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Checking references for intended status: Informational ---------------------------------------------------------------------------- == Unused Reference: 'RFC1918' is defined on line 783, but no explicit reference was found in the text ** Obsolete normative reference: RFC 3315 (Obsoleted by RFC 8415) ** Obsolete normative reference: RFC 3736 (Obsoleted by RFC 8415) == Outdated reference: A later version (-13) exists of draft-ietf-6man-addr-select-opt-08 == Outdated reference: A later version (-06) exists of draft-ietf-v6ops-enterprise-incremental-ipv6-02 -- Obsolete informational reference (is this intentional?): RFC 3484 (Obsoleted by RFC 6724) Summary: 2 errors (**), 0 flaws (~~), 4 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group F. Templin 3 Internet-Draft Boeing Research & Technology 4 Intended status: Informational April 18, 2013 5 Expires: October 20, 2013 7 Operational Guidance for IPv6 Deployment in IPv4 Sites using ISATAP 8 draft-templin-v6ops-isops-19.txt 10 Abstract 12 Many end user sites in the Internet today still have predominantly 13 IPv4 internal infrastructures. These sites range in size from small 14 home/office networks to large corporate enterprise networks, but 15 share the commonality that IPv4 provides satisfactory internal 16 routing and addressing services for most applications. As more and 17 more IPv6-only services are deployed, however, end user devices 18 within such sites will increasingly require at least basic IPv6 19 functionality. This document therefore provides operational guidance 20 for deployment of IPv6 within predominantly IPv4 sites using the 21 Intra-Site Automatic Tunnel Addressing Protocol (ISATAP). 23 Status of this Memo 25 This Internet-Draft is submitted in full conformance with the 26 provisions of BCP 78 and BCP 79. 28 Internet-Drafts are working documents of the Internet Engineering 29 Task Force (IETF). Note that other groups may also distribute 30 working documents as Internet-Drafts. The list of current Internet- 31 Drafts is at http://datatracker.ietf.org/drafts/current/. 33 Internet-Drafts are draft documents valid for a maximum of six months 34 and may be updated, replaced, or obsoleted by other documents at any 35 time. It is inappropriate to use Internet-Drafts as reference 36 material or to cite them other than as "work in progress." 38 This Internet-Draft will expire on October 20, 2013. 40 Copyright Notice 42 Copyright (c) 2013 IETF Trust and the persons identified as the 43 document authors. All rights reserved. 45 This document is subject to BCP 78 and the IETF Trust's Legal 46 Provisions Relating to IETF Documents 47 (http://trustee.ietf.org/license-info) in effect on the date of 48 publication of this document. Please review these documents 49 carefully, as they describe your rights and restrictions with respect 50 to this document. Code Components extracted from this document must 51 include Simplified BSD License text as described in Section 4.e of 52 the Trust Legal Provisions and are provided without warranty as 53 described in the Simplified BSD License. 55 Table of Contents 57 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 58 2. Enabling IPv6 Services using ISATAP . . . . . . . . . . . . . 4 59 3. SLAAC Services . . . . . . . . . . . . . . . . . . . . . . . . 5 60 3.1. Advertising ISATAP Router Behavior . . . . . . . . . . . . 5 61 3.2. ISATAP Host Behavior . . . . . . . . . . . . . . . . . . . 6 62 3.3. Reference Operational Scenario - Shared Prefix Model . . . 6 63 3.4. Reference Operational Scenario - Individual Prefix 64 Model . . . . . . . . . . . . . . . . . . . . . . . . . . 9 65 3.5. SLAAC Site Administration Guidance . . . . . . . . . . . . 12 66 3.6. Loop Avoidance . . . . . . . . . . . . . . . . . . . . . . 14 67 3.7. Interface Identifier Compatibility Considerations . . . . 14 68 4. Manual Configuration . . . . . . . . . . . . . . . . . . . . . 15 69 5. Scaling Considerations . . . . . . . . . . . . . . . . . . . . 15 70 6. Site Renumbering Considerations . . . . . . . . . . . . . . . 16 71 7. Path MTU Considerations . . . . . . . . . . . . . . . . . . . 16 72 8. Alternative Approaches . . . . . . . . . . . . . . . . . . . . 17 73 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 74 10. Security Considerations . . . . . . . . . . . . . . . . . . . 17 75 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18 76 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18 77 12.1. Normative References . . . . . . . . . . . . . . . . . . . 18 78 12.2. Informative References . . . . . . . . . . . . . . . . . . 18 79 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 20 81 1. Introduction 83 End user sites in the Internet today currently use IPv4 routing and 84 addressing internally for core operating functions such as web 85 browsing, filesharing, network printing, e-mail, teleconferencing and 86 numerous other site-internal networking services. Such sites 87 typically have an abundance of public or private IPv4 addresses for 88 internal networking, and are separated from the public Internet by 89 firewalls, packet filtering gateways, proxies, address translators 90 and other site border demarcation devices. To date, such sites have 91 had little incentive to enable IPv6 services internally [RFC1687]. 