Subject: Re: [dhcwg] DHCPv6 Stateful Prefix Length

From: "Durand, Alain" <[email-masked]>
Date: Fri, 28 Sep 2007 10:35:22 -0400

I've heard too that something was coming in that space, but I've lost track of its status.

   - Alain.

----- Original Message -----
From: Bernie Volz (volz) <[email-masked]>
To: Durand, Alain; RamaSubramanian KrishnaMurthi <[email-masked]>; [email-masked] <[email-masked]>
Sent: Fri Sep 28 10:26:50 2007
Subject: RE: [dhcwg] DHCPv6 Stateful Prefix Length

I'm not convinced of that yet. I think Tim Chown is writing an I-D about
this topic (perhaps he already has)?

From the Chicago minutes
(http://www3.ietf.org/proceedings/07jul/minutes/dhc.txt):

---
Extensions to DHCPv6 for prefix and default router information

Tim Chown led a discussion of handling rogue RAs in an IPv6
deployment.  The motivation for this presentation is that
administrators of operational networks, mostly universities are
comfortable with DHCP, but are finding problems with 'rogue Router
Advertisments'.  One possible alternative is to avoid RAs and use DHCP
for prefix and default router information. 

Bogus RAs can originate from several sources:

1) configuration error - sometimes with long lifetime
2) User-induced accidents: host acting as 6to4 router from home
3) malice

Arkko said that it's not clear DHCP is the right way to deal with
these problems.  Dave Thaler pointed out that SeND is the official
solution to this problem, so creating another solution does not
improve the situation.  Thaler also pointed out that, with the
revision to the "on-link assumption" in RFC 2461bis, there may be a
need for passing prefix information in DHCP.  Alain Durand expressed
interest in using DHCP for prefix and default router information.  Tim
Chown promised to publish a draft documenting the problem. 
---

If we were to consider such an option, there needs to be a lot of
thought as to what happens if you have BOTH an RA and DHCPv6 option and
they conflict in what they are telling the client. This also gets
complicated because you could have "normal" RAs, SeND RAs,
unauthenticated DHCPv6, and authenticated DHCPv6. And, you also need to
add manual configuration to that too (though that might be easy enough
to let it always "win"). I'm not even sure what happens today if there
is conflicting information from RAs (SeND or not).

- Bernie

-----Original Message-----
From: Alain Durand [mailto:[email-masked]] 
Sent: Friday, September 28, 2007 9:57 AM
To: Bernie Volz (volz); RamaSubramanian KrishnaMurthi; [email-masked]
Subject: Re: [dhcwg] DHCPv6 Stateful Prefix Length

As we have seen in the DHCPv6 bake-off, this is not implemented by every
body and creates inter issues. It would be much cleaner to have such an
option.

    - Alain.

On 9/28/07 8:56 AM, "Bernie Volz (volz)" <[email-masked]> wrote:

> A host should use information from the Router Advertisements (in
> particular, from the Prefix Information Options in the RA).
> 
> If there is no information in the RA about a prefix that contains the
> address, then /128 should be assumed.
> 
> - Bernie
> 
> -----Original Message-----
> From: RamaSubramanian KrishnaMurthi [mailto:[email-masked]]
> Sent: Friday, September 28, 2007 1:42 AM
> To: [email-masked]
> Subject: [dhcwg] DHCPv6 Stateful Prefix Length
> 
> Hi all,
>    I don't whether this question has been asked early or not.
> 
>     Can the DHCPv6 Stateful server send Prefix length of the IPv6
> Address that is being sent to client ? Is there any RFC that talks
about
> ?
>  
>   If the DHCPv6 Stateful server doesn't send the prefix length what
the
> prefix value that dhcpv6 stateful client should assume ?
>     
>  
> Yours ever
> -RamaSubbu SK
> 
> 
>  
>
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