Resenting with fewer names recipients
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-------- Forwarded Message --------
Subject: Re: [mpls] [spring] Special purpose labels in
draft-hegde-spring-traffic-accounting-for-sr-paths
Date: Fri, 17 Nov 2017 02:45:18 +0000
From: Stewart Bryant <stewart.bry...@gmail.com>
To: Mach Chen <mach.c...@huawei.com>, stephane.litkow...@orange.com
<stephane.litkow...@orange.com>, Robert Raszuk <rob...@raszuk.net>,
Alexander Vainshtein <alexander.vainsht...@ecitele.com>
CC: mpls <m...@ietf.org>, spring <spring@ietf.org>, Clarence Filsfils
<cfils...@cisco.com>, draft-hegde-spring-traffic-accounting-for-sr-paths
<draft-hegde-spring-traffic-accounting-for-sr-pa...@ietf.org>, Michael
Gorokhovsky <michael.gorokhov...@ecitele.com>,
draft-ietf-spring-oam-usec...@ietf.org
<draft-ietf-spring-oam-usec...@ietf.org>, Zafar Ali (zali) <z...@cisco.com>
I would like to ask a fundamental question here.
Do we need transit counters for only MPLS-SR, or do we need it for
MPLS-LDP as well?
If we need it for both, then we need to have this discussion in a
general MPLS context and not in an MPLS-SR specific context.
At least some of the methods described here would work for both.
Also WRT the proposal to do ingress collection, if nodal paths are used,
that only tells us the approximate path, not the hotspot which I
understand to be the original goal.
- Stewart
On 16/11/2017 14:46, Mach Chen wrote:
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:mpls-boun...@ietf.org] *On Behalf Of
*stephane.litkow...@orange.com
*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; draft-ietf-spring-oam-usec...@ietf.org; 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:mpls-boun...@ietf.org] *On Behalf Of *Robert Raszuk
*Sent:* Thursday, November 16, 2017 16:23
*To:* Alexander Vainshtein
*Cc:* spring; Clarence Filsfils; mpls; Michael Gorokhovsky;
draft-ietf-spring-oam-usec...@ietf.org
<mailto:draft-ietf-spring-oam-usec...@ietf.org>;
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"
<alexander.vainsht...@ecitele.com
<mailto:alexander.vainsht...@ecitele.com>> 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: alexander.vainsht...@ecitele.com
<mailto:alexander.vainsht...@ecitele.com>
*From:*mpls [mailto:mpls-boun...@ietf.org
<mailto:mpls-boun...@ietf.org>] *On Behalf Of *Greg Mirsky
*Sent:* Thursday, November 16, 2017 4:28 AM
*To:* Xuxiaohu <xuxia...@huawei.com <mailto:xuxia...@huawei.com>>
*Cc:* draft-hegde-spring-traffic-accounting-for-sr-paths
<draft-hegde-spring-traffic-accounting-for-sr-pa...@ietf.org
<mailto:draft-hegde-spring-traffic-accounting-for-sr-pa...@ietf.org>>;
spring <spring@ietf.org <mailto:spring@ietf.org>>; Zafar Ali (zali)
<z...@cisco.com <mailto:z...@cisco.com>>; mpls <m...@ietf.org
<mailto:m...@ietf.org>>
*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 <xuxia...@huawei.com
<mailto:xuxia...@huawei.com>> 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:xuxia...@huawei.com <mailto:xuxia...@huawei.com>
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<gregimir...@gmail.com
<mailto:gregimir...@gmail.com>>;draft-hegde-spring-traffic-accounting-for-sr-paths<draft-hegde-spring-traffic-accounting-for-sr-pa...@ietf.org
<mailto:draft-hegde-spring-traffic-accounting-for-sr-pa...@ietf.org>>;mpls<m...@ietf.org
<mailto:m...@ietf.org>>;spring<spring@ietf.org
<mailto:spring@ietf.org>>
*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,
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 <spring-boun...@ietf.org
<mailto:spring-boun...@ietf.org>> on behalf of Greg Mirsky
<gregimir...@gmail.com <mailto:gregimir...@gmail.com>>
*Date: *Wednesday, November 15, 2017 at 11:10 AM
*To: *"draft-hegde-spring-traffic-accounting-for-sr-pa...@ietf.org
<mailto:draft-hegde-spring-traffic-accounting-for-sr-pa...@ietf.org>"
<draft-hegde-spring-traffic-accounting-for-sr-pa...@ietf.org
<mailto:draft-hegde-spring-traffic-accounting-for-sr-pa...@ietf.org>>,
"m...@ietf.org <mailto:m...@ietf.org>" <m...@ietf.org
<mailto:m...@ietf.org>>, "spring@ietf.org
<mailto:spring@ietf.org>" <spring@ietf.org <mailto:spring@ietf.org>>
*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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