93 End-user sites that currently use IPv4 services internally come in 94 endless sizes and varieties. For example, a home network behind a 95 Network Address Translator (NAT) may consist of a single link 96 supporting a few laptops, printers etc. As a larger example, a small 97 business may consist of one or a few offices with several networks 98 connecting considerably larger numbers of computers, routers, 99 handheld devices, printers, faxes, etc. Moving further up the scale, 100 large financial institutions, major retailers, large corporations, 101 etc. may consist of hundreds or thousands of branches worldwide that 102 are tied together in a complex global enterprise network. Additional 103 examples include personal-area networks, mobile vehicular networks, 104 disaster relief networks, tactical military networks, various forms 105 of Mobile Ad-hoc Networks (MANETs), etc. 107 With the proliferation of IPv6 services, however, existing IPv4 sites 108 will increasingly require a means for enabling IPv6 services so that 109 hosts within the site can communicate with IPv6-only correspondents. 110 Such services must be deployable with minimal configuration, and in a 111 fashion that will not cause disruptions to existing IPv4 services. 112 The Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) 113 [RFC5214] provides a simple-to-use service that sites can deploy in 114 the near term to meet these requirements. 116 ISATAP has also often been mentioned with respect to IPv6 deployment 117 in enterprise networks [RFC4057][RFC4852] 118 [I-D.ietf-v6ops-enterprise-incremental-ipv6]. ISATAP can therefore 119 be considered as an IPv6 solution alternative based on candidate 120 enterprise network characteristics. 122 This document provides operational guidance for using ISATAP to 123 enable IPv6 services within predominantly IPv4 sites while causing no 124 disruptions to existing IPv4 services. The terminology of ISATAP 125 (see: [RFC5214], Section 3) applies also to this document. 127 2. Enabling IPv6 Services using ISATAP 129 Existing sites within the Internet will soon need to enable IPv6 130 services. Larger sites typically obtain provider independent IPv6 131 prefixes from an Internet registry and advertise the prefixes into 132 the IPv6 routing system on their own behalf, i.e., they act as an 133 Internet Service Provider (ISP) unto themselves. Smaller sites that 134 wish to enable IPv6 can arrange to obtain public IPv6 prefixes from 135 an ISP, where the prefixes may be either purely native or the near- 136 native prefixes offered by 6rd [RFC5969]. Alternatively, the site 137 can obtain prefixes independently of an ISP e.g., via a tunnel broker 138 [RFC3053], by using one of its public IPv4 addresses to form a 6to4 139 prefix [RFC3056], etc. In any case, after obtaining IPv6 prefixes 140 the site can automatically enable IPv6 services internally by 141 configuring ISATAP. 143 The ISATAP service uses a Non-Broadcast, Multiple Access (NBMA) 144 tunnel virtual interface model [RFC2491][RFC2529] based on IPv6-in- 145 IPv4 encapsulation [RFC4213]. The encapsulation format can further 146 use Differentiated Service (DS) [RFC2983] and Explicit Congestion 147 Notification (ECN) [RFC3168] mapping between the inner and outer IP 148 headers to ensure expected per-hop behavior within well-managed 149 sites. 151 The ISATAP service is based on two node types known as advertising 152 ISATAP routers and ISATAP hosts. (While out of scope for thie 153 document, a third node type known as non-advertising ISATAP routers 154 is defined in [I-D.templin-isupdate].) Each node may further have 155 multiple ISATAP interfaces (i.e., one interface for each site), and 156 may act as an advertising ISATAP router on some of those interfaces 157 and a simple ISATAP host on others. Hence, the node type is 158 considered on a per-interface basis. 160 Advertising ISATAP routers configure their ISATAP interfaces as 161 advertising router interfaces (see: [RFC4861], Section 6.2.2). 162 ISATAP hosts configure their ISATAP interfaces as simple host 163 interfaces and also coordinate their autoconfiguration operations 164 with advertising ISATAP routers. In this sense, advertising ISATAP 165 routers are "servers" while ISATAP hosts are "clients" in the service 166 model. 168 Advertising ISATAP routers arrange to add their IPv4 address to the 169 site's Potential Router List (PRL) so that ISATAP clients can 170 discover them, as discussed in Sections 8.3.2 and 9 of [RFC5214]. 171 Alternatively, site administrators could include IPv4 anycast 172 addresses in the PRL and assign each such address to multiple 173 advertising ISATAP routers. In that case, IPv4 routing within the 174 site would direct the ISATAP client to the nearest advertising ISATAP 175 router. 177 After the PRL is published, ISATAP clients within the site can 178 automatically perform unicast IPv6 Neighbor Discovery Router 179 Solicitation (RS) / Router Advertisement (RA) exchanges with 180 advertising ISATAP routers using IPv6-in-IPv4 encapsulation 181 [RFC4861][RFC5214]. In the exchange, the IPv4 source address of the 182 RS and the destination address of the RA are an IPv4 address of the 183 client, while the IPv4 destination address of the RS and the source 184 address of the RA are an IPv4 address of the server found in the PRL. 185 Similarly, the IPv6 source address of the RS is a link-local ISATAP 186 address that embeds the client's IPv4 address, while the source 187 address of the RA is a link-local ISATAP address that embeds the 188 server's IPv4 address. (The destination addresses of the RS and RA 189 may be either the neighbor's link-local ISATAP address or a link- 190 scoped multicast address depending on the implementation.) 192 Following router discovery, ISATAP clients can configure and assign 193 IPv6 addresses and/or prefixes using Stateless Address 194 AutoConfiguration (SLAAC) [RFC4862][RFC5214]. While out of scope for 195 this document, use of the Dynamic Host Configuration Protocol for 196 IPv6 (DHCPv6) [RFC3315] is also possible pending future updates (see: 197 [I-D.templin-isupdate]). 199 3. SLAAC Services 201 Predominantly IPv4 sites can enable SLAAC services for ISATAP clients 202 that need to communicate with IPv6 correspondents. SLAAC services 203 are enabled using either the "shared" or "individual" prefix model. 