Re: [Autoconf] Using DHCPv6 without link-local? Support only EUI-64 interfaces?

Alexandru Petrescu <> Mon, 02 August 2010 12:29 UTC

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Date: Mon, 02 Aug 2010 14:29:37 +0200
From: Alexandru Petrescu <>
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Subject: Re: [Autoconf] Using DHCPv6 without link-local? Support only EUI-64 interfaces?
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Le 02/08/2010 14:07, Teco Boot a écrit :
> Op 2 aug 2010, om 10:51 heeft Alexandru Petrescu het volgende
> geschreven:
>> I was thinking about the same thing as you say: if RFC5889 forbids
>> link local addresses and new Charter wants DHCP then how could both
>> work?
> The document doesn't say "forbid".

Right, RFC5889-to-be does not say "forbid".

> Note that while link-local addresses are assumed to be "on link",
> the utility of link-local addresses is limited as described in
> Section 6.

Ok, DHCPv6 could leave with this, thinking that the utility of 
link-local addresses is only  during the initial DHCP exchanges 
(Solicit-Advertise I believe).

5889-to-be (without WG discussion Maastricht):
>    Note that while an IPv6 link-local address is assigned to each
>    interface as per [RFC4291], in general link-local addresses are of
>    limited utility on links with undetermined connectivity, as
>    connectivity to neighbors may be constantly changing.  The known
>    limitations are:
>    o  There is no mechanism to ensure that IPv6 link-local addresses are
>       unique across multiple links, hence they cannot be used to
>       reliably identify routers (it is often desirable to identify a
>       router with an IP address).
>    o  Routers cannot forward any packets with link-local source or
>       destination addresses to other links (as per [RFC4291]), while
>       most of the time, routers need to be able to forward packets to/
>       from different links.

Although DHCP Relay sits on a router, DHCP is not "most of the time" in 
that a DHCP Relay will use its global address although the Client sent a 
Solicit using its link-local address - Relay duplicates the packet.

>    Therefore, autoconfiguration solutions should be encouraged to
>    primarily focus on configuring IP addresses that are not IPv6 link-
>    local.

This is fine, because DHCP would configure an IP address on Client which 
is not link-local but global.

Of course this DHCPv6-LL analysis should change when we get the more 
final RFC5889-to-be text.