Subject: Re: [RFC net-next 1/2] net: allow user to set IPv6 nexthop for IPv4 route

From: Andy Gospodarek <[email-masked]>
Date: Fri, 27 Mar 2015 10:35:23 -0400

On Fri, Mar 27, 2015 at 09:23:57AM -0400, Sowmini Varadhan wrote:
> On Thu, Mar 26, 2015 at 5:05 PM, Andy Gospodarek
> <[email-masked]> wrote:
> > This adds kernel infrastructure to allow userspace (read: routing protocols) to
> > support adding IPv6 next-hops to IPv4 routes.  This is essentially added to
> > support a feature of MP-BGP outlined in RFC-5549.
> >
> > Thise does not encompass all that is needed to support RFC-5549, but this
> > demonstrates the netlink infrastructure needed to correctly enable the kernel
> > infrastructure that would support this RFC.  For more informtion the full RFC
> > is here: http://www.ietf.org/rfc/rfc5549.txt.
> 
> Is there some impact to redirect behavior? RFC 5549 does not seem to
> discuss it at all, but the firsthop would be processing (and
> potentially sending)
> an icmp redirect to the host. I dont think there is a good way to construct
> this, either with icmpv4 or icmpv6, and maybe some checks are needed to
> not even try, when the IP mix-match is encountered.
> 

You are correct that there is not a great way to construct this since
the frames at strictly IPv4 frames.  I'll have to dig into this a bit
more to see if there is something worth doing for this case.