204 In the shared prefix model, all advertising ISATAP routers advertise 205 a common prefix (e.g., 2001:db8::/64) to ISATAP clients within the 206 site. In the individual prefix model, advertising ISATAP router 207 advertise individual prefixes (e.g., 2001:db8:0:1::/64, 2001:db8:0: 208 2::/64, 2001:db8:0:3::/64, etc.) to ISATAP clients within the site. 209 Note that combinations of the shared and individual prefix models are 210 also possible, in which some of the site's ISATAP routers advertise 211 shared prefixes and others advertise individual prefixes. 213 The following sections discuss operational considerations for 214 enabling ISATAP SLAAC services within predominantly IPv4 sites. 216 3.1. Advertising ISATAP Router Behavior 218 Advertising ISATAP routers that support SLAAC services send RA 219 messages in response to RS messages received on an advertising ISATAP 220 interface. SLAAC services are enabled when advertising ISATAP 221 routers advertise non-link-local IPv6 prefixes in Prefix Information 222 Options (PIOs) with the A flag set to 1[RFC4861]. When there are 223 multiple advertising ISATAP routers, the routers can advertise a 224 shared IPv6 prefix or individual IPv6 prefixes. 226 3.2. ISATAP Host Behavior 228 ISATAP hosts resolve the PRL and send RS messages to obtain RA 229 messages from an advertising ISATAP router. When the host receives 230 RA messages, it uses SLAAC to configure IPv6 addresses from any 231 advertised prefixes with the A flag set to 1 as specified in 232 [RFC4862][RFC5214] then assigns the addresses to the ISATAP 233 interface. The host also assigns any of the advertised prefixes with 234 the L flag set to 1 to the ISATAP interface. (Note that the IPv6 235 link-local prefix fe80::/64 is always considered on-link on an ISATAP 236 interface.) 238 3.3. Reference Operational Scenario - Shared Prefix Model 240 Figure 1 depicts an example ISATAP network topology for allowing 241 hosts within a predominantly IPv4 site to configure ISATAP services 242 using SLAAC with the shared prefix model. The example shows two 243 advertising ISATAP routers ('A', 'B'), two ISATAP hosts ('C', 'D'), 244 and an ordinary IPv6 host ('E') outside of the site in a typical 245 deployment configuration. In this model, routers 'A' and 'B' both 246 advertise the same (shared) IPv6 prefix 2001:db8::/64 into the IPv6 247 routing system, and also advertise the prefix in the RA messages they 248 send to ISATAP clients. 250 .-(::::::::) 2001:db8:1::1 251 .-(::: IPv6 :::)-. +-------------+ 252 (:::: Internet ::::) | IPv6 Host E | 253 `-(::::::::::::)-' +-------------+ 254 `-(::::::)-' 255 ,~~~~~~~~~~~~~~~~~, 256 ,----|companion gateway|--. 257 / '~~~~~~~~~~~~~~~~~' : 258 / |. 259 ,-' `. 260 ; +------------+ +------------+ ) 261 : | Router A | | Router B | / 262 : | (isatap) | | (isatap) | : 263 : | 192.0.2.1 | | 192.0.2.1 | ; 264 + +------------+ +------------+ \ 265 fe80::*:192.0.2.1 fe80::*:192.0.2.1 266 | 2001:db8::/64 2001:db8::/64 | 267 | ; 268 : IPv4 Site -+-' 269 `-. (PRL: 192.0.2.1) .) 270 \ _) 271 `-----+--------)----+'----' 272 fe80::*:192.0.2.18 fe80::*:192.0.2.34 273 2001:db8::*:192.0.2.18 2001:db8::*:192.0.2.34 274 +--------------+ +--------------+ 275 | (isatap) | | (isatap) | 276 | Host C | | Host D | 277 +--------------+ +--------------+ 279 (* == "0000:5efe", i.e., the organizational unique code for ISATAP, 280 per Section 6.1 of [RFC5214]) 282 Figure 1: Example ISATAP Network Topology using Shared Prefix Model 284 With reference to Figure 1, advertising ISATAP routers 'A' and 'B' 285 within the IPv4 site connect to the IPv6 Internet either directly or 286 via a companion gateway. The routers advertise the shared prefix 287 2001:db8::/64 into the IPv6 Internet routing system either as a 288 singleton /64 or as part of a shorter aggregated IPv6 prefix. For 289 the purpose of this example, we also assume that the IPv4 site is 290 configured within multiple IPv4 subnets - each with an IPv4 prefix 291 length of /28. 293 Advertising ISATAP routers 'A' and 'B' both configure the IPv4 294 anycast address 192.0.2.1 on a site-interior IPv4 interface, then 295 configure an advertising ISATAP router interface for the site with 296 link-local ISATAP address fe80::5efe:192.0.2.1. The site 297 administrator then places the single IPv4 address 192.0.2.1 in the 298 site's PRL. 'A' and 'B' then both advertise the anycast address/ 299 prefix into the site's IPv4 routing system so that ISATAP clients can 300 locate the router that is topologically closest. (Note: advertising 301 ISATAP routers can also use individual IPv4 unicast addresses instead 302 of, or in addition to, a shared IPv4 anycast address. In that case, 303 the PRL will contain multiple IPv4 addresses of advertising routers - 304 some of which may be anycast and others unicast.) 306 ISATAP host 'C' connects to the site via an IPv4 interface with 307 address 192.0.2.18/28, and also configures an ISATAP host interface 308 with link-local ISATAP address fe80::5efe:192.0.2.18 over the IPv4 309 interface. 'C' next resolves the PRL, and sends an RS message to the 310 IPv4 address 192.0.2.1, where IPv4 routing will direct it to the 311 closest of either 'A' or 'B'. Assuming 'A' is closest, 'C' receives 312 an RA from 'A' then configures a default IPv6 route with next-hop 313 address fe80::5efe:192.0.2.1 via the ISATAP interface and processes 314 the IPv6 prefix 2001:db8::/64 advertised in the PIO. If the A flag 315 is set in the PIO, 'C' uses SLAAC to automatically configure the IPv6 316 address 2001:db8::5efe:192.0.2.18 (i.e., an address with an ISATAP 317 interface identifier) and assigns it to the ISATAP interface. If the 318 L flag is set, 'C' also assigns the prefix 2001:db8::/64 to the 319 ISATAP interface, and the IPv6 address becomes a true ISATAP address. 