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Beeram 4 Intended status: Standards Track Juniper Networks 5 Expires: June 22, 2018 T. Parikh 6 Verizon 7 T. Saad 8 Cisco Systems 9 December 19, 2017 11 Signaling RSVP-TE tunnels on a shared MPLS forwarding plane 12 draft-ietf-mpls-rsvp-shared-labels-00.txt 14 Abstract 16 As the scale of MPLS RSVP-TE networks has grown, so the number of 17 Label Switched Paths (LSPs) supported by individual network elements 18 has increased. Various implementation recommendations have been 19 proposed to manage the resulting increase in control plane state. 21 However, those changes have had no effect on the number of labels 22 that a transit Label Switching Router (LSR) has to support in the 23 forwarding plane. That number is governed by the number of LSPs 24 transiting or terminated at the LSR and is directly related to the 25 total LSP state in the control plane. 27 This document defines a mechanism to prevent the maximum size of the 28 label space limit on an LSR from being a constraint to control plane 29 scaling on that node. That is, it allows many more LSPs to be 30 supported than there are forwarding plane labels available. 32 This work introduces the notion of pre-installed 'per Traffic 33 Engineering (TE) link labels' that can be shared by MPLS RSVP-TE LSPs 34 that traverse these TE links. This approach significantly reduces 35 the forwarding plane state required to support a large number of 36 LSPs. This couples the feature benefits of the RSVP-TE control plane 37 with the simplicity of the Segment Routing MPLS forwarding plane. 39 This document also introduces the ability to mix different types of 40 label operations along the path of an LSP, thereby allowing the 41 ingress router or an external controller to influence how to 42 optimally place a LSP in the network. 44 Requirements Language 46 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 47 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 48 "OPTIONAL" in this document are to be interpreted as described in BCP 49 14 [RFC2119] [RFC8174] when, and only when, they appear in all 50 capitals, as shown here. 52 Status of This Memo 54 This Internet-Draft is submitted in full conformance with the 55 provisions of BCP 78 and BCP 79. 57 Internet-Drafts are working documents of the Internet Engineering 58 Task Force (IETF). Note that other groups may also distribute 59 working documents as Internet-Drafts. The list of current Internet- 60 Drafts is at http://datatracker.ietf.org/drafts/current/. 62 Internet-Drafts are draft documents valid for a maximum of six months 63 and may be updated, replaced, or obsoleted by other documents at any 64 time. It is inappropriate to use Internet-Drafts as reference 65 material or to cite them other than as "work in progress." 67 This Internet-Draft will expire on June 22, 2018. 69 Copyright Notice 71 Copyright (c) 2017 IETF Trust and the persons identified as the 72 document authors. All rights reserved. 74 This document is subject to BCP 78 and the IETF Trust's Legal 75 Provisions Relating to IETF Documents 76 (http://trustee.ietf.org/license-info) in effect on the date of 77 publication of this document. Please review these documents 78 carefully, as they describe your rights and restrictions with respect 79 to this document. Code Components extracted from this document must 80 include Simplified BSD License text as described in Section 4.e of 81 the Trust Legal Provisions and are provided without warranty as 82 described in the Simplified BSD License. 84 Table of Contents 86 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 87 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 88 3. Allocation of TE Link Labels . . . . . . . . . . . . . . . . 5 89 4. Segment Routed RSVP-TE Tunnel Setup . . . . . . . . . . . . . 5 90 5. Delegating Label Stack Imposition . . . . . . . . . . . . . . 