< draft-ietf-rift-applicability-08.txt		draft-ietf-rift-applicability-09.txt >
	RIFT WG Yuehua. Wei, Ed.		RIFT WG Yuehua. Wei, Ed.
	Internet-Draft Zheng. Zhang		Internet-Draft Zheng. Zhang
	Intended status: Informational ZTE Corporation		Intended status: Informational ZTE Corporation
	Expires: 11 May 2022 Dmitry. Afanasiev		Expires: 15 June 2022 Dmitry. Afanasiev
	Yandex		Yandex
	P. Thubert		P. Thubert
	Cisco Systems		Cisco Systems
	Jaroslaw. Kowalczyk		Jaroslaw. Kowalczyk
	Orange Polska		Orange Polska
	7 November 2021		12 December 2021
	RIFT Applicability		RIFT Applicability
	draft-ietf-rift-applicability-08		draft-ietf-rift-applicability-09
	Abstract		Abstract
	This document discusses the properties, applicability and operational		This document discusses the properties, applicability and operational
	considerations of RIFT in different network scenarios. It intends to		considerations of RIFT in different network scenarios. It intends to
	provide a rough guide how RIFT can be deployed to simplify routing		provide a rough guide how RIFT can be deployed to simplify routing
	operations in Clos topologies and their variations.		operations in Clos topologies and their variations.
	Status of This Memo		Status of This Memo
	skipping to change at page 1, line 39 ¶		skipping to change at page 1, line 39 ¶
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at https://datatracker.ietf.org/drafts/current/.		Drafts is at https://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	This Internet-Draft will expire on 11 May 2022.		This Internet-Draft will expire on 15 June 2022.
	Copyright Notice		Copyright Notice
	Copyright (c) 2021 IETF Trust and the persons identified as the		Copyright (c) 2021 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents (https://trustee.ietf.org/		Provisions Relating to IETF Documents (https://trustee.ietf.org/
	license-info) in effect on the date of publication of this document.		license-info) in effect on the date of publication of this document.
	Please review these documents carefully, as they describe your rights		Please review these documents carefully, as they describe your rights
	and restrictions with respect to this document. Code Components		and restrictions with respect to this document. Code Components
	extracted from this document must include Simplified BSD License text		extracted from this document must include Revised BSD License text as
	as described in Section 4.e of the Trust Legal Provisions and are		described in Section 4.e of the Trust Legal Provisions and are
	provided without warranty as described in the Simplified BSD License.		provided without warranty as described in the Revised BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
	2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3		2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
	3. Problem Statement of Routing in Modern IP Fabric Fat Tree		3. Problem Statement of Routing in Modern IP Fabric Fat Tree
	Networks . . . . . . . . . . . . . . . . . . . . . . . . 5		Networks . . . . . . . . . . . . . . . . . . . . . . . . 5
	4. Applicability of RIFT to Clos IP Fabrics . . . . . . . . . . 5		4. Applicability of RIFT to Clos IP Fabrics . . . . . . . . . . 5
	4.1. Overview of RIFT . . . . . . . . . . . . . . . . . . . . 5		4.1. Overview of RIFT . . . . . . . . . . . . . . . . . . . . 5
	4.2. Applicable Topologies . . . . . . . . . . . . . . . . . . 8		4.2. Applicable Topologies . . . . . . . . . . . . . . . . . . 8
	skipping to change at page 6, line 32 ¶		skipping to change at page 6, line 32 ¶
	normally just the default route, propagates one hop south and is "re-		normally just the default route, propagates one hop south and is "re-
	advertised" by nodes at next lower level.		advertised" by nodes at next lower level.