321 In the same fashion, ISATAP host 'D' configures its IPv4 interface 322 with address 192.0.2.34/28 and configures its ISATAP interface with 323 link-local ISATAP address fe80::5efe:192.0.2.34. 'D' next performs 324 an RS/RA exchange that is serviced by 'B', then uses SLAAC to 325 autoconfigure the address 2001:db8::5efe:192.0.2.34 and a default 326 IPv6 route with next-hop address fe80::5efe:192.0.2.1. Finally, IPv6 327 host 'E' connects to an IPv6 network outside of the site. 'E' 328 configures its IPv6 interface in a manner specific to its attached 329 IPv6 link, and autoconfigures the IPv6 address 2001:db8:1::1. 331 Following this autoconfiguration, when host 'C' inside the site has 332 an IPv6 packet to send to host 'E' outside the site, it prepares the 333 packet with source address 2001:db8::5efe:192.0.2.18 and destination 334 address 2001:db8:1::1. 'C' then uses IPv6-in-IPv4 encapsulation to 335 forward the packet to the IPv4 address 192.0.2.1 which will be 336 directed to 'A' based on IPv4 routing. 'A' in turn decapsulates the 337 packet and forwards it into the public IPv6 Internet where it will be 338 conveyed to 'E' via normal IPv6 routing. In the same fashion, host 339 'D' uses IPv6-in-IPv4 encapsulation via its default router 'B' to 340 send IPv6 packets to IPv6 Internet hosts such as 'E'. 342 When host 'E' outside the site sends IPv6 packets to ISATAP host 'C' 343 inside the site, the IPv6 routing system may direct the packet to 344 either of 'A' or 'B'. If the site is not partitioned internally, the 345 router that receives the packet can use ISATAP to statelessly forward 346 the packet directly to 'C'. If the site may be partitioned 347 internally, however, the packet must first be forwarded to 'C's 348 serving router based on IPv6 routing information. This implies that, 349 in a partitioned site, the advertising ISATAP routers must connect 350 within a full or partial mesh of IPv6 links, and must either run a 351 dynamic IPv6 routing protocol or configure static routes so that 352 incoming IPv6 packets can be forwarded to the correct serving router. 354 In this example, 'A' can configure the IPv6 route 2001:db8::5efe: 355 192.0.2.32/124 with the IPv6 address of the next hop toward 'B' in 356 the mesh network as the next hop, and 'B' can configure the IPv6 357 route 2001:db8::5efe:192.0.2.16/124 with the IPv6 address of the next 358 hop toward 'A' as the next hop. (Notice that the /124 prefixes 359 properly cover the /28 prefix of the IPv4 address that is embedded 360 within the IPv6 address.) In that case, when 'A' receives a packet 361 from the IPv6 Internet with destination address 2001:db8::5efe: 362 192.0.2.34, it first forwards the packet toward 'B' over an IPv6 mesh 363 link. 'B' in turn uses ISATAP to forward the packet into the site, 364 where IPv4 routing will direct it to 'D'. In the same fashion, when 365 'B' receives a packet from the IPv6 Internet with destination address 366 2001:db8::5efe:192.0.2.18, it first forwards the packet toward 'A' 367 over an IPv6 mesh link. 'A' then uses ISATAP to forward the packet 368 into the site, where IPv4 routing will direct it to 'C'. 370 Finally, when host 'C' inside the site connects to host 'D' inside 371 the site, it has the option of using the native IPv4 service or the 372 ISATAP IPv6-in-IPv4 encapsulation service. When there is operational 373 assurance that IPv4 services between the two hosts are available, the 374 hosts may be better served to continue to use legacy IPv4 services in 375 order to avoid encapsulation overhead and to avoid any IPv4 376 protocol-41 filtering middleboxes that may be in the path. If 'C' 377 and 'D' may be in different IPv4 network partitions, however, IPv6- 378 in-IPv4 encapsulation should be used with one or both of routers 'A' 379 and 'B' serving as intermediate gateways. 381 3.4. Reference Operational Scenario - Individual Prefix Model 383 Figure 2 depicts an example ISATAP network topology for allowing 384 hosts within a predominantly IPv4 site to configure ISATAP services 385 using SLAAC with the individual prefix model. The example shows two 386 advertising ISATAP routers ('A', 'B'), two ISATAP hosts ('C', 'D'), 387 and an ordinary IPv6 host ('E') outside of the site in a typical 388 deployment configuration. In the figure, ISATAP routers 'A' and 'B' 389 both advertise different prefixes taken from the aggregated prefix 390 2001:db8::/48, with 'A' advertising 2001:db8:0:1::/64 and 'B' 391 advertising 2001:db8:0:2::/64. 393 .-(::::::::) 2001:db8:1::1 394 .-(::: IPv6 :::)-. +-------------+ 395 (:::: Internet ::::) | IPv6 Host E | 396 `-(::::::::::::)-' +-------------+ 397 `-(::::::)-' 398 ,~~~~~~~~~~~~~~~~~, 399 ,----|companion gateway|--. 400 / '~~~~~~~~~~~~~~~~~' : 401 / |. 402 ,-' `. 403 ; +------------+ +------------+ ) 404 : | Router A | | Router B | / 405 : | (isatap) | | (isatap) | : 406 : | 192.0.2.1 | | 192.0.2.1 | ; 407 + +------------+ +------------+ \ 408 fe80::*:192.0.2.17 fe80::*:192.0.2.33 409 2001:db8:0:1::/64 2001:db8:0:2::/64 410 | ; 411 : IPv4 Site -+-' 412 `-. (PRL: 192.0.2.1) .) 413 \ _) 414 `-----+--------)----+'----' 415 fe80::*:192.0.2.18 fe80::*:192.0.2.34 416 2001:db8:0:1::*:192.0.2.18 2001:db8:0:2::*:192.0.2.34 417 +--------------+ +--------------+ 418 | (isatap) | | (isatap) | 419 | Host C | | Host D | 420 +--------------+ +--------------+ 422 (* == "0000:5efe") 424 Figure 2: Example ISATAP Network Topology using Individual Prefix 425 Model 427 With reference to Figure 2, advertising ISATAP routers 'A' and 'B' 428 within the IPv4 site connect to the IPv6 Internet either directly or 429 via a companion gateway. Router 'A' advertises the individual prefix 430 2001:db8:0:1::/64 into the IPv6 Internet routing system, and router 431 'B' advertises the individual prefix 2001:db8:0:2::/64. The routers 432 could instead both advertise a shorter shared prefix such as 2001: 433 db8::/48 into the IPv6 routing system, but in that case they would 434 need to configure a mesh of IPv6 links between themselves in the same 435 fashion as described for the shared prefix model in Section 3.4. For 436 the purpose of this example, we also assume that the IPv4 site is 437 configured within multiple IPv4 subnets - each with an IPv4 prefix 438 length of /28. 