Re: [Lsr] WG Adoption Call for "IGP Flexible Algorithms (Flex-Algorithm) In IP Networks" - draft-bonica-lsr-ip-flexalgo-01

Gyan Mishra <> Fri, 04 December 2020 05:28 UTC

Return-Path: <>
Received: from localhost (localhost []) by (Postfix) with ESMTP id CA7103A0AF6 for <>; Thu, 3 Dec 2020 21:28:47 -0800 (PST)
X-Virus-Scanned: amavisd-new at
X-Spam-Flag: NO
X-Spam-Score: -2.087
X-Spam-Status: No, score=-2.087 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_FROM=0.001, HTML_MESSAGE=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_REMOTE_IMAGE=0.01, URIBL_BLOCKED=0.001] autolearn=ham autolearn_force=no
Authentication-Results: (amavisd-new); dkim=pass (2048-bit key)
Received: from ([]) by localhost ( []) (amavisd-new, port 10024) with ESMTP id A4HsjQnuxmw8 for <>; Thu, 3 Dec 2020 21:28:45 -0800 (PST)
Received: from ( [IPv6:2607:f8b0:4864:20::535]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by (Postfix) with ESMTPS id A37ED3A0ADA for <>; Thu, 3 Dec 2020 21:28:45 -0800 (PST)
Received: by with SMTP id e23so2821486pgk.12 for <>; Thu, 03 Dec 2020 21:28:45 -0800 (PST)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=n2icTpbDo5g2vI980MJW9AlUKVW/4GprA878kCuS3Gk=; b=viCJ8uZlAIUW+nepLEKqfJ60uz/v119KX/rx2w8iPklIQz2jEkqeckGeP0nn+5goPE dLRYDeMxbaAoxYGebZpneoasOiWiRn2bVBTh3EucX79UeL+kBK7i0oTo9X2AgC/8gf/G WTO9JE6eblxXM+XBi4T2880TXkdEEIMtU+6uxAUanTBlUZEQvSBUoSc52UMJkTF/dJq5 e+8K2f6bMmRMdeem5ZPLgZY++60tRKsVS6n+IxxJQejoNlDWt3kt4QJFXX9Xj/7CVl8H HnBF4W3WEVL1zOzMHxm5SmLIp/DiO+M91CQJ99+666rpIBZs7RogaI+1hsqIIgTt/Lak XBTA==
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=n2icTpbDo5g2vI980MJW9AlUKVW/4GprA878kCuS3Gk=; b=KNBJA4VOYqT0dezaAbFY3G8emGcMWacH5m2pmqFzcn9JTX62u3lmYx2dRCGTn39g5w LJpo9njmFxIQHBaCafXAn6fV3XLqcgdRwu/Oo+nIMKuwA/ToCcFxwnxSTkqsm337uUqe 4FzAV4IvePpy23unyBnvFXONdcAWsh9ljwu6gLVwHZaRIwdpPaPUe8ZRR6RPYZsIU9Je AKS3nIIwciTcaMKJTH5OShkWq1ueMo6ZZM769Qi/DqUiVSgQ7BPX+D1zHUCQw3CO9vow XKGQquvAFWKCQgndhLfpn9H8YpBTkSQaMPwdKeE6BFgEAOxuFoLE5aAvILyiOo0TdDfk bViQ==
X-Gm-Message-State: AOAM531ZSegMJWATcv938ujFSg6EBMT8VVuHHmssJ5Bcq44MYpPh39j3 hEFbCVdE3n5waxgKqKvCCiEAA9sgfXbGZd1By0A=
X-Google-Smtp-Source: ABdhPJwhsd1+J27uxVScm8cms95UTiOIqdZiVY4eGmMGGNcAS1FY+fctGoaMnkBCjMvqSLezxtNUvtA4HsKWHBPGuAY=
X-Received: by 2002:a62:5543:0:b029:19d:930f:9a17 with SMTP id j64-20020a6255430000b029019d930f9a17mr2312662pfb.20.1607059724948; Thu, 03 Dec 2020 21:28:44 -0800 (PST)
MIME-Version: 1.0
References: <> <>
In-Reply-To: <>
From: Gyan Mishra <>
Date: Fri, 4 Dec 2020 00:28:34 -0500
Message-ID: <>
To: Jeff Tantsura <>
Cc: "Acee Lindem (acee)" <>, Robert Raszuk <>, Tony Li <>, lsr <>
Content-Type: multipart/alternative; boundary="00000000000009d7cc05b59cc0ab"
Archived-At: <>
Subject: Re: [Lsr] WG Adoption Call for "IGP Flexible Algorithms (Flex-Algorithm) In IP Networks" - draft-bonica-lsr-ip-flexalgo-01
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: Fri, 04 Dec 2020 05:28:48 -0000

