Re: [spring] I-D Action: draft-ietf-spring-srv6-network-programming-06.txt

[Gyan Mishra <[e-mail]>]

On Fri, Dec 20, 2019 at 1:22 AM Gyan Mishra <[e-mail]> wrote:

>
>
> On Thu, Dec 19, 2019 at 8:45 PM Brian E Carpenter <
> [e-mail]> wrote:
>
>> On 20-Dec-19 12:01, Robert Raszuk wrote:
>> >>   And where is it forwarded to, since we are already at the DA?
>> >
>> > PSP operates at the n-1 segment end of the SR path so naturally after
>> swapping DA it is forwarded to the segment end. Note that we are all along
>> operating on the encapsulated header ... original packet including its
>> original IPv6 header is sitting as passenger here.
>> >
>> > So last segment here will received encapsulated IPv6 packet will
>> decapsulate it and fwd based on the original DA.
>> >
>> > Seems very simple :)
>>
>> Right, but the language in the PSP sub-section does not talk about
>> decapsulation. I think the root problem may be using the word "pop", which
>> is relevant in the MPLS label stack context but not here, without
>> additional definition.
>>
>
>   [Gyan] I agree with what Brian is saying that pop in MPLS PHP or UHP you
> are popping an MPLS label 4 byte shim, where here you are removing the SRH
> header.  Not a really a pop.  The MPLS shim is an encapsulation since it’s
> sits between the L2 and L3 header.  I think if we fix the verbiage and
> change from pop to remove we may want to come up with some other name like
> PSR & USR if “remove” was used.
>
>>
      With both SRv6 and MPLS within their respective domains when the
packet comes in from external to the domain on the PE-CE attachment circuit
with MPLS the label  4 byte shim imposition or encapsulation happens on the
PE upon forwarding on any MPLS enabled “core”  interface PE-P link.  With
SRv6 the 6in6 encapsulation occurs when a packet from the PE-CE attachment
circuit originating from outside the SRv6 domain hits the SRv6 source node
ingress PE which 6in6 encapsulates the packet from the CE and then adds the
SRH header to source route the packet through the SRv6 domain.  With mpls
the label disposition happens with PHP on egress P penultimate node.  So
that de-encapsulation with SRv6 ends up mapping to USD end.x SID function
where the original 6in6 encapsulation done on the SRv6 source node is now
removed.  So big difference here in nomenclature with PSP and USP removing
SRH and not performing any de-encapsulation which is decoupled to a
separate USD function.

>
>>     Brian
>>
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> --
>
> Gyan S. Mishra
>
> IT Network Engineering & Technology
>
> Verizon Communications Inc. (VZ)
>
> 13101 Columbia Pike FDC1 3rd Floor
>
> Silver Spring, MD 20904
>
> United States
>
> Phone: [phone]
>
> Email: [e-mail]
>
> www.linkedin.com/in/networking-technologies-consultant
>
> --

Gyan S. Mishra

IT Network Engineering & Technology

Verizon Communications Inc. (VZ)

13101 Columbia Pike FDC1 3rd Floor

Silver Spring, MD 20904

United States

Phone: [phone]

Email: [e-mail]

www.linkedin.com/in/networking-technologies-consultant