[frr] 2 MPLS Questions

Vincent Jardin vincent.jardin at 6wind.com
Sat Mar 18 06:31:59 EDT 2017


+Thomas to be on track.


Le 18 mars 2017 06:19:47 Vivek Venkatraman <vivek at 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.
>
> This behavior should already be supported.
>
> 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.
>
> On Thu, Mar 16, 2017 at 10:45 AM, Jeff Tantsura <jefftant at 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 at 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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>
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>
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