Hi Sasha, 

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

________________________________________
From: Alexander Vainshtein <Alexander.Vainshtein=40rbbn....@dmarc.ietf.org>
Sent: Saturday, July 27, 2024 5:27
To: draft-dong-spring-srv6-inter-layer-programm...@ietf.org
Cc: spring@ietf.org
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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