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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) No issues found here. Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 MPLS Working Group Maria Napierala 3 Internet Draft AT&T 4 Intended Status: Standards Track 5 Expires: March 4, 2014 Eric C. Rosen 6 IJsbrand Wijnands 7 Cisco Systems, Inc. 9 September 4, 2013 11 Using LDP Multipoint Extensions on Targeted LDP Sessions 13 draft-ietf-mpls-targeted-mldp-04.txt 15 Abstract 17 Label Distribution Protocol (LDP) can be used to set up Point-to- 18 Multipoint (P2MP) and Multipoint-to-Multipoint (MP2MP) Label Switched 19 Paths. However, the specification for the Multipoint Extensions to 20 LDP presupposes that the two endpoints of an LDP session are directly 21 connected. The LDP base specification allows for the case where the 22 two endpoints of an LDP session are not directly connected; such a 23 session is known as a "Targeted LDP" session. This document provides 24 the specification for using the LDP Multipoint Extensions over a 25 Targeted LDP session. 27 Status of this Memo 29 This Internet-Draft is submitted to IETF in full conformance with the 30 provisions of BCP 78 and BCP 79. 32 Internet-Drafts are working documents of the Internet Engineering 33 Task Force (IETF), its areas, and its working groups. Note that 34 other groups may also distribute working documents as Internet- 35 Drafts. 37 Internet-Drafts are draft documents valid for a maximum of six months 38 and may be updated, replaced, or obsoleted by other documents at any 39 time. It is inappropriate to use Internet-Drafts as reference 40 material or to cite them other than as "work in progress." 42 The list of current Internet-Drafts can be accessed at 43 http://www.ietf.org/ietf/1id-abstracts.txt. 45 The list of Internet-Draft Shadow Directories can be accessed at 46 http://www.ietf.org/shadow.html. 48 Copyright and License Notice 50 Copyright (c) 2013 IETF Trust and the persons identified as the 51 document authors. All rights reserved. 53 This document is subject to BCP 78 and the IETF Trust's Legal 54 Provisions Relating to IETF Documents 55 (http://trustee.ietf.org/license-info) in effect on the date of 56 publication of this document. Please review these documents 57 carefully, as they describe your rights and restrictions with respect 58 to this document. Code Components extracted from this document must 59 include Simplified BSD License text as described in Section 4.e of 60 the Trust Legal Provisions and are provided without warranty as 61 described in the Simplified BSD License. 63 Table of Contents 65 1 Introduction .......................................... 3 66 2 Targeted mLDP and the Upstream LSR .................... 3 67 2.1 Selecting the Upstream LSR ............................ 3 68 2.2 Sending data from U to D .............................. 4 69 3 Applicability of Targeted mLDP ........................ 5 70 4 LDP Capabilities ...................................... 5 71 5 Targeted mLDP with Unicast Replication ................ 6 72 6 Targeted mLDP with Multicast Tunneling ................ 7 73 7 IANA Considerations ................................... 8 74 8 Security Considerations ............................... 8 75 9 Acknowledgments ....................................... 8 76 10 Authors' Addresses .................................... 9 77 11 Normative References .................................. 9 78 1. Introduction 80 The Label Distribution Protocol (LDP) extensions for setting up 81 Point-to-MultiPoint (P2MP) Label Switched Paths (LSPs) and 82 Multipoint-to-Multipoint (MP2MP) LSPs are specified in [mLDP]. This 83 set of extensions is generally known as "Multipoint LDP" (mLDP). 85 A pair of Label Switched Routers (LSRs) that are the endpoints of an 86 LDP session are considered to be "LDP peers". When a pair of LDP 87 peers are "directly connected" (e.g., they are connected by a layer 2 88 medium, or are otherwise considered to be neighbors by the network's 89 interior routing protocol), the LDP session is said to be a "directly 90 connected" LDP session. When the pair of LDP peers are not directly 91 connected, the session between them is said to be a "Targeted" LDP 92 session. 94 The base specification for mLDP does not explicitly cover the case 95 where the LDP multipoint extensions are used over a targeted LDP 96 session. This document provides that specification. 