Re: [v6ops] DHCPv6/SLAAC Make Hosts Confusing-//RE: new draft: draft-liu-bonica-v6ops-dhcpv6-slaac-problem

Alexandru Petrescu <> Tue, 29 October 2013 13:04 UTC

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Date: Tue, 29 Oct 2013 14:03:50 +0100
From: Alexandru Petrescu <>
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To: Gert Doering <>
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Subject: Re: [v6ops] DHCPv6/SLAAC Make Hosts Confusing-//RE: new draft: draft-liu-bonica-v6ops-dhcpv6-slaac-problem
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Le 28/10/2013 17:12, Gert Doering a écrit :
> Hi,
> On Mon, Oct 28, 2013 at 04:16:26PM +0100, Alexandru Petrescu wrote:
>> I thought the goal was to not modify RA, whereas the above does
>> modify the RA to include a DNS resolver.
> Uh.  *That* train has sailed 6 years ago with RFC5006...


But in this thread some say we should no longer do DHCP-typical-info in
the RA, and at the same time they propose to do it, provided the backend
info comes from a DHCP server.  Hence my question about whether a
delegated prefix (another DHCP-typical-info) would be ok for this
concept. (I author an earlier draft in this space).

>> If yes, would it be ok to include a Prefix Delegation option as
>> well in the RA? (not an RFC4191 option, but a new Prefix Delegation
>> option pasted from DHCPv6 Prefix Delegation).
> What use would that be?  The benefit of RA is that "everyone can see
> them and the information contained applies to *all* consumers, and is
> periodically refreshed without having to poll".  PD is, by
> definition, very specific to the device where you delegate to...

I tend to agree that RA's content is generally valid for everyone
receiving that RA, and that typically RAs are multicasted to all nodes
on a link.

However, there are some specific cases where the RA is unicast to
particular nodes and contain information specific to that node.  For
example in Proxy Mobile IPv6 RFC5213 an access router sends an RA to a
particular mobile host attaching to it, and it puts inside a prefix to
make believe that particular node to be at its home.  Each node has a
different home prefix.  Another example is in Fast Mobile IPv6 protocol
RFC4068 where a Proxy RA contains an address specific to a mobile.  A
more remote example is that of RPL RFC6550 which uses a new ICMP message
'RPL Control Message' remotely similar to RA, and whose destination is

Apart from that, the use case I am considering is fast exchanges of IP
messages to establish quickly short-lived communications (10ms IP
establishment address/defroute, and app-layer communications during a
few minutes).  Used in vehicular communications.  A vehicle containing a
cellular link (SIM subscription) may offer Internet connectivity to a
SIM-less vehicle nearby - mobile billboard vehicle, like in this figure
(check the "Free WiFi" banner).


> This thread is full of weirdness.
> Gert Doering -- NetMaster