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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in RFCs) == Unused Reference: 'RFC2547' is defined on line 256, but no explicit reference was found in the text == Outdated reference: A later version (-15) exists of draft-ietf-l2tpext-l2tp-base-14 -- Obsolete informational reference (is this intentional?): RFC 2547 (Obsoleted by RFC 4364) == Outdated reference: A later version (-05) exists of draft-ietf-l3vpn-ipsec-2547-01 Summary: 10 errors (**), 0 flaws (~~), 7 warnings (==), 8 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group W. Mark Townsley 3 Internet-Draft cisco Systems 4 Ted Seely 5 October 2004 Sprint 7 Encapsulation of MPLS over Layer 2 Tunneling Protocol Version 3 9 Status of this Memo 11 By submitting this Internet-Draft, I certify that any applicable 12 patent or other IPR claims of which I am aware have been disclosed, 13 and any of which I become aware will be disclosed, in accordance with 14 RFC 3668. 16 Internet-Drafts are working documents of the Internet Engineering 17 Task Force (IETF), its areas, and its working groups. Note that 18 other groups may also distribute working documents as 19 Internet-Drafts. 21 Internet-Drafts are draft documents valid for a maximum of six months 22 and may be updated, replaced, or obsoleted by other documents at any 23 time. It is inappropriate to use Internet-Drafts as reference 24 material or to cite them other than as "work in progress". 26 The list of current Internet-Drafts can be accessed at 27 http://www.ietf.org/ietf/1id-abstracts.txt . 29 The list of Internet-Draft Shadow Directories can be accessed at 30 http://www.ietf.org/shadow.html . 32 Copyright Notice 34 Copyright (C) The Internet Society (2004). All Rights Reserved. 36 Abstract 38 The Layer 2 Tunneling Protocol, Version 3, (L2TPv3) defines a 39 protocol for tunneling a variety of payload types over IP networks. 40 This document defines how to carry an MPLS label or label stack and 41 its payload over L2TPv3. This enables an application which 42 traditionally requires an MPLS-enabled core network to utilize an 43 L2TPv3 encapsulation over an IP network instead. 45 Contents 47 Status of this Memo.......................................... 1 49 1. Introduction.............................................. 2 51 2. MPLS over L2TPv3 Encoding................................. 2 53 3. Assigning the L2TPv3 Session ID and Cookie................ 4 55 4. Applicability............................................. 4 57 5. Security Considerations................................... 5 59 6. IANA Considerations....................................... 5 61 7. Acknowledgments........................................... 6 63 8. References................................................ 6 64 8.1 Normative References.................................. 6 65 8.2 Informative References................................ 6 67 9. Contacts.................................................. 6 69 Specification of Requirements 71 In this document, several words are used to signify the requirements 72 of the specification. These words are often capitalized. The key 73 words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", 74 "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document 75 are to be interpreted as described in [RFC2119]. 77 1. Introduction 79 This document defines how to encapsulate an MPLS label or label stack 80 and its payload over L2TPv3. After defining the MPLS over L2TPv3 81 encapsulation procedure, other MPLS over IP encapsulation options 82 including IP, GRE and IPsec are discussed in context with MPLS over 83 L2TPv3 in an Applicability section. This document only describes 84 encapsulation and does not concern itself with all possible MPLS- 85 based applications which may be enabled over L2TPv3. 87 2. MPLS over L2TPv3 Encoding 89 MPLS over L2TPv3 allows tunneling of an MPLS stack [RFC3032] over an 90 IP network utilizing the L2TPv3 encapsulation defined in [L2TPv3]. 92 +-+-+-+-+-+-+-+-+-+-+ 93 | IP | 94 +-+-+-+-+-+-+-+-+-+-+ 95 | L2TPv3 | 96 +-+-+-+-+-+-+-+-+-+-+ 97 | MPLS Label Stack | 98 +-+-+-+-+-+-+-+-+-+-+ 100 Figure 2.1 MPLS Stack over L2TPv3/IP 102 For reference, the L2TPv3 encapsulation carrying a single MPLS label 103 is as follows: 105 0 1 2 3 106 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 107 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 108 | Session ID | 109 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 110 | Cookie (optional, maximum 64 bits)... 111 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 112 ... | 113 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Label 114 | Label | Exp |S| TTL | Stack 115 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Entry 117 Figure 2.2 MPLS label over L2TPv3 encapsulation 119 Session ID 121 The L2TPv3 Session ID is a 32-bit identifier field locally 122 selected as a lookup key for the context of an L2TP Session. An 123 L2TP Session contains necessary context for processing a received 124 L2TP packet. At a minimum, such context contains whether the 125 Cookie (see description below) is present and the value it was 126 assigned, as well as what type of tunneled encapsulation follows 127 (i.e., Frame Relay, Ethernet, MPLS, etc). 129 Cookie 131 The L2TPv3 Cookie field contains a variable length (maximum 64 132 bits) randomly assigned value. It is intended to provide an 133 additional level of guarantee that a data packet has been directed 134 to the proper L2TP session by the Session ID. While the Session 135 ID may be encoded and assigned any value (perhaps optimizing for 136 local lookup capabilities, redirection in a distributed forwarding 137 architecture, etc.), the Cookie MUST be selected as a random 138 value, with the added restriction that it not be the same as a 139 recently used value for a given Session ID. A well-chosen Cookie 140 will prevent inadvertent misdirection of a stray packet containing 141 a recently reused Session ID, a Session ID that is subject to 142 packet corruption, and protection against some specific malicious 143 packet insertion attacks as described in more detail in Section 144 4.2 of this document. 