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Checking references for intended status: Experimental ---------------------------------------------------------------------------- == Outdated reference: A later version (-20) exists of draft-ietf-babel-rfc6126bis-17 -- Obsolete informational reference (is this intentional?): RFC 5549 (Obsoleted by RFC 8950) Summary: 0 errors (**), 0 flaws (~~), 2 warnings (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group T. Bastian 3 Internet-Draft Ecole Normale Superieure, Paris 4 Updates: 6126bis (if approved) J. Chroboczek 5 Intended status: Experimental IRIF, University of Paris-Diderot 6 Expires: April 23, 2021 October 20, 2020 8 IPv4 routes with an IPv6 next-hop in the Babel routing protocol 9 draft-ietf-babel-v4viav6-00 11 Abstract 13 This document defines an extension to the Babel routing protocol that 14 allows annoncing routes to an IPv4 prefix with an IPv6 next-hop, 15 which makes it possible for IPv4 traffic to flow through interfaces 16 that have not been assigned an IPv4 address. 18 Status of This Memo 20 This Internet-Draft is submitted in full conformance with the 21 provisions of BCP 78 and BCP 79. 23 Internet-Drafts are working documents of the Internet Engineering 24 Task Force (IETF). Note that other groups may also distribute 25 working documents as Internet-Drafts. The list of current Internet- 26 Drafts is at https://datatracker.ietf.org/drafts/current/. 28 Internet-Drafts are draft documents valid for a maximum of six months 29 and may be updated, replaced, or obsoleted by other documents at any 30 time. It is inappropriate to use Internet-Drafts as reference 31 material or to cite them other than as "work in progress." 33 This Internet-Draft will expire on April 23, 2021. 35 Copyright Notice 37 Copyright (c) 2020 IETF Trust and the persons identified as the 38 document authors. All rights reserved. 40 This document is subject to BCP 78 and the IETF Trust's Legal 41 Provisions Relating to IETF Documents 42 (https://trustee.ietf.org/license-info) in effect on the date of 43 publication of this document. Please review these documents 44 carefully, as they describe your rights and restrictions with respect 45 to this document. Code Components extracted from this document must 46 include Simplified BSD License text as described in Section 4.e of 47 the Trust Legal Provisions and are provided without warranty as 48 described in the Simplified BSD License. 50 Table of Contents 52 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 53 1.1. Specification of Requirements . . . . . . . . . . . . . . 3 54 2. Protocol operation . . . . . . . . . . . . . . . . . . . . . 3 55 2.1. Announcing v4-over-v6 routes . . . . . . . . . . . . . . 3 56 2.2. Receiving v4-over-v6 routes . . . . . . . . . . . . . . . 3 57 2.3. Prefix and seqno requests . . . . . . . . . . . . . . . . 4 58 2.4. Other TLVs . . . . . . . . . . . . . . . . . . . . . . . 4 59 3. Backwards compatibility . . . . . . . . . . . . . . . . . . . 4 60 4. Protocol encoding . . . . . . . . . . . . . . . . . . . . . . 5 61 4.1. Prefix encoding . . . . . . . . . . . . . . . . . . . . . 5 62 4.2. Changes for existing TLVs . . . . . . . . . . . . . . . . 5 63 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 64 6. Security Considerations . . . . . . . . . . . . . . . . . . . 6 65 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 66 7.1. Normative References . . . . . . . . . . . . . . . . . . 7 67 7.2. Informative References . . . . . . . . . . . . . . . . . 7 68 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 70 1. Introduction 72 Traditionally, a routing table maps a network prefix of a given 73 address family to a next-hop address in the same address family. The 74 sole purpose of this next-hop address is to serve as an input to a 75 protocol that will map it to a link-layer address, Neighbour 76 Discovery (ND) [RFC4861] in the case of IPv6, Address Resolution 77 (ARP) [RFC0826] in the case of IPv4. Therefore, there is no reason 78 why the address family of the next hop address should match that of 79 the prefix being announced: an IPv6 next-hop yields a link-layer 80 address that is suitable for forwarding both IPv6 or IPv4 traffic. 82 We call a route towards an IPv4 prefix that uses an IPv6 next hop a 83 "v4-over-v6" route. Since an IPv6 next-hop can use a link-local 84 address that is autonomously configured, the use of v4-over-v6 routes 85 enables a mode of operation where the network core has no statically 86 assigned IP addresses of either family, thus significantly reducing 87 the amount of manual configuration. 89 This document describes an extension that allows the Babel routing 90 protocol [RFC6126bis] to announce routes towards IPv6 prefixes with 91 IPv4 next hops. The extension is inspired by a previously defined 92 extension to the BGP protocol [RFC5549]. 