idnits 2.17.1 draft-ietf-mpls-ldp-applic-00.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- ** Looks like you're using RFC 2026 boilerplate. This must be updated to follow RFC 3978/3979, as updated by RFC 4748. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- == No 'Intended status' indicated for this document; assuming Proposed Standard == It seems as if not all pages are separated by form feeds - found 0 form feeds but 6 pages Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- ** The document seems to lack an Introduction section. ** The document seems to lack an IANA Considerations section. (See Section 2.2 of https://www.ietf.org/id-info/checklist for how to handle the case when there are no actions for IANA.) ** The document seems to lack separate sections for Informative/Normative References. All references will be assumed normative when checking for downward references. ** The abstract seems to contain references ([MPLS-FRAMEWORK], [MPLS-ARCH], [LDP]), which it shouldn't. Please replace those with straight textual mentions of the documents in question. Miscellaneous warnings: ---------------------------------------------------------------------------- -- The document seems to lack a disclaimer for pre-RFC5378 work, but may have content which was first submitted before 10 November 2008. If you have contacted all the original authors and they are all willing to grant the BCP78 rights to the IETF Trust, then this is fine, and you can ignore this comment. If not, you may need to add the pre-RFC5378 disclaimer. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (October 1999) is 8959 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Missing Reference: 'RFC2457' is mentioned on line 72, but not defined == Unused Reference: 'RFC2547' is defined on line 208, but no explicit reference was found in the text -- Possible downref: Non-RFC (?) normative reference: ref. 'LDP' -- Possible downref: Non-RFC (?) normative reference: ref. 'MPLS-ARCH' -- Possible downref: Non-RFC (?) normative reference: ref. 'MPLS-FRAMEWORK' ** Obsolete normative reference: RFC 1771 (Obsoleted by RFC 4271) ** Obsolete normative reference: RFC 2385 (Obsoleted by RFC 5925) ** Obsolete normative reference: RFC 2547 (Obsoleted by RFC 4364) Summary: 8 errors (**), 0 flaws (~~), 4 warnings (==), 5 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Network Working Group Bob Thomas 2 Internet Draft Cisco Systems, Inc. 3 Expiration Date: April 2000 4 Eric Gray 5 Lucent Technologies 7 October 1999 9 LDP Applicability 11 draft-ietf-mpls-ldp-applic-00.txt 13 Status of this Memo 15 This document is an Internet-Draft and is in full conformance with 16 all provisions of Section 10 of RFC2026. 18 Internet-Drafts are working documents of the Internet Engineering 19 Task Force (IETF), its areas, and its working groups. Note that 20 other groups may also distribute working documents as Internet- 21 Drafts. 23 Internet-Drafts are draft documents valid for a maximum of six months 24 and may be updated, replaced, or obsoleted by other documents at any 25 time. It is inappropriate to use Internet-Drafts as reference 26 material or to cite them other than as "work in progress." 28 The list of current Internet-Drafts can be accessed at 29 http://www.ietf.org/ietf/1id-abstracts.txt 31 The list of Internet-Draft Shadow Directories can be accessed at 32 http://www.ietf.org/shadow.html. 34 Abstract 36 Multiprotocol Label Switching (MPLS) is a method for forwarding 37 packets that uses short, fixed-length values carried by packets, 38 called labels, to determine packet nexthops ([MPLS-FRAMEWORK], 39 [MPLS-ARCH]). A fundamental concept in MPLS is that two Label 40 Switching Routers (LSRs) must agree on the meaning of the labels used 41 to forward traffic between and through them. This common 42 understanding is achieved by using a set of procedures, called a 43 label distribution protocol, by which one LSR informs another of 44 label bindings it has made. This document describes the 45 applicability of a set of such procedures called LDP (for Label 46 Distribution Protocol) [LDP]. 48 1. LDP Applicability 50 A label distribution protocol is a set of procedures by which one 51 Label Switching Router (LSR) informs another of the meaning of labels 52 used to forward traffic between and through them. 54 The MPLS architecture allows for the possibility of more than a 55 single method for distributing labels, and a number of different 56 label distribution protocols are being standardized. Existing 57 protocols have been extended so that label distribution can be 58 piggybacked on them, and new protocols have been defined for the 59 explicit purpose of distributing labels. 61 This document describes the applicability of the Label Distribution 62 Protocol (LDP), a new protocol for label distribution designed to 63 support label distribution for hop-by-hop MPLS forwarding. 65 LDP, together with an IP routing plane and software to program ATM 66 switch or Frame Relay switch cross-connect tables, can implement IP 67 in a network of ATM and/or Frame Relay switches without requiring an 68 overlay or the use of ATM-specific or Frame Relay-specific addressing 69 or routing. 71 LDP is also useful in situations that require efficient hop-by-hop 72 routed tunnels, such as MPLS-based VPN architectures [RFC2457] and 73 tunneling between BGP border routers. 75 In addition, LDP includes a mechanism that makes it possible to 76 extend it to support MPLS features that go beyond best effort hop- 77 by-hop forwarding. 79 As a stand-alone protocol for distributing labels LDP does not rely 80 on the presence of specific routing protocols at every hop along an 81 LSP path in order to establish an LSP. Hence LDP is useful in 82 situations in which an LSP must traverse nodes which may not all 83 support a common piggybacked approach to distributing labels. 