Linux IPv6 routing strange behaviour

Max Tulyev maxtul at
Thu Aug 15 13:08:01 CEST 2013

I have some additional info about the issue I found.

Even if no traffic and no full-view, but a lot of interfaces (tunnel
broker node is a good sample), the static routes are duplicating.

That is definitely NOT a route cache described below, as route cache is
pointing to the HOST, not to the network.

On 15.08.13 13:54, Hannes Frederic Sowa wrote:
> 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:
> <>
> Greetings,
>   Hannes

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