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'1') (Obsoleted by RFC 5944) == Outdated reference: A later version (-06) exists of draft-ietf-ipsec-nat-reqts-04 == Outdated reference: A later version (-08) exists of draft-ietf-ipsec-nat-t-ike-05 Summary: 4 errors (**), 0 flaws (~~), 17 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Mobile IP Working Group F. Adrangi, Ed. 3 Internet-Draft intel 4 Expires: October 10, 2003 H. Levkowetz, Ed. 5 ipUnplugged 6 April 11, 2003 8 Problem Statement: Mobile IPv4 Traversal of VPN Gateways 9 11 Status of this Memo 13 This document is an Internet-Draft and is in full conformance with 14 all provisions of Section 10 of RFC2026. 16 Internet-Drafts are working documents of the Internet Engineering 17 Task Force (IETF), its areas, and its working groups. Note that other 18 groups may also distribute working documents as Internet-Drafts. 20 Internet-Drafts are draft documents valid for a maximum of six months 21 and may be updated, replaced, or obsoleted by other documents at any 22 time. It is inappropriate to use Internet-Drafts as reference 23 material or to cite them other than as "work in progress." 25 The list of current Internet-Drafts can be accessed at http:// 26 www.ietf.org/ietf/1id-abstracts.txt. 28 The list of Internet-Draft Shadow Directories can be accessed at 29 http://www.ietf.org/shadow.html. 31 This Internet-Draft will expire on October 10, 2003. 33 Copyright Notice 35 Copyright (C) The Internet Society (2003). All Rights Reserved. 37 Abstract 39 Deploying Mobile-IP v4 in networks which are connected to the 40 internet through a VPN (Virtual Private Network) gateway presents 41 some problems which do not currently have well-described solutions. 42 This document aims to describe and illustrate these problems, and 43 propose some guidelines for possible solutions. 45 Table of Contents 47 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 48 1.1 Overview of the Problem . . . . . . . . . . . . . . . . . . 3 49 1.2 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 4 50 2. MIP and VPN Deployment Scenarios . . . . . . . . . . . . . . 4 51 2.1 MIPv4 HA(s) Inside the Intranet behind a VPN Gateway . . . . 5 52 2.2 VPN Gateway and MIPv4 HA(s) in parallel . . . . . . . . . . 6 53 2.3 Combined VPN Gateway and MIPv4 HA . . . . . . . . . . . . . 7 54 2.4 MIPv4 HA(s) Outside the VPN domain . . . . . . . . . . . . . 7 55 2.5 Combined VPN Gateway and MIPv4 HA(s) on the Local Link . . . 8 56 3. Deployment Scenarios Selection . . . . . . . . . . . . . . . 9 57 4. Problem statement . . . . . . . . . . . . . . . . . . . . . 9 58 4.1 Registering in co-located mode . . . . . . . . . . . . . . . 11 59 4.2 Registering via an FA . . . . . . . . . . . . . . . . . . . 12 60 4.3 Summary: MIP Incompatibilities with IPsec-based VPN 61 Gateways . . . . . . . . . . . . . . . . . . . . . . . . . . 13 62 5. Solution Guidelines . . . . . . . . . . . . . . . . . . . . 14 63 5.1 Preservation of Existing VPN Infrastructure . . . . . . . . 14 64 5.2 Software Upgrades to Existing VPN Client and Gateways . . . 14 65 5.3 IPsec Protocol . . . . . . . . . . . . . . . . . . . . . . . 14 66 5.4 Multi-Vendor Interoperability . . . . . . . . . . . . . . . 14 67 5.5 MIPv4 Protocol . . . . . . . . . . . . . . . . . . . . . . . 14 68 5.6 Handoff Overhead . . . . . . . . . . . . . . . . . . . . . . 15 69 5.7 Scalability, Availability, Reliability, and Performance . . 15 70 5.8 Functional Entities . . . . . . . . . . . . . . . . . . . . 15 71 5.9 Implications of Intervening NAT Gateways . . . . . . . . . . 15 72 5.10 Security Implications . . . . . . . . . . . . . . . . . . . 15 73 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 16 74 Normative References . . . . . . . . . . . . . . . . . . . . 16 75 Informative References . . . . . . . . . . . . . . . . . . . 16 76 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 17 77 Intellectual Property and Copyright Statements . . . . . . . 18 79 1. Introduction 81 Mobile IP [1] agents are being deployed in enterprise networks to 82 enable mobility across wired and wireless LANs while roaming inside 83 the enterprise intranet. With the growing deployment of IEEE 802.11 84 access points ("hot spots") in public places such as hotels, 85 airports, and convention centers, and wireless WAN data networks such 86 as GPRS, the need for enabling mobile users to maintain their 87 transport connections and constant reachability while connecting back 88 to their target "home" networks protected by Virtual Private 89 Network (VPN) technology is increasing. This implies that Mobile IP 90 and VPN technologies have to coexist and function together in order 91 to provide mobility and security to the enterprise mobile users. 