Is there an assumption that some other monitoring exists so that there
is knowledge of whetehr the link is up to control advertising the new
adjacency SID?
Yours,
Joel
On 8/15/2024 6:32 AM, 韩柳燕 wrote:
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 doesn't 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
Get Outlook for Android <https://aka.ms/AAb9ysg>
------------------------------------------------------------------------
*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
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