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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: Proposed Standard 5 Expires: October 20, 2012 Eric C. Rosen 6 IJsbrands Wijnands 7 Cisco Systems, Inc. 9 April 20, 2012 11 Using LDP Multipoint Extensions on Targeted LDP Sessions 13 draft-napierala-mpls-targeted-mldp-03.txt 15 Abstract 17 Label Distribution Protocol (LDP) can be used to set up 18 Point-to-Multipoint (P2MP) and Multipoint-to-Multipoint (MP2MP) Label 19 Switched Paths. The existing specification for this functionality 20 assumes that a pair of LDP neighbors are directly connected. 21 However, the LDP base specification allows for the case where a pair 22 of LDP neighbors are not directly connected; the LDP session between 23 such a pair of neighbors is known as a "Targeted LDP" session. This 24 document specifies the use of the LDP P2MP/MP2MP 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) 2012 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 1.1 Specification of requirements ......................... 3 67 1.2 Targeted mLDP ......................................... 3 68 1.3 Targeted mLDP and the Upstream LSR .................... 3 69 1.3.1 Selecting the Upstream LSR ............................ 3 70 1.3.2 Sending data from U to D .............................. 4 71 1.4 Applicability of Targeted mLDP ........................ 5 72 1.5 LDP Capabilities ...................................... 5 73 2 Targeted mLDP with Unicast Replication ................ 5 74 3 Targeted mLDP with Multicast Tunneling ................ 6 75 4 IANA Considerations ................................... 8 76 5 Security Considerations ............................... 8 77 6 Acknowledgments ....................................... 8 78 7 Authors' Addresses .................................... 8 79 8 Normative References .................................. 9 81 1. Introduction 83 1.1. Specification of requirements 85 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 86 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 87 document are to be interpreted as described in [RFC2119]. 89 1.2. Targeted mLDP 91 The Label Distribution Protocol (LDP) extensions for setting up 92 Point-to-MultiPoint (P2MP) Label Switched Paths (LSPs) and 93 Multipoint-to-Multipoint (MP2MP) LSPs are specified in [mLDP]. This 94 set of extensions is generally known as "Multipoint LDP" (mLDP). 96 A pair of Label Switched Routers (LSRs) that are the endpoints of an 97 LDP session are considered to be "LDP neighbors". When a pair of LDP 98 neighbors are "directly connected" (e.g., they are connected by a 99 layer 2 medium, or are otherwise considered to be neighbors by the a 100 network's interior routing protocol), the LDP session is said to be a 101 "directly connected" LDP session. When the pair of LDP neighbors are 102 not directly connected, the session between them is said to be a 103 "Targeted" LDP session. 105 The base specification for mLDP does not explicitly cover the case 106 where the LDP multipoint extensions are used over a targeted LDP 107 session. This document provides that specification. 109 We will use the term "Multipoint" to mean "either P2MP or MP2MP". 111 1.3. Targeted mLDP and the Upstream LSR 113 1.3.1. Selecting the Upstream LSR 115 In mLDP, a multipoint LSP (MP-LSP) has a unique identifier that is an 116 ordered pair of the form . The first element of 117 the ordered pair is the IP address of the MP-LSP's "root node". The 118 second element of the ordered pair is an identifier that is unique in 119 the context of the root node. 121 If LSR D is setting up the MP-LSP , D must determine the 122 "upstream LSR" for . In [mLDP], the upstream LSR for , 123 U, is defined to be the "next hop" on D's path to R, and "next hop" 124 is tacitly assumed to mean "IGP next hop". It is thus assumed that 125 there is a direct LDP session between D and U. In this 126 specification, we extend the notion of "upstream LSR" to cover the 127 following cases: 129 - U is the "BGP next hop" on D's path to R, where U and D are not 130 IGP neighbors, and where there is a Targeted LDP session between 131 U and D. In this case, we allow D to select U as the "upstream 132 LSR" for . 