	+---------------+ +----------------+		+---------------+ +----------------+
	| ToF | | ToF | LEVEL 2		| ToF | | ToF | LEVEL 2
	+ ++------+--+--+-+ ++-+--+----+-----+		+ ++------+--+--+-+ ++-+--+----+-----+
	| | | | | | | | | ^		| | | | | | | | | ^
	+ | | | +-------------------------+ |		+ | | | +-------------------------+ |
	Distance | +-------------------+ | | | | |		Distance | +-------------------+ | | | | |
	Vector | | | | | | | | +		Vector | | | | | | | | +
	South | | | | +--------+ | | | Link+State		South | | | | +--------+ | | | Link-State
	+ | | | | | | | | Flooding		+ | | | | | | | | Flooding
	| | | +----------------+ | | | North		| | | +----------------+ | | | North
	v | | | | | | | | +		v | | | | | | | | +
	++---+-+ +------+ +-+----+ ++----++ |		++---+-+ +------+ +-+----+ ++----++ |
	|SPINE | |SPINE | | SPINE| | SPINE| | LEVEL 1		|SPINE | |SPINE | | SPINE| | SPINE| | LEVEL 1
	+ ++----++ ++---+-+ +-+--+-+ ++----++ |		+ ++----++ ++---+-+ +-+--+-+ ++----++ |
	+ | | | | | | | | | ^ N		+ | | | | | | | | | ^ N
	Distance | +-------+ | | +--------+ | | | E		Distance | +-------+ | | +--------+ | | | E
	Vector | | | | | | | | | +------>		Vector | | | | | | | | | +------>
	South | +-------+ | | | +------+ | | | |		South | +-------+ | | | +------+ | | | |
	skipping to change at page 24, line 17 ¶		skipping to change at page 24, line 17 ¶
	Note that in the case of Positive Disaggregation, the first ToF		Note that in the case of Positive Disaggregation, the first ToF
	node(s) that announces a more-specific route attracts all the traffic		node(s) that announces a more-specific route attracts all the traffic
	for that route and may suffer from a transient incast. A ToP node		for that route and may suffer from a transient incast. A ToP node
	that defers injecting the longer prefix in the FIB, in order to		that defers injecting the longer prefix in the FIB, in order to
	receive more advertisements and spread the packets better, also keeps		receive more advertisements and spread the packets better, also keeps
	on sending a portion of the traffic to the black hole in the		on sending a portion of the traffic to the black hole in the
	meantime. In the case of Negative Disaggregation, the last ToF		meantime. In the case of Negative Disaggregation, the last ToF
	node(s) that injects the route may also incur an incast issue; this		node(s) that injects the route may also incur an incast issue; this
	problem would occur if a prefix that becomes totally unreachable is		problem would occur if a prefix that becomes totally unreachable is
	disaggregated, but doing so is mostly useless and is not recommended.		disaggregated.
	5.7. Mobile Edge and Anycast		5.7. Mobile Edge and Anycast
	When a physical or a virtual node changes its point of attachement in		When a physical or a virtual node changes its point of attachement in
	the fabric from a previous-leaf to a next-leaf, new routes must be		the fabric from a previous-leaf to a next-leaf, new routes must be
	installed that supersede the old ones. Since the flooding flows		installed that supersede the old ones. Since the flooding flows
	northwards, the nodes (if any) between the previous-leaf and the		northwards, the nodes (if any) between the previous-leaf and the
	common parent are not immediately aware that the path via previous-		common parent are not immediately aware that the path via previous-
	leaf is obsolete, and a stale route may exist for a while. The		leaf is obsolete, and a stale route may exist for a while. The
	common parent needs to select the freshest route advertisement in		common parent needs to select the freshest route advertisement in
	skipping to change at page 28, line 26 ¶		skipping to change at page 28, line 26 ¶
	| | | | | |		| | | | | |
	| +----------------+ | |		| +----------------+ | |
	| +----------------+ |		| +----------------+ |
	| | | | | |		| | | | | |
	+----------+--+ +--+----------+		+----------+--+ +--+----------+
	| ToR1 | | ToR2 | Spine		| ToR1 | | ToR2 | Spine
	+--+------+---+ +--+-------+--+		+--+------+---+ +--+-------+--+
	+---+ | | | | | | +---+		+---+ | | | | | | +---+
	| +-----------------+ | | |		| +-----------------+ | | |
	| | | +-------------+ | |		| | | +-------------+ | |
	+ | + | | +-----------------+ |		| | | | | +-----------------+ |
	X | X | +--------x-----+ | X |		| | | | +--------------+ | | |
	+ | + | | | + |		| | | | | | | |
	+---+ +---+ +---+ +---+		+---+ +---+ +---+ +---+
	| | | | | | | |		| | | | | | | |
	+---+ +---+ ...............+---+ +---+		+---+ +---+ ............. +---+ +---+
	SV(1) SV(2) SV(n-1) SV(n) Leaf		SV(1) SV(2) SV(n-1) SV(n) Leaf
	Figure 11: Dual-homing servers		Figure 11: Dual-homing servers
	In the single plane, the worst condition is disaggregation of every
	other servers at the same level. Suppose the links from ToR1 (Top of
	Rack) to all the leaves become not available. All the servers'
	routes are disaggregated and the FIB of the servers will be expanded
	with n-1 more specific routes.