7 91 5.1. Stacking at the Ingress . . . . . . . . . . . . . . . . . 8 92 5.1.1. Stack to Reach Delegation Hop . . . . . . . . . . . . 8 93 5.1.2. Stack to Reach Egress . . . . . . . . . . . . . . . . 9 94 5.2. Explicit Delegation . . . . . . . . . . . . . . . . . . . 10 95 5.3. Automatic Delegation . . . . . . . . . . . . . . . . . . 10 96 5.3.1. Effective Transport Label-Stack Depth (ETLD) . . . . 10 98 6. Mixing TE Link Labels and Regular Labels in an RSVP-TE Tunnel 11 99 7. Construction of Label Stacks . . . . . . . . . . . . . . . . 12 100 8. Facility Backup Protection . . . . . . . . . . . . . . . . . 13 101 8.1. Link Protection . . . . . . . . . . . . . . . . . . . . . 13 102 8.2. Node Protection . . . . . . . . . . . . . . . . . . . . . 14 103 9. Quantifying TE Link Labels . . . . . . . . . . . . . . . . . 14 104 10. Protocol Extensions . . . . . . . . . . . . . . . . . . . . . 14 105 10.1. Requirements . . . . . . . . . . . . . . . . . . . . . . 14 106 10.2. Attribute Flags TLV: TE Link Label . . . . . . . . . . . 15 107 10.3. RRO Label Subobject Flag: TE Link Label . . . . . . . . 15 108 10.4. Attribute Flags TLV: LSI-D . . . . . . . . . . . . . . . 15 109 10.5. RRO Label Subobject Flag: Delegation Label . . . . . . . 16 110 10.6. Attributes Flags TLV: LSI-D-S2E . . . . . . . . . . . . 16 111 10.7. Attributes TLV: ETLD . . . . . . . . . . . . . . . . . . 16 112 11. OAM Considerations . . . . . . . . . . . . . . . . . . . . . 17 113 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 17 114 13. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 17 115 14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 116 14.1. Attribute Flags: TE Link Label, LSI-D, LSI-D-S2E . . . . 18 117 14.2. Attribute TLV: ETLD . . . . . . . . . . . . . . . . . . 18 118 14.3. Record Route Label Sub-object Flags: TE Link Label, 119 Delegation Label . . . . . . . . . . . . . . . . . . . . 18 120 15. Security Considerations . . . . . . . . . . . . . . . . . . . 19 121 16. References . . . . . . . . . . . . . . . . . . . . . . . . . 19 122 16.1. Normative References . . . . . . . . . . . . . . . . . . 19 123 16.2. Informative References . . . . . . . . . . . . . . . . . 20 124 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21 126 1. Introduction 128 The scaling of RSVP-TE [RFC3209] control plane implementations can be 129 improved by adopting the guidelines and mechanisms described in 130 [RFC2961] and [I-D.ietf-teas-rsvp-te-scaling-rec]. These documents 131 do not make any difference to the forwarding plane state required to 132 handle the control plane state. The forwarding plane state remains 133 unchanged and is directly proportional to the total number of Label 134 Switching Paths (LSPs) supported by the control plane. 136 This document describes a mechanism that prevents the size of the 137 platform specific label space on a Label Switching Router (LSR) from 138 being a constraint to pushing the limits of control plane scaling on 139 that node. 141 This work introduces the notion of pre-installed 'per Traffic 142 Engineering (TE) link labels' that are allocated by an LSR. Each 143 such label is installed in the MPLS forwarding plane with a 'pop' 144 operation and the instruction to forward the received packet over the 145 TE link. An LSR advertises this label in the Label object of a Resv 146 message as LSPs are set up and they are recorded hop by hop in the 147 Record Route object (RRO) of the Resv message as it traverses the 148 network. To make use of this feature, the ingress Label Edge Router 149 (LER) pushes a stack of labels [RFC3031] as received in the RRO. 150 These 'TE link labels' can be shared by MPLS RSVP-TE LSPs that 151 traverse the same TE link. 153 This forwarding plane behavior fits in the MPLS architecture 154 [RFC3031] and is same as that exhibited by Segment Routing (SR) 155 [I-D.ietf-spring-segment-routing] when using an MPLS forwarding plane 156 and a series of adjacency segments. This work couples the feature 157 benefits of the RSVP-TE control plane with the simplicity of the 158 Segment Routing MPLS forwarding plane. The RSVP-TE tunnels that use 159 this shared forwarding plane can co-exist with MPLS-SR LSPs 160 [I-D.ietf-spring-segment-routing-mpls] as described in 161 [I-D.ietf-teas-sr-rsvp-coexistence-rec]. 