98 We will use the term "Multipoint" to mean "either P2MP or MP2MP". 100 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 101 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 102 document are to be interpreted as described in [RFC2119]. 104 2. Targeted mLDP and the Upstream LSR 106 2.1. Selecting the Upstream LSR 108 In mLDP, a multipoint LSP (MP-LSP) has a unique identifier that is an 109 ordered pair of the form . The first element of 110 the ordered pair is the IP address of the MP-LSP's "root node". The 111 second element of the ordered pair is an identifier that is unique in 112 the context of the root node. 114 If LSR D is setting up the MP-LSP , D must determine the 115 "upstream LSR" for . In [mLDP], the upstream LSR for , 116 U, is defined to be the "next hop" on D's path to R, and "next hop" 117 is tacitly assumed to mean "IGP next hop". It is thus assumed that 118 there is a direct LDP session between D and U. In this 119 specification, we extend the notion of "upstream LSR" to cover the 120 following cases: 122 - U is the "BGP next hop" on D's path to R, where U and D are not 123 necessarily IGP neighbors, and where there is a Targeted LDP 124 session between U and D. In this case, we allow D to select U as 125 the "upstream LSR" for . 127 - If the "next hop interface" on D's path to R is an RSVP-TE P2P 128 tunnel whose remote endpoint is U, and if there is known to be an 129 RSVP-TE P2P tunnel from U to D, and if there is a Targeted LDP 130 session between U and D, then we allow D to select U as the 131 "upstream LSR" for . This is useful when D and U are part 132 of a network area that is fully meshed via RSVP-TE P2P tunnels. 134 The particular method used to select an "upstream LSR" is determined 135 by the Service Provider (SP), and must be made known a priori (i.e., 136 by provisioning) to all the LSRs involved. 138 Other methods than the two specified above MAY be used; however the 139 specification of other methods is outside the scope of this document. 141 2.2. Sending data from U to D 143 By using Targeted mLDP, we can construct an MP-LSP containing 144 an LSR U, where U has one or more downstream LSR neighbors (D1, ..., 145 Dn) to which it is not directly connected. In order for a data 146 packet to travel along this MP-LSP, U must have some way of 147 transmitting the packet to D1, ..., Dn. We will cover two methods of 148 transmission: 150 - Unicast Replication. 152 In this method, U creates n copies of the packet, and unicasts 153 each copy to exactly one of D1, ..., Dn. 155 - Multicast tunneling. 157 In this method, U becomes the root node of a multicast tunnel, 158 with D1, ..., Dn as leaf nodes. When a packet traveling along 159 the MP-LSP arrives at U, U transmits it through the 160 multicast tunnel, and as a result it arrives at D1, ..., Dn. 162 When this method is used, it may be desirable to carry traffic of 163 multiple MP-LSPs through a single multicast tunnel. We specify 164 procedures that allow for the proper demultiplexing of the MP- 165 LSPs at the leaf nodes of the multicast tunnel. We do not assume 166 that all the leaf nodes of the tunnel are on all the MP-LSPs 167 traveling through the tunnel; thus some of the tunnel leaf nodes 168 may need to discard some of the packets received through the 169 tunnel. For example, suppose MP-LSP contains node U with 170 downstream LSRs D1 and D2, while MP-LSP contains node U 171 with downstream LSRs D2 and D3. Suppose also that there is a 172 multicast tunnel with U as root and with D1, D2, and D3 as leaf 173 nodes. U can aggregate both MP-LSPs in this one tunnel. 174 However, D1 will have to discard packets that are traveling on 175 , while D3 will have to discard packets that are traveling 176 on . 178 3. Applicability of Targeted mLDP 180 When LSR D is setting up MP-LSP , it MUST NOT use targeted mLDP 181 unless D implements a procedure that can select, as the "upstream 182 LSR" for , an LSR U that is a Targeted mLDP peer of D. See 183 section 2.1. 185 Whether D uses Targeted mLDP when this condition holds is determined 186 by provisioning, or by other methods that are outside the scope of 187 this specification. 