440 Advertising ISATAP routers 'A' and 'B' both configure individual IPv4 441 unicast addresses 192.0.2.17/28 and 192.0.2.33/28 (respectively) 442 instead of, or in addition to, a shared IPv4 anycast address. Router 443 'A' then configures an advertising ISATAP router interface for the 444 site with link-local ISATAP address fe80::5efe:192.0.2.17, while 445 router 'B' configures an advertising ISATAP router interface for the 446 site with link-local ISATAP address fe80::5efe:192.0.2.33. The site 447 administrator then places the IPv4 addresses 192.0.2.17 and 448 192.0.2.33 in the site's PRL. 'A' and 'B' then both advertise their 449 IPv4 addresses into the site's IPv4 routing system. 451 ISATAP host 'C' connects to the site via an IPv4 interface with 452 address 192.0.2.18/28, and also configures an ISATAP host interface 453 with link-local ISATAP address fe80::5efe:192.0.2.18 over the IPv4 454 interface. 'C' next resolves the PRL, and sends an RS message to the 455 IPv4 address 192.0.2.17, where IPv4 routing will direct it to 'A'. 456 'C' then receives an RA from 'A' then configures a default IPv6 route 457 with next-hop address fe80::5efe:192.0.2.17 via the ISATAP interface 458 and processes the IPv6 prefix 2001:db8:0:1:/64 advertised in the PIO. 459 If the A flag is set in the PIO, 'C' uses SLAAC to automatically 460 configure the IPv6 address 2001:db8:0:1::5efe:192.0.2.18 (i.e., an 461 address with an ISATAP interface identifier) and assigns it to the 462 ISATAP interface. If the L flag is set, 'C' also assigns the prefix 463 2001:db8:0:1::/64 to the ISATAP interface, and the IPv6 address 464 becomes a true ISATAP address. 466 In the same fashion, ISATAP host 'D' configures its IPv4 interface 467 with address 192.0.2.34/28 and configures its ISATAP interface with 468 link-local ISATAP address fe80::5efe:192.0.2.34. 'D' next performs 469 an RS/RA exchange that is serviced by 'B', then uses SLAAC to 470 autoconfigure the address 2001:db8:0:2::5efe:192.0.2.34 and a default 471 IPv6 route with next-hop address fe80::5efe:192.0.2.33. Finally, 472 IPv6 host 'E' connects to an IPv6 network outside of the site. 'E' 473 configures its IPv6 interface in a manner specific to its attached 474 IPv6 link, and autoconfigures the IPv6 address 2001:db8:1::1. 476 Following this autoconfiguration, when host 'C' inside the site has 477 an IPv6 packet to send to host 'E' outside the site, it prepares the 478 packet with source address 2001:db8::5efe:192.0.2.18 and destination 479 address 2001:db8:1::1. 'C' then uses IPv6-in-IPv4 encapsulation to 480 forward the packet to the IPv4 address 192.0.2.17 which will be 481 directed to 'A' based on IPv4 routing. 'A' in turn decapsulates the 482 packet and forwards it into the public IPv6 Internet where it will be 483 conveyed to 'E' via normal IPv6 routing. In the same fashion, host 484 'D' uses IPv6-in-IPv4 encapsulation via its default router 'B' to 485 send IPv6 packets to IPv6 Internet hosts such as 'E'. 487 When host 'E' outside the site sends IPv6 packets to ISATAP host 'C' 488 inside the site, the IPv6 routing system will direct the packet to 489 'A' since 'A' advertises the individual prefix that matches 'C's 490 destination address. 'A' can then use ISATAP to statelessly forward 491 the packet directly to 'C'. If 'A' and 'B' both advertise the shared 492 shorter prefix 2001:db8::/48 into the IPv6 routing system, however 493 packets coming from 'E' may be directed to either 'A' or 'B'. In 494 that case, the advertising ISATAP routers must connect within a full 495 or partial mesh of IPv6 links the same as for the shared prefix 496 model, and must either run a dynamic IPv6 routing protocol or 497 configure static routes so that incoming IPv6 packets can be 498 forwarded to the correct serving router. 500 In this example, 'A' can configure the IPv6 route 2001:db8:0:2::/64 501 with the IPv6 address of the next hop toward 'B' in the mesh network 502 as the next hop, and 'B' can configure the IPv6 route 2001:db8: 503 0.1::/64 with the IPv6 address of the next hop toward 'A' as the next 504 hop. Then, when 'A' receives a packet from the IPv6 Internet with 505 destination address 2001:db8:0:2::5efe:192.0.2.34, it first forwards 506 the packet toward 'B' over an IPv6 mesh link. 'B' in turn uses 507 ISATAP to forward the packet into the site, where IPv4 routing will 508 direct it to 'D'. In the same fashion, when 'B' receives a packet 509 from the IPv6 Internet with destination address 2001:db8:0:1::5efe: 510 192.0.2.18, it first forwards the packet toward 'A' over an IPv6 mesh 511 link. 'A' then uses ISATAP to forward the packet into the site, 512 where IPv4 routing will direct it to 'C'. 514 Finally, when host 'C' inside the site connects to host 'D' inside 515 the site, it has the option of using the native IPv4 service or the 516 ISATAP IPv6-in-IPv4 encapsulation service. When there is operational 517 assurance that IPv4 services between the two hosts are available, the 518 hosts may be better served to continue to use legacy IPv4 services in 519 order to avoid encapsulation overhead and to avoid any IPv4 520 protocol-41 filtering middleboxes that may be in the path. If 'C' 521 and 'D' may be in different IPv4 network partitions, however, IPv6- 522 in-IPv4 encapsulation should be used with one or both of routers 'A' 523 and 'B' serving as intermediate gateways. 