163 RSVP-TE using a shared MPLS forwarding plane offers the following 164 benefits: 166 1. Shared Labels: The transit label on a TE link is shared among 167 RSVP-TE tunnels traversing the link and is used independent of 168 the ingress and egress of the LSPs. 170 2. Faster LSP setup time: No forwarding plane state needs to be 171 programmed during LSP setup and teardown resulting in faster time 172 for provisioning and deprovisioning LSPs. 174 3. Hitless re-routing: New transit labels are not required during 175 make-before-break (MBB) in scenarios where the new LSP instance 176 traverses the exact same path as the old LSP instance. This 177 saves the ingress LER and the services that use the tunnel from 178 needing to update the forwarding plane with new tunnel labels and 179 so makes MBB events faster. Periodic MBB events are relatively 180 common in networks that deploy the 'auto-bandwidth' feature on 181 RSVP-TE LSPs to monitor bandwidth utilization and periodically 182 adjust LSP bandwidth. 184 4. Mix and match labels: Both 'TE link labels' and regular labels 185 can be used on transit hops for a single RSVP-TE tunnel (see 186 Section 6). This allows backward compatibility with transit LSRs 187 that provide regular labels in Resv messages. 189 No additional extensions are required to routing protocols (IGP-TE) 190 in order to support this shared MPLS forwarding plane. 191 Functionalities such as bandwidth admission control, LSP priorities, 192 preemption, auto-bandwidth and Fast Reroute continue to work with 193 this forwarding plane. 195 The signaling procedures and extensions discussed in this document do 196 not apply to Point to Multipoint (P2MP) RSVP-TE Tunnels. 198 2. Terminology 200 The following terms are used in this document: 202 TE link label: An incoming label at an LSR that will be popped by 203 the LSR with the packet being forwarded over a specific outgoing 204 TE link to a neighbor. 206 Shared MPLS forwarding plane: An MPLS forwarding plane where every 207 participating LSR uses TE link labels on every LSP. 209 Segment Routed RSVP-TE tunnel: An MPLS RSVP-TE tunnel that requests 210 the use of a shared MPLS forwarding plane at every hop of the LSP. 212 3. Allocation of TE Link Labels 214 An LSR that participates in a shared MPLS forwarding plane MUST 215 allocate a unique TE link label for each TE link. When an LSR 216 encounters a TE link label at the top of the label stack it MUST pop 217 the label and forward the packet over the TE link to the downstream 218 neighbor on the RSVP-TE tunnel. 220 Multiple TE link labels MAY be allocated for the TE link to 221 accommodate tunnels requesting no protection, link-protection and 222 node-protection over the specific TE link. 224 Implementations that maintain per label bandwidth accounting at each 225 hop must aggregate the reservations made for all the LSPs using the 226 shared TE link label. 228 4. Segment Routed RSVP-TE Tunnel Setup 230 This section provides an example of how the RSVP-TE signaling 231 procedure works to set up a tunnel utilizing a shared MPLS forwarding 232 plane. The sample topology below is used to explain the example. 233 Labels shown at each node are TE link labels that, when present at 234 the top of the label stack, indicate that they should be popped and 235 that the packet should be forwarded on the TE link to the neighbor. 