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Checking references for intended status: Informational ---------------------------------------------------------------------------- == Unused Reference: 'RFC1918' is defined on line 781, 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reference: RFC 3315 (Obsoleted by RFC 8415) ** Obsolete normative reference: RFC 3736 (Obsoleted by RFC 8415) == Outdated reference: A later version (-13) exists of draft-ietf-6man-addr-select-opt-03 == Outdated reference: A later version (-04) exists of draft-templin-isupdate-03 -- Obsolete informational reference (is this intentional?): RFC 3484 (Obsoleted by RFC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 May 09, 2012 5 Expires: November 10, 2012 7 Operational Guidance for IPv6 Deployment in IPv4 Sites using ISATAP 8 draft-templin-v6ops-isops-17.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 November 10, 2012. 40 Copyright Notice 42 Copyright (c) 2012 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 . . . . . . . . . . . . . 3 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 banks, restaurants, major retailers, large corporations, etc. 101 may consist of hundreds or thousands of branches worldwide that are 102 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. This document therefore 115 provides operational guidance for using ISATAP to enable IPv6 116 services within predominantly IPv4 sites while causing no disruptions 117 to existing IPv4 services. The terminology of ISATAP (see: 118 [RFC5214], Section 3) applies also to this document. 120 2. Enabling IPv6 Services using ISATAP 122 Existing sites within the Internet will soon need to enable IPv6 123 services. Larger sites typically obtain provider independent IPv6 124 prefixes from an Internet registry and advertise the prefixes into 125 the IPv6 routing system on their own behalf, i.e., they act as an 126 Internet Service Provider (ISP) unto themselves. Smaller sites that 127 wish to enable IPv6 can arrange to obtain public IPv6 prefixes from 128 an ISP, where the prefixes may be either purely native or the near- 129 native prefixes offered by 6rd [RFC5969]. Alternatively, the site 130 can obtain prefixes independently of an ISP e.g., via a tunnel broker 131 [RFC3053], by using one of its public IPv4 addresses to form a 6to4 132 prefix [RFC3056], etc. (Note however that experience shows that the 133 6to4 method has some problems in current deployments that can lead to 134 connectivity failures [RFC6343].) In any case, after obtaining IPv6 135 prefixes the site can automatically enable IPv6 services internally 136 by configuring ISATAP. 138 The ISATAP service uses a Non-Broadcast, Multiple Access (NBMA) 139 tunnel virtual interface model [RFC2491][RFC2529] based on IPv6-in- 140 IPv4 encapsulation [RFC4213]. The encapsulation format can further 141 use Differentiated Service (DS) [RFC2983] and Explicit Congestion 142 Notification (ECN) [RFC3168] mapping between the inner and outer IP 143 headers to ensure expected per-hop behavior within well-managed 144 sites. 146 The ISATAP service is based on two node types known as advertising 147 ISATAP routers and ISATAP hosts. (A third node type known as non- 148 advertising ISATAP routers is defined in [I-D.templin-isupdate] but 149 out of scope for this document.) Each node may further have multiple 150 ISATAP interfaces (i.e., one interface for each site), and may act as 151 an advertising ISATAP router on some of those interfaces and a simple 152 ISATAP host on others. Hence, the node type is considered on a per- 153 interface basis. 155 Advertising ISATAP routers configure their ISATAP interfaces as 156 advertising router interfaces (see: [RFC4861], Section 6.2.2). 157 ISATAP hosts configure their ISATAP interfaces as simple host 158 interfaces and also coordinate their autoconfiguration operations 159 with advertising ISATAP routers. In this sense, advertising ISATAP 160 routers are "servers" while ISATAP hosts are "clients" in the service 161 model. 163 Advertising ISATAP routers arrange to add their IPv4 address to the 164 site's Potential Router List (PRL) so that ISATAP clients can 165 discover them, as discussed in Sections 8.3.2 and 9 of [RFC5214]. 166 Alternatively, site administrators could include IPv4 anycast 167 addresses in the PRL and assign each such address to multiple 168 advertising ISATAP routers. In that case, IPv4 routing within the 169 site would direct the ISATAP client to the nearest advertising ISATAP 170 router. 172 After the PRL is published, ISATAP clients within the site can 173 automatically perform unicast IPv6 Neighbor Discovery Router 174 Solicitation (RS) / Router Advertisement (RA) exchanges with 175 advertising ISATAP routers using IPv6-in-IPv4 encapsulation 177 [RFC4861][RFC5214]. In the exchange, the IPv4 source address of the 178 RS and the destination address of the RA are an IPv4 address of the 179 client, while the IPv4 destination address of the RS and the source 180 address of the RA are an IPv4 address of the server found in the PRL. 181 Similarly, the IPv6 source address of the RS is a link-local ISATAP 182 address that embeds the client's IPv4 address, while the source 183 address of the RA is a link-local ISATAP address that embeds the 184 server's IPv4 address. (The destination addresses of the RS and RA 185 may be either the neighbor's link-local ISATAP address or a link- 186 scoped multicast address depending on the implementation.) 