Re: IPv6 nexthop for IPv4

2015-03-26 15:53 GMT+01:00 Sowmini Varadhan [off-list ref]:

On Thu, Mar 26, 2015 at 10:39 AM, Bjørnar Ness [off-list ref] wrote:

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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.

If it does not support IPv6 I guess the route command will fail! This
is a bad argument
against this. Dont see the point of limiting nexthop to L2

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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.

Did you look at RFC5549 and MP-BGP?

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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.

Point is we dont need another software encapsulation for this to work.
It can work
more or less "out-of-the-box" if ipv4 nexthops can be ipv6

Say you have 10 racks with 40 servers in each, two links to each
server to each TOR,
and you want to run a full L3 BGP routed network here. The
configuration/addressing
overhead we need today is enormous. With neighbor discovery and IPv6 nexthops,
this configuration can be done totally dynamic using link-local addresses.

I know people are working on this, but as I wrote in the first mail, I
just hope it gets done
"right", not hacky like this (POC):

https://ams-ix.net/downloads/RFC5549/

-- 
Bj(/)rnar