Re: [Lsr] New draft on Flex-Algorithm Bandwidth Constraints

"Dongjie (Jimmy)" <> Tue, 02 March 2021 01:48 UTC

Return-Path: <>
Received: from localhost (localhost []) by (Postfix) with ESMTP id BB4553A0AD1 for <>; Mon, 1 Mar 2021 17:48:44 -0800 (PST)
X-Virus-Scanned: amavisd-new at
X-Spam-Flag: NO
X-Spam-Score: -1.299
X-Spam-Status: No, score=-1.299 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, HTML_MESSAGE=0.001, HTTPS_HTTP_MISMATCH=0.1, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001, URI_NOVOWEL=0.5] autolearn=no autolearn_force=no
Received: from ([]) by localhost ( []) (amavisd-new, port 10024) with ESMTP id QcqvGE-Ly8Hs for <>; Mon, 1 Mar 2021 17:48:42 -0800 (PST)
Received: from ( []) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by (Postfix) with ESMTPS id CBFB73A0ACB for <>; Mon, 1 Mar 2021 17:48:41 -0800 (PST)
Received: from (unknown []) by (SkyGuard) with ESMTP id 4DqKgH2kKJz67v8m; Tue, 2 Mar 2021 09:44:27 +0800 (CST)
Received: from ( by ( with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256) id 15.1.2106.2; Tue, 2 Mar 2021 02:48:38 +0100
Received: from ( by ( with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.2106.2; Tue, 2 Mar 2021 09:48:35 +0800
Received: from ([]) by ([]) with mapi id 15.01.2106.006; Tue, 2 Mar 2021 09:48:35 +0800
From: "Dongjie (Jimmy)" <>
To: Robert Raszuk <>, Tony Li <>
CC: Gyan Mishra <>, DECRAENE Bruno IMT/OLN <>, Shraddha Hegde <>, Rajesh M <>, "" <>, William Britto A J <>
Thread-Topic: [Lsr] New draft on Flex-Algorithm Bandwidth Constraints
Thread-Index: AQHXDBIWT9mc4YXF3E+r+hn24uWzgqpraLCAgAA/MgCAAsPaAIAAi0gAgAAb7gCAANqMoA==
Date: Tue, 2 Mar 2021 01:48:35 +0000
Message-ID: <>
References: <> <> <> <> <> <> <>
In-Reply-To: <>
Accept-Language: en-US, zh-CN
Content-Language: zh-CN
X-MS-Has-Attach: yes
x-originating-ip: []
Content-Type: multipart/related; boundary="_004_f358ab68753c4c8390364dcf8dbda949huaweicom_"; type="multipart/alternative"
MIME-Version: 1.0
X-CFilter-Loop: Reflected
Archived-At: <>
Subject: Re: [Lsr] New draft on Flex-Algorithm Bandwidth Constraints
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Link State Routing Working Group <>
List-Unsubscribe: <>, <>
List-Archive: <>
List-Post: <>
List-Help: <>
List-Subscribe: <>, <>
X-List-Received-Date: Tue, 02 Mar 2021 01:48:45 -0000

Hi Robert,

I have similar question as yours: whether the proposed mechanism is based on static or dynamic bandwidth/latency metric?

If static, it is easy for Flex-Algo based distributed computation, while the result may not be that helpful, as Tony said, all traffic may be steered to the same link.

If dynamic, the changes in the metric will result in dynamic computation with Flex-Algo constraints, thus more need to be considered: measurement and advertisement of dynamic metrics, overhead in dynamic computation, loop prevention during dynamic computation and convergence, the possibility of an unacceptable result… And with all this overhead in mind, it is better to understand what would be the gains, can it help to reduce the congestion or packet drop? Or what possible problem it is targeted to solve?