188 Following router discovery, ISATAP clients can configure and assign 189 IPv6 addresses and/or prefixes using Stateless Address 190 AutoConfiguration (SLAAC) [RFC4862][RFC5214]. While out of scope for 191 this document, use of the Dynamic Host Configuration Protocol for 192 IPv6 (DHCPv6) [RFC3315] is also possible when necessary updates to 193 the ISATAP base specification are implemented [I-D.templin-isupdate]. 195 3. SLAAC Services 197 Predominantly IPv4 sites can enable SLAAC services for ISATAP clients 198 that need to communicate with IPv6 correspondents. SLAAC services 199 are enabled using either the "shared" or "individual" prefix model. 200 In the shared prefix model, all advertising ISATAP routers advertise 201 a common prefix (e.g., 2001:db8::/64) to ISATAP clients within the 202 site. In the individual prefix model, advertising ISATAP router 203 advertise individual prefixes (e.g., 2001:db8:0:1::/64, 2001:db8:0: 204 2::/64, 2001:db8:0:3::/64, etc.) to ISATAP clients within the site. 205 Note that combinations of the shared and individual prefix models are 206 also possible, in which some of the site's ISATAP routers advertise 207 shared prefixes and others advertise individual prefixes. 209 The following sections discuss operational considerations for 210 enabling ISATAP SLAAC services within predominantly IPv4 sites. 212 3.1. Advertising ISATAP Router Behavior 214 Advertising ISATAP routers that support SLAAC services send RA 215 messages in response to RS messages received on an advertising ISATAP 216 interface. SLAAC services are enabled when advertising ISATAP 217 routers advertise non-link-local IPv6 prefixes in Prefix Information 218 Options (PIOs) with the A flag set to 1[RFC4861]. When there are 219 multiple advertising ISATAP routers, the routers can advertise a 220 shared IPv6 prefix or individual IPv6 prefixes. 222 3.2. ISATAP Host Behavior 224 ISATAP hosts resolve the PRL and send RS messages to obtain RA 225 messages from an advertising ISATAP router. When the host receives 226 RA messages, it uses SLAAC to configure IPv6 addresses from any 227 advertised prefixes with the A flag set to 1 as specified in 228 [RFC4862][RFC5214] then assigns the addresses to the ISATAP 229 interface. The host also assigns any of the advertised prefixes with 230 the L flag set to 1 to the ISATAP interface. (Note that the IPv6 231 link-local prefix fe80::/64 is always considered on-link on an ISATAP 232 interface.) 234 3.3. Reference Operational Scenario - Shared Prefix Model 236 Figure 1 depicts an example ISATAP network topology for allowing 237 hosts within a predominantly IPv4 site to configure ISATAP services 238 using SLAAC with the shared prefix model. The example shows two 239 advertising ISATAP routers ('A', 'B'), two ISATAP hosts ('C', 'D'), 240 and an ordinary IPv6 host ('E') outside of the site in a typical 241 deployment configuration. In this model, routers 'A' and 'B' both 242 advertise the same (shared) IPv6 prefix 2001:db8::/64 into the IPv6 243 routing system, and also advertise the prefix in the RA messages they 244 send to ISATAP clients. 246 .-(::::::::) 2001:db8:1::1 247 .-(::: IPv6 :::)-. +-------------+ 248 (:::: Internet ::::) | IPv6 Host E | 249 `-(::::::::::::)-' +-------------+ 250 `-(::::::)-' 251 ,~~~~~~~~~~~~~~~~~, 252 ,----|companion gateway|--. 253 / '~~~~~~~~~~~~~~~~~' : 254 / |. 255 ,-' `. 256 ; +------------+ +------------+ ) 257 : | Router A | | Router B | / 258 : | (isatap) | | (isatap) | : 259 : | 192.0.2.1 | | 192.0.2.1 | ; 260 + +------------+ +------------+ \ 261 fe80::*:192.0.2.1 fe80::*:192.0.2.1 262 | 2001:db8::/64 2001:db8::/64 | 263 | ; 264 : IPv4 Site -+-' 265 `-. (PRL: 192.0.2.1) .) 266 \ _) 267 `-----+--------)----+'----' 268 fe80::*:192.0.2.18 fe80::*:192.0.2.34 269 2001:db8::*:192.0.2.18 2001:db8::*:192.0.2.34 270 +--------------+ +--------------+ 271 | (isatap) | | (isatap) | 272 | Host C | | Host D | 273 +--------------+ +--------------+ 275 (* == "5efe") 277 Figure 1: Example ISATAP Network Topology using Shared Prefix Model 279 With reference to Figure 1, advertising ISATAP routers 'A' and 'B' 280 within the IPv4 site connect to the IPv6 Internet either directly or 281 via a companion gateway. The routers advertise the shared prefix 282 2001:db8::/64 into the IPv6 Internet routing system either as a 283 singleton /64 or as part of a shorter aggregated IPv6 prefix if the 284 routing system will not accept prefixes as long as a /64. For the 285 purpose of this example, we also assume that the IPv4 site is 286 configured within multiple IPv4 subnets - each with an IPv4 prefix 287 length of /28. 289 Advertising ISATAP routers 'A' and 'B' both configure the IPv4 290 anycast address 192.0.2.1 on a site-interior IPv4 interface, then 291 configure an advertising ISATAP router interface for the site with 292 link-local ISATAP address fe80::5efe:192.0.2.1. The site 293 administrator then places the single IPv4 address 192.0.2.1 in the 294 site's PRL. 