netdev - Re: IPv6 nexthop for IPv4

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Date:	Thu, 26 Mar 2015 10:29:14 -0400
From:	Sowmini Varadhan <sowmini05@...il.com>
To:	Bjørnar Ness <bjornar.ness@...il.com>
Cc:	netdev <netdev@...r.kernel.org>
Subject: Re: IPv6 nexthop for IPv4

On Thu, Mar 26, 2015 at 9:16 AM, Bjørnar Ness <bjornar.ness@...il.com> wrote:
> Hello, hope this is the right place to ask.
>
> Does anyone know if there is work beeing done in natively supporting
> IPv6 nexthops for IPv4?

What problem are you trying to solve? Do you want to tunnel your
ipv4 packet through IPv6? there are a number of tunneling mechanisms
in linux for this.


>
> I know that "some" Linux switch software company is working on this, but
> I am afraid the functionality will be more of a "hack".
>
> The benefit of this is stateless configuration (rfc5549), using IPv6 link-local
> neighbor address as IPv4 nexthop, beeing able to do for example:
>
> ip route add 10.0.0.0/16 via fe80::225:90ff:fed3:bfb4/64 dev sfp0

Trying to understand what the desired behavior is, for the route
above: if I send a packet from 10.0.0.1 to 10.0.0.2, you want the dst-mac
to be the mac address of e80::225:90ff:fed3:bfb4???
how do you know that fe80::225:90ff:fed3:bfb4 supports ipv4
forwarding on the receiving interface (and if it does, why didn't it
advertise itself as an IPv4 router on that interface)?

>
> This is somehow possible now by exploiting static arp entries and
> "unused" IPv4 addresses for nexthop, but is far from ideal.
>
> Hope someone will be able to provide some insight on what is planned
> in this area, and weather this direct functionality will ever make it
> into the kernel.
>
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