93 The goal of this draft is to: 95 o Identify and describe practical deployment scenarios for Mobile IP 96 and VPN in enterprise and operator environments. 98 o Identify example usage scenarios for remote users roaming outside 99 the "home" network protected by a VPN gateway. 101 o Articulate the problems resulting from Mobile IP and VPN 102 coexistence. Specify a set of framework guidelines to evaluate 103 proposed solutions, supporting multi-vendor seamless IPv4 mobility 104 across IPsec-based VPN gateways. 106 1.1 Overview of the Problem 108 Real life networks typically consist of three different domains from 109 a corporate point of view. The first domain is the Internet (i.e., 110 the untrusted external network). The second domain is the trusted 111 intranet (also referred to as VPN Domain in this document). 112 The third domain is the DMZ, which is between the Internet and the 113 intranet. 115 Access to the intranet is typically guarded by both a firewall and a 116 VPN device. The intranet can only be accessed by respecting the 117 security policies in the firewall and the VPN device. 119 When MIP is deployed in a corporate network behind a VPN device, 120 roaming between these two different domains (i.e., the untrusted 121 Internet and the trusted intranet) becomes problematic. It would be 122 desirable to have seamless session mobility between the two domains, 123 because MIP was designed for session mobility regardless of the 124 network point of attachment. Unfortunately, the current MIP 125 standards fall short of this promise for an important customer 126 segment, corporate users behind VPN gateways. 128 Because current standards do not provide for session mobility across 129 these two domains the possibility of finding a solution to this 130 problem has been investigated. The goal is to provide seamless 131 session mobility when the mobile node moves between these two domains 132 or between subnets in either domain. 134 From the beginning it was also assumed that VPNs and 135 firewalls were to be taken as more or less granted because they have 136 much wider deployments than MIP at the present. Therefore any 137 solutions would need to minimize impact on existing VPN and 138 firewall deployments, related standards and "de facto" standards. 140 1.2 Terminology 142 MIPv4 Mobile IP for IPv4 [1] 144 MIPv6 Mobile IP for IPv6 146 VPN Virtual Private Network 148 GW Gateway 150 VPN Domain 151 An intranet protected by a VPN gateway. 153 DMZ 154 (DeMilitarized Zone) A small network inserted as a "neutral 155 zone" between a company's private network and the outside 156 public network to prevent outside users from getting direct 157 access to the company's private network 159 Home Network 160 A network, possibly virtual, having a network prefix matching 161 that of a mobile node's home address. 163 Home Agent 164 A router on a mobile node's home network which tunnels 165 datagrams for delivery to the mobile node when it is away 166 from home, and maintains current location information for the 167 mobile node. 169 2. MIP and VPN Deployment Scenarios 171 This section describes a set of deployment scenarios where MIP agents 172 and VPN gateways have to coexist to provide mobility and security. 174 The intention is to identify practical deployment scenarios for MIP 175 and VPNs where MIP technology might be extended to solve problems 176 resulting from the desire for co-existence. 178 In all scenarios, "MN" refers to a mobile node that runs both MIP and 179 IPsec-based VPN client software. The foreign network might or 180 might not employ a foreign agent. And, the term "Intranet" 181 refers to a private network protected by a VPN gateway and perhaps a 182 layer-3 transparent or non-transparent firewall. Please note that 183 firewalls are purposely omitted from the following scenarios, 184 because they may be installed in a number of different ways, and the 185 fact that this draft's focus is the relationship between MIP and VPN. 187 The following sub-sections introduce five representative 188 combinations of MIPv4 HA and VPN gateway placement. 