Subject: [dhcwg] Re: purpose of m/o bit

From: "da Silva, Ron" <[email-masked]>
Date: Fri, 27 May 2005 09:30:37 -0400

> To me, assuming the current specs, the following would make sense:

One of the permutations missing in your algorithm is if a device is
configured for always-full-DHCPv6 on an interface AND it receives RA
with AAC set...I presume in that case the device would get multiple
addresses, right?

-ron

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From: Ralph Droms <[email-masked]>
Date: Fri, 27 May 2005 09:44:42 -0400

Ron - Use of AAC on specific prefixes advertised in RAs, as controlled
by the A bit in a prefix information option, is independent of the use
of DHCP ... so you're right, if there are prefixes in an RA with the A
bit set, and the M and/or O bits are set in that RA, the host would
configure both AAC addresses and DHCP-assigned addresses.

I didn't include anything about AAC in the analysis I posted because I
think they are completely independent...

- Ralph

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From: Iljitsch van Beijnum <[email-masked]>
Date: Fri, 27 May 2005 18:12:53 +0200

> with AAC set...I presume in that case the device would get multiple

Like Ralph, I didn't include those because stateless  
autoconfiguration happens independent from DHCPv6.

But now that you ask...

Over in shim6/multi6 we're thinking about multihoming mechanisms  
where security is derived from "hash-based addresses": the hash over  
certain information is used as an interface identifier. It would be  
nice to be able to implement all of this in middleboxes rather than /  
in addition to hosts, but then we need to have a way to assign a  
specific address to a host. In order to provide "legacy" IPv6  
connectivity we need to do stateless address autoconfig, but it would  
be nice if we could make the hosts in question ignore those addresses  
and just use the hash-based one obtained from a DHCP server.

(Note that the above goes several steps further than the official wg  
consensus, just thinking ahead.)

I guess there are two ways to do this: an ND/RA option that tells a  
host how to use stateless autoconfig and/or DHCP derived addresses,  
or a DHCPv6 option that does the same. I.e., such an option could  
tell the host "don't use stateless autoconfig".

Thinking about this stuff, I wondered:

- how does the DHCP server know which prefixes are on-link for the host?

- what happens when the DHCP server assigns an address that the  
router doesn't recognize as on-link?