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([2607:fb90:4ae8:860c:106e:e783:56ba:92f6]) by smtp.gmail.com with ESMTPSA id gm10sm3516495pjb.4.2021.04.09.21.22.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 09 Apr 2021 21:22:18 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable From: Jeff Tantsura Mime-Version: 1.0 (1.0) Subject: Re: I-D Action: draft-filsfils-6man-structured-flow-label-00.txt Date: Fri, 9 Apr 2021 21:22:16 -0700 Message-Id: References: <34787b4f-fdfb-953a-4458-ca410ba70c08@gmail.com> Cc: Ron Bonica , 6man@ietf.org, draft-filsfils-6man-structured-flow-label@ietf.org In-Reply-To: <34787b4f-fdfb-953a-4458-ca410ba70c08@gmail.com> To: Brian E Carpenter X-Mailer: iPhone Mail (18D70) Archived-At: X-BeenThere: ipv6@ietf.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: "IPv6 Maintenance Working Group \(6man\)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 10 Apr 2021 04:22:25 -0000 To my memory, around 2015 Tom Herbert submitted a kernel patch that would ch= ange flow label based on RTO, and this has been successfully used for =E2=80= =9Cself healing fabrics=E2=80=9D in large DCs to rebalance flows. Since ever= y piece of silicon in DC that takes flow label into consideration when hashi= ng the traffic uses full 20 bits - repurposing part of it would break it. This and similar solutions would need to be addressed. Regards, Jeff > On Apr 9, 2021, at 20:39, Brian E Carpenter w= rote: >=20 > =EF=BB=BFOn 09-Apr-21 10:12, Ron Bonica wrote: >> Clarence, >>=20 >> Draft-filsfils-6man-structured-flow-label addresses a real problem. Howev= er, it may have issues with regard to backwards compatibility and IPv6 exten= sibility. Each is addressed below. >>=20 >> Backwards Compatibility >> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=20 >> In the draft, you divide the flow label into 4 FLC bits and 16 FLE bits. T= he 4 FLC bits carry per-packet control information and are not used for ECMP= load-balancing. The 16 FLE bits are as defined in RFC 6437. >>=20 >> This raises the issue of backwards compatibility. Many legacy devices IPv= 6 devices use all 20 bits of the flow label as defined in RFC 6437. As you s= ay in Section 4, this could cause packets belonging to a single flow to be d= istributed among multiple paths. So, the degree of packet reordering at the u= ltimate destination node will increase to an unacceptable level. >=20 > And the use of the flow label for server-farm load balancing will be compl= etely broken. That's why this idea is a non-starter outside a limited domain= . >=20 > Brian >=20 >>=20 >> IPv6 Extensibility >> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=20 >>=20 >> Over the past decade, there have been several proposals that take the fol= lowing form: >>=20 >> - An IPv6 source node needs to convey some piece of information to every n= ode along the packet's delivery path >> - Field X in the IPv6 header is longer than it needs to be >> - So, we can borrow a few bits from Field X to convey this information. >>=20 >> This approach is flawed for the following reasons: >>=20 >> - It can cause backwards compatibility issues, as described above >> - It only works a few times, until there are no more bits to be borrowed i= n the base IPv6 header >>=20 >> IPv6 includes a Hop-by-hop Options header. It's purpose is to convey info= rmation from the source node to every node along the packet's delivery path.= Sadly, it was implemented badly so that it can be used as a DoS vector. The= refore, network operators generally filter it. >>=20 >> A better approach would be: >>=20 >> - to avoid borrowing bits from the IPv6 header >> - to use the HBH Option for its intended purpose >>=20 >> This will require rehabilitation of the HBH option. Bob Hinden and Gorry = Fairhurst have made a good start towards this goal in draft-hinden-6man-hbh-= processing. We vendors will also need to get behind the rehabilitation effor= t, revising our implementations so that it can no longer be used as a DoS ve= ctor. In turn, network operators will also need to get behind the rehabilita= tion effort. >>=20 >> While this may not be the path of least resistance, it will contribute to= the future extensibility of IPv6. Let's do the right thing. >>=20 >> = Ron >>=20 >>=20 >>=20 >>=20 >>=20 >>> On 17-Mar-21 05:49, internet-drafts@ietf.org wrote: >>>=20 >>> A New Internet-Draft is available from the on-line Internet-Drafts direc= tories. >>>=20 >>>=20 >>> Title : Structured Flow Label >>> Authors : Clarence Filsfils >>> Ahmed Abdelsalam >>> Shay Zadok >>> Xiaohu Xu >>> Weiqiang Cheng >>> Daniel Voyer >>> Pablo Camarillo Garvia >>> Filename : draft-filsfils-6man-structured-flow-label-00.txt >>> Pages : 12 >>> Date : 2021-03-16 >>>=20 >>=20 >>=20 >> Juniper Business Use Only >>=20 >> -------------------------------------------------------------------- >> IETF IPv6 working group mailing list >> ipv6@ietf.org >> Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 >> -------------------------------------------------------------------- >>=20 >=20 > -------------------------------------------------------------------- > IETF IPv6 working group mailing list > ipv6@ietf.org > Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 > --------------------------------------------------------------------