netdev - Re: IPv6 nexthop for IPv4

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Date:	Thu, 26 Mar 2015 10:53:56 -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 10:39 AM, Bjørnar Ness <bjornar.ness@...il.com> wrote:

>>> 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???
>
> Absolutely, correct.

What if the current node does not want to support ipv6? This sounds
pretty "creative", if this can work, you might as well make the nexthop to
be the L2 address of the gw.

> Basically because you either added the route manually, or it was provided
> by fe80::225:90ff:fed3:bfb4 itself via some routing protocol (MP-BGP)
>
> This will be the same as any other route. How do you know it forwards traffic..

because you would be running a routing protocol that manages reachability
of the gw and the route. RIP, OSPF, BGP etc all have a lot of mechanisms
to monitor liveness of the route and of the nexthop, which has to be of
the same address family as the route itself.

>
> In large routed setups, address management in general and lack of IPv4 addresses
> can become a big hassle. Beeing able to get a ipv6 neighbor for a ipv4
> route would
> make this process a lot simpler.

Yes, that's the motivation behind all the tunneling/transition mechanisms
in the various ipv6 working groups.

--Sowmini
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