190 2.1 MIPv4 HA(s) Inside the Intranet behind a VPN Gateway 192 MIPv4 HAs are deployed inside the Intranet protected by a VPN 193 gateway, and are not directly reachable by the MNs outside the 194 Intranet. 196 ..Foreign Network.. .....VPN Domain..(Intranet)..... 197 . . . . 198 . +----+ +----+ . +----+ +-------+ +-------+ . 199 . |MNs | | FA | . | VPN| | Router| | VPN/HA| . 200 . |away| | | .<=========>| | | 1..n | | 1..n | . 201 . +----+ +----+ . | GW | +-------+ +-------+ . 202 . . +----+ . 203 ................... . +-------+ +-------+ . 204 . | CN | | MNs | . 205 . | 1..n | | home | . 206 . +-------+ +-------+ . 207 . . 208 ................................ 210 Figure 1 212 Direct application of MIPv4 standards [1] is successfully used to 213 provide mobility for users inside the Intranet. However, mobile 214 users outside the Intranet can only access the intranet resources 215 (e.g., MIP agents) through the VPN gateway, which will allow only 216 authenticated IPsec traffic inside. This implies that the MIPv4 217 traffic has to run inside IPsec, which leads to two distinct 218 problems: 220 1. When the foreign network has an FA deployed (as in e.g. CDMA 221 2000), MIPv4 registration becomes impossible because the traffic 222 between MN and VPN gateway, which is what the FA sees, is 223 encrypted and the FA is not set up to decrypt it. 225 2. In co-located mode, successful registration is possible but the 226 VPN tunnel has to be re-negotiated every time the MN changes its 227 point of network attachment. 229 These problems are articulated in Section 4. 231 This deployment scenario may not be common yet, but it is practical 232 and becoming important as there is an increasing need for providing 233 corporate remote users with continuous access to the Intranet 234 resources. 236 2.2 VPN Gateway and MIPv4 HA(s) in parallel 238 A MIPv4 HA is deployed in parallel with the VPN gateway, and it is 239 directly reachable by MNs inside or outside the Intranet. 241 ..Foreign Network.. .....VPN Domain..(Intranet)..... 242 . . . . 243 . +----+ +----+ . +----+ +-------+ . 244 . |MNs | | FA | . | VPN| | Router| . 245 . |away| | | .<=========>| | | 1..n | . 246 . +----+ +----+ . | GW | +-------+ . 247 . . +----+ . 248 . . +----+ +-------+ +-------+ . 249 . .<=========>| HA | | CN | | MNs | . 250 ................... | | | 1..n | | home | . 251 +----+ +-------+ +-------+ . 252 . . 253 ................................ 255 Figure 2 257 The MIPv4 HA has a public interface connected to the Internet, and a 258 private interface attached to the Intranet. Mobile users will most 259 likely have a virtual home network associated with the MIPv4 HA's 260 private interface, so that the mobile users are always away from home 261 and hence registered with the MIPv4 HA. Furthermore, in deployments 262 where the VPN gateway and the HA are placed in a corporate DMZ, this 263 implies that MIPv4 traffic will always be routed through the 264 DMZ (regardless of whether MNs are located outside or inside the 265 Intranet), which may not be acceptable by IT departments in large 266 corporations. 268 This deployment can be used with two different configurations: "MIPv4 269 inside IPsec-ESP tunnel" and "IPsec-ESP inside MIPv4 tunnel". The 270 "MIPv4 inside IPsec-ESP tunnel" has the same problems as the scenario 271 of Section 2.1. The "IPsec-ESP inside MIPv4 tunnel" does not have 272 problems described in Section 2.1, however it will require some 273 modifications to the routing logic of the MIPv4 HA or the VPN 274 gateway. 276 2.3 Combined VPN Gateway and MIPv4 HA 278 This is similar to deployment scenario described in Section 2.2, with 279 the exception that the VPN gateway and MIPv4 HA are running on the 280 same physical machine. 282 ..Foreign Network.. .....VPN Domain..(Intranet)..... 283 . . . . 284 . +----+ +----+ . +----+ +-------+ . 285 . |MNs | | FA | . | VPN| | Router| . 286 . |away| | | .<==========| GW | | 1..n | . 287 . +----+ +----+ . | + | +-------+ . 288 . . | HA | . 289 ................... +----+ +-------+ +-------+ . 290 . | CN | | MNs | . 291 . | 1..n | | home | . 292 . +-------+ +-------+ . 293 . . 294 ................................ 296 Figure 3 298 Running MIPv4 HA and VPN on the same machine resolves routing 299 related issues that exist in Section 2.2 when a "IPsec-ESP inside 300 MIPv4 tunnel" configuration is used. However, it does not promote 301 multi-vendor interoperability in environments where MIPv4 HA and VPN 302 technologies must be acquired from different vendors. 