Hi Jeff,

2017-03-20, Jeff Tantsura:
I think it is a requirement to have something efficient to trigger a lookup in any {routing table, vrf interface, netns}.

I hadn't tried (because no need). I thought we might achieve something like that by forwarding the packet on 'lo', or on a vrf interface, or on a veth device: wouldn't this kind of next hop specification trigger a re-enter of the packet in the IP stack after the pop operation ?
[jeff] would’t this be a tad inefficient? :)

Well, I was not implying that the above would be efficient, and I would actually have the same concern as you have.
But to be honest I also lack hard facts to back this concern: e.g. I don't know whether going through a vrf interface is a small or high cost.

Best,

-Thomas






On Thu, Mar 16, 2017 at 10:45 AM, Jeff Tantsura <jefftant@gmail.com> wrote:
Donald,

Wrt PHP, this is incorrect, PHP node MUST not perform IP lookup, or in fact any lookup after POP. In most cases (labeled services, L2/L3 VPN) there's another label(s) in the stack, looking it up would be fatal.

Regards,
Jeff

> On Mar 15, 2017, at 08:05, Donald Sharp <sharpd@cumulusnetworks.com> wrote:
>
> David/Roopa -
>
> Olivier asked me about these two issues yesterday in the FRR Technical
> Meeting.  I just wanted to make sure I didn't loose track of these
> questions that he had:
>
> 1) More than 2 labels in the kernel at a time, when will this be
> allowed in the kernel?
>
>   -> David is currently working on this issue.  When he is done it
> will be upstreamed.  So soonish(tm).
>
> 2) PenUltimate Hop Popping:
>
> I know this issue is not trivial to solve. In fact, once the POP
> instruction perform, the packet must re-enter in the IP packet
> processing to determine what action must apply. A possible solution
> would be to process this packet as a new incoming IP packet when
> output interface is the loopback disregarding the IP address value.
> But, this issue is less urgent than the first one. Our OSPF Segment
> Routing implementation could announce if the router works in
> PenUltimate Hop Poping mode or not. So, for the moment, the option is
> force to yes.
>
> thanks!
>
> donald
>
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