Linux IPv6 routing strange behaviour

Hannes Frederic Sowa hannes at
Thu Aug 15 12:54:11 CEST 2013

On Thu, Aug 15, 2013 at 11:35:50AM +0100, Phil Mayers wrote:
> On 15/08/13 11:31, Hannes Frederic Sowa wrote:
> >On Thu, Aug 15, 2013 at 07:39:23AM +0200, Mikael Abrahamsson wrote:
> >>On Wed, 14 Aug 2013, Max Tulyev wrote:
> >>
> >>>What is the soultion? There are *MILLIONS* of flows in the backbone...
> >>
> >>The solution is not to use a flow routing platform in the core. This
> >>lesson was learnt at the end of the 90ties.
> >>
> >>So until the linux ipv6 forwarding code is fixed to do stateless
> >>forwarding, it's just not suited for your application.
> >
> >Some time ago I started working on nh-exceptions, but it is a very
> >delicate change. I hope I can look at this again as soon as I have some
> >more free time. Because the data structures are already in place for
> >IPv4 in the generic routing code it should be not such a big patch.
> I guess I'm a little bit confused by this thread.
> Why are nh-exceptions relevant to *forwarding* (as opposed to the host 
> side of the stack, which of course needs to cache all kinds of bits 
> per-destination)

It is a common lookup path where the per host routing nodes get cloned and
reinserted back into the fib.

> Or is that what you're saying - the host-based bits will live as 
> "exceptions" on top of a stateless FIB?

Yes, that would be the end result of this change. Also these entries will be
added on demand, so, normally there won't be a lot of exceptions.

This is a recent presentation about the IPv4 routing cache removal:



More information about the ipv6-ops mailing list