134 - If the "next hop interface" on D's path to R is an RSVP-TE P2P 135 tunnel whose remote endpoint is U, and if there is known to be an 136 RSVP-TE P2P tunnel from U to D, and if there is a Targeted LDP 137 session between U and D, then we allow D to select U as the 138 "upstream LSR" for . This is useful when D and U are part 139 of a network area that is fully meshed via RSVP-TE P2P tunnels. 141 The particular method used to select an "upstream LSR" is determined 142 by the SP. Other methods than the ones above MAY be used. 144 1.3.2. Sending data from U to D 146 By using Targeted mLDP, we can construct an MP-LSP containing 147 an LSR U, where U has one or more downstream LSR neighbors (D1, ..., 148 Dn) to which it is not directly connected. In order for a data 149 packet to travel along this MP-LSP, U must have some way of 150 transmitting the packet to D1, ..., Dn. We will cover two methods of 151 transmission: 153 - Unicast Replication. 155 In this method, U creates n copies of the packet, and unicasts 156 each copy to exactly one of D1, ..., Dn. 158 - Multicast tunneling. 160 In this method, U becomes the root node of a multicast tunnel, 161 with D1, ..., Dn as leaf nodes. When a packet traveling along 162 the MP-LSP arrives at U, U transmits it through the 163 multicast tunnel, and as a result it arrives at D1, ..., Dn. 165 When this method is used, it may be desirable to carry traffic of 166 multiple MP-LSPs through a single multicast tunnel. We specify 167 procedures that allow for the proper demultiplexing of the MP- 168 LSPs at the leaf nodes of the multicast tunnel. We do not assume 169 that all the leaf nodes of the tunnel are on all the MP-LSPs 170 traveling through the tunnel; thus some of the tunnel leaf nodes 171 may need to discard some of the packets received through the 172 tunnel. For example, suppose MP-LSP contains node U with 173 downstream LSRs D1 and D2, while MP-LSP contains node U 174 with downstream LSRs D2 and D3. Suppose also that there is a 175 multicast tunnel with U as root and with D1, D2, and D3 as leaf 176 nodes. U can aggregate both MP-LSPs in this one tunnel. 177 However, D1 will have to discard packets that are traveling on 178 , while D3 will have to discard packets that are traveling 179 on . 181 1.4. Applicability of Targeted mLDP 183 When LSR D is setting up MP-LSP , it MUST NOT use targeted mLDP 184 unless D can select the "upstream LSR" for using one of the 185 procedures discussed in section 1.3.1. 187 Whether D uses Targeted mLDP when this condition holds is determined 188 by provisioning, or by other methods that are outside the scope of 189 this specification. 191 When Targeted mLDP is used, the choice between unicast replication 192 and multicast tunneling is determined by provisioning, or by other 193 methods that are outside the scope of this specification. 195 1.5. LDP Capabilities 197 Per [mLDP], any LSR that needs to set up an MP-LSP must support the 198 procedures of [LDP-CAP], and in particular must send and receive the 199 P2MP Capability and/or the MP2MP Capability. This specification does 200 not define any new capabilities; the advertisement of the P2MP and/or 201 MP2MP Capabilities on a Targeted LDP session means that the 202 advertising LSR is capable of following the procedures of this 203 document. 205 Some of the procedures of this document require the use of upstream- 206 assigned labels [LDP-UP]. In order to use upstream-assigned labels 207 as part of Targeted mLDP, an LSR must advertise the LDP Upstream- 208 Assigned Label Capability [LDP-UP] on the Targeted LDP session. 