Best regards,

From: Lsr [] On Behalf Of Robert Raszuk
Sent: Tuesday, March 2, 2021 4:22 AM
To: Tony Li <>
Cc: Gyan Mishra <>om>; DECRAENE Bruno IMT/OLN <>om>; Shraddha Hegde <>et>; Rajesh M <>et>;; William Britto A J <>
Subject: Re: [Lsr] New draft on Flex-Algorithm Bandwidth Constraints

Hi Tony,

Constructing arbitrary topologies with bw constrain is useful work. For example I want to create a topology without links of the capacity less then 1 Gbps. All cool. Of course if I have a case where two nodes have 10 L3 1Gbps links nicely doing ECMP I will not include those which may be a problem.

However my observation is precisely related to your last sentence.

Is this extension to be used with static or dynamic data ? If static all fine. But as William replied to me earlier link delay may be dynamically computed and may include queue wait time. That to me means something much different if Flex-Algo topologies will become dynamically adjustable. And I am not saying this is not great idea .. My interest here is just to understand the current scope.


On Mon, Mar 1, 2021 at 7:42 PM Tony Li <<>> wrote:

Hi William, Gyan, Robert, Tony, et. al.,

Please permit me to wax a bit philosophic here.

William is exactly correct that the goal is not to make FlexAlgo deal with reservations like RSVP does.  Without some kind of setup protocol or global computation, that’s simply not possible. Moreover that’s not the real problem that we’re out to solve.

Reservations are just a first order approximation to a traffic flow in any case. We characterize them as having a fixed constant bandwidth, but we all know that that is far from the truth. Each flow is diurnal and fractally bursty. Every user who ever clicks on a link creates bandwidth demand and while the Law of Large Numbers helps us out with some averages we all know that we have no good way of characterizing the traffic that we’re trying to carry. Claiming that it is a single 12Gbps LSP is truly a huge over simplification and a good step towards solving the real problem.

So what is the real problem that we’re trying to solve?

We are trying to not drop packets.

Dropping packets is bad because it forces retransmissions and impacts someone’s Internet experience. Dropping packets is our response to congestion events. If we could manage to have a network that never congested and always delivered packets without giant latency, all would be good.

To date, we have created traffic engineering mechanisms to help us steer traffic so that we could delivery traffic without congesting. It has been a means to an end. The mechanisms that we’ve created have a non-trivial overhead and approximate our goals, but they do NOT preclude, anticipate, or avoid congestion. They do not react when we have unexpected inputs. We do extensive pre-computation to deal with even single failures and have no serious mechanisms that handle multiple failures.

Right now, FlexAlgo does nothing to help with bandwidth management. Wiilliam et. al., are proposing some first steps, which are to be encouraged. Much more will be needed, not to recreate legacy mechanisms but because we should be striving for a more sophisticated, real-time approach to bandwidth management and congestion avoidance.


On Mar 1, 2021, at 2:24 AM, William Britto A J <<>> wrote:

Hi Gyan,

This draft aims to provide the protocol constructs to define a flex-algorithm which is suitable for sending high bandwidth traffic. Flex-Algo is a very useful feature for network consolidation use-cases which requires different metric-types for SPF. We are trying introduce the protocol constructs to simplify the use of metric based on bandwidth via Flex-Algo.

This draft does not attempt to do bandwidth management nor reservation like what RSVP does. For LDP based networks that use igp metric relative to bandwidth, Flex-Algo provides an easy alternate.


From: Gyan Mishra <<>>
Date: Saturday, 27 February 2021 at 9:40 PM
To: Robert Raszuk <<>>
Cc: DECRAENE Bruno IMT/OLN <<>>, Rajesh M <<>>, Shraddha Hegde <<>>, William Britto A J <<>>,<> <<>>
Subject: Re: [Lsr] New draft on Flex-Algorithm Bandwidth Constraints
[External Email. Be cautious of content]

Hi William & Co-authors

From first read of the draft it does appear your are trying to apply RSVP TE PCALC path and reserve message link attributes constraints such as concept of affinity bits to exclude low bandwidth or delay of individual links without taking into account all of what RSVP TE is reserving of bandwidth in the end to end path with the Path and Reserve message.  As mentioned Looking at individual links will not provide the end to end path view or bandwidth requirements for the entire path to be reserved as accomplished by RSVP TE.

