RE: [spring] I-D Action: draft-ietf-spring-srv6-network-programming-10.txt

[Ron Bonica <[e-mail]>]

Beyond that, SRv6 nodes examine the O-flag, even when Segments Left is equal to 0. So, when the SRH is removed, O-flag functionality isn't available at the ultimate segment endpoint.

                                                          Ron


From: spring <[e-mail]> On Behalf Of Greg Mirsky
Sent: Friday, February 28, 2020 11:22 AM
To: Robert Raszuk <[e-mail]>
Cc: John Scudder <jgs=[e-mail]>; SPRING WG <[e-mail]>; 6man WG <[e-mail]>
Subject: Re: [spring] I-D Action: draft-ietf-spring-srv6-network-programming-10.txt

Hi Robert,
you've asked about a possible operational drawback of PSP. I think that for OAM PSP has decremental effect on the usefulness of performance measurements as there's no obvious information to identify the path a packet traversed.

Regards,
Greg

On Fri, Feb 28, 2020 at 2:55 AM Robert Raszuk <[e-mail]<mailto:[e-mail]>> wrote:
Hi John,

> I have an additional observation, or question, about Dan's scenario. Almost all communication is bidirectional.
> Presumably this means a router that's the tail end of an SRv6 path in one direction is the head end in the other.

While your observation is correct that most TCP connections are bidir SR in a lot of cases can operate only in one direction. Needless to say it can also be used with UDP streaming.

To extend Ketan's OTT video example let me observe that in a lot of transactions queries from clients are tiny and do not TE capabilities while responses are huge and bursty and may indeed benefit from special handling.

Sure if you think of applications like VPNs than you are right ... regardless of the size of the packets proper tagging must occur in either direction - but this is just one use of SRv6 perhaps not even the major one.

- - -

Now as one friend just asked me offline - putting all IPv6 dogmas aside - what is the technical issue with removing previously applied extension header from the packet within a given operator's network ? What breaks when you do that ?

Thx,
R.


On Thu, Feb 27, 2020 at 10:11 PM John Scudder <jgs=[e-mail]<mailto:[e-mail]>> wrote:
I have an additional observation, or question, about Dan's scenario... Almost all communication is bidirectional. Presumably this means a router that's the tail end of an SRv6 path in one direction is the head end in the other. Doesn't a head end need to add an SRH? If I've gotten that right, then we can extend Ron's list with one more item. That is, apparently the ultimate segment endpoint:

* Can process a SID, received as an IPv6 DA, on the fast path
* Cannot process an SRH on receipt, even if Segments Left equal 0, on the fast path.
* Can add an SRH on transmission, on the fast path

Even though strictly speaking the second and third bullet points aren't mutually exclusive, it's a little difficult to imagine a real router that would have both these properties simultaneously. Perhaps I'm not being creative enough in imagining deployment scenarios? Since this scenario is claimed as an important reason this problematic feature is needed, it would be great if someone who understands it would elucidate, thanks.

One further point, Ron says "I wonder whether it is a good idea to stretch the IPv6 standard to accommodate IPv6-challenged devices." I also wonder this, especially because these devices will have a relatively limited lifetime in the network.[*] I don't find the cost/benefit attractive of making a permanent detrimental change to the IPv6 architecture to accommodate a temporary deployment issue.

Regards,

-John

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