210 2. Targeted mLDP with Unicast Replication 212 When unicast replication is used, the mLDP procedures are exactly the 213 same as described in [mLDP], with the following exception. If LSR D 214 is setting up MP-LSP , its "upstream LSR" is selected according 215 to the procedures of section 1.3.1, and is not necessarily the "IGP 216 next hop" on D's path to R. 218 Suppose that LSRs D1 and D2 are both setting up the P2MP MP-LSP 219 , and that LSR U is the upstream LSR on each of their paths to 220 R. D1 and D2 each binds a label to , and each uses a label 221 mapping message to inform U of the label binding. Suppose D1 has 222 assigned label L1 to and D2 has assigned label L2 to . 223 (Note that L1 and L2 could have the same value or different values; 224 D1 and D2 do not coordinate their label assignments.) When U has a 225 packet to transmit on the MP-LSP , it makes a copy of the 226 packet, pushes on label L1, and unicasts the resulting packet to D1. 227 It also makes a second copy of the packet, pushes on label L2, and 228 then unicasts the resulting packet to D2. 230 This procedure also works when the MP-LSP is a MP2MP LSP. 231 Suppose that in addition to labels L1 and L2 described above, U has 232 assigned label L3 for traffic received from D1, and label L4 233 for traffic received from D2. When U processes a packet with 234 label L3 at the top of its label stack, it knows the packet is from 235 D1, so U sends a unicast copy of the packet to D2, after swapping L3 236 for L2. U does not send a copy back to D1. 238 Note that all labels used in this procedure are downstream-assigned 239 labels. 241 The method of unicast is a local matter, outside the scope of this 242 specification. The only requirement is that D1 will receive the copy 243 of the packet carrying label L1, and that D1 will process the packet 244 by looking up label L1. (And similarly, D2 must receive the copy of 245 the packet carrying label L2, and must process the packet by looking 246 up label L2.) 248 Note that if the method of unicast is MPLS, U will need to push 249 another label on each copy of the packet before transmitting it. 250 This label needs to ensure that delivery of the packet to the 251 appropriate LSR, D1 or D2. Use of penultimate-hop popping for that 252 label is perfectly legitimate. 254 3. Targeted mLDP with Multicast Tunneling 256 Suppose that LSRs D1 and D2 are both setting up MP-LSP , and 257 that LSR U is the upstream LSR on each of their paths to R. Since 258 multicast tunneling is being used, when U has a packet to send on 259 this MP-LSP, it does not necessarily send two copies, one to D1 and 260 one to D2. It may send only one copy of the packet, which will get 261 replicated somewhere downstream in the multicast tunnel. Therefore, 262 the label that gets bound to the MP-LSP must be an upstream-assigned 263 label, assigned by U. This requires a change from the procedures of 264 [mLDP]. D1 and D2 do not send label mapping messages to U; instead 265 they send label request messages to U, asking U to assign a label to 266 the MP-LSP . U responds with a label mapping message containing 267 an upstream-assigned label, L (using the procedures specified in 268 [LDP-UP]). As part of the same label mapping message, U also sends 269 an Interface TLV (as specified in [LDP-UP]) identifying the multicast 270 tunnel in which data on the MP-LSP will be carried. When U transmits 271 a packet on this tunnel, it first pushes on the upstream-assigned 272 label L, and then pushes on the label that corresponds to the 273 multicast tunnel. 275 If the numerical value L of the upstream-assigned label is the value 276 3, defined in [LDP] and [RFC3032] as "Implicit NULL", then the 277 specified multicast tunnel will carry only the specified MP-LSP. 278 That is, aggregation of multiple MP-LSPs into a single multicast 279 tunnel is not being done. In this case, no upstream-assigned label 280 is pushed onto a packet that is transmitted through the multicast 281 tunnel. 