[spring] Re: My question at the mike about draft-dong-spring-srv6-inter-layer-programming

["Dongjie (Jimmy)" <[e-mail]>]

Hi Sasha, 

Thanks for your question at the mic. Please see some replies inline: 

________________________________________
From: Alexander Vainshtein <Alexander.Vainshtein=[e-mail]>
Sent: Saturday, July 27, 2024 5:27
To: [e-mail]
Cc: [e-mail]
Subject: [spring] My question at the mike about draft-dong-spring-srv6-inter-layer-programming

Hi all,
Just repeating the question about the draft<https://datatracker.ietf.org/doc/html/draft-dong-spring-srv6-inter-layer-programming-08> I’ve asked at he mike at the SPRING WG session today.


  *   Suppose that there is an underlay link between a pair of IP nodes  that is not “visible in he L3 topology”. To me this means that there no P-capable (logical) interfaces associated with the endpoints of this underlay link

[Jie] The interface of the underlay link is not L3-capable, while it still can have some packet processing capability.  You may consider it as a layer-2 logical interface. 


  *   Suppose further that one of these nodes (the upstream one) allocates and advertises an SID with End.XU behavior for this underlay link

  *   The upstream node receives an IPv6 packets with the tops SRv6 SID on it being the End.XU. It strips this SID (this the common behavior of all End-like SIDs) and send the resulting IPv6 packet across the link to the downstream node/\.
Now the question: How should the downstream node process the received packet if its local endpoint of the undelay link s not associated with an IP-capable logical interface?

[Jie] Similar to what I said above, the receiving interface is not L3-capable, while it can receive and process the packet properly in layer-2, the inner L3 packet header can be processed by the node. 


If the endpoints of the underlay ink are associated with L3 interfaces in both nodes, the link becomes visible in L3 topology, and a regular End.X SID can be allocated and advertised for it.

[Jie] As described in the draft, making it an L3 adjacency between the two endpoints is both challenging and unnecessary. And operator does not want this link to be visible in L3 topology. Thus regular End.X SID does not meet the requirement here.

 
Hope this help to answer your question. 

Best regards,
Jie


Hopefully this clarifies my question.

Regards,
Sasha




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