Hi Stephane,
If you want to do transit measurement, you have to pay some cost.
The difference is how large the cost is, one, two or multiple labels.
For E2E measurement, it could be much easier. A single label
(could be local or global) is inserted immediately follow the
last label of the SR path. Since there is only one label, the
path label could be put into the stack at the beginning, no
matter whether the measurement is enable or not. With this, it
will not affect the entropy.
Best regards,
Mach
*From:*mpls [mailto:[email protected]] *On Behalf Of
*[email protected] <mailto:[email protected]>
*Sent:* Thursday, November 16, 2017 6:49 PM
*To:* Robert Raszuk; Alexander Vainshtein
*Cc:* mpls; spring; Clarence Filsfils;
draft-hegde-spring-traffic-accounting-for-sr-paths; Michael
Gorokhovsky; [email protected]
<mailto:[email protected]>; Zafar Ali (zali)
*Subject:* Re: [mpls] [spring] Special purpose labels in
draft-hegde-spring-traffic-accounting-for-sr-paths
Hi,
Yes today we do not have any CLI command on any router to get
paths statistics for LDP (I mean Ingress to Egress) as LDP is
based on MP2P LSPs, so a transit node does not have the knowledge
of the source. From an operational point of view, what we do
today is that we collect netflow statistics on core routers, we
project the label stack onto the routing with an external tool to
get the Ingress to Egress LDP traffic including the mapping of
the flows on the links.
Now for RSVP, we do have such statistics as the LSP is P2P and
has states on every node.
Robert mentioned correctly that SR-TE (especially with MPLS
dataplane) has limited TE features (we cannot mimic all what RSVP
does in SRTE without adding too much complexity).
Thus, is it a problem (transit node stats) worth to be solved ?
If yes, where do we accept to put the complexity ? For a stats
issue I would rather prefer to move the complexity to an external
tool that can do correlations or whatever operations rather than
getting it in the forwarding plane…
IMO, that’s a “nice to have” problem to solve getting that we do
not have this for LDP and we know the limitations of SR-TE MPLS.
However, Ingress stats per SRTE LSP are for sure mandatory to get !
The main drawback I see with the proposed solution is that it
mimics what Entropy label does with a solution which is similar
and at the same time cannot replace entropy label as the provided
entropy is far from being sufficient (this is not the goal I
know, but I was looking for potential use case optimizations). So
in a network running entropy label and this mechanism, a router
will need to find the ELI/EL and hash, then find another special
label to build the stats (maybe tomorrow there will be a third
one to look at and a fourth one…). That starts to be a big
overhead for the forwarding plane.
Brgds,
Stephane
*From:*mpls [mailto:[email protected]] *On Behalf Of *Robert
Raszuk
*Sent:* Thursday, November 16, 2017 16:23
*To:* Alexander Vainshtein
*Cc:* spring; Clarence Filsfils; mpls; Michael Gorokhovsky;
[email protected]
<mailto:[email protected]>;
draft-hegde-spring-traffic-accounting-for-sr-paths; Zafar Ali (zali)
*Subject:* Re: [mpls] [spring] Special purpose labels in
draft-hegde-spring-traffic-accounting-for-sr-paths
Folks,
This thread started and the requirements reported clearly stated
that all what we need is the ability to account per path traffic
on egress nodes.
Now out of the sudden I see requirement popping up to be able to
measure per path in transit nodes.
Well you can do it today with SRv6 if your hardware allows or you
can do it with RSVP-TE.
SR-MPLS is replacing LDP and adds ability for limited TE. But
SR-MPLS never intended to become connection oriented protocol nor
architecture.
So I recommend we take a step back here. Or if you like first go
and fix basic MPLS LDP LSPs to allow per end to end path
accounting in transit nodes then come back here to ask for the
same in SR-MPLS. Not the other way around.
Thx
r.
On Nov 16, 2017 16:12, "Alexander Vainshtein"
<[email protected]
<mailto:[email protected]>> wrote:
Greg,
I concur with your position: let’s first of all agree that
ability to measure traffic carried by an SR-TE LSP in a specific
transit node is a require OAM function for SR.
I have looked up the SR OAM Use Cases
<https://datatracker.ietf.org/doc/draft-ietf-spring-oam-usecase/?include_text=1>
draft, and I did not find any relevant use cases there.
The only time measurements are mentioned is a reference to an
expired implementation report
<https://tools.ietf.org/html/draft-leipnitz-spring-pms-implementation-report-00>
draft discussing delay measurements. Since delay measurements are
in any case based on synthetic traffic, and are always end-to-end
(one-way or two-way), this reference is not relevant, IMHO, for
this discussion.