'A' and 'B' then both advertise the anycast address/ 295 prefix into the site's IPv4 routing system so that ISATAP clients can 296 locate the router that is topologically closest. (Note: advertising 297 ISATAP routers can also use individual IPv4 unicast addresses instead 298 of, or in addition to, a shared IPv4 anycast address. In that case, 299 the PRL will contain multiple IPv4 addresses of advertising routers - 300 some of which may be anycast and others unicast.) 302 ISATAP host 'C' connects to the site via an IPv4 interface with 303 address 192.0.2.18/28, and also configures an ISATAP host interface 304 with link-local ISATAP address fe80::5efe:192.0.2.18 over the IPv4 305 interface. 'C' next resolves the PRL, and sends an RS message to the 306 IPv4 address 192.0.2.1, where IPv4 routing will direct it to the 307 closest of either 'A' or 'B'. Assuming 'A' is closest, 'C' receives 308 an RA from 'A' then configures a default IPv6 route with next-hop 309 address fe80::5efe:192.0.2.1 via the ISATAP interface and processes 310 the IPv6 prefix 2001:db8::/64 advertised in the PIO. If the A flag 311 is set in the PIO, 'C' uses SLAAC to automatically configure the IPv6 312 address 2001:db8::5efe:192.0.2.18 (i.e., an address with an ISATAP 313 interface identifier) and assigns it to the ISATAP interface. If the 314 L flag is set, 'C' also assigns the prefix 2001:db8::/64 to the 315 ISATAP interface, and the IPv6 address becomes a true ISATAP address. 317 In the same fashion, ISATAP host 'D' configures its IPv4 interface 318 with address 192.0.2.34/28 and configures its ISATAP interface with 319 link-local ISATAP address fe80::5efe:192.0.2.34. 'D' next performs 320 an RS/RA exchange that is serviced by 'B', then uses SLAAC to 321 autoconfigure the address 2001:db8::5efe:192.0.2.34 and a default 322 IPv6 route with next-hop address fe80::5efe:192.0.2.1. Finally, IPv6 323 host 'E' connects to an IPv6 network outside of the site. 'E' 324 configures its IPv6 interface in a manner specific to its attached 325 IPv6 link, and autoconfigures the IPv6 address 2001:db8:1::1. 327 Following this autoconfiguration, when host 'C' inside the site has 328 an IPv6 packet to send to host 'E' outside the site, it prepares the 329 packet with source address 2001:db8::5efe:192.0.2.18 and destination 330 address 2001:db8:1::1. 'C' then uses IPv6-in-IPv4 encapsulation to 331 forward the packet to the IPv4 address 192.0.2.1 which will be 332 directed to 'A' based on IPv4 routing. 'A' in turn decapsulates the 333 packet and forwards it into the public IPv6 Internet where it will be 334 conveyed to 'E' via normal IPv6 routing. In the same fashion, host 335 'D' uses IPv6-in-IPv4 encapsulation via its default router 'B' to 336 send IPv6 packets to IPv6 Internet hosts such as 'E'. 338 When host 'E' outside the site sends IPv6 packets to ISATAP host 'C' 339 inside the site, the IPv6 routing system may direct the packet to 340 either of 'A' or 'B'. If the site is not partitioned internally, the 341 router that receives the packet can use ISATAP to statelessly forward 342 the packet directly to 'C'. If the site may be partitioned 343 internally, however, the packet must first be forwarded to 'C's 344 serving router based on IPv6 routing information. This implies that, 345 in a partitioned site, the advertising ISATAP routers must connect 346 within a full or partial mesh of IPv6 links, and must either run a 347 dynamic IPv6 routing protocol or configure static routes so that 348 incoming IPv6 packets can be forwarded to the correct serving router. 350 In this example, 'A' can configure the IPv6 route 2001:db8::5efe: 351 192.0.2.32/124 with the IPv6 address of the next hop toward 'B' in 352 the mesh network as the next hop, and 'B' can configure the IPv6 353 route 2001:db8::5efe:192.0.2.16/124 with the IPv6 address of the next 354 hop toward 'A' as the next hop. (Notice that the /124 prefixes 355 properly cover the /28 prefix of the IPv4 address that is embedded 356 within the IPv6 address.) In that case, when 'A' receives a packet 357 from the IPv6 Internet with destination address 2001:db8::5efe: 358 192.0.2.34, it first forwards the packet toward 'B' over an IPv6 mesh 359 link. 'B' in turn uses ISATAP to forward the packet into the site, 360 where IPv4 routing will direct it to 'D'. In the same fashion, when 361 'B' receives a packet from the IPv6 Internet with destination address 362 2001:db8::5efe:192.0.2.18, it first forwards the packet toward 'A' 363 over an IPv6 mesh link. 'A' then uses ISATAP to forward the packet 364 into the site, where IPv4 routing will direct it to 'C'. 366 Finally, when host 'C' inside the site connects to host 'D' inside 367 the site, it has the option of using the native IPv4 service or the 368 ISATAP IPv6-in-IPv4 encapsulation service. When there is operational 369 assurance that IPv4 services between the two hosts are available, the 370 hosts may be better served to continue to use legacy IPv4 services in 371 order to avoid encapsulation overhead and to avoid any IPv4 372 protocol-41 filtering middleboxes that may be in the path. If 'C' 373 and 'D' may be in different IPv4 network partitions, however, IPv6- 374 in-IPv4 encapsulation should be only used with one or both of routers 375 'A' and 'B' serving as intermediate gateways. 