85 2. Feature Overview 87 LDP associates a Forwarding Equivalence Class (FEC) [MPLS-ARCH] with 88 each label it distributes. Two LSRs which use LDP to exchange FEC- 89 label binding information are known as "LDP Peers", and we speak of 90 there being an "LDP Session" between them. 92 LDP uses TCP for session communication. Use of TCP ensures that 93 session messages are reliably delivered, and that distributed labels 94 and state information associated with LSPs need not be refreshed 95 periodically. 97 LDP includes a mechanism by which an LSR can discover potential LDP 98 peers. The discovery mechanism makes it unnecessary for operators to 99 explicitly configure each LSR with its LDP peers. 101 When an LSR discovers another LSR it follows the LDP session setup 102 procedure to establish an LDP session. By means of this procedure 103 the LSRs establish a session TCP connection and use it to negotiate 104 parameters for the session, such as the label distribution method to 105 be used (see below). After the LSRs agree on the parameters, the 106 session is operational and the LSRs use the TCP connection for label 107 distribution. 109 LDP supports two different methods for label distribution. An LSR 110 using Downstream Unsolicited distribution advertises FEC-label 111 bindings to its peers when it is ready to forward packets in the FEC 112 by means of MPLS. An LSR using Downstream on Demand distribution 113 provides FEC-label bindings to a peer in response to specific 114 requests from the peer for a label for the FEC. 116 LDP allows LSRs flexibility in strategies for retaining learned 117 labels. An LSR using liberal label retention stores all labels 118 learned from peers regardless of whether it currently needs them for 119 forwarding, whereas one using conservative label retention stores 120 only labels for which it has immediate use and releases unneeded 121 labels to the peer that advertised them. 123 In addition, LDP allows flexibility in strategies for when to 124 advertise FEC-label bindings. An LSR using independent control mode 125 advertises FEC-label bindings to peers whenever it sees fit, whereas 126 one using ordered control advertises bindings only when it has 127 previously received a label for the FEC from the FEC nexthop or it is 128 an MPLS egress for the FEC. 130 Downstream on Demand distribution with conservative label retention 131 and ordered control is appropriate in situations where labels are a 132 relatively scarce resource that must be conserved, and Downstream 133 Unsolicited distribution with liberal label retention and independent 134 control is appropriate where labels are plentiful and need not be 135 carefully conserved. However, the protocol permits other 136 combinations of distribution method, label retention mode and control 137 mode, including hybrid variants of them. 139 LDP defines a mechanism for loop detection to protect against 140 forwarding loops in LSPs that traverse non-TTL MPLS clouds; see 141 [MPLS-ARCH] for discussion of situations which may benefit from this 142 mechanism. The loop detection mechanism is optional in the sense 143 that it may be disabled by LSR configuration. However, an LDP- 144 compliant LSR must implement it. 146 LDP includes an extension mechanism which supports the development of 147 vendor-private and experimental features. This mechanism defines 148 procedures for introducing new types of messages and TLVs, methods an 149 LSR can use for detecting such messages and TLVs, and procedures an 150 LSR must follow when it receives a message or TLV it does not 151 implement. While it is not possible to make every future enhancement 152 backwards compatible, these procedures facilitate the introduction of 153 new capabilities in MPLS networks that include older implementations 154 that do not recognize them. 156 3. Scalability Considerations 158 The following factors may influence the scalability of LDP 159 implementations: 161 - LDP label distribution is incremental, requiring no periodic 162 refresh of FEC-label bindings. 164 - In situations were label resources may be scarce (ATM and Frame 165 Relay links) the use of the Downstream on Demand distribution 166 method with conservative label retention ensures that only those 167 labels required to support normally-routed paths are allocated 168 and distributed. 170 - In situations where label resources are not scarce, the use of 171 the Downstream Unsolicited method with liberal label retention 172 ensures that changes in FEC nexthop from one LDP peer to another 173 require no distribution action to update previously distributed 174 labels. 176 - Limitations on the number of TCP connections an LSR supports 177 limit the number of LDP peers the LSR can support. 179 - Use of the optional path vector based loop detection mechanism 180 imposes additional memory and processing requirements on an LSR, 181 as well as additional LDP traffic. Both impact scalability. 183 4. Security Considerations 185 LDP defines the optional use of the TCP MD5 Signature Option to 186 protect against the introduction of spoofed TCP segments into LDP 187 session connection streams. LDP use of the TCP MD5 Signature Option 188 is similar to BGP [RFC1771] use of the option specified in [RFC2385]. 190 5. References 192 [LDP] L. Andersson, P. Doolan, N. Feldman, A. Fredette, B. Thomas, 193 "LDP Specification", Work in Progress, June 1999. 195 [MPLS-ARCH] E. Rosen, A. Viswanathan, R. Callon, "Multiprotocol Label 196 Switching Architecture", Work in Progress, July 1998. 198 [MPLS-FRAMEWORK] R. Callon, P. Doolan, N. Feldman, A. Fredette, G. 199 Swallow, A. Viswanathan, "A Framework for Multiprotocol Label 200 Switching", Work in Progress, November 1997. 202 [RFC1771] Y. Rekhter, T. Li, "A Border Gateway Protocol 4 (BGP-4)", 203 RFC 1771, March 1995. 205 [RFC2385] Heffernan, A., "Protection of BGP Sessions via the TCP MD5 206 Signature Option", RFC 2385, August 1998. 208 [RFC2547] E. Rosen, Y. Rekhter, " BGP/MPLS VPNs", RFC 2547, March 209 1999. 211 6. Author Information 213 Eric Gray Bob Thomas 214 Lucent Technologies, Inc Cisco Systems, Inc. 215 P.O. Box 710 250 Apollo Dr. 216 Durham, NH 03824 Chelmsford, MA 01824 217 Phone: 603-659-3386 Phone: 978-244-8078 218 email: ewgray@lucent.com email: rhthomas@cisco.com