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Pignataro 5 Expires: November 9, 2009 Cisco Systems 6 May 8, 2009 8 Load Balancing for Mesh Softwires 9 draft-ietf-softwire-lb-03 11 Status of this Memo 13 This Internet-Draft is submitted to IETF in full conformance with the 14 provisions of BCP 78 and BCP 79. 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 Internet- 19 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 This Internet-Draft will expire on November 9, 2009. 34 Copyright Notice 36 Copyright (c) 2009 IETF Trust and the persons identified as the 37 document authors. All rights reserved. 39 This document is subject to BCP 78 and the IETF Trust's Legal 40 Provisions Relating to IETF Documents in effect on the date of 41 publication of this document (http://trustee.ietf.org/license-info). 42 Please review these documents carefully, as they describe your rights 43 and restrictions with respect to this document. 45 Abstract 47 Payloads carried over a Softwire mesh service as defined by BGP 48 Encapsulation Subsequent Address Family Identifier (SAFI) information 49 exchange often carry a number of identifiable, distinct flows. It 50 can in some circumstances be desirable to distribute these flows over 51 the equal cost multiple paths (ECMPs) that exist in the packet 52 switched network. Currently, the payload of a packet entering the 53 Softwire can only be interpreted by the ingress and egress routers. 54 Thus the load balancing decision of a core router is only based on 55 the encapsulating header, presenting much less entropy than available 56 in the payload or the encapsulated header since the Softwire 57 encapsulation acts in a tunneling fashion. This document describes a 58 method for achieving comparable load balancing efficiency in a 59 network carrying Softwire mesh service over Layer Two Tunneling 60 Protocol - Version 3 (L2TPv3) over IP or Generic Routing 61 Encapsulation (GRE) encapsulation to what would be achieved without 62 such encapsulation. 64 Table of Contents 66 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 67 1.1. Requirements Language . . . . . . . . . . . . . . . . . . . 3 68 2. Load Balancing Block sub-TLV . . . . . . . . . . . . . . . . . 3 69 2.1. Applicability to Tunnel Types . . . . . . . . . . . . . . . 4 70 2.2. Encapsulation Considerations . . . . . . . . . . . . . . . 5 71 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5 72 4. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 73 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5 74 6. Normative References . . . . . . . . . . . . . . . . . . . . . 6 75 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6 77 1. Introduction 79 Consider the case of a router R1 which encapsulates a packet P into a 80 Softwire bound to router R3. R2 is a router on the shortest path 81 from R1 to R3. R2's shortest path to R3 involves equal cost multiple 82 paths (ECMPs). The goal is for R2 to be able to choose which path to 83 use on the basis of the full entropy of packet P. 85 This is achieved by carrying in the encapsulation header a signature 86 of the inner header, hence enhancing the entropy of the flows as seen 87 by the core routers. The signature is carried as part of one of the 88 fields of the encapsulation header. To aid with better description 89 in the document, we define the generic term "load balancing field" to 90 mean such a value that is specific to an encapsulation type. For 91 example, for L2TPv3-over-IP [RFC3931] encapsulation, the load 92 balancing field is the Session Identifier (Session ID). For GRE 93 [RFC2784] encapsulation, the key field [RFC2890], if present, 94 represents the load balancing field. This mechanism assumes that 95 core routers base their load balancing decisions on a flow definition 96 that includes the load balancing field. This is an obvious and 97 generic functionality as, for example, for L2TPv3-over-IP tunnels, 98 the Session ID is at the same well-known constant offset as the TCP/ 99 UDP ports in the encapsulating header. 101 The "Encapsulation SAFI" [RFC5512] is extended such that a contiguous 102 block of the load balancing field is bound to the Softwire advertised 103 by a BGP next-hop. On a per-inner flow basis, the ingress PE selects 104 one value of the load balancing field from the block to preserve per- 105 flow ordering, and at the same time to enhance the entropy across 106 flows. 108 1.1. Requirements Language 110 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 111 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 112 document are to be interpreted as described in RFC 2119 [RFC2119]. 114 2. Load Balancing Block sub-TLV 116 This document defines a new sub-TLV for use with the Tunnel 117 Encapsulation Attribute defined in [RFC5512]. The new sub-TLV is 118 referred to as the "Load Balancing Block sub-TLV" and MAY be included 119 in any Encapsulation SAFI UPDATE message where load balancing is 120 desired. 122 The sub-TLV type of the Load Balancing Block sub-TLV is 5. The sub- 123 TLV length is 2 octets. The value represents the length of the block 124 in bits and it MUST NOT exceed the size of the load balancing field. 