377 3.4. Reference Operational Scenario - Individual Prefix Model 379 Figure 2 depicts an example ISATAP network topology for allowing 380 hosts within a predominantly IPv4 site to configure ISATAP services 381 using SLAAC with the individual prefix model. The example shows two 382 advertising ISATAP routers ('A', 'B'), two ISATAP hosts ('C', 'D'), 383 and an ordinary IPv6 host ('E') outside of the site in a typical 384 deployment configuration. In the figure, ISATAP routers 'A' and 'B' 385 both advertise different prefixes taken from the aggregated prefix 386 2001:db8::/48, with 'A' advertising 2001:db8:0:1::/64 and 'B' 387 advertising 2001:db8:0:2::/64. 389 .-(::::::::) 2001:db8:1::1 390 .-(::: IPv6 :::)-. +-------------+ 391 (:::: Internet ::::) | IPv6 Host E | 392 `-(::::::::::::)-' +-------------+ 393 `-(::::::)-' 394 ,~~~~~~~~~~~~~~~~~, 395 ,----|companion gateway|--. 396 / '~~~~~~~~~~~~~~~~~' : 397 / |. 398 ,-' `. 399 ; +------------+ +------------+ ) 400 : | Router A | | Router B | / 401 : | (isatap) | | (isatap) | : 402 : | 192.0.2.1 | | 192.0.2.1 | ; 403 + +------------+ +------------+ \ 404 fe80::*:192.0.2.17 fe80::*:192.0.2.33 405 2001:db8:0:1::/64 2001:db8:0:2::/64 406 | ; 407 : IPv4 Site -+-' 408 `-. (PRL: 192.0.2.1) .) 409 \ _) 410 `-----+--------)----+'----' 411 fe80::*:192.0.2.18 fe80::*:192.0.2.34 412 2001:db8:0:1::*:192.0.2.18 2001:db8:0:2::*:192.0.2.34 413 +--------------+ +--------------+ 414 | (isatap) | | (isatap) | 415 | Host C | | Host D | 416 +--------------+ +--------------+ 418 (* == "5efe") 420 Figure 2: Example ISATAP Network Topology using Individual Prefix 421 Model 423 With reference to Figure 2, advertising ISATAP routers 'A' and 'B' 424 within the IPv4 site connect to the IPv6 Internet either directly or 425 via a companion gateway. Router 'A' advertises the individual prefix 426 2001:db8:0:1::/64 into the IPv6 Internet routing system, and router 427 'B' advertises the individual prefix 2001:db8:0:2::/64. The routers 428 could instead both advertise a shorter shared prefix such as 2001: 429 db8::/48 into the IPv6 routing system, but in that case they would 430 need to configure a mesh of IPv6 links between themselves in the same 431 fashion as described for the shared prefix model in Section 3.4. For 432 the purpose of this example, we also assume that the IPv4 site is 433 configured within multiple IPv4 subnets - each with an IPv4 prefix 434 length of /28. 436 Advertising ISATAP routers 'A' and 'B' both configure individual IPv4 437 unicast addresses 192.0.2.17/28 and 192.0.2.33/28 (respectively) 438 instead of, or in addition to, a shared IPv4 anycast address. Router 439 'A' then configures an advertising ISATAP router interface for the 440 site with link-local ISATAP address fe80::5efe:192.0.2.17, while 441 router 'B' configures an advertising ISATAP router interface for the 442 site with link-local ISATAP address fe80::5efe:192.0.2.33. The site 443 administrator then places the IPv4 addresses 192.0.2.17 and 444 192.0.2.33 in the site's PRL. 'A' and 'B' then both advertise their 445 IPv4 addresses into the site's IPv4 routing system so that ISATAP 446 clients can locate the router that is topologically closest. (Note: 447 advertising ISATAP routers can also use an IPv4 anycast address 448 instead of, or in addition to, their IPv4 uncast address.) 450 ISATAP host 'C' connects to the site via an IPv4 interface with 451 address 192.0.2.18/28, and also configures an ISATAP host interface 452 with link-local ISATAP address fe80::5efe:192.0.2.18 over the IPv4 453 interface. 'C' next resolves the PRL, and sends an RS message to the 454 IPv4 address 192.0.2.17, where IPv4 routing will direct it to 'A'. 455 'C' then receives an RA from 'A' then configures a default IPv6 route 456 with next-hop address fe80::5efe:192.0.2.17 via the ISATAP interface 457 and processes the IPv6 prefix 2001:db8:0:1:/64 advertised in the PIO. 458 If the A flag is set in the PIO, 'C' uses SLAAC to automatically 459 configure the IPv6 address 2001:db8:0:1::5efe:192.0.2.18 (i.e., an 460 address with an ISATAP interface identifier) and assigns it to the 461 ISATAP interface. If the L flag is set, 'C' also assigns the prefix 462 2001:db8:0:1::/64 to the ISATAP interface, and the IPv6 address 463 becomes a true ISATAP address. 465 In the same fashion, ISATAP host 'D' configures its IPv4 interface 466 with address 192.0.2.34/28 and configures its ISATAP interface with 467 link-local ISATAP address fe80::5efe:192.0.2.34. 'D' next performs 468 an RS/RA exchange that is serviced by 'B', then uses SLAAC to 469 autoconfigure the address 2001:db8:0:2::5efe:192.0.2.34 and a default 470 IPv6 route with next-hop address fe80::5efe:192.0.2.33. Finally, 471 IPv6 host 'E' connects to an IPv6 network outside of the site. 