	Sometimes, people may prefer to disaggregate from ToR to servers from		Sometimes, people may prefer to disaggregate from ToR to servers from
	start on, i.e. the servers have couple tens of routes in FIB from		start on, i.e. the servers have couple tens of routes in FIB from
	start on beside default routes to avoid breakages at rack level.		start on beside default routes to avoid breakages at rack level.
	Full disaggregation of the fabric could be achieved by configuration		Full disaggregation of the fabric could be achieved by configuration
	supported by RIFT.		supported by RIFT.
	5.11. Fabric With A Controller		5.11. Fabric With A Controller
	There are many different ways to deploy the controller. One		There are many different ways to deploy the controller. One
	possibility is attaching a controller to the RIFT domain from ToF and		possibility is attaching a controller to the RIFT domain from ToF and
	skipping to change at page 31, line 25 ¶		skipping to change at page 31, line 25 ¶
	|Spine11| |Spine12| |Spine21| |Spine22| LEVEL 1		|Spine11| |Spine12| |Spine21| |Spine22| LEVEL 1
	+-+---+-+ ++----+-+ +-+---+-+ ++----+-+		+-+---+-+ ++----+-+ +-+---+-+ ++----+-+
	| | | | | | | |		| | | | | | | |
	| +---------+ | | +---------+ |		| +---------+ | | +---------+ |
	| +-------+ | | | +-------+ | |		| +-------+ | | | +-------+ | |
	| | | | | | | |		| | | | | | | |
	+-+---+-+ +--+--+-+ +-+---+-+ +--+--+-+		+-+---+-+ +--+--+-+ +-+---+-+ +--+--+-+
	| | | | | | | |		| | | | | | | |
	|Leaf111| |Leaf112| |Leaf121| |Leaf122| LEVEL 0		|Leaf111| |Leaf112| |Leaf121| |Leaf122| LEVEL 0
	+-+-----+ ++------+ +-----+-+ +-----+-+		+-+-----+ ++------+ +-----+-+ +-----+-+
	+ + + ^ |		+ + + ^ +
	PrefixA PrefixB PrefixA | PrefixC		PrefixA PrefixB PrefixA | PrefixC
	|		|
	+ traffic		+ traffic
	Figure 14: Anycast		Figure 14: Anycast
	If the traffic comes from ToF to Leaf111 or Leaf121 which has anycast		If the traffic comes from ToF to Leaf111 or Leaf121 which has anycast
	prefix PrefixA, RIFT can deal with this case well. But if the		prefix PrefixA, RIFT can deal with this case well. But if the
	traffic comes from Leaf122, it arrives Spine21 or Spine22 at level 1.		traffic comes from Leaf122, it arrives Spine21 or Spine22 at level 1.
	But Spine21 or Spine22 doesn't know another PrefixA attaching		But Spine21 or Spine22 doesn't know another PrefixA attaching
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