189 When Targeted mLDP is used, the choice between unicast replication 190 and multicast tunneling is determined by provisioning, or by other 191 methods that are outside the scope of this specification. It is 192 presupposed that all nodes will have a priori knowledge of whether to 193 use unicast replication or to use multicast tunneling. If the 194 latter, it is presupposed that all nodes will have a priori knowledge 195 of the type of multicast tunneling to use. 197 4. LDP Capabilities 199 Per [mLDP], any LSR that needs to set up an MP-LSP must support the 200 procedures of [LDP-CAP], and in particular must send and receive the 201 P2MP Capability and/or the MP2MP Capability. This specification does 202 not define any new capabilities; the advertisement of the P2MP and/or 203 MP2MP Capabilities on a Targeted LDP session means that the 204 advertising LSR is capable of following the procedures of this 205 document. 207 Some of the procedures of this document require the use of upstream- 208 assigned labels [LDP-UP]. In order to use upstream-assigned labels 209 as part of Targeted mLDP, an LSR must advertise the LDP Upstream- 210 Assigned Label Capability [LDP-UP] on the Targeted LDP session. 212 5. Targeted mLDP with Unicast Replication 214 When unicast replication is used, the mLDP procedures are exactly the 215 same as described in [mLDP], with the following exception. If LSR D 216 is setting up MP-LSP , its "upstream LSR" is selected according 217 to the procedures of section 2.1, and is not necessarily the "IGP 218 next hop" on D's path to R. 220 Suppose that LSRs D1 and D2 are both setting up the P2MP MP-LSP 221 , and that LSR U is the upstream LSR on each of their paths to 222 R. D1 and D2 each binds a label to , and each uses a label 223 mapping message to inform U of the label binding. Suppose D1 has 224 assigned label L1 to and D2 has assigned label L2 to . 225 (Note that L1 and L2 could have the same value or different values; 226 D1 and D2 do not coordinate their label assignments.) When U has a 227 packet to transmit on the MP-LSP , it makes a copy of the 228 packet, pushes on label L1, and unicasts the resulting packet to D1. 229 It also makes a second copy of the packet, pushes on label L2, and 230 then unicasts the resulting packet to D2. 232 This procedure also works when the MP-LSP is a MP2MP LSP. 233 Suppose that in addition to labels L1 and L2 described above, U has 234 assigned label L3 for traffic received from D1, and label L4 235 for traffic received from D2. When U processes a packet with 236 label L3 at the top of its label stack, it knows the packet is from 237 D1, so U sends a unicast copy of the packet to D2, after swapping L3 238 for L2. U does not send a copy back to D1. 240 Note that all labels used in this procedure are downstream-assigned 241 labels. 243 The method of unicast is a local matter, outside the scope of this 244 specification. The only requirement is that D1 will receive the copy 245 of the packet carrying label L1, and that D1 will process the packet 246 by looking up label L1. (And similarly, D2 must receive the copy of 247 the packet carrying label L2, and must process the packet by looking 248 up label L2.) 250 Note that if the method of unicast is MPLS, U will need to push 251 another label on each copy of the packet before transmitting it. 252 This label needs to ensure that delivery of the packet to the 253 appropriate LSR, D1 or D2. Use of penultimate-hop popping for that 254 label is perfectly legitimate. 256 6. Targeted mLDP with Multicast Tunneling 258 Suppose that LSRs D1 and D2 are both setting up MP-LSP , and 259 that LSR U is the upstream LSR on each of their paths to R. Since 260 multicast tunneling is being used, when U has a packet to send on 261 this MP-LSP, it does not necessarily send two copies, one to D1 and 262 one to D2. It may send only one copy of the packet, which will get 263 replicated somewhere downstream in the multicast tunnel. Therefore, 264 the label that gets bound to the MP-LSP must be an upstream-assigned 265 label, assigned by U. This requires a change from the procedures of 266 [mLDP]. D1 and D2 do not send label mapping messages to U; instead 267 they send label request messages to U, following the procedures of 268 Section 4 of [LDP-UP], asking U to assign a label to the MP-LSP 269 . U responds with a label mapping message containing an 270 upstream-assigned label, L (using the procedures specified in [LDP- 271 UP]). As part of the same label mapping message, U also sends an 272 Interface TLV (as specified in [LDP-UP]) identifying the multicast 273 tunnel in which data on the MP-LSP will be carried. When U transmits 274 a packet on this tunnel, it first pushes on the upstream-assigned 275 label L, and then pushes on the label that corresponds to the 276 multicast tunnel. 