'E' 472 configures its IPv6 interface in a manner specific to its attached 473 IPv6 link, and autoconfigures the IPv6 address 2001:db8:1::1. 475 Following this autoconfiguration, when host 'C' inside the site has 476 an IPv6 packet to send to host 'E' outside the site, it prepares the 477 packet with source address 2001:db8::5efe:192.0.2.18 and destination 478 address 2001:db8:1::1. 'C' then uses IPv6-in-IPv4 encapsulation to 479 forward the packet to the IPv4 address 192.0.2.17 which will be 480 directed to 'A' based on IPv4 routing. 'A' in turn decapsulates the 481 packet and forwards it into the public IPv6 Internet where it will be 482 conveyed to 'E' via normal IPv6 routing. In the same fashion, host 483 'D' uses IPv6-in-IPv4 encapsulation via its default router 'B' to 484 send IPv6 packets to IPv6 Internet hosts such as 'E'. 486 When host 'E' outside the site sends IPv6 packets to ISATAP host 'C' 487 inside the site, the IPv6 routing system will direct the packet to 488 'A' since 'A' advertises the individual prefix that matches 'C's 489 destination address. 'A' can then use ISATAP to statelessly forward 490 the packet directly to 'C'. If 'A' and 'B' both advertise the shared 491 shorter prefix 2001:db8::/48 into the IPv6 routing system, however 492 packets coming from 'E' may be directed to either 'A' or 'B'. In 493 that case, the advertising ISATAP routers must connect within a full 494 or partial mesh of IPv6 links the same as for the shared prefix 495 model, and must either run a dynamic IPv6 routing protocol or 496 configure static routes so that incoming IPv6 packets can be 497 forwarded to the correct serving router. 499 In this example, 'A' can configure the IPv6 route 2001:db8:0:2::/64 500 with the IPv6 address of the next hop toward 'B' in the mesh network 501 as the next hop, and 'B' can configure the IPv6 route 2001:db8: 502 0.1::/64 with the IPv6 address of the next hop toward 'A' as the next 503 hop. Then, when 'A' receives a packet from the IPv6 Internet with 504 destination address 2001:db8:0:2::5efe:192.0.2.34, it first forwards 505 the packet toward 'B' over an IPv6 mesh link. 'B' in turn uses 506 ISATAP to forward the packet into the site, where IPv4 routing will 507 direct it to 'D'. In the same fashion, when 'B' receives a packet 508 from the IPv6 Internet with destination address 2001:db8:0:1::5efe: 509 192.0.2.18, it first forwards the packet toward 'A' over an IPv6 mesh 510 link. 'A' then uses ISATAP to forward the packet into the site, 511 where IPv4 routing will direct it to 'C'. 513 Finally, when host 'C' inside the site connects to host 'D' inside 514 the site, it has the option of using the native IPv4 service or the 515 ISATAP IPv6-in-IPv4 encapsulation service. When there is operational 516 assurance that IPv4 services between the two hosts are available, the 517 hosts may be better served to continue to use legacy IPv4 services in 518 order to avoid encapsulation overhead and to avoid any IPv4 519 protocol-41 filtering middleboxes that may be in the path. If 'C' 520 and 'D' may be in different IPv4 network partitions, however, IPv6- 521 in-IPv4 encapsulation should be used with one or both of routers 'A' 522 and 'B' serving as intermediate gateways. 524 3.5. SLAAC Site Administration Guidance 526 In common practice, firewalls, gateways and packet filtering devices 527 of various forms are often deployed in order to divide the site into 528 separate partitions. In both the shared and individual prefix models 529 described above, the entire site can be represented by the aggregate 530 IPv6 prefix assigned to the site, while each site partition can be 531 represented by "sliver" IPv6 prefixes taken from the aggregate. In 532 order to provide a simple service that does not interact poorly with 533 the site topology, site administrators should therefore institute an 534 address plan to align IPv6 sliver prefixes with IPv4 site partition 535 boundaries. 537 For example, in the shared prefix model in Section 3.3, the aggregate 538 prefix is 2001:db8::/64, and the sliver prefixes are 2001:db8::5efe: 539 192.0.2.0/124, 2001:db8::5efe:192.0.2.16/124, 2001:db8::5efe: 540 192.0.2.32/124, etc. In the individual prefix model in Section 3.4, 541 the aggregate prefix is 2001:db8::/48 and the sliver prefixes are 542 2001:db8:0:0::/64, 2001:db8:0:1::/64, 2001:db8:0:2::/64, etc. 544 When individual prefixes are used, site administrators can configure 545 advertising ISATAP routers to advertise different individual prefixes 546 to different sets of clients, e.g., based on the client's IPv4 subnet 547 prefix such that the IPv6 prefixes are congruent with the IPv4 548 addressing plan. (For example, administrators can configure each 549 advertising ISATAP router to provide services only to certain sets of 550 ISATAP clients through inbound IPv6 Access Control List (ACL) entries 551 that match the IPv4 subnet prefix embedded in the ISATAP interface 552 identifier of the IPv6 source address). When a shared prefix is 553 used, site administrators instead configure the ISATAP routers to 554 advertise the shared prefix to all clients. 