Hi Sasha,
Thanks a lot for your question at the meeting and via the email discussions.
I would like to add some clarifications. The new SRv6 behaviors does not
require IGP based link discovery and advertisement for the underlay connection
between the two endpoints, which is needed for End.X behavior. It is more
adaptable to the network situation and has application advantages. Because for
large networks, the nodes at both ends may span different metropolitan areas
networks or even backbone networks, and may not be in the same IGP domain due
to the limited size of IGP. The new SRv6 behaviors in this draft do not require
IGP to be enabled as the control protocol between the two end nodes of the
underlay link and doesn39t require this link to be visible in L3 topology.
Best regards,
Liuyan
----邮件原文----发件人："Dongjie \\(Jimmy\\)"
<jie.dong=40huawei....@dmarc.ietf.org>收件人：Alexander Vainshtein
<Alexander.Vainshtein=40rbbn....@dmarc.ietf.org>,"draft-dong-spring-srv6-inter-layer-programm...@ietf.org"
<draft-dong-spring-srv6-inter-layer-programm...@ietf.org>抄 送:
"spring@ietf.org" <spring@ietf.org>发送时间：2024-08-05 11:38:21主题：RE: My question
at the mike aboutdraft-dong-spring-srv6-inter-layer-programming
Hi Sasha,
Thanks a lot for your comments during the SPRING session and in the follow-up
mails. Please see some replies inline with [Jie]:
From: Alexander Vainshtein
[mailto:Alexander.Vainshtein=40rbbn....@dmarc.ietf.org] Sent: Sunday, July 28,
2024 1:05 AM To: Dongjie (Jimmy) <jie.d...@huawei.com>
draft-dong-spring-srv6-inter-layer-programm...@ietf.org Cc: spring@ietf.org
Subject: Re: My question at the mike about
draft-dong-spring-srv6-inter-layer-programming
Jie,
Lots of thanks for your email.
First, I would like to apologize for not responding to your emails earlier.
[Jie] No problem, it is always good to know your opinion no matter early or
late:)
I think that there is a certain mismatch of terminology that have resulted in
misunderstanding.
[Jie] I also realized this, and have checked with my colleague who is closer to
the implementation.
In my (and, AFAIK, relatively common) terminology frames received from a Layer
2 logical interface are disposed based solely in their L2 header. (In the case
of Ethernet this would include Destination and Source MAC addresses and zero,
one or two VLAN tags - but not the "true" Ethertype that follows these tags.
Other L2 media uses similar arrangements). I.e., the node that receives
Ethernet frames from what it considers a L2 interface cannot differentiate
between, say, IPv4, ARP, IPv6 and MPLS.
[Jie] Agreed, although to my understanding MPLS sits between layer 2 and layer
3.
It is the ability to differentiate between different protocols based on the
"true" Ethertype and, say, look up the Destination IPv6 address in the
appropriate FIB (which is required for SRv6) that makes an interface a L3 one
from my POV.
[Jie] Agree that for an interface to process SRv6 packets, it needs to be
associated with some L3 functionality. While it does not need to be a full L3
interface which is visible in the routing topology. In other word, the L3
adjacency is better to be avoided. We can add some clarification in next
update.
Regarding your concern about L3 interfaces involving adjacencies, I also think
this is unfounded. It is quite easy to make an IGP adjacency unusable for
normal IP forwarding by assigning maximum cost to the corresponding link -but
using Adj-SIDs allocated and advertised for such a link in SR-TE policies that
are set up by the appropriate controller.
[Jie] The primary goal here is not about how to make an IGP adjacency unusable
in IP routing, it is about how to avoid the challenge and cost of establishing
IGP adjacency between two remote endpoints (they can even belong to different
IGP domains). As since the underlay interface and path can be created/deleted
dynamically, adding such link using Adj-SIDs to IGP would also impact the
protocol stability.
Thus it would be beneficial to distinguish it from the L3 Adj-SIDs/End.X SIDs
in SPRING, and its advertisement can also be separate from the control plane
mechanisms for Adj-SIDs/End.X SIDs.
Hope this helps to clarify the intent of this effort.
Best regards,
Jie
Hopefully these notes will be useful
Regards,
Sasha
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--------------------------------------------------------------------------------
From: Dongjie (Jimmy) <jie.dong=40huawei....@dmarc.ietf.org> Sent: Saturday,
July 27, 2024 7:59:30 AM To: Alexander Vainshtein
<alexander.vainsht...@rbbn.com>
draft-dong-spring-srv6-inter-layer-programm...@ietf.org
<draft-dong-spring-srv6-inter-layer-programm...@ietf.org> Cc: spring@ietf.org
<spring@ietf.org> Subject: [EXTERNAL] Re: My question at the mike about
draft-dong-spring-srv6-inter-layer-programming
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 Disclaimer This e-mail together with any
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