237 +---+100 +---+150 +---+200 +---+250 +---+ 238 | A |-----| B |-----| C |-----| D |-----| E | 239 +---+ +---+ +---+ +---+ +---+ 240 |110 |450 |550 |650 |850 241 | | | | | 242 | |400 |500 |600 |800 243 | +---+ +---+ +---+ +---+ 244 +-------| F |-----|G |-----|H |-----|I | 245 +---+300 +---+350 +---+700 +---+ 247 Figure 1: Sample Topology - TE Link Labels 249 Consider two tunnels: 251 RSVP-TE tunnel T1: From A to E on path A-B-C-D-E 253 RSVP-TE tunnel T2: From F to E on path F-B-C-D-E 255 Both tunnels share the TE links B-C, C-D, and D-E. 257 RSVP-TE is used to signal the setup of tunnel T1 (using the TE link 258 label attributes flag defined in Section 10.2). When LSR D receives 259 the Resv message from the egress LER E, it checks the next-hop TE 260 link (D-E) and provides the TE link label (250) in the Resv message 261 for the tunnel placing the label value in the Label object and also 262 in the Label subobject carried in the RRO and setting the TE link 263 label flag as defined in Section 10.3. 265 Similarly, LSR C provides the TE link label (200) for the TE link 266 C-D, and LSR B provides the TE link label (150) for the TE link B-C. 268 For tunnel T2, the transit LSRs provide the same TE link labels as 269 described for tunnel T1 as the links B-C, C-D, and D-E are common 270 between the two LSPs. 272 The ingress LERs (A and F) will push the same stack of labels (from 273 top of stack to bottom of stack) {150, 200, 250} for tunnels T1 and 274 T2 respectively. 276 It should be noted that a transit LSR does not swap the top TE link 277 label on an incoming packet (the label that it advertised in the Resv 278 message it sent). All it has to do is pop the top label and forward 279 the packet. 281 The values in the Label subobjects in the RRO are of interest to the 282 ingress LERs in order to construct the stack of labels to impose on 283 the packets. 285 If, in this example, there was another RSVP-TE tunnel T3 from F to I 286 on path F-B-C-D-E-I, then this would also share the TE links B-C, 287 C-D, and D-E and additionally traverse link E-I. The label stack 288 used by F would be {150, 200, 250, 850}. Hence, regardless of the 289 ingress and egress LERs from where the LSPs start and end, they will 290 share LSR labels at shared hops in the shared MPLS forwarding plane. 292 There MAY be local operator policy at the ingress LER that influences 293 the maximum depth of the label stack that can be pushed for a Segment 294 Routed RSVP-TE tunnel. Prior to signaling the LSP, the ingress LER 295 may decide that it would be unable to push a label stack containing 296 one label for each hop along the path. In this case the LER can 297 choose either to not signal a Segment Routed RSVP-TE tunnel (using 298 normal LSP signaling instead), or can adopt the techniques described 299 in Section 5 or Section 6. 301 5. Delegating Label Stack Imposition 303 One or more transit LSRs can assist the ingress LER by imposing part 304 of the label stack required for the path. Consider the example in 305 Figure 2 with an RSVP-TE tunnel from A to L on path 306 A-B-C-D-E-F-G-H-I-J-K-L. In this case, the LSP is too long for LER A 307 to impose the full label stack, so it uses the assistance of 308 delegation hops LSR D and LSR I to impose parts of the label stack. 310 Each delegation hop allocates a delegation label to represent a set 311 of labels that will be pushed at this hop. When a packet arrives at 312 a delegation hop LSR with a delegation label, the LSR pops the label 313 and pushes a set of labels before forwarding the packet. 315 1250d 316 +---+100p +---+150p +---+200p +---+250p +---+300p +---+ 317 | A |------| B |------| C |------| D |------| E |------| F | 318 +---+ +---+ +---+ +---+ +---+ +---+ 319 |350p 320 | 321 1500d | 322 +---+ 600p+---+ 550p+---+ 500p+---+ 450p+---+ 400p+---+ 323 | L |------| K |------| J |------| I |------| H |------+ G + 324 +---+ +---+ +---+ +---+ +---+ +---+ 326 Notation :