Subject: [Mip4] adver lifetime / (re)registration process / FA CoA

From: Matthias Guentert <[email-masked]>
Date: Mon, 20 Sep 2010 22:40:58 +0200

Hello list members

I am doing a small simulation to measure the hand-off latency on
rfc2002 / rfc3344. Now I am asking myself how the registration process
is working in detail:

If a MN is at home and receives advertisement messages in a certain
interval from it's home agent, in which interval should it
(re)-register at the home/foreign agent? Does/Should the MN read the
'lifetime' field received by the advertisement extension and send
registration request out in this interval? Or is the (re)registering
interval detached from the advertisement lifetime?

RFC3344 states on page 20: [...]

_Registration Lifetime_

The longest lifetime (measured in seconds) that this
agent is willing to accept in any Registration Request.
A value of 0xffff indicates infinity. This field has no
relation to the "Lifetime" field within the ICMP Router
Advertisement portion of the Agent Advertisement.

[...]

This is not clear to me. Should there anyway be such a repetitive
re-registration process?

Another question, which does not fit to the subject line:

How is mobile node able to talk to a foreign agent when working in
shared / FA CoA mode? Unfortunately I coudn't find any documents on
this.

Let's assume the following IP addresses

* MN: 192.168.1.4
* HA: 192.168.1.10/24
* FA: 192.168.10.10/24

If the mobile node now moves to the foreign network and keeps it's
home address it will in fact be able to receive broadcast messages
coming from the foreign agent but i will not able to
register/receive/send any data because it's IP address is not
reachable through a route. So how is this working?

I really would be happy if someone could shed some light on this.

TIA, Matthias

---

From: "Charles E. Perkins" <[email-masked]>
Date: Mon, 20 Sep 2010 13:53:31 -0700

Hello Matthias,

Answers below:

> Advertisement portion of the Agent Advertisement.

Since the lifetimes are unrelated, the advertisement
lifetime doesn't have much effect on the registration
lifetime (and vice-versa).

> This is not clear to me. Should there anyway be such a repetitive

The re-registration interval can be over 18 hours long,
so it's not a terrible burden on the network capacity or
the node processing (for most nodes, anyway).

> reachable through a route. So how is this working?

This is the fundamental point of Mobile IP.  The foreign
agent makes sure that it treats the mobile node as neighboring
through one of its network interfaces.  The registration
signaling enables the home agent to deliver packets to the
foreign agent, which then relays each such packet to the
mobile node.

Regards,
Charlie P.

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From: Matthias Guentert <[email-masked]>
Date: Mon, 20 Sep 2010 23:25:32 +0200

Hello Charles

Thank you very much for your really quick reply.

> lifetime (and vice-versa).

Are there any typical values/intervals at which a mobile node should
send out re-registrations?

> foreign agent, which then relays each such packet to the

To get it right: Does the FA in shared CoA mode setup its network
interface to listen on the same IP address as the home agent while
serving a mobile node abroad?

Regards, Matthias

---

From: "Charles E. Perkins" <[email-masked]>
Date: Mon, 20 Sep 2010 14:51:25 -0700

Hello Matthias,

> send out re-registrations?

I reckon there are typical values that are decided
by the operators, but I don't know of specific
examples.

> serving a mobile node abroad?

No, the foreign agent receives encapsulated packets that are
addressed directly to the CoA (i.e., the foreign agent).
After decapsulating each such packet, the FA sees the mobile
node's address and delivers it (e.g., over the air link).

Regards,
Charlie P.