BU is supposed to do this.
> However, other nodes on the link will still have their NCE pointing to
> the HA. This leads me to suggest that the MN MUST send an NA (with
> 'O'=1) on the _home link only_ to stop the HA from proxying. 
> ND has link
> scope only and does not affect other links with which the MN may be
> connected to different visited networks (at the same time that it is
> connected to the home link using a different interface).

RFC 3775 already says that the mobile node should sent a Neighbor
Advertisement with the 'O' flag set after it receives the binding ack
from the home agent.

   After receiving the Binding Acknowledgement for its Binding Update to
   its home agent, the mobile node MUST multicast onto the home link (to
   the all-nodes multicast address) a Neighbor Advertisement [12], to
   advertise the mobile node's own link-layer address for its own home
   address.  The Target Address in this Neighbor Advertisement MUST be
   set to the mobile node's home address, and the Advertisement MUST
   include a Target Link-layer Address option specifying the mobile
   node's link-layer address.  The mobile node MUST multicast such a
   Neighbor Advertisement for each of its home addresses, as defined by
   the current on-link prefixes, including its link-local address and
   site-local address.  The Solicited Flag (S) in these Advertisements
   MUST NOT be set, since they were not solicited by any Neighbor
   Solicitation.  The Override Flag (O) in these Advertisements MUST be
   set, indicating that the Advertisements SHOULD override any existing
   Neighbor Cache entries at any node receiving them.

> 3. When the MN returns home, we should have a consistent 
> semantics about
> de-registration regardless of other networks the MN may be 
> connected to.
> Limiting the actions to a) NA ('O'=1), followed by, b) Dereg-BU on the
> particular home link, I believe we can achieve that.

Currently, RFC 3775 specifies b) followed by a). For changing the order,
we might need a separate discussion. Not on this thread.

Vijay
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---

From: Suresh Krishnan <[email-masked]>
Date: Wed, 09 Jul 2008 15:44:20 -0400

Hi Vijay,

>    Neighbor Cache entries at any node receiving them.

Yes. This is the case. But what "override" means is defined by RFC4861 
and not by RFC3775.

Let's say the MN has a home address HoA_X and and the HA is defending 
this address. Another node A on the same link has been communicating 
with the MN through the HA and has a neighbor cache entry that looks 
like this

HoA_X : LLaddr_of_HA : REACHABLE

Receipt of the NA from the MN with a different LL addr will set it to

HoA_X : LLaddr_of_HA : STALE (if O=0 in the NA)

or

HoA_X : LLaddr_of_MN : STALE (if O=1 in the NA)

In either case the receiving node A has to perform NUD before 
communicating to the MN. So there will be a disruption of service.

Cheers
Suresh