556 Advertising ISATAP routers can advertise prefixes with the (A, L) 557 flags set to (1,0) so that ISATAP clients will use SLAAC to 558 autoconfigure IPv6 addresses with ISATAP interface identifiers from 559 the prefixes and assign them to the receiving ISATAP interface, but 560 they will not assign the prefix itself to the ISATAP interface. In 561 that case, the advertising router must assign the sliver prefix for 562 the site partition to the advertising ISATAP interface. In this way, 563 the advertising router considers the addresses covered by the sliver 564 prefix as true ISATAP addresses, but the ISATAP clients themselves do 565 not. This configuration enables a hub-and-spokes architecture which 566 in some cases may be augmented by route optimization based on the 567 receipt of ICMPv6 Redirects. 569 Site administrators can implement address selection policy rules 570 [RFC3484] through explicit configurations in each ISATAP client. 571 Site administrators implement this policy by configuring address 572 selection policy rules in each ISATAP client in order to give 573 preference to IPv4 destination addresses over destination addresses 574 derived from one of the client's IPv6 sliver prefixes. 576 For example, site administrators can configure each ISATAP client 577 associated with a sliver prefix such as 2001:db8::5efe:192.0.2.64/124 578 to add the prefix to its address selection policy table with a lower 579 precedence than the prefix ::ffff:0:0/96. In this way, IPv4 580 addresses are preferred over IPv6 addresses from within the same 581 sliver. The prefix could be added to each ISATAP client either 582 manually, or through an automated service such as a DHCP option 583 [I-D.ietf-6man-addr-select-opt] discovered by the client, e.g., using 584 Stateless DHCPv6 [RFC3736]. In this way, clients will use IPv4 585 communications to reach correspondents within the same IPv4 site 586 partition, and will use IPv6 communications to reach correspondents 587 in other partitions and/or outside of the site. 589 It should be noted that sliver prefixes longer than /64 cannot be 590 advertised for SLAAC purposes. Also, sliver prefixes longer than /64 591 do not allow for interface identifier rewriting by address 592 translators. These factors may favor the individual prefix model in 593 some deployment scenarios, while the flexibility afforded by the 594 shared prefix model may be more desirable in others. Additionally, 595 if the network is small then the shared prefix model works well. If 596 the network is large, however, a better alternative may be to deploy 597 separate ISATAP routers in each partition and have each advertise 598 their own individual prefix. 600 Finally, site administrators should configure ISATAP routers to not 601 send ICMPv6 Redirect messages to inform a source client of a better 602 next hop toward the destination unless there is strong assurance that 603 the client and the next hop are within the same IPv4 site partition. 605 3.6. Loop Avoidance 607 In sites that provide IPv6 services through ISATAP with SLAAC as 608 described in this section, site administrators must take operational 609 precautions to avoid routing loops. For example, each advertising 610 ISATAP router should drop any incoming IPv6 packets that would be 611 forwarded back to itself via another of the site's advertising 612 routers. Additionally, each advertising ISATAP router should drop 613 any encapsulated packets received from another advertising router 614 that would be forwarded back to that same advertising router. This 615 corresponds to the mitigation documented in Section 3.2.3 of 616 [RFC6324], but other mitigations specified in that document can also 617 be employed. 619 Note that IPv6 packets with link-local ISATAP addresses are exempt 620 from these checks, since they cannot be forwarded by an IPv6 router 621 and may be necessary for router-to-router coordinations. 623 3.7. Interface Identifier Compatibility Considerations 625 [RFC5214] Section 6.1 specifies the setting of the "u" bit in the 626 Modified EUI-64 interface identifier format used by ISATAP. 627 Implementations that comply with the specification set the "u" bit to 628 1 when the IPv4 address is known to be globally unique, however some 629 legacy implementations unconditionally set the "u" bit to 0. 631 Implementations interpret the ISATAP interface identifier only within 632 the link to which the corresponding ISATAP prefix is assigned, hence 633 the value of the "u" bit is interpreted only within the context of an 634 on-link prefix and not within a global context. Implementers are 635 responsible for ensuring that their products are interoperable, 636 therefore implementations must make provisions for ensuring "u" bit 637 compatibility for intra-link communications. 639 Site administrators should accordingly configure access control list 640 entries and other literal representations of ISATAP interface 641 identifiers such that both values of the "u" bit are accepted. For 642 example, if the site administrator configures an access control list 643 entry that matches the prefix "fe80::0000:5efe:192.0.2.0/124" they 644 should also configure a companion list entry that matches the prefix 645 "fe80::0200:5efe:192.0.2.0/124. 