94 1.1. Specification of Requirements 96 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 97 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 98 "OPTIONAL" in this document are to be interpreted as described in BCP 99 14 [RFC2119] [RFC8174] when, and only when, they appear in all 100 capitals, as shown here. 102 2. Protocol operation 104 The Babel protocol fully supports double-stack operation: all data 105 that represent a neighbour address or a network prefix are tagged by 106 an Address Encoding (AE), a small integer that identifies the address 107 family (IPv4 or IPv6) of the address of prefix, and describes how it 108 is encoded. This extension defines a new AE, called v4-over-v6, 109 which has the same format as the existing AE for IPv4 addresses. 110 This new AE is only allowed in TLVs that carry network prefixes: TLVs 111 that carry a neighbour address use the normal encodings for IPv6 112 addresses. 114 2.1. Announcing v4-over-v6 routes 116 A Babel node that needs to announce an IPv4 route over an interface 117 that has no assigned IPv4 address MAY make a v4-over-v6 announcement. 118 In order to do so, it first establishes an IPv6 next-hop address in 119 the usual manner (either by sending the Babel packet over IPv6, or by 120 including a Next Hop TLV containing an IPv6 address); it then sends 121 an Update with AE equal to TBD containing the IPv4 prefix being 122 announced. 124 If the outgoing interface has been assigned an IPv4 address, then, in 125 the interest of maximising compatibility with existing routers, the 126 sender SHOULD prefer an ordinary IPv4 announcement; even in that 127 case, however, it MAY use a v4-over-v6 announcement. A node SHOULD 128 NOT send both ordinary IPv4 and v4-over-v6 annoucements for the same 129 prefix over a single interface (if the update is sent to a multicast 130 address) or to a single neighbour (if sent to a unicast address), 131 since doing that doubles the amount of routing traffic while 132 providing no benefit. 134 2.2. Receiving v4-over-v6 routes 136 Upon reception of an Update TLV with a v4-over-v6 AE, a Babel node 137 computes the IPv6 next-hop, as described in Section 4.6.9 of 138 [RFC6126bis]. If no IPv6 next-hop exists, then the Update MUST be 139 silently ignored. If an IPv6 next-hop exists, then the node MAY 140 acquire the route being announced, as described in Section 3.5.3 of 141 [RFC6126bis]; the parameters of the route are as follows: 143 o the prefix, plen, router-id, seqno, metric MUST be computed as for 144 an IPv4 route, as described in Section 4.6.9 of [RFC6126bis]; 146 o the next-hop MUST be computed as for an IPv6 route, as described 147 in Section 4.6.9 of [RFC6126bis]: it is taken from the last 148 preceding Next-Hop TLV with an AE field equal to 2 or 3; if no 149 such entry exists, and if the Update TLV has been sent in a Babel 150 packet carried over IPv6, then the next-hop is the network-layer 151 source address of the packet. 153 As usual, a node MAY ignore the update, e.g., due to filtering 154 (Appendix C of [RFC6126bis]). If a node cannot install v4-over-v6 155 routes, eg., due to hardware or software limitations, then routes to 156 an IPv4 prefix with an IPv6 next-hop MUST NOT be selected, as 157 described in Section 3.5.3 of [RFC6126bis]. 159 2.3. Prefix and seqno requests 161 Prefix and seqno requests are used to request an update for a given 162 prefix. Since they are not related to a specific Next-Hop, there is 163 no semantic difference between ordinary IPv4 and v4-over-v6 requests. 165 A node SHOULD NOT send requests of either kind with the AE field 166 being set to TBD (v4-over-v6); instead, it SHOULD request IPv4 167 updates using requests with the AE field being set to 1 (IPv4). 169 When receiving requests, AEs 1 (IPv4) and TBD (v4-over-v6) MUST be 170 treated in the same manner: the receiver processes the request as 171 described in Section 3.8 of [RFC6126bis]. If an Update is sent, then 172 it MAY be sent with AE 1 or TBD, as described in Section 2.1 above, 173 irrespective of which AE was used in the request. 175 When receiving a request with AE 0 (wildcard), the receiver SHOULD 176 send a full route dump, as described in Section 3.8.1.1 of 177 [RFC6126bis]. Any IPv4 routes contained in the route dump MAY use 178 either AE 1 or AE TBD, as described in Section 2.1 above. 180 2.4. Other TLVs 182 The only other TLV defined by [RFC6126bis] that carries an AE field 183 is the IHU TLV. IHU TLVs MUST NOT carry the AE TBD (v4-over-v6). 185 3. Backwards compatibility 187 This protocol extension adds no new TLVs or sub-TLVs. 189 This protocol extension uses a new AE. As discussed in Appendix D of 190 [RFC6126bis] and specified in the same document, implementations that 191 do not understand the present extension will silently ignore the 192 various TLVs that use this new AE. As a result, incompatible 193 versions will ignore v4-over-v6 routes. They will also ignore 194 requests with AE TBD, which, as stated in Section 2.3, are NOT 195 RECOMMENDED. 