525 3.5. SLAAC Site Administration Guidance 527 In common practice, firewalls, gateways and packet filtering devices 528 of various forms are often deployed in order to divide the site into 529 separate partitions. In both the shared and individual prefix models 530 described above, the entire site can be represented by the aggregate 531 IPv6 prefix assigned to the site, while each site partition can be 532 represented by "sliver" IPv6 prefixes taken from the aggregate. In 533 order to provide a simple service that does not interact poorly with 534 the site topology, site administrators should therefore institute an 535 address plan to align IPv6 sliver prefixes with IPv4 site partition 536 boundaries. 538 For example, in the shared prefix model in Section 3.3, the aggregate 539 prefix is 2001:db8::/64, and the sliver prefixes are 2001:db8::5efe: 540 192.0.2.0/124, 2001:db8::5efe:192.0.2.16/124, 2001:db8::5efe: 541 192.0.2.32/124, etc. In the individual prefix model in Section 3.4, 542 the aggregate prefix is 2001:db8::/48 and the sliver prefixes are 543 2001:db8:0:0::/64, 2001:db8:0:1::/64, 2001:db8:0:2::/64, etc. 545 When individual prefixes are used, site administrators can configure 546 advertising ISATAP routers to advertise different individual prefixes 547 to different sets of clients, e.g., based on the client's IPv4 subnet 548 prefix such that the IPv6 prefixes are congruent with the IPv4 549 addressing plan. (For example, administrators can configure each 550 advertising ISATAP router to provide services only to certain sets of 551 ISATAP clients through inbound IPv6 Access Control List (ACL) entries 552 that match the IPv4 subnet prefix embedded in the ISATAP interface 553 identifier of the IPv6 source address). When a shared prefix is 554 used, site administrators instead configure the ISATAP routers to 555 advertise the shared prefix to all clients. 557 Advertising ISATAP routers can advertise prefixes with the (A, L) 558 flags set to (1,0) so that ISATAP clients will use SLAAC to 559 autoconfigure IPv6 addresses with ISATAP interface identifiers from 560 the prefixes and assign them to the receiving ISATAP interface, but 561 they will not assign the prefix itself to the ISATAP interface. In 562 that case, the advertising router must assign the sliver prefix for 563 the site partition to the advertising ISATAP interface. In this way, 564 the advertising router considers the addresses covered by the sliver 565 prefix as true ISATAP addresses, but the ISATAP clients themselves do 566 not. This configuration enables a hub-and-spokes architecture which 567 in some cases may be augmented by route optimization based on the 568 receipt of ICMPv6 Redirects. 570 Site administrators can implement address selection policy rules 571 [RFC3484] through explicit configurations in each ISATAP client. 572 Site administrators implement this policy by configuring address 573 selection policy rules in each ISATAP client in order to give 574 preference to IPv4 destination addresses over destination addresses 575 derived from one of the client's IPv6 sliver prefixes. 577 For example, site administrators can configure each ISATAP client 578 associated with a sliver prefix such as 2001:db8::5efe:192.0.2.64/124 579 to add the prefix to its address selection policy table with a lower 580 precedence than the prefix ::ffff:0:0/96. In this way, IPv4 581 addresses are preferred over IPv6 addresses from within the same 582 sliver. The prefix could be added to each ISATAP client either 583 manually, or through an automated service such as a DHCP option 584 [I-D.ietf-6man-addr-select-opt] discovered by the client, e.g., using 585 Stateless DHCPv6 [RFC3736]. In this way, clients will use IPv4 586 communications to reach correspondents within the same IPv4 site 587 partition, and will use IPv6 communications to reach correspondents 588 in other partitions and/or outside of the site. 590 It should be noted that sliver prefixes longer than /64 cannot be 591 advertised for SLAAC purposes. Also, sliver prefixes longer than /64 592 do not allow for interface identifier rewriting by address 593 translators. These factors may favor the individual prefix model in 594 some deployment scenarios, while the flexibility afforded by the 595 shared prefix model may be more desirable in others. Additionally, 596 if the network is small then the shared prefix model works well. If 597 the network is large, however, a better alternative may be to deploy 598 separate ISATAP routers in each partition and have each advertise 599 their own individual prefix. 601 Finally, site administrators should configure ISATAP routers to not 602 send ICMPv6 Redirect messages to inform a source client of a better 603 next hop toward the destination unless there is strong assurance that 604 the client and the next hop are within the same IPv4 site partition. 606 3.6. Loop Avoidance 608 In sites that provide IPv6 services through ISATAP with SLAAC as 609 described in this section, site administrators must take operational 610 precautions to avoid routing loops. For example, each advertising 611 ISATAP router should drop any incoming IPv6 packets that would be 612 forwarded back to itself via another of the site's advertising 613 routers. Additionally, each advertising ISATAP router should drop 614 any encapsulated packets received from another advertising router 615 that would be forwarded back to that same advertising router. This 616 corresponds to the mitigation documented in Section 3.2.3 of 617 [RFC6324], but other mitigations specified in that document can also 618 be employed. 620 Note that IPv6 packets with link-local ISATAP addresses are exempt 621 from these checks, since they cannot be forwarded by an IPv6 router 622 and may be necessary for router-to-router coordinations. 624 3.7. Interface Identifier Compatibility Considerations 626 [RFC5214] Section 6.1 specifies the setting of the "u" bit in the 627 Modified EUI-64 interface identifier format used by ISATAP. 