Re: [dhcwg] Comments on 22 rev of the draft

Martin Stiemerling <Martin.Stiemerling@ccrle.nec.de> Thu, 24 January 2002 09:37 UTC

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Date: Thu, 24 Jan 2002 10:28:50 +0100
From: Martin Stiemerling <Martin.Stiemerling@ccrle.nec.de>
To: Vijay Bhaskar A K <vijayak@india.hp.com>
Cc: dhcwg@ietf.org
Subject: Re: [dhcwg] Comments on 22 rev of the draft
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--On Donnerstag, Januar 24, 2002 00:10:27 +0530 Vijay Bhaskar A K 
<vijayak@india.hp.com> wrote:

>> What possible use can there be in allowing the client to select the
>> prefix  that it wants?
>
> Please go through the follow scenario.  Router is advertising  3ffe::/64
> prefix and a host has generated an address of prefix  3ffe::/64  using
> router  advertisements.  Now, the host  needs  some  more  addresses  of
> prefix  3ffe::/64.  It chooses to use stateful  autoconf  (dhcpv6).  The

The client has nothing to choose! When the IPv6 router says in his router 
advertisements "use stateless autoconfiguration" (Flags in router 
advertisement are M=0, O=0), the client has to use stateless 
autoconfiguration, i.e. form an IPv6 address with the advertised prefix. 
When the router says "use stateful autoconfiguration" (Flags in router 
advertisement are M=1, O=1), the client has to use stateful 
autoconfiguration, i.e. request an IPv6 address from a DHCPv6 server. See 
RFC 2641, section 4.2, and RFC 2462, section 5.2.

We can't change the base IPv6 specification for DHCPv6.

> server  sends  advertise  saying  that,  it can  allocate  addresses  in
> 3ffe::/64  and  5ffe::/64.  Since,  the  client's  wish  is to get  only
> 3ffe::/64,  it can tell the server its  preference  for the prefix while
> sending  Request.  This will help in server not allocating the addresses
> that the client doesn't want.
>
> Moreover, if the client wants to communicate  with the external site, it
> requires  global  rather  than site local  addresses.  Here also, it can
> show the preference.
>
> DHCP clients are intended to arrange for ad-hoc
>> connections.   Under what circumstances would the client have any
>> knowledge  of what prefixes might be better than others?
>
> Obviosuly, the client using the stateless  autoconf,  knows the prefixes
> in the link, (by router advertisements).  From the Advertise messages of
> the various servers, it knows about the prefixes in the link.
>
>
>
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>



Martin Stiemerling

NEC Europe Ltd. -- Network Laboratories      Martin.Stiemerling@ccrle.nec.de
IPv4: http://www.ccrle.nec.de             IPv6: http://www.ipv6.ccrle.nec.de

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