647 4. Manual Configuration 649 When no autoconfiguration services are available (e.g., if there are 650 no advertising ISATAP routers present), site administrators can use 651 manual configuration to assign IPv6 addresses with ISATAP interface 652 identifiers to the ISATAP interfaces of clients. Otherwise, site 653 administrators should avoid manual configurations that would in any 654 way invalidate the assumptions of the autoconfiguration service. For 655 example, manually configured addresses may not be automatically 656 renumbered during a site-wide renumbering event, which could 657 subsequently result in communication failures. 659 5. Scaling Considerations 661 Section 3 depicts ISATAP network topologies with only two advertising 662 ISATAP routers within the site. In order to support larger numbers 663 of ISATAP clients (and/or multiple site partitions), the site can 664 deploy more advertising ISATAP routers to support load balancing and 665 generally shortest-path routing. 667 Such an arrangement requires that the advertising ISATAP routers 668 participate in an IPv6 routing protocol instance so that IPv6 669 addresses/prefixes can be mapped to the correct ISATAP router. The 670 routing protocol instance can be configured as either a full mesh 671 topology involving all advertising ISATAP routers, or as a partial 672 mesh topology with each advertising ISATAP router associating with 673 one or more companion gateways. Each such companion gateway would in 674 turn participate in a full mesh between all companion gateways. 676 6. Site Renumbering Considerations 678 Advertising ISATAP routers distribute IPv6 prefixes to ISATAP clients 679 within the site. If the site subsequently reconnects to a different 680 ISP, however, the site must renumber to use addresses derived from 681 the new IPv6 prefixes [RFC1900][RFC4192][RFC5887]. 683 For IPv6 services provided by SLAAC, site renumbering in the event of 684 a change in an ISP-served IPv6 prefix entails a simple renumbering of 685 IPv6 addresses and/or prefixes that are assigned to the ISATAP 686 interfaces of clients within the site. In some cases, filtering 687 rules (e.g., within site border firewall filtering tables) may also 688 require renumbering, but this operation can be automated and limited 689 to only one or a few administrative "touch points". 691 In order to renumber the ISATAP interfaces of clients within the site 692 using SLAAC, advertising ISATAP routers need only schedule the 693 services offered by the old ISP for deprecation and begin to 694 advertise the IPv6 prefixes provided by the new ISP. ISATAP client 695 interface address lifetimes will eventually expire, and the host will 696 renumber its interfaces with addresses derived from the new prefixes. 697 ISATAP clients should also eventually remove any deprecated SLAAC 698 prefixes from their address selection policy tables, but this action 699 is not time-critical. 701 Finally, site renumbering in the event of a change in an ISP-served 702 IPv6 prefix further entails locating and rewriting all IPv6 addresses 703 in naming services, databases, configuration files, packet filtering 704 rules, documentation, etc. If the site has published the IPv6 705 addresses of any site-internal nodes within the public Internet DNS 706 system, then the corresponding resource records will also need to be 707 updated during the renumbering operation. This can be accomplished 708 via secure dynamic updates to the DNS. 710 7. Path MTU Considerations 712 IPv6-in-IPv4 encapsulation overhead effectively reduces the size of 713 IPv6 packets that can traverse the tunnel in relation to the actual 714 Maximum Transmission Unit (MTU) of the underlying IPv4 network path 715 between the encapsulator and decapsulator. Two methods for 716 accommodating IPv6 path MTU discovery over IPv6-in-IPv4 tunnels 717 (i.e., the static and dynamic methods) are documented in Section 3.2 718 of [RFC4213]. 720 The static method places a "safe" upper bound on the size of IPv6 721 packets permitted to enter the tunnel, however the method can be 722 overly conservative when larger IPv4 path MTUs are available. The 723 dynamic method can accommodate much larger IPv6 packet sizes in some 724 cases, but can fail silently if the underlying IPv4 network path does 725 not return the necessary error messages. 727 This document notes that sites that include well-managed IPv4 links, 728 routers and other network middleboxes are candidates for use of the 729 dynamic MTU determination method, which may provide for a better 730 operational IPv6 experience in the presence of IPv6-in-IPv4 tunnels. 731 The dynamic MTU determination method can potentially also present a 732 larger MTU to IPv6 correspondents outside of the site, since IPv6 733 path MTU discovery is considered robust even over the wide area in 734 the public IPv6 Internet. 736 8. Alternative Approaches 738 [RFC4554] proposes a use of VLANs for IPv4-IPv6 coexistence in 739 enterprise networks. The ISATAP approach provides a more flexible 740 and broadly-applicable alternative, and with fewer administrative 741 touch points. 