From: Scott Morris (swm@emanon.com)
Date: Wed Feb 26 2003 - 20:20:23 GMT-3
The foreign agent care-of-address is the "typical" way that mobile IP
works. And it's the announcement of the FA itself saying to the home
agent that 'I know how to get to x.x.x.x' (done through a tunnel). So
for routing purposes, the FA becomes the care-of-address in order to get
to x.x.x.x...
The colocate care-of-address actually implies that sometimes a mobile
node moves onto a roaming network that either has no FA's, or all of the
FA's are busy. This is when it can become it's "own" FA using a
colocated care-of-address. The specifics of how to get one aren't in
the mobile IP RFC's, but DHCP is the primary method. At that point, the
mobile node technically has two addresses, it's "normal" mobile one, and
an address within the roaming networks' scope. It is also possible to
have a pre-determined colocated address configured on the mobile node
So you the network engineer MAY determine things depending on which end
of the problem you are on! If you are on the mobile node/home agent
side, there's nothing you can do. If you are engineering the foreign
agent/roaming network then you are in control of this, and may set up
extra things in order to facilitate this interaction (or not). It would
depend on the mobile node software though as to whether it would take
effect.
If a colocated c/o address is used, the the mobile node will not attempt
to register with the FA router. It will just start sending IP packets
as if it were its own FA.
Hope that helps.
Scott
-----Original Message-----
From: ccie2be [mailto:ccie2be@nyc.rr.com]
Sent: Wednesday, February 26, 2003 5:33 PM
To: Group Study; swm@emanon.com
Subject: Re: Amazing but true
Hi,
Here's the original post regarding care-of-addresses used with Mobile
IP.
With Mobile IP there are 2 types of care-of addresses:
1) Care-of-address acquired from a Foreign Agent
2) Colocated care-of-address
The Cisco docs does a good job of explaining what these are but doesn't
say anything about what determines which type of address is used or why
1 type should be used versus the other.
Do I, as the network engineer, determine which type of address is used?
Does this depend on what mobile node software is installed on the client
or is this configured on the router, and if so, how?
Please help me understand this. Thanks, Jim
----- Original Message -----
From: "Scott Morris" <swm@emanon.com>
To: "'ccie2be'" <ccie2be@nyc.rr.com>
Sent: Wednesday, February 26, 2003 5:30 PM
Subject: RE: Amazing but true
> What was/were the original questions?
>
> Scott
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> Of ccie2be
> Sent: Wednesday, February 26, 2003 2:50 PM
> To: Group Study
> Subject: Amazing but true
>
>
> Hi everyone,
>
> Over the past few weeks, several times I've posted a question
> regarding the two types of care-of-addresses used with Mobile IP. My
> question concerned what detemines which type of address is used and
> whether the type used is something that's configured on the router or
> determined by some other means - perhaps the software installed on the
> mobile client.
>
> What surprises me though is that there hasn't been one single
> response! I don't understand how that could be. I've searched thru
> both the Group Study archieves and Cisco's documentation and found
> nothing addressing this question. I also know that mobile IP is fair
> game for the lab, so I'm amazed that this question continues to go
> unanswered.
>
> And, though I can't understand why that is I've come up with 2
> theories:
>
> a) nobody knows
> b) nobody cares
>
> I can't imagine that nobody on groupstudy knows this - this is
> probably the most knowledgable group of networking professional in the
> world - so let's nix that idea.
>
> Could it be that nobody cares? That's also hard to imagine.
> Everyday, questions seemingly far more esoteric are posted and
> responded to. Besides, there must be at least a few people who might
> need to implement Mobile IP in the near future and they would
> certainly need to know about this. And, even if nobody at the moment
> needed to know about this for work, most people on group study seemed
> to be very intellectually curious So, let's nix this theory as well.
>
> Well, I hope this sparks some discussion, and maybe, in the process,
> generates the answer to the original question.
>
> What do you think?
>
> Jim
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