628 Implementations that comply with the specification set the "u" bit to 629 1 when the IPv4 address is known to be globally unique, however some 630 legacy implementations unconditionally set the "u" bit to 0. 632 Implementations interpret the ISATAP interface identifier only within 633 the link to which the corresponding ISATAP prefix is assigned, hence 634 the value of the "u" bit is interpreted only within the context of an 635 on-link prefix and not within a global context. Implementers are 636 responsible for ensuring that their products are interoperable, 637 therefore implementations must make provisions for ensuring "u" bit 638 compatibility for intra-link communications. 640 Site administrators should accordingly configure access control list 641 entries and other literal representations of ISATAP interface 642 identifiers such that both values of the "u" bit are accepted. For 643 example, if the site administrator configures an access control list 644 entry that matches the prefix "fe80::0000:5efe:192.0.2.0/124" they 645 should also configure a companion list entry that matches the prefix 646 "fe80::0200:5efe:192.0.2.0/124. 648 4. Manual Configuration 650 When no autoconfiguration services are available (e.g., if there are 651 no advertising ISATAP routers present), site administrators can use 652 manual configuration to assign IPv6 addresses with ISATAP interface 653 identifiers to the ISATAP interfaces of clients. Otherwise, site 654 administrators should avoid manual configurations that would in any 655 way invalidate the assumptions of the autoconfiguration service. For 656 example, manually configured addresses may not be automatically 657 renumbered during a site-wide renumbering event, which could 658 subsequently result in communication failures. 660 5. Scaling Considerations 662 Section 3 depicts ISATAP network topologies with only two advertising 663 ISATAP routers within the site. In order to support larger numbers 664 of ISATAP clients (and/or multiple site partitions), the site can 665 deploy more advertising ISATAP routers to support load balancing and 666 generally shortest-path routing. 668 Such an arrangement requires that the advertising ISATAP routers 669 participate in an IPv6 routing protocol instance so that IPv6 670 addresses/prefixes can be mapped to the correct ISATAP router. The 671 routing protocol instance can be configured as either a full mesh 672 topology involving all advertising ISATAP routers, or as a partial 673 mesh topology with each advertising ISATAP router associating with 674 one or more companion gateways. Each such companion gateway would in 675 turn participate in a full mesh between all companion gateways. 677 6. Site Renumbering Considerations 679 Advertising ISATAP routers distribute IPv6 prefixes to ISATAP clients 680 within the site. If the site subsequently reconnects to a different 681 ISP, however, the site must renumber to use addresses derived from 682 the new IPv6 prefixes [RFC6879]. 684 For IPv6 services provided by SLAAC, site renumbering in the event of 685 a change in an ISP-served IPv6 prefix entails a simple renumbering of 686 IPv6 addresses and/or prefixes that are assigned to the ISATAP 687 interfaces of clients within the site. In some cases, filtering 688 rules (e.g., within site border firewall filtering tables) may also 689 require renumbering, but this operation can be automated and limited 690 to only one or a few administrative "touch points". 692 In order to renumber the ISATAP interfaces of clients within the site 693 using SLAAC, advertising ISATAP routers need only schedule the 694 services offered by the old ISP for deprecation and begin to 695 advertise the IPv6 prefixes provided by the new ISP. ISATAP client 696 interface address lifetimes will eventually expire, and the host will 697 renumber its interfaces with addresses derived from the new prefixes. 698 ISATAP clients should also eventually remove any deprecated SLAAC 699 prefixes from their address selection policy tables, but this action 700 is not time-critical. 702 Finally, site renumbering in the event of a change in an ISP-served 703 IPv6 prefix further entails locating and rewriting all IPv6 addresses 704 in naming services, databases, configuration files, packet filtering 705 rules, documentation, etc. If the site has published the IPv6 706 addresses of any site-internal nodes within the public Internet DNS 707 system, then the corresponding resource records will also need to be 708 updated during the renumbering operation. This can be accomplished 709 via secure dynamic updates to the DNS. 711 7. Path MTU Considerations 713 IPv6-in-IPv4 encapsulation overhead effectively reduces the size of 714 IPv6 packets that can traverse the tunnel in relation to the actual 715 Maximum Transmission Unit (MTU) of the underlying IPv4 network path 716 between the encapsulator and decapsulator. Two methods for 717 accommodating IPv6 path MTU discovery over IPv6-in-IPv4 tunnels 718 (i.e., the static and dynamic methods) are documented in Section 3.2 719 of [RFC4213]. 721 The static method places a "safe" upper bound on the size of IPv6 722 packets permitted to enter the tunnel, however the method can be 723 overly conservative when larger IPv4 path MTUs are available. The 724 dynamic method can accommodate much larger IPv6 packet sizes in some 725 cases, but can fail silently if the underlying IPv4 network path does 726 not return the necessary error messages. 728 This document notes that sites that include well-managed IPv4 links, 729 routers and other network middleboxes are candidates for use of the 730 dynamic MTU determination method, which may provide for a better 731 operational IPv6 experience in the presence of IPv6-in-IPv4 tunnels. 