Re: [v6ops] DAD again [was: draft-ietf-v6ops-host-addr-availability discussion]

Gert Doering <> Fri, 13 November 2015 15:43 UTC

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Date: Fri, 13 Nov 2015 16:43:19 +0100
From: Gert Doering <>
To: "Hemant Singh \(shemant\)" <>
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Subject: Re: [v6ops] DAD again [was: draft-ietf-v6ops-host-addr-availability discussion]
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On Fri, Nov 13, 2015 at 03:34:11PM +0000, Hemant Singh (shemant) wrote:
> >Otherwise, there is no way to ensure uniqueness on non-directly-connected interfaces - think "loopback on a router on the other side of the planet".
> The router on the other side of the planet has a tunnel to the upstream router and thus the two routers are in the same routed domain.  In the same routed domain, an interface on a router responds to ND NS messages for address resolution.  Thus the interface has to also perform DAD for its IPv6 address(es).

Well, if you take an address that belongs to a connected /64 and glue that
to your loopback interface, what you say is true - there will be ND NS
queries for that address, and you better should do DAD.

In the normal case for loopback interfaces, these intentionally are *not*
numbered out of connected networks, but coming out of separately assigned
number space (like, DHCPv6PD, or manually configured).  Why would anyone
send a ND NS for such an address in the first place?  Nobody knows that
it "could be on a link here".

And no, the router on the other side of the planet has no "tunnel" to 
your routing domain.  It's just a router having a loopack address, 
chosen to show that your concerns about loopback address DAD are a bit

Gert Doering
        -- NetMaster
have you enabled IPv6 on something today...?

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