Subject: [Mip6] Further information on Mobile Prefix Advertisement

From: christophe preguica <[email-masked]>
Date: Tue, 02 Dec 2003 10:15:21 +0100

Hi,

I would like to have further information on the contents of the mobile 
prefix advertisement message in the mobile IPv6 draft...
The draft says:
"In this mechanism, mobile nodes away from home receive Mobile Prefix 
Advertisements messages. These messages include Prefix Information 
Options for the prefixes configured on the home subnet interface(s) of 
the home agent."
Does this mean that:
1 - all manually configured prefixes on the interface of the HA are 
advertised in the MPA message as they are in the RA.
2 - the HA router addresses learned in the RA of the other HAs (used for 
DHAAD)
3 - the global addresses of the HA on this interface (like 2 above)
4 - the "dynamic" prefixes created based on the addresses on the 
interface of the HA, means the same behavior as RA if the dynamic 
behavior is set.

A RA contains all this data, what should contain a MPA ?
Moreover, are prefixes advertised whether or not they are 
on-link/off-link, with the bit A not set ?

Regards,

Chris.

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From: "T.J. Kniveton" <[email-masked]>
Date: Tue, 02 Dec 2003 19:25:35 -0800

Christophe,

The purpose of Mobile Prefix Advertisements is to allow the MN to get 
prefix information while it's away from home, in order to configure a 
valid home address that will be served by a Home Agent. Keep that in mind.

If the Home Agent(s) has prefixes configured on the interface which is 
connected to the home network, it puts them in the MPA, along with any 
prefixes being advertised by other Home Agents on the same link (home 
network).

> advertised in the MPA message as they are in the RA. 

YES

>
> 2 - the HA router addresses learned in the RA of the other HAs (used 
> for DHAAD) 

Well, yes, the other HAs will include the prefix their address(es) is 
constructed from in prefix information options, so YES

> 3 - the global addresses of the HA on this interface (like 2 above) 

Addresses don't go into prefix information options, prefixes do. What do 
you mean by this?

> interface of the HA, means the same behavior as RA if the dynamic 

I'm not sure what sort of "dynamic" behavior you're talking about.Are 
you thinking of some case where the router will dynamicall configure 
what prefixes are available on a link? Or network renumbering?

> A RA contains all this data, what should contain a MPA ? 

It is spelled out in the rest of the section you quoted (10.6.1)

> on-link/off-link, with the bit A not set ?

Prefixes should be advertised if they are ON the LINK of the home 
network, and that means they are served by, and advertised by, one or 
more HAs, who send the MPA.

TJ

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From: christophe preguica <[email-masked]>
Date: Thu, 04 Dec 2003 13:33:49 +0100

Thanks for your feedback.
So if I understand well...

According to the mobility draft (10.6.3): "Set the Managed Address 
Configuration (M) flag if the corresponding flag has been set in any of 
the Router Advertisements from which the prefix information has been 
learned (including the ones sent by this home agent)." So the HA 
advertises all the prefixes received in RA from the HA neighbors and the 
ones included in the RA sent by the HA itself.
So added to your remarks, the HA advertises:
- its configured prefixes (AdvPrefixList )
- the ones of its neighbors (normally the sames)
- only prefixes on-link, whatever the bit A.

What I called "dynamic" was that a router advertises:
- prefixes configured to be advertised in RA
- by default the ones associated to an address on the interface the RA 
is to be sent from. I called them "dynamic" but the word is not 
appropriate (see RFC 2461, 6.2.1): "Default: all prefixes that the 
router advertises via routing protocols as being on-link for the 
interface from which the advertisement is sent."
Both these prefixes are part of the AdvPrefixList.

Regards,

Chris.

T.J. Kniveton wrote:

> Addresses don't go into prefix information options, prefixes do. What 
> do you mean by this?
>
>>