733 Finally, since all ISATAP tunnels terminate at a host, transport 734 protocols that perform packet size negotiations will see an IPv6 MTU 735 that accounts for the encapsulation headers and therefore will avoid 736 sending encapsulated packets that exceed the IPv4 path MTU. 738 8. Alternative Approaches 740 [RFC4554] proposes a use of VLANs for IPv4-IPv6 coexistence in 741 enterprise networks. The ISATAP approach provides a more flexible 742 and broadly-applicable alternative, and with fewer administrative 743 touch points. 745 The tunnel broker service [RFC3053] uses point-to-point tunnels that 746 require end users to establish an explicit administrative 747 configuration of the tunnel far end, which may be outside of the 748 administrative boundaries of the site. 750 6to4 [RFC3056] and Teredo [RFC4380] provide "last resort" unmanaged 751 automatic tunneling services when no other means for IPv6 752 connectivity is available. These services are given lower priority 753 when the ISATAP managed service and/or native IPv6 services are 754 enabled. 756 6rd [RFC5969] enables a stateless prefix delegation capability based 757 on IPv4-embedded IPv6 prefixes, whereas ISATAP enables a stateful 758 prefix delegation capability based on native IPv6 prefixes. 760 9. IANA Considerations 762 This document has no IANA considerations. 764 10. Security Considerations 766 In addition to the security considerations documented in [RFC5214], 767 sites that use ISATAP should take care to ensure that no routing 768 loops are enabled [RFC6324]. Additional security concerns with IP 769 tunneling are documented in [RFC6169]. 771 11. Acknowledgments 773 The following are acknowledged for their insights that helped shape 774 this work: Dmitry Anipko, Fred Baker, Ron Bonica, Brian Carpenter, 775 Remi Despres, Thomas Henderson, Philip Homburg, Lee Howard, Ray 776 Hunter, Joel Jaeggli, John Mann, Gabi Nakibly, Christopher Palmer, 777 Hemant Singh, Mark Smith, Ole Troan, and Gunter Van de Velde. 779 12. References 781 12.1. Normative References 783 [RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and 784 E. Lear, "Address Allocation for Private Internets", 785 BCP 5, RFC 1918, February 1996. 787 [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., 788 and M. Carney, "Dynamic Host Configuration Protocol for 789 IPv6 (DHCPv6)", RFC 3315, July 2003. 791 [RFC3736] Droms, R., "Stateless Dynamic Host Configuration Protocol 792 (DHCP) Service for IPv6", RFC 3736, April 2004. 794 [RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms 795 for IPv6 Hosts and Routers", RFC 4213, October 2005. 797 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 798 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 799 September 2007. 801 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 802 Address Autoconfiguration", RFC 4862, September 2007. 804 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 805 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 806 March 2008. 808 12.2. Informative References 810 [I-D.ietf-6man-addr-select-opt] 811 Matsumoto, A., Fujisaki, T., and T. Chown, "Distributing 812 Address Selection Policy using DHCPv6", 813 draft-ietf-6man-addr-select-opt-08 (work in progress), 814 January 2013. 816 [I-D.ietf-v6ops-enterprise-incremental-ipv6] 817 Chittimaneni, K., Chown, T., Howard, L., Kuarsingh, V., 818 Pouffary, Y., and E. Vyncke, "Enterprise IPv6 Deployment 819 Guidelines", 820 draft-ietf-v6ops-enterprise-incremental-ipv6-02 (work in 821 progress), February 2013. 823 [I-D.templin-isupdate] 824 Templin, F., "ISATAP Updates", draft-templin-isupdate-04 825 (work in progress), May 2012. 827 [RFC1687] Fleischman, E., "A Large Corporate User's View of IPng", 828 RFC 1687, August 1994. 830 [RFC2491] Armitage, G., Schulter, P., Jork, M., and G. Harter, "IPv6 831 over Non-Broadcast Multiple Access (NBMA) networks", 832 RFC 2491, January 1999. 834 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 835 Domains without Explicit Tunnels", RFC 2529, March 1999. 837 [RFC2983] Black, D., "Differentiated Services and Tunnels", 838 RFC 2983, October 2000. 840 [RFC3053] Durand, A., Fasano, P., Guardini, I., and D. Lento, "IPv6 841 Tunnel Broker", RFC 3053, January 2001. 843 [RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains 844 via IPv4 Clouds", RFC 3056, February 2001. 846 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 847 of Explicit Congestion Notification (ECN) to IP", 848 RFC 3168, September 2001. 850 [RFC3484] Draves, R., "Default Address Selection for Internet 851 Protocol version 6 (IPv6)", RFC 3484, February 2003. 853 [RFC4057] Bound, J., "IPv6 Enterprise Network Scenarios", RFC 4057, 854 June 2005. 856 [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through 857 Network Address Translations (NATs)", RFC 4380, 858 February 2006. 860 [RFC4554] Chown, T., "Use of VLANs for IPv4-IPv6 Coexistence in 861 Enterprise Networks", RFC 4554, June 2006. 863 [RFC4852] Bound, J., Pouffary, Y., Klynsma, S., Chown, T., and D. 865 Green, "IPv6 Enterprise Network Analysis - IP Layer 3 866 Focus", RFC 4852, April 2007. 868 [RFC5969] Townsley, W. and O. Troan, "IPv6 Rapid Deployment on IPv4 869 Infrastructures (6rd) -- Protocol Specification", 870 RFC 5969, August 2010. 872 [RFC6169] Krishnan, S., Thaler, D., and J. Hoagland, "Security 873 Concerns with IP Tunneling", RFC 6169, April 2011. 875 [RFC6324] Nakibly, G. and F. Templin, "Routing Loop Attack Using 876 IPv6 Automatic Tunnels: Problem Statement and Proposed 877 Mitigations", RFC 6324, August 2011. 879 [RFC6879] Jiang, S., Liu, B., and B. Carpenter, "IPv6 Enterprise 880 Network Renumbering Scenarios, Considerations, and 881 Methods", RFC 6879, February 2013. 883 Author's Address 885 Fred L. Templin 886 Boeing Research & Technology 887 P.O. Box 3707 MC 7L-49 888 Seattle, WA 98124 889 USA 891 Email: fltemplin@acm.org