197 Using a new AE introduces a new compression state, used to parse the 198 network prefixes. As this compression state is separate from other 199 AEs' states, it will not interfere with the compression state of 200 unextended nodes. 202 This extension reuses the next-hop state from AEs 2 and 3 (IPv6), but 203 makes no changes to the way it is updated, and therefore causes no 204 compatibility issues. 206 As mentioned in Section 2.1, ordinary IPv4 announcements are 207 preferred to v4-over-v6 announcements when the outgoing interface has 208 an assigned IPv4 address; doing otherwise would prevent routers that 209 do not implement this extension from learning the route being 210 announced. 212 4. Protocol encoding 214 This extension defines the v4-over-v6 AE, whose value is TBD. This 215 AE is solely used to tag network prefixes, and MUST NOT be used to 216 tag peers' addresses, eg. in Next-Hop or IHU TLVs. 218 This extension defines no new TLVs or sub-TLVs. 220 4.1. Prefix encoding 222 Network prefixes tagged with AE TBD MUST be encoded and decoded as 223 prefixes tagged with AE 1 (IPv4), as described in Section 4.3.1 of 224 [RFC6126bis]. 226 A new compression state for AE TBD (v4-over-v6) distinct from that of 227 AE 1 (IPv4) is introduced, and MUST be used for address compression 228 of prefixes tagged with AE TBD, as described in Section 4.6.9 of 229 [RFC6126bis] 231 4.2. Changes for existing TLVs 233 The following TLVs MAY be tagged with AE TBD: 235 o Update (Type = 8) 237 o Route Request (Type = 9) 238 o Seqno Request (Type = 10) 240 As AE TBD is suitable only to tag network prefixes, IHU (Type = 5) 241 and Next-Hop (Type = 7) TLVs MUST NOT be tagged with AE TBD. Such 242 TLVs MUST be silently ignored. 244 4.2.1. Update 246 An Update (Type = 8) TLV with AE = TBD is constructed as described in 247 Section 4.6.9 of [RFC6126bis] for AE 1 (IPv4), with the following 248 specificities: 250 o Prefix. The Prefix field is constructed according to the 251 Section 4.1 above. 253 o Next hop. The next hop is determined as described in Section 2.2 254 above. 256 4.2.2. Other valid TLVs tagged with AE = TBD 258 Any other valid TLV tagged with AE = TBD MUST be constructed and 259 decoded as described in Section 4.6 of [RFC6126bis]. Network 260 prefixes within MUST be constructed and decoded as described in 261 Section 4.1 above. 263 5. IANA Considerations 265 IANA is requested to allocate a value (4 suggested) in the "Babel 266 Address Encodings" registry as follows: 268 +-----+------------+-----------------+ 269 | AE | Name | Reference | 270 +-----+------------+-----------------+ 271 | TBD | v4-over-v6 | (this document) | 272 +-----+------------+-----------------+ 274 6. Security Considerations 276 This extension does not fundamentally change the security properties 277 of the Babel protocol: as described in Section 6 of [RFC6126bis], 278 Babel must be protected by a suitable cryptographic mechanism in 279 order to be made secure. 281 However, enabling this extension will allow IPv4 traffic to flow 282 through sections of a network that have not been assigned IPv4 283 addresses, which, in turn, might allow IPv4 traffic to reach areas of 284 the network that were previously inaccessible to such traffic. If 285 this is undesirable, the flow of IPv4 traffic must be restricted by 286 the use of suitable filtering rules (Appendix C of [RFC6126bis]) 287 together with matching access control rules in the data plane. 289 7. References 291 7.1. Normative References 293 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 294 Requirement Levels", BCP 14, RFC 2119, 295 DOI 10.17487/RFC2119, March 1997. 297 [RFC6126bis] 298 Chroboczek, J. and D. Schinazi, "The Babel Routing 299 Protocol", draft-ietf-babel-rfc6126bis-17 (work in 300 progress), February 2020. 302 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 303 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 304 May 2017. 306 7.2. Informative References 308 [RFC0826] Plummer, D., "An Ethernet Address Resolution Protocol: Or 309 Converting Network Protocol Addresses to 48.bit Ethernet 310 Address for Transmission on Ethernet Hardware", STD 37, 311 RFC 826, DOI 10.17487/RFC0826, November 1982. 313 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 314 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 315 DOI 10.17487/RFC4861, September 2007. 317 [RFC5549] Le Faucheur, F. and E. Rosen, "Advertising IPv4 Network 318 Layer Reachability Information with an IPv6 Next Hop", 319 RFC 5549, DOI 10.17487/RFC5549, May 2009. 321 Authors' Addresses 323 Theophile Bastian 324 Ecole Normale Superieure, Paris 325 France 327 Email: contact@tobast.fr 328 Juliusz Chroboczek 329 IRIF, University of Paris-Diderot 330 Case 7014 331 75205 Paris Cedex 13 332 France 334 Email: jch@irif.fr