From: Scott Morris (swm@emanon.com)
Date: Sat May 28 2005 - 17:22:35 GMT-3
The client software on the MN will take care of all this.
How does your workstation normally work? You have an IP address, a netmask
and (presumably) a default gateway. One of the first things you do (at
least on Windows) is ARP for your default gateway. You either find it or
you don't.
If you are a windows machine, you actually also send out a multicast to the
AllRouters address and presumably listen for IRDP alternatives as well.
So if you aren't on your native network, your mobile client software will
figure this out. In addition when it hears an IRDP announcement, it now has
confirmation of being someplace else (since the announced gateway is not
going to be on it's own configured subnet). We take a lot of this for
granted since we live in a DHCP world most of the time, and this magic just
happens!
So with IRDP comes the MN registration process. That tags to the FA who
talks to the HA (either through an existing or setting up a tunneled
connection) and the MN binding table gets populated.
Assuming that the HA does not NEED to be where the actual network/host
normally resides, it's simply a router that allows for /32 routes to be
learned, registered and then redistributed into the IGP back home so
everyone else knows where this /32 is instead of the /24 it may normally be
part of.
As I said, there's a time involved with the registration, so after a while
the /32 route the HA learns will timeout and not be renewed. When this
happens, we assume that either the client has shut off (and no routing needs
to happen in that direction) or that it will show up back on the network
where the original /24 exists (so normal routing resumes).
It's a client-driven concept though. IRDP is only used to announce to the
MN client software of a way to get someplace.
Scott
PS. Look who's talking! :) I'm doing this between chores! Got home last
nite from teaching a class, then had to fix my own network this morning from
a bizzare cable meltdown. So I'm recovering and catching up on the e-mails!
Playing games too! And bouncing my daughter too... So I'm doing well at
multitasking!
Have a great weekend!
-----Original Message-----
From: ccie2be [mailto:ccie2be@nyc.rr.com]
Sent: Saturday, May 28, 2005 4:05 PM
To: 'Scott Morris'; 'Stephen Fisher'
Cc: ccielab@groupstudy.com
Subject: RE: Mobile IP and IRDP
Thanks Scott for getting back to me.
I think, however, we're not on exactly the same page.
So, let me try to explain the issue differently.
When a MN goes to a foreign network, the MN KNOWS it's on the foreign
network because it hears the IRDP announcements made by the FA. In fact,
IRDP is required to be configured on the FA.
Now, when the MN returns to it home network, how does the MN know its on its
how network and not some other foreign network. After all, the HA does NOT
have to be configured with IRDP.
Also, the HA needs to know immediately when MN returns to its home network
since it would not be good if the HA is still tunneling packets to the MN
when the MN is NOT away.
So, without IRDP configured on the HA, how does the MN and HA know the MN
has returned to the home network?
Thanks again, Tim
PS: What's wrong with you? What are doing on GS on a 3 day holiday
weekend? As for me, I'm still trying to become a ccie but you already have
4 of them, so what's your excuse? Are the issues I raise so interesting and
provocative its difficult to rip yourself away? :-)
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Scott Morris
Sent: Saturday, May 28, 2005 2:43 PM
To: 'ccie2be'; 'Stephen Fisher'
Cc: ccielab@groupstudy.com
Subject: RE: Mobile IP and IRDP
During the registration process, there is also a time mechanism involved.
So, you register (can even be AAA-driven) and for that time period you are
in the mobility binding table.
Bear in mind that there is a software that resides on the client PC to
handle this registration and stuff as well!
But after the time period, especially if not renewed (much like DHCP lease)
then the mobility binding (/32) expires and defaults back to wherever the
route normally exists.
HTH,
Scott
-----Original Message-----
From: ccie2be [mailto:ccie2be@nyc.rr.com]
Sent: Saturday, May 28, 2005 1:16 PM
To: swm@emanon.com; 'Stephen Fisher'
Cc: ccielab@groupstudy.com
Subject: RE: Mobile IP and IRDP
Thanks, Scott.
But, do you know what mechanism is used when a MN returns to its home
network to inform the MN that it is now back on its home network?
Since IRDP doesn't have to be configured on the HA, there must be some way
MN learn this so that they can deregister their binding on the HA.
Tim
-----Original Message-----
From: Scott Morris [mailto:swm@emanon.com]
Sent: Saturday, May 28, 2005 1:08 PM
To: 'Stephen Fisher'; 'ccie2be'
Cc: ccielab@groupstudy.com
Subject: RE: Mobile IP and IRDP
IRDP is done on the FA. The MN will wander around a network, and as it
wanders on someplace that is not its own native network it will need to know
about the gateway to get out. That's the problem that IRDP solves.
The HA simply sits around and waits to hear /32 CoA announcements from the
FA regarding stations that are wandering.
HTH,
Scott
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Stephen Fisher
Sent: Saturday, May 28, 2005 12:44 PM
To: ccie2be
Cc: ccielab@groupstudy.com
Subject: Re: Mobile IP and IRDP
On Fri, May 27, 2005 at 04:40:04PM -0400, ccie2be wrote:
> Now, it makes sense to me that IRDP needs to be configured on the FA
> router. It also seems to me that IRDP should also be configured on the
> HA interfaces where MN exist so that MN's know they are on the Home
> Network.
>
> But, in the examples on the Doc-CD and in the Cisco Press, IRDP isn't
> configured on the HA.
>
> Do you know why that is?
That's a good question.. the way I understand it, the MN knows it is on its
home network when its assigned address (such as through DHCP) matches its
usual IP address. The Cisco Press Mobile IP book also mentions comparing
its usual address to the prefixes received in IRDP announcements so now I'm
not sure either.
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