+1 for IP flex algo for operators toolbox


On Thu, Dec 3, 2020 at 10:54 PM Jeff Tantsura <>

> I’m very much in favor of being able to provide a number of technologies
> that help operators with different requirements and constraints to provide
> their services in a most optimized way, hence my support for flex-algo,
> either labeled or not as a technology on the dynamic spectrum of the
> solution space.
> One can achieve similar results on a single topology with a centralized
> controller, there are trade-offs in either, extremities on either side are
> counterproductive .
> Regards,
> Jeff
> On Dec 3, 2020, at 17:47, Gyan Mishra <> wrote:
> In fact the concept of traffic engineering has been around for a long time
> using simple IGP metric manipulation to steer traffic using the IGP.
> I had designed in my past life a costing algorithm where you use highest
> bandwidth links and lowest latency as the crow flies point A to point B
> such that you take the highest bandwidth lowest latency path based on a
> formula for path instantiation.  This is the essence of flex algo basically
> an engineered algorithm algo xyz for a sub routing instance instantiation.
> This concept works well for global table or single routing instance,
> however if you have multiple VPNs and you want to realize per VPN coloring
> capabilities it is much different then use of flex algo with a single IGP
> global table routing following a single algo or multiple sub set algo’s.
> That’s where RSVP TE PCALC path computation and bandwidth and link
> attributes came into play in an MPLS context.
> However, now trying to expand traditional RSVP TE to provide per VRF VPN
> mapping and coloring is now a daunting painful and non scalable solution.
> Now requires with RSVP static routes and VRF next hop rewrite to map each
> VPN to a different color steered statically to a different loopback egress
> PE iBGP next hop then the default iBGP global table next hop.
> That’s where the advent of SR with SR-TE now fills that much needed gap of
> per VRF coloring to build the same as we had in the RSVP world loose path
> prefix sid or strict path adjacency sid path instantiation now done via
> centralized controller.
> The gap where flex algo comes into play is unique but I think is a tool on
> the operator toolbox which prior to IP flex algo provided additional
> steering granularity and path instantiation control used in conjunction
> with SR-TE.
> The gap IP flex algo fills is internet providers global table routing
> being able to create logical traffic steering constructs where MPLS or SR
> does not exist.
> So that is a huge much needed gap as not all operators on the public core
> have MPLS or SR and would like an alternative.
> This could be used in both core and data center space as well IP based
> infrastructure.
> RSVP TE and SR have their niche and now IP flex algo fills yet another
> somewhat mutually exclusive niche.
> Kind Regards
> Gyan
> On Thu, Dec 3, 2020 at 8:18 PM Jeff Tantsura <>
> wrote:
>> Anything else than IGP metric based SPT is considered TE. Looking
>> holistically - topology virtualization (or similar) could have been a
>> better name.
>> Cheers,
>> Jeff
>> On Dec 3, 2020, 4:25 PM -0800, Robert Raszuk <>et>, wrote:
>> Hi Tony,
>> The moment I hit "Send" I knew that this response may be coming as it
>> really depends what is one's definition of TE.
>> If indeed IGP TE is anything more then SPF - then sure we can call it a
>> TE feature.
>> However, while a very useful and really cool proposal, my point is to
>> make sure this is not oversold - that's all.
>> Best,
>> R.
>> On Fri, Dec 4, 2020 at 1:13 AM Tony Li <> wrote:
>>> Hi Robert,
>>> > However I really do not think that what Flexible Algorithm offers can
>>> be compared or even called as Traffic Engineering (MPLS or SR).
>>> >
>>> > Sure Flex Algo can accomplish in a very elegant way with little cost
>>> multi topology routing but this is not full TE. It can also direct traffic
>>> based on static or dynamic network preferences (link colors, rtt drops etc
>>> ... ),  but again it is not taking into account load of the entire network
>>> and IMHO has no way of accomplish TE level traffic distribution.
>>> >
>>> > Just to make sure the message here is proper.
>>> It’s absolutely true that FlexAlgo (IP or SR) has limitations. There’s
>>> no bandwidth reservation. There’s no dynamic load balancing. No, it’s not a
>>> drop in replacement for RSVP. No, it does not supplant SR-TE and a good
>>> controller. Etc., etc., etc….
>>> However I don’t feel that it’s fair to say that FlexAlgo can’t be called
>>> Traffic Engineering.  After all TE is a very broad topic. Everything that
>>> we’ve done that’s more sophisticated than simple SPF falls in the area of
>>> Traffic Engineering.  Link coloring and SRLG alone clearly fall into that
>>> bucket.
>>> I’ll grant you that it may not have the right TE features for your
>>> application, but that doesn’t mean that it’s not sufficient for some.
>>> Please don’t mislead people by saying that it’s not Traffic Engineering.
>>> Regards,
>>> Tony
>>> _______________________________________________
>> Lsr mailing list
>> _______________________________________________
>> Lsr mailing list
> --
> <>
> *Gyan Mishra*
> *Network Solutions A**rchitect *
> *M 301 502-134713101 Columbia Pike
> <,+MD?entry=gmail&source=g> *Silver
> Spring, MD
> <,+MD?entry=gmail&source=g>
> --


*Gyan Mishra*

*Network Solutions A**rchitect *

*M 301 502-134713101 Columbia Pike *Silver Spring, MD