278 If the numerical value L of the upstream-assigned label is the value 279 3, defined in [LDP] and [RFC3032] as "Implicit NULL", then the 280 specified multicast tunnel will carry only the specified MP-LSP. 281 That is, aggregation of multiple MP-LSPs into a single multicast 282 tunnel is not being done. In this case, no upstream-assigned label 283 is pushed onto a packet that is transmitted through the multicast 284 tunnel. 286 Various types of multicast tunnel may be used. The choice of tunnel 287 type is determined by provisioning, or by some other method that is 288 outside the scope of this document. [LDP-UP] specifies encodings 289 allowing U to identify an mLDP MP-LSP, and RSVP-TE P2MP LSP, as well 290 as other types of multicast tunnel. 292 Procedures for tunneling MP2MP LSPs through P2MP or MP2MP LSPs are 293 outside the scope of this document. 295 If the multicast tunnel is an mLDP MP-LSP or an RSVP-TE P2MP LSP, 296 when U transmits a packet on the MP-LSP , the upstream-assigned 297 label L will be the second label in the label stack. Penultimate-hop 298 popping MUST NOT be done, because the top label provides the context 299 in which the second label is to be interpreted. See [RFC5331]. 301 When LSR U uses these procedures to inform LSR D that a particular 302 MP-LSP is being carried in a particular multicast tunnel, U and D 303 MUST take appropriate steps to ensure that packets U sends into this 304 tunnel will be received by D. The exact steps to take depend on the 305 tunnel type. As long as U is D's upstream LSR for any MP-LSP that 306 has been assigned to this tunnel, D must remain joined to the tunnel. 308 Note that U MAY assign the same multicast tunnel for multiple 309 different MP-LSPs. However, U MUST assign a distinct upstream- 310 assigned label to each MP-LSP. This allows the packets traveling 311 through the tunnel to be demultiplexed into the proper MP-LSPs. 313 If U has an MP-LSP with downstream LSRs D1 and D2, and an MP- 314 LSP with downstream LSRs D2 and D3, U may assign both MP-LSPs 315 to the same multicast tunnel. In this case, D3 will receive packets 316 traveling on . However, the upstream-assigned label carried 317 by those packets will not be recognized by D3, hence D3 will discard 318 those packets. Similarly, D1 will discard the packets. 320 This document does not specify any rules for deciding whether to 321 aggregate two or more MP-LSPs into a single multicast tunnel. Such 322 rules are outside the scope of this document. 324 Except for the procedures explicitly detailed in this document, the 325 procedures of [mLDP] and [LDP-UP] apply unchanged. 327 7. IANA Considerations 329 This document has no considerations for IANA. 331 8. Security Considerations 333 This document raises no new security considerations beyond those 334 discussed in [LDP], [LDP-UP], and [RFC5331]. 336 9. Acknowledgments 338 The authors wish to thank Lizhong Jin and Lizhen Bin for their 339 comments. 341 10. Authors' Addresses 343 Maria Napierala 344 AT&T Labs 345 200 Laurel Avenue, Middletown, NJ 07748 346 USA 347 E-mail: mnapierala@att.com 349 Eric C. Rosen 350 Cisco Systems, Inc. 351 1414 Massachusetts Avenue 352 Boxborough, MA, 01719 353 USA 354 E-mail: erosen@cisco.com 356 IJsbrand Wijnands 357 Cisco Systems, Inc. 358 De kleetlaan 6a Diegem 1831 359 Belgium 360 E-mail: ice@cisco.com 362 11. Normative References 364 [LDP] Loa Andersson, Ina Minei, Bob Thomas, editors, "LDP 365 Specification", RFC 5036, October 2007 367 [LDP-CAP] Bob Thomas, Kamran Raza, Shivani Aggarwal, Rahul Aggarwal, 368 Jean-Louis Le Roux, "LDP Capabilities", RFC 5561, July 2009 370 [mLDP] IJsbrand Wijnands, Ina Minei, Kireeti Kompella, Bob Thomas, 371 "Label Distribution Protocol Extensions for Point-to-Multipoint and 372 Multipoint-to-Multipoint Label Switched Paths", RFC 6388, November 373 2011 375 [LDP-UP] Rahul Aggarwal, Jean-Louis Le Roux, "MPLS Upstream Label 376 Assignment for LDP", RFC 6389, November 2011 378 [RFC2119] "Key words for use in RFCs to Indicate Requirement 379 Levels.", Bradner, March 1997 381 [RFC3032] Eric Rosen, et. al., "MPLS Label Stack Encoding", RFC 3032, 382 January 2001 384 [RFC5331] Rahul Aggarwal, Yakov Rekhter, Eric Rosen, "MPLS Upstream 385 Label Assignment and Context-Specific Label Space", RFC 5331, August 386 2009