[jeff] to better phrase - no router, beside the one allocating service labels could lookup/touch them, this is true for PHP or any other case. In PHP case, after most outer label has been looked up and a fully resolved adj provided, the rest of the label stack MUST not be looked up (payload)On Mar 20, 2017, at 09:38, Thomas Morin <thomas.morin@orange.com> wrote:Hi everyone,
2017-03-18, Vincent Jardin:
+Thomas to be on track.
Vincent, you'll tell if what is below helped or not :)
Le 18 mars 2017 06:19:47 Vivek Venkatraman <vivek@cumulusnetworks.com> a écrit :
This is correct. By definition, if a router is the penultimate hop, it means the actual egress is downstream and has signaled (advertised) an implicit-null label to this router. The router doing the PHP knows the next hop to forward to (the egress) without doing any additional lookup.
(Note that with BGP/MPLS VPNs this is the typical behavior, but it is not a mandatory behavior: the egress router may have advertise a real label (i.e. not implicit null) in which case the penultimate router will swap the topmost label of the stack, not seeing/touching the vpn label. This is also a behavior that relates to the use of MPLS for transit, but with MPLS-over-GRE or MPLS-over-UDP, MPLS can be used with IP transit, in which case this behavior is not used).
[jeff] would’t this be a tad inefficient? :)
This behavior should already be supported.
Yes, I can confirm that forwarding via a neighbor on an interface based on the incoming MPLS label is supported.
This is what we use in bagpipe IP VPN 'linux' driver [1].
What is not supported (if I remember right) is the ability on the egress to terminate a label and perform a (route) lookup. That is needed to really be able to support any L2/L3 VPN service properly.
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 ?
-Thomas
[1] http://git.openstack.org/cgit/openstack/networking-bagpipe/tree/networking_bagpipe/bagpipe_bgp/vpn/ipvpn/mpls_linux_dataplane.py#n194
_______________________________________________
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
>
> _______________________________________________
> frr mailing list
> frr@lists.nox.tf
> https://lists.nox.tf/listinfo/frr
_______________________________________________
frr mailing list
frr@lists.nox.tf
https://lists.nox.tf/listinfo/frr
frr mailing list
frr@lists.nox.tf
https://lists.nox.tf/listinfo/frr