Subject: [dhcwg] Multiple IP addresses for DHCPv6 clients

From: "Achint Setia" <[email-masked]>
Date: Thu, 5 May 2005 22:44:21 +0800

Hi,

The DHCPv6 RFC 3315 mentions that the client can send multiple IAs in a
packet. I have the following queries regarding the same:-

1.	If the client wants to request multiple IP addresses from the
server, should it send as many IA_Addr in a single IA_NA (i.e under the
same IAID) in the SOLICIT message or send multiple IA_NAs each with a
single IA Address field. I am asking this because the server identifies
a client binding by the triplet <DUID,  IA_Type, IAID> which means in
case of the first option, there have to be multiple addresses in the
same binding.

2.	Suppose after getting an address, the client wants to get
another address. Should it send another SOLICIT with a new IAID or can
it use the previous IAID to get the new address (assuming multiple
addresses per binding)

3.	The RFC says in section 18.1.3 (Creation and Transmission of
Renew Messages) "The server may also add new addresses to the IA"

What are the possible scenarios in which the server can itself chose to
send multiple IP addresses to the client without going through the
normal 4 way 

Handshake. Can we use this as a solution to the issue (2) I mentioned?

I'll appreciate your help in this regard.

Thanks,

Achint Setia,

Microsoft.

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From: Ted Lemon <[email-masked]>
Date: Thu, 5 May 2005 11:46:11 -0500

On May 5, 2005, at 9:44 AM, Achint Setia wrote:
> If the client wants to request multiple IP addresses from the  
> server, should it send as many IA_Addr in a single IA_NA (i.e under  
> the same IAID) in the SOLICIT message or send multiple IA_NAs each  
> with a single IA Address field. I am asking this because the server  
> identifies a client binding by the triplet <DUID,  IA_Type, IAID>  
> which means in case of the first option, there have to be multiple  
> addresses in the same binding.
The word "identity" in the phrase "identity association" refers to  
the identity that the client presents to the network.   When a client  
wishes to present more than one identity to the network, it uses more  
than one identity association.   The reason for wanting more than one  
IP address is to present more than one identity.   So if a client  
wants more than one IP address, it should present more than one IA_ID.
>  Suppose after getting an address, the client wants to get another  
> address. Should it send another SOLICIT with a new IAID or can it  
> use the previous IAID to get the new address (assuming multiple  
> addresses per binding)
It has to do an additional solicit.   It's okay to renew all the IAs  
at once, though.
>  The RFC says in section 18.1.3 (Creation and Transmission of Renew  
> Messages) “The server may also add new addresses to the IA”
>
> What are the possible scenarios in which the server can itself  
> chose to send multiple IP addresses to the client without going  
> through the normal 4 way
>
No.   The reason a server would send more than one address in an IA  
is to handle the case where a site is multi-homed.   In this case, a  
client is presenting a single identity to the network, but may need  
more than one IP address because the site is multi-homed, so the  
server sends the client two IP addresses for its single identity.    
This is completely orthogonal to the question of presenting multiple  
identities, and so you can't use this facility to acquire multiple IP  
addresses for the client.