146 Label Stack Entry 148 An MPLS label as defined in [RFC3032]. 150 The optional L2-Specific-Sublayer defined in [L2TPv3] is generally 151 not present for MPLS over L2TPv3. 153 Generic IP encapsulation procedures such as MTU considerations, 154 handling of TTL, EXP and DSCP bits, etc. are the same as the "Common 155 Procedures" for IP encapsulation of MPLS defined in Section 5 of 156 [MPLS-IP-GRE] and are not reiterated here. 158 3. Assigning the L2TPv3 Session ID and Cookie 160 Much like an MPLS label, the L2TPv3 Session ID and Cookie must be 161 selected and exchanged between participating nodes before L2TPv3 can 162 operate. These values may be configured manually, or distributed via 163 a signaling protocol. This document concerns itself only with the 164 encapsulation of MPLS over L2TPv3, so the particular method of 165 assigning the Session ID and Cookie for a given application is out of 166 scope here. 168 4. Applicability 170 The methods defined [MPLS-IP-GRE], [MPLS-IPSEC] and this document all 171 describe methods for carrying MPLS over an IP network. Cases where 172 MPLS over L2TPv3 may be applicable compared to other alternatives are 173 discussed here. 175 The use of IP or GRE to carry MPLS labels increases the opportunity 176 for MPLS label spoofing attacks. It is generally simpler to have 177 one's border routers refuse to accept an MPLS packet than to 178 configure a router to refuse to accept certain MPLS packets carried 179 in IP or GRE to or from certain IP sources or destinations. When ACLs 180 fail or are not available, L2TPv3 provides an additional level of 181 protection at the PE itself against packet spoofing attacks (much 182 like IPsec provides an additional level of protection at the PE 183 rather than relying on ACL filters). MPLS over L2TPv3 may be 184 favorable compared to [MPLS-IP-GRE], if: 186 Two routers are "adjacent" over an L2TPv3 tunnel that exists for 187 some reason outside the scope of this document, and those two 188 routers need to send MPLS packets over that adjacency. 190 Implementation considerations dictate the use of MPLS over L2TPv3. 191 For example, some hardware device might only be able to handle 192 L2TPv3 encapsulations in its fastpath. 194 (The above two applicability statements were adopted from [MPLS-IP- 195 GRE]) 197 In summary, L2TPv3 can provide a balance between the limited security 198 against IP spoofing attacks offered by [MPLS-IP-GRE] vs. the greater 199 security and associated operational and processing overhead offered 200 by [MPLS-IPSEC]. Further, MPLS over L2TPv3 may be faster in some 201 hardware, particularly if it is already optimized to classify 202 incoming L2TPv3 packets carrying IP framed in a variety of ways. That 203 is, IP encapsulated by HDLC or Frame Relay over L2TPv3 may be 204 considered not that far removed from IP encapsulated by MPLS over 205 L2TPv3. 207 5. Security Considerations 209 The L2TPv3 Cookie does not provide cryptographic security. However, 210 when used with a sufficiently random 64-bit value which is kept 211 secret from a hacker, the L2TPv3 Cookie may be used as a simple yet 212 effective packet source authentication check which is quite resistent 213 to brute force packet spoofing attacks. It also alleviates the need 214 to rely solely on filter lists based on a list of valid source IP 215 addresses, and thwarts attacks which could benefit by spoofing a 216 permitted source IP address. 218 L2TPv3 tunnels may also be secured using IPsec. When using IPsec, 219 the tunnel head and the tunnel tail should be treated as the 220 endpoints of a Security Association. The MPLS over L2TPv3 221 encapsulated packets should be considered as originating at the 222 tunnel head and as being destined for the tunnel tail; IPsec 223 transport mode should thus be used. Key distribution may be done 224 either manually or automatically. 226 Security is also discussed as part of the applicability discussion in 227 section 4 of this document. 229 6. IANA Considerations 231 There are no IANA considerations for this document. 233 7. Acknowledgments 235 Thanks to Robert Raszuk, Clarence Filsfils and Eric Rosen for their 236 review of this document. Some text was adopted from [MPLS-IP-GRE]. 238 8. References 240 8.1 Normative References 242 [L2TPv3] J. Lau, M. Townsley, I. Goyret, "Layer Two Tunneling 243 Protocol (Version 3)", work in progress, 244 draft-ietf-l2tpext-l2tp-base-14.txt, June 2004. 246 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 247 Requirement Levels", BCP 14, RFC 2119, March 1997. 249 [MPLS-IP-GRE] T. Worster, Y. Rekhter, E. Rosen, "Encapsulating 250 MPLS in IP or Generic Routing Encapsulation (GRE)", 251 work in progress, draft-ietf-mpls-in-ip-or-gre-08.txt, 252 June 2004. 254 8.2 Informative References 256 [RFC2547] E. Rosen, Y. Rekhter, "BGP/MPLS VPNs", RFC 2547, March 1999. 258 [RFC3032] R. Rosen, et. al., "MPLS Label Stack Encoding," RFC 3032, 259 January 2001. 261 [MPLS-IPSEC] E. Rosen, J. De Clercq, O/ Paridaens, Y. T'Joens, 262 C. Sargor, "Use of PE-PE IPsec in RFC2547 VPNs", 263 work in progress, draft-ietf-l3vpn-ipsec-2547-01.txt, 264 August 2003. 266 9. Contacts 268 W. Mark Townsley 269 cisco Systems 270 7025 Kit Creek Road 271 Research Triangle Park, NC 27709 272 mark@townsley.net 274 Ted Seely 275 Sprint 276 tseely@sprint.net 277 Intellectual Property Statement 279 The IETF takes no position regarding the validity or scope of any 280 Intellectual Property Rights or other rights that might be claimed to 281 pertain to the implementation or use of the technology described in 282 this document or the extent to which any license under such rights 283 might or might not be available; nor does it represent that it has 284 made any independent effort to identify any such rights. 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