As Tony and Robert have mentioned I agree this is a good first step but does need more refinement to make useful.

Kind Regards


On Sat, Feb 27, 2021 at 7:24 AM Robert Raszuk <<>> wrote:
Hi William & co-authors,

I read the draft and have two basic questions.

Both bw & delay can be used as defined in the draft to construct new forwarding topologies. But how practical such topologies would be in the real life when 40GB links may be heavily occupied with bursty traffic and 10G links can sit idle ? I suppose you are trying to address the case where say 12 gbps holographic stream needs to be sent across a network.. But then I don't think if sending it in a single flow instead of spreading into many sub-flows and use as much as possible ecmp would not be a better option.

Likewise how good is my accumulated link delay value if in between there are deep buffer network elements and say egress queuing to each link (which max is unaccounted for in your draft) can significantly alter the end to end delay ? Have you consider to add MAX_EGRESS_QUEUE_DELAY on a per link basis (still as static value).  So if some traffic is delay sensitive we will have a much better accuracy not to get into a trap of queuing related delays.

Thx a lot,

On Fri, Feb 26, 2021 at 8:37 AM William Britto A J <<>> wrote:

We would like to draw your attention to a new ID:<;!!NEt6yMaO-gk!U3HBQwaZL7T4mjz-MUHE7VjFtnOyNghGDh5vwJXUXkHdMxlravmRvJwdZ8sz2YPxkw$>

The draft talks about introducing link bandwidth related constraints in Flex-Algorithm which can be used to define a Flex-Algorithm based on bandwidth based metric.

Please review. Any questions and comments are welcome.


From:<> <<>>
Date: Monday, 22 February 2021 at 10:56 PM
To: Bruno Decraene <<>>, Rajesh M <<>>, Rajesh M <<>>, Shraddha Hegde <<>>, William Britto A J <<>>, William Britto A J <<>>
Subject: New Version Notification for draft-hegde-lsr-flex-algo-bw-con-00.txt
[External Email. Be cautious of content]

A new version of I-D, draft-hegde-lsr-flex-algo-bw-con-00.txt
has been successfully submitted by Shraddha Hegde and posted to the
IETF repository.

Name:           draft-hegde-lsr-flex-algo-bw-con
Revision:       00
Title:          Flexible Algorithms Bandwidth Constraints
Document date:  2021-02-22
Group:          Individual Submission
Pages:          21
URL:  ;!!NEt6yMaO-gk!QGg36p91zPfVMznYY91xs-zx70Qp5BE1nJx-Thnl14sTCkvwgOjEzjGBtD3v6TruoA$<;!!NEt6yMaO-gk!QGg36p91zPfVMznYY91xs-zx70Qp5BE1nJx-Thnl14sTCkvwgOjEzjGBtD3v6TruoA$>

   Many networks configure the link metric relative to the link
   capacity.  High bandwidth traffic gets routed as per the link
   capacity.  Flexible algorithms provides mechanisms to create
   constraint based paths in IGP.  This draft documents a set of
   bandwidth related constraints to be used in Flexible Algorithms.

Please note that it may take a couple of minutes from the time of submission
until the htmlized version and diff are available at<;!!NEt6yMaO-gk!U3HBQwaZL7T4mjz-MUHE7VjFtnOyNghGDh5vwJXUXkHdMxlravmRvJwdZ8vQC8uTvg$>g$>.

The IETF Secretariat

Juniper Business Use Only
Lsr mailing list<><;!!NEt6yMaO-gk!U3HBQwaZL7T4mjz-MUHE7VjFtnOyNghGDh5vwJXUXkHdMxlravmRvJwdZ8umPEf2Zg$>
Lsr mailing list<><;!!NEt6yMaO-gk!U3HBQwaZL7T4mjz-MUHE7VjFtnOyNghGDh5vwJXUXkHdMxlravmRvJwdZ8umPEf2Zg$>

Gyan Mishra
Network Solutions Architect
M 301 502-1347
13101 Columbia Pike
Silver Spring, MD

Juniper Business Use Only
Lsr mailing list<>