283 Various types of multicast tunnel may be used. The choice of tunnel 284 type is determined by provisioning, or by some other method that is 285 outside the scope of this document. [LDP-UP] specifies encodings 286 allowing U to identify an mLDP MP-LSP, and RSVP-TE P2MP LSP, as well 287 as other types of multicast tunnel. 289 This document does not specify procedures for tunneling one or more 290 MP2MP LSPs through P2MP tunnels. While it is possible to do this, it 291 is highly RECOMMENDED that MP2MP LSPs be tunneled through MP2MP LSPs 292 (unless, of course, unicast replication is being used). 294 If the multicast tunnel is an mLDP MP-LSP or an RSVP-TE P2MP LSP, 295 when U transmits a packet on the MP-LSP , the upstream-assigned 296 label L will be the second label in the label stack. Penultimate-hop 297 popping MUST NOT be done, because the top label provides the context 298 in which the second label is to be interpreted. See [RFC5331]. 300 When LSR U uses these procedures to inform LSR D that a particular 301 MP-LSP is being carried in a particular multicast tunnel, U and D 302 MUST take appropriate steps to ensure that packets U sends into this 303 tunnel will be received by D. The exact steps to take depend on the 304 tunnel type. As long as U is D's upstream LSR for any MP-LSP that 305 has been assigned to this tunnel, D must remain joined to the tunnel. 307 Note that U MAY assign the same multicast tunnel for multiple 308 different MP-LSPs. However, U MUST assign a distinct upstream- 309 assigned label to each MP-LSP. This allows the packets traveling 310 through the tunnel to be demultiplexed into the proper MP-LSPs. 312 If U has an MP-LSP with downstream LSRs D1 and D2, and an MP- 313 LSP with downstream LSRs D2 and D3, U may assign both MP-LSPs 314 to the same multicast tunnel. In this case, D3 will receive packets 315 traveling on . However, the upstream-assigned label carried 316 by those packets will not be recognized by D3, hence D3 will discard 317 those packets. Similarly, D1 will discard the packets. 319 This document does not specify any rules for deciding whether to 320 aggregate two or more MP-LSPs into a single multicast tunnel. Such 321 rules are outside the scope of this document. 323 Except for the procedures explicitly detailed in this document, the 324 procedures of [mLDP] and [LDP-UP] apply unchanged. 326 4. IANA Considerations 328 This document has no considerations for IANA. 330 5. Security Considerations 332 This document raises no new security considerations beyond those 333 discussed in [LDP], [LDP-UP], and [RFC5331]. 335 6. Acknowledgments 337 The authors wish to think Lizhong Jin for his comments. 339 7. Authors' Addresses 341 Maria Napierala 342 AT&T Labs 343 200 Laurel Avenue, Middletown, NJ 07748 344 E-mail: mnapierala@att.com 346 Eric C. Rosen 347 Cisco Systems, Inc. 348 1414 Massachusetts Avenue 349 Boxborough, MA, 01719 350 E-mail: erosen@cisco.com 351 IJsbrand Wijnands 352 Cisco Systems, Inc. 353 De kleetlaan 6a Diegem 1831 354 Belgium 355 E-mail: ice@cisco.com 357 8. Normative References 359 [LDP] Loa Andersson, Ina Minei, Bob Thomas, editors, "LDP 360 Specification", RFC 5036, October 2007 362 [LDP-CAP] Bob Thomas, Kamran Raza, Shivani Aggarwal, Rahul Aggarwal, 363 Jean-Louis Le Roux, "LDP Capabilities", RFC 5561, July 2009 365 [mLDP] IJsbrand Wijnands, Ina Minei, Kireeti Kompella, Bob Thomas, 366 "Label Distribution Protocol Extensions for Point-to-Multipoint and 367 Multipoint-to-Multipoint Label Switched Paths", RFC 6388, November 368 2011 370 [LDP-UP] Rahul Aggarwal, Jean-Louis Le Roux, "MPLS Upstream Label 371 Assignment for LDP", RFC 6389, November 2011 373 [RFC2119] "Key words for use in RFCs to Indicate Requirement 374 Levels.", Bradner, March 1997 376 [RFC3032] Eric Rosen, et. al., "MPLS Label Stack Encoding", RFC 3032, 377 January 2001 379 [RFC5331] Rahul Aggarwal, Yakov Rekhter, Eric Rosen, "MPLS Upstream 380 Label Assignment and Context-Specific Label Space", RFC 5331, August 381 2009