[dev] [frr] 2 MPLS Questions

Amine Kherbouche amine.kherbouche at 6wind.com
Thu Apr 6 10:09:10 EDT 2017


On 6 April 2017 at 15:36, David Ahern <dsa at cumulusnetworks.com> wrote:

> net-next tree has the patch set increasing number of labels. Allows up
> to 30 labels for ingress (ip->mpls) and routing (mpls->mpls).
>
> An mpls_route is limited to 4096 bytes (number of nexthops + labels); an
> lwt (ingress) route is under 128 bytes. With the latest set users of
> N-labels takes the performance hit of each additional label.


I think that having 30 stacked labels is useless, regardless of the
performance
issue, like Jeff said, the worst case covers 5 labels. I don't inderstand
this waste.


> On 3/23/17 1:34 PM, Amine Kherbouche wrote:
> > Olivier,
> >
> >     The best for me, is to have the possibility to recompile the MPLS
> >     kernel module with the new value the MAX_LABEL_STACK and then let
> >     our Segment Routing implementation read this value to determine
> >     what's feasible.
> >
> > Yes but we still need a default value.
> > You have also to see the perf impact, now the current mpls entry size in
> > linux kernel is under
> > a cache line, even using 12 stacked labels, we are always under a cache
> > line but beyond
> > this value we're going to see performance issue.
> >
>



-- 
Amine
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