125 This format is very similar to the variable-length subnet masking 126 (VLSM) used in IP addresses to allow arbitrary length prefixes. The 127 block is determined by extracting the initial sequence of 'block 128 size' bits from the load balancing field. 130 If a load balancing field is not signaled (e.g., if the Encapsulation 131 sub-TLV is not included in an advertisement as in the case of GRE 132 without a Key), then the Load Balancing Block sub-TLV MUST NOT be 133 included. 135 The smaller the value field of the Load Balancing Block sub-TLV, the 136 larger the space for per-flow identification, and hence the better 137 entropy for potential load-balancing in the core; in addition, the 138 lower the polarization when mapping flows to ECMP paths. However, 139 reducing the load balancing block size consumes more L2TPv3 Session 140 IDs or GRE keys, resulting in potentially less number of supported 141 services. A typical deployment would need to arbitrate between this 142 trade-off. 144 As an example, Assume that there is a Softwire set up between R1 and 145 R3 with L2TPv3-over-IP tunnel type. Assume that R3 encodes the 146 Session ID with value 0x1234ABCD in the encapsulation sub-TLV. It 147 also includes the load balancing block sub-TLV and encodes the value 148 24. This should be interpreted as follows: 150 o If an ingress router does not understand Load Balancing Block sub- 151 TLV, it continues to use the Session ID 0x1234ABCD and 152 encapsulates all packets with that Session ID, 154 o If an ingress router understands Load Balancing Block sub-TLV, it 155 picks the first 24 bits out of the Session ID (0x1234AB) to be 156 used as the block and fills in the lower-order 8 bits with a per- 157 flow identifier (e.g. it can be determined based on the inner 158 packet's source, destination addresses and TCP/UDP ports). This 159 selection preserves per-flow ordering of packets. 161 This requirement and solution applies equally to GRE where the key 162 plays the same role as the Session ID in L2TPv3. 164 Needless to say, if an egress router does not support load balancing 165 block sub-TLV, the Softwire continues to operate with a single load 166 balancing field that all ingress routers encapsulate with. 168 2.1. Applicability to Tunnel Types 170 The load balancing block sub-TLV is applicable to Tunnel types that 171 define a load balancing field. This document defines load balancing 172 fields for tunnel types 1 (L2TPv3 over IP) and 2 (GRE) as follows: 174 o L2TPv3 over IP - Session ID. Special care needs to be taken to 175 always create a non-zero Session ID. When an egress router 176 includes a load balancing sub-TLV, it MUST encode the Session ID 177 field of the Encapsulation sub-TLV in a way that ensures that the 178 most significant bits of the Session ID after extracting the block 179 are non-zero. 181 o GRE - GRE key 183 This document does not define a load balancing field for the IP in IP 184 Tunnel Type (tunnel types 7). Future tunnel types that desire to use 185 the load balancing sub-TLV MUST define a load balancing field that is 186 part of the encapsulating header. 188 2.2. Encapsulation Considerations 190 Fields included in the encapsulation header besides the load 191 balancing field are not affected by the load balancing block sub-TLV. 192 All other encapsulation fields are shared between variations of the 193 load balancing field. For example, for L2TPv3-over-IP tunnel type, 194 if the optional cookie is included in the Encapsulation sub-TLV by 195 the egress router during Softwire signaling, it applies to all the 196 "Session ID" values derived at the ingress router after applying the 197 load balancing block as described in this document. 199 3. IANA Considerations 201 IANA is requested to assign the Type of 5 for the Load Balancing 202 Block sub-TLV, in the BGP Tunnel Encapsulation Attribute Sub-TLVs 203 registry (number space created as part of the publication of 204 [RFC5512]): 206 Sub-TLV name Type 207 ------------- ----- 208 Load Balancing Block 5 210 4. Security Considerations 212 There are no additional security risks introduced by this design. 214 5. Acknowledgements 216 The authors would like to thank Stewart Bryant, Mark Townsley, Rajiv 217 Asati, Kireeti Kompella, and Robert Raszuk for their review and 218 comments. 220 6. Normative References 222 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 223 Requirement Levels", BCP 14, RFC 2119, March 1997. 225 [RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. 226 Traina, "Generic Routing Encapsulation (GRE)", RFC 2784, 227 March 2000. 229 [RFC2890] Dommety, G., "Key and Sequence Number Extensions to GRE", 230 RFC 2890, September 2000. 232 [RFC3931] Lau, J., Townsley, M., and I. Goyret, "Layer Two Tunneling 233 Protocol - Version 3 (L2TPv3)", RFC 3931, March 2005. 235 [RFC5512] Mohapatra, P. and E. Rosen, "The BGP Encapsulation 236 Subsequent Address Family Identifier (SAFI) and the BGP 237 Tunnel Encapsulation Attribute", RFC 5512, April 2009. 239 Authors' Addresses 241 Clarence Filsfils 242 Cisco Systems 243 Brussels, 244 Belgium 246 Email: cfilsfil@cisco.com 248 Pradosh Mohapatra 249 Cisco Systems 250 170 W. Tasman Drive 251 San Jose, CA 95134 252 USA 254 Email: pmohapat@cisco.com 255 Carlos Pignataro 256 Cisco Systems 257 7200 Kit Creek Road, PO Box 14987 258 Research Triangle Park, NC 27709 259 USA 261 Email: cpignata@cisco.com