Hi,
Just as a point of reference, for VLAN tag stacks, the outermost VLAN
tag is always first in the list.
Regarding relax the ordering or not, I may not be answering exactly the
same question, but I would say that you want a have a canonical order
(to allow for easy and efficient comparison), and forcing everyone to
have to sort the label stack before using it would probably just be
regarded as a wart.
Thanks,
Rob
On 14/07/2017 22:31, Acee Lindem (acee) wrote:
Hi Tarek, Jeff,
Typically, YANG indices are added to YANG lists to simply imply
ordering. I don’t believe there is absolutely any value in trying to
enforce the semantics of a precise label position on this index. It is
fairly obvious that the first label in the list is the first label in
the stack, the second label in the list is the second label in the
stack, and so on… Hopefully, the other YANG model authors will agree
with me on this point and the “Index 0 as top” convention should be
relaxed. Is there a YANG doctor in the house???
Now, we currently specify the top label as the first label in the list
while Jeff has proposed that the bottom label be the first label.
Surely, there is an existing convention within MPLS RFCs and drafts
and we should be consistent. I’d research myself but I have a ton of
other things to do prior to leaving for Prague tomorrow. When someone
refers to the first label, is the top or bottom label? I have always
been referring to the first label as the top label (with all due
respect to C stack implementations).
Thanks,
Acee
From: "Tarek Saad (tsaad)" <[email protected] <mailto:[email protected]>>
Date: Thursday, July 13, 2017 at 1:12 PM
To: Jeff Haas <[email protected] <mailto:[email protected]>>, Xufeng Liu
<[email protected] <mailto:[email protected]>>
Cc: Greg Mirsky <[email protected]
<mailto:[email protected]>>, "[email protected]
<mailto:[email protected]>"
<[email protected]
<mailto:[email protected]>>, "[email protected]
<mailto:[email protected]>" <[email protected] <mailto:[email protected]>>,
"[email protected]
<mailto:[email protected]>"
<[email protected]
<mailto:[email protected]>>, Routing WG
<[email protected] <mailto:[email protected]>>
Subject: Re: MPLS label and LSE data models
Resent-From: <[email protected] <mailto:[email protected]>>
Resent-To: <[email protected] <mailto:[email protected]>>,
Yingzhen Qu <[email protected] <mailto:[email protected]>>,
Acee Lindem <[email protected] <mailto:[email protected]>>, Christian Hopps
<[email protected] <mailto:[email protected]>>, <[email protected]
<mailto:[email protected]>>
Resent-Date: Thursday, July 13, 2017 at 1:12 PM
Hi Jeff and Xufeng,
Sorry, catching up on this thread. Yes, we've made a change for
the MPLS label-stack from "leaf-list" to a "list with key index"
to address having multiple labels of same value in the same stack.
We noted an assumption in the description that index 0 is the top
of the stack followed by the remainder of the labels in the stack.
However, you have a point about enforcing index (n-1) being
present before accepting index n. There is some discussion on
'preceding-sibling' and 'following-sibling' with some
recommendations in rfc6087.. I'll need to check if enforcing such
"when" check is good idea in YANG.
Another idea (not so elegant) is relax this "index 0 as top" and
just accept the lowest index of the list as the top followed by
the remainder labels (as sorted in index increasing order).
Regards,
Tarek
-----Original Message-----
From: Jeffrey Haas <[email protected] <mailto:[email protected]>>
Date: Thursday, July 13, 2017 at 12:51 PM
To: Xufeng Liu <[email protected] <mailto:[email protected]>>
Cc: Greg Mirsky <[email protected]
<mailto:[email protected]>>,
"[email protected]
<mailto:[email protected]>"
<[email protected]
<mailto:[email protected]>>, "[email protected]
<mailto:[email protected]>" <[email protected] <mailto:[email protected]>>,
"[email protected]
<mailto:[email protected]>"
<[email protected]
<mailto:[email protected]>>, "[email protected]
<mailto:[email protected]>" <[email protected] <mailto:[email protected]>>
Subject: Re: MPLS label and LSE data models
Resent-From: <[email protected] <mailto:[email protected]>>
Resent-To: Tarek Saad <[email protected] <mailto:[email protected]>>,
<[email protected] <mailto:[email protected]>>, <[email protected]
<mailto:[email protected]>>, <[email protected]
<mailto:[email protected]>>, <[email protected]
<mailto:[email protected]>>, <[email protected]
<mailto:[email protected]>>, <[email protected]
<mailto:[email protected]>>, <[email protected]
<mailto:[email protected]>>, <[email protected]
<mailto:[email protected]>>, <[email protected]
<mailto:[email protected]>>
Resent-Date: Thursday, July 13, 2017 at 12:42 PM
Xufeng,
On Thu, Jul 13, 2017 at 04:14:18PM +0000, Xufeng Liu wrote:
> Thanks for looking at this. You are right, but we are still
discussing various approaches for the static MPLS and the
conclusion has not been reached yet.
> We'd like to hear what you think and appreciate your comments.
To offer a suggestion, order the stack from bottom (lowest
number) to top
(highest). Require that bottom of stack be element index zero.
My yang constraints are a bit weak but I believe you can
construct an XPath
that requires that a node of index 0 must be present.
The above two suggestions don't help with the issues of
needing to sort the
list by index in order to generate the stack, but it does at
least remove
any possible ambiguity about the critical bottom of stack
semantic.
-- Jeff
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