743 The tunnel broker service [RFC3053] uses point-to-point tunnels that 744 require end users to establish an explicit administrative 745 configuration of the tunnel far end, which may be outside of the 746 administrative boundaries of the site. 748 6to4 [RFC3056] and Teredo [RFC4380] provide "last resort" unmanaged 749 automatic tunneling services when no other means for IPv6 750 connectivity is available. These services are given lower priority 751 when the ISATAP managed service and/or native IPv6 services are 752 enabled. 754 6rd [RFC5969] enables a stateless prefix delegation capability based 755 on IPv4-embedded IPv6 prefixes, whereas ISATAP enables a stateful 756 prefix delegation capability based on native IPv6 prefixes. 758 9. IANA Considerations 760 This document has no IANA considerations. 762 10. Security Considerations 764 In addition to the security considerations documented in [RFC5214], 765 sites that use ISATAP should take care to ensure that no routing 766 loops are enabled [RFC6324]. Additional security concerns with IP 767 tunneling are documented in [RFC6169]. 769 11. Acknowledgments 771 The following are acknowledged for their insights that helped shape 772 this work: Dmitry Anipko, Fred Baker, Ron Bonica, Brian Carpenter, 773 Remi Despres, Thomas Henderson, Philip Homburg, Lee Howard, Ray 774 Hunter, Joel Jaeggli, John Mann, Gabi Nakibly, Christopher Palmer, 775 Hemant Singh, Mark Smith, Ole Troan, and Gunter Van de Velde. 777 12. References 779 12.1. Normative References 781 [RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and 782 E. Lear, "Address Allocation for Private Internets", 783 BCP 5, RFC 1918, February 1996. 785 [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., 786 and M. Carney, "Dynamic Host Configuration Protocol for 787 IPv6 (DHCPv6)", RFC 3315, July 2003. 789 [RFC3736] Droms, R., "Stateless Dynamic Host Configuration Protocol 790 (DHCP) Service for IPv6", RFC 3736, April 2004. 792 [RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms 793 for IPv6 Hosts and Routers", RFC 4213, October 2005. 795 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 796 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 797 September 2007. 799 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 800 Address Autoconfiguration", RFC 4862, September 2007. 802 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 803 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 804 March 2008. 806 12.2. Informative References 808 [I-D.ietf-6man-addr-select-opt] 809 Matsumoto, A., Fujisaki, T., Kato, J., and T. Chown, 810 "Distributing Address Selection Policy using DHCPv6", 811 draft-ietf-6man-addr-select-opt-03 (work in progress), 812 February 2012. 814 [I-D.templin-isupdate] 815 Templin, F., "ISATAP Updates", draft-templin-isupdate-03 816 (work in progress), May 2012. 818 [RFC1687] Fleischman, E., "A Large Corporate User's View of IPng", 819 RFC 1687, August 1994. 821 [RFC1900] Carpenter, B. and Y. Rekhter, "Renumbering Needs Work", 822 RFC 1900, February 1996. 824 [RFC2491] Armitage, G., Schulter, P., Jork, M., and G. Harter, "IPv6 825 over Non-Broadcast Multiple Access (NBMA) networks", 826 RFC 2491, January 1999. 828 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 829 Domains without Explicit Tunnels", RFC 2529, March 1999. 831 [RFC2983] Black, D., "Differentiated Services and Tunnels", 832 RFC 2983, October 2000. 834 [RFC3053] Durand, A., Fasano, P., Guardini, I., and D. Lento, "IPv6 835 Tunnel Broker", RFC 3053, January 2001. 837 [RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains 838 via IPv4 Clouds", RFC 3056, February 2001. 840 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 841 of Explicit Congestion Notification (ECN) to IP", 842 RFC 3168, September 2001. 844 [RFC3484] Draves, R., "Default Address Selection for Internet 845 Protocol version 6 (IPv6)", RFC 3484, February 2003. 847 [RFC4192] Baker, F., Lear, E., and R. Droms, "Procedures for 848 Renumbering an IPv6 Network without a Flag Day", RFC 4192, 849 September 2005. 851 [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through 852 Network Address Translations (NATs)", RFC 4380, 853 February 2006. 855 [RFC4554] Chown, T., "Use of VLANs for IPv4-IPv6 Coexistence in 856 Enterprise Networks", RFC 4554, June 2006. 858 [RFC5887] Carpenter, B., Atkinson, R., and H. Flinck, "Renumbering 859 Still Needs Work", RFC 5887, May 2010. 861 [RFC5969] Townsley, W. and O. Troan, "IPv6 Rapid Deployment on IPv4 862 Infrastructures (6rd) -- Protocol Specification", 863 RFC 5969, August 2010. 865 [RFC6169] Krishnan, S., Thaler, D., and J. Hoagland, "Security 866 Concerns with IP Tunneling", RFC 6169, April 2011. 868 [RFC6324] Nakibly, G. and F. Templin, "Routing Loop Attack Using 869 IPv6 Automatic Tunnels: Problem Statement and Proposed 870 Mitigations", RFC 6324, August 2011. 872 [RFC6343] Carpenter, B., "Advisory Guidelines for 6to4 Deployment", 873 RFC 6343, August 2011. 875 Author's Address 877 Fred L. Templin 878 Boeing Research & Technology 879 P.O. Box 3707 MC 7L-49 880 Seattle, WA 98124 881 USA 883 Email: fltemplin@acm.org