Subject: [Mip4] A question about Agent discovery

From: "Zhang DaWei-E13742" <[email-masked]>
Date: Mon, 25 Sep 2006 11:59:08 +0800

Hi,all
 
    How Mobile Node find it needs to re-register when it entered a new
foreign network while there are no FA in old or new foreign net?
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From: "Bjorn Andersson" <[email-masked]>
Date: Mon, 25 Sep 2006 08:46:16 +0300

> foreign network while there are no FA in old or new foreign net?

This is not specificied by the RFC but upto the implementation. One
way is to do DHCP discovery when an link change is reported by the
operating system. When the MN gets a new IP adresses, that it has got
either via DHCP or manually configured or by some other means, it can
then register the colocated care-of address.

  Bjorn

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From: Vijay Devarapalli <[email-masked]>
Date: Mon, 25 Sep 2006 07:30:36 -0700

> foreign network while there are no FA in old or new foreign net?

each link change should be treated as potentially
attaching to a new IP subnet. take a look at RFC 4436.

Vijay

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From: Alexandru Petrescu <[email-masked]>
Date: Mon, 25 Sep 2006 16:51:10 +0200

Bjorn Andersson wrote:
> operating system.

Remark a "link change" reported by a card doesn't necessarily mean a
subnet change.  A subnet change happens when the subnet prefix has
changed.  Also, the card sometimes reports up/down but it connects to
same subnet.

> When the MN gets a new IP adresses, that it has got either via DHCP 
> or manually configured or by some other means, it can then register 
> the colocated care-of address.

Going further on the DHCP line...

Movement detection on MN can be implemented by comparing the MAC address
  of the first message coming from the DHCP Server (or Relay).  DHCP has
several scenarios of message exchange.

For example, the initial exchange is a 4 message exchange (disover,
offer, request, ack) but subsequent exchanges are shorter (e.g. renew,
ack, or rebind, ack).

Normally (heh) a handover should involve only (renew, ack), thus the MAC
address of the ack should be used as a differentiator for movement
detection.

Otherwise, the MN could do (discover, offer, req, ack) each time it
changes its AP, in which case it should compare the MAC address of offer.

If (renew, ack) returns error somehow, then MN knows it has changed
subnet, because it is forced to do discover, offer, request, ack.  So in
this case no need to compare the MAC address.

In all cases, implementing movement detection for MIP4 MN using DHCPv4
necessarily implies modifying the DHCP implementation (not the rfc).

Alex