I have added the authors of the SR OAM Use Cases draft to tis thread.
Regards,
Sasha
Office: +972-39266302 <tel:+972%203-926-6302>
Cell: +972-549266302 <tel:+972%2054-926-6302>
Email: [email protected]
<mailto:[email protected]>
*From:*mpls [mailto:[email protected]
<mailto:[email protected]>] *On Behalf Of *Greg Mirsky
*Sent:* Thursday, November 16, 2017 4:28 AM
*To:* Xuxiaohu <[email protected] <mailto:[email protected]>>
*Cc:* draft-hegde-spring-traffic-accounting-for-sr-paths
<[email protected]
<mailto:[email protected]>>;
spring <[email protected] <mailto:[email protected]>>; Zafar Ali
(zali) <[email protected] <mailto:[email protected]>>; mpls
<[email protected] <mailto:[email protected]>>
*Subject:* Re: [mpls] [spring] Special purpose labels in
draft-hegde-spring-traffic-accounting-for-sr-paths
Dear All,
I cannot imagine that operators will agree to deploy network that
lacks critical OAM tools to monitor performance and troubleshoot
the network. True, some will brave the challenge and be the early
adopters but even they will likely request that the OAM toolbox
be sufficient to support their operational needs. I see that this
work clearly describes the problem and why ability to quantify
the flow behavior at internal nodes is important for efficient
network operation. First let's discuss whether the case and
requirement towards OAM is real and valid. Then we can continue
to discussion of what measurement method to use.
Regards,
Greg
On Thu, Nov 16, 2017 at 10:05 AM, Xuxiaohu <[email protected]
<mailto:[email protected]>> wrote:
Concur. Although it has some values, it's not cost-efficient
from my point of view. Network simplicity should be the first
priority object. Hence we would have to make some compromise.
Best regards,
Xiaohu
------------------------------------------------------------------------
徐小虎Xuxiaohu
M：+86-13910161692 <tel:+86-13910161692>
E：[email protected] <mailto:[email protected]>
产品与解决方案-网络战略与业务发展部
Products & Solutions-Network Strategy & Business Development Dept
*发件人：***Zafar Ali (zali)
*收件人：***Greg Mirsky<[email protected]
<mailto:[email protected]>>;draft-hegde-spring-traffic-accounting-for-sr-paths<[email protected]
<mailto:[email protected]>>;mpls<[email protected]
<mailto:[email protected]>>;spring<[email protected]
<mailto:[email protected]>>
*主**题：***Re: [mpls] [spring] Special purpose labels in
draft-hegde-spring-traffic-accounting-for-sr-paths
*时间：***2017-11-16 02:24:10
Hi,
This draft breaks the SR architecture. I am quoting a snippet
from abstract of SR Architecture document
https://tools.ietf.org/html/draft-ietf-spring-segment-routing-13
<https://tools.ietf.org/html/draft-ietf-spring-segment-routing-13>,
which states:
“SR allows to enforce a flow through any topological path
while maintaining per-flow state only at the ingress nodes to
the SR domain.”
In addition to creating states at transit and egress nodes,
the procedure also affects the data plane and makes it
unscalable. It also makes controller job much harder and
error prune. In summary, I find the procedure very complex
and unscalable.
Thanks
Regards … Zafar
*From: *spring <[email protected]
<mailto:[email protected]>> on behalf of Greg Mirsky
<[email protected] <mailto:[email protected]>>
*Date: *Wednesday, November 15, 2017 at 11:10 AM
*To:
*"[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: *[spring] Special purpose labels in
draft-hegde-spring-traffic-accounting-for-sr-paths
Hi Shraddha,
thank you for very well written and thought through draft. I
have these questions I'd like to discuss:
* Have you thought of using not one special purpose label
for both SR Path Identifier and SR Path Identifier+Source
SID cases but request two special purpose labels, one for
each case. Then the SR Path Identifier would not have to
lose the bit for C flag.
* And how you envision to collect the counters along the
path? Of course, a Controller may query LSR for all
counters or counters for the particular flow (SR Path
Identifier+Source SID). But in addition I'd propose to
use in-band mechanism, perhaps another special purpose
label, to trigger the LSR to send counters of the same
flow with the timestamp out-band to the predefined Collector.
* And the last, have you considered ability to flush
counters per flow. In Scalability Considerations you've
stated that counters are maintained as long as collection
of statistics is enabled. If that is on the node scope,
you may have to turn off/on the collection to flush off
some old counters. I think that finer granularity, per
flow granularity would be useful for operators. Again,
perhaps the flow itself may be used to signal the end of
the measurement and trigger release of counters.
Regards,
Greg
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