304 2.4 MIPv4 HA(s) Outside the VPN domain 306 In this scenario, MIPv4 HAs are deployed outside the Intranet (e.g., 307 in an operator network), as depicted in Figure 4 below. 309 ..Foreign Network.. .....VPN Domain..(Intranet)..... 310 . . . . 311 . +----+ +----+ . +----+ +-------+ . 312 . |MNs | | FA | . | VPN| | Router| . 313 . |away| | | .<==========| GW | | 1..n | . 314 . +----+ +----+ . | | +-------+ . 315 . . | | . 316 ................... | | +-------+ +-------+ . 317 | | | CN | | MNs | . 318 .....MIPv4 Home.... | | | 1..n | | home | . 319 . .<=========>| | +-------+ +-------+ . 320 . +------+ . +----+ . 321 . | HAs | . . . 322 . | 1..n | . ................................ 323 . +------+ . 324 ................... 326 Figure 4 328 In this deployment scenario the goal is to provide remote users with 329 continuous access to the Intranet resources while they are roaming 330 outside the Intranet only (i.e., mobility is not supported inside the 331 Intranet). In this case it is most practical to run IPsec-ESP inside 332 a MIPv4 tunnel, as the MNs can register with the HA without 333 establishing an IPsec tunnel to the VPN gateway. This should work 334 without any technical problems. The 'home network' will be a virtual 335 home network, located at the HA, from which it is possible to reach 336 the Corporate intranet trough the VPN gateway. 338 2.5 Combined VPN Gateway and MIPv4 HA(s) on the Local Link 340 This is similar to the deployment scenario described in Section 2.3, 341 with the difference that the VPN gateway/HA is sitting on the local 342 link. In this the VPN gateway and HA would most naturaly be 343 co-located in the same box, although this is in no way a requirement. 345 ..Foreign Network.. .....VPN Domain..(Intranet)..... 346 . . . . 347 . +----+ +----+ . +------+ +-------+ +-------+ . 348 . |MNs | | FA | . | Fire | | Router| | VPN/HA| . 349 . |away| | | .<=======>| wall | | 1..n | | 1..n | . 350 . +----+ +----+ . | | +-------+ +-------+ . 351 . . | NAT | . 352 ................... +------+ +-------+ +-------+ . 353 . | CN | | MNs | . 354 . | 1..n | | home | . 355 . +-------+ +-------+ . 356 . . 357 ................................ 359 Figure 5 361 This deployment works today without any technical problems with 362 IPsec-ESP running inside a MIPv4 tunnel. And it has the same 363 problems as in Section 2.3 if MIPv4 is run inside the IPsec-ESP 364 tunnel. This is not common or practical for large deployments (on 365 the order of thousands of users) because of the large and distributed 366 security perimeter. 368 3. Deployment Scenarios Selection 370 The deployment scenarios described in Section 2 were evaluated to 371 identify the ones most in need of solving. The evaluation was done 372 based on two main criteria: 1) Is the deployment scenario common and 373 practical? and 2) Does the deployment scenario reveal any problems 374 resulting from MIPv4 and VPN coexistence? 376 There was a consensus about importance and practicality of the 377 scenario in Section 2.1 because of rising needs to provide corporate 378 remote users with continuous access to their Intranet resources. 379 After analyzing each scenario one realizes that problems occurring in 380 scenarios in Section 2.2 and Section 2.4 are either the same as or a 381 subset of the ones in scenario in Section 2.1. (The scenarios in 382 Section 2.3 and Section 2.5 do not have functional problems, but also 383 do not permit multi-vendor deployment). A solution for the 384 deployment scenario in Section 2.1 is therefore seen as essential, 385 and this in turn can also be applied to solve problems in other 386 scenarios. For the remainder of this draft, we will articulate the 387 roaming scenarios, the problems, and the solution guidelines relevant 388 to the scenario in Section 2.1. 390 4. Problem statement 392 This section describes roaming scenarios corresponding to the 393 deployment scenario in Section 2.1 where an MN needs to have 394 continuous access to the Intranet resources regardless of whether it 395 is roaming inside or outside the Intranet, and their associated 396 problems. The scenarios are constructed based on a multi-subnetted, 397 MIPv4-enabled Intranet (hereafter, referred to as Intranet or VPN 398 domain) protected by an IPsec-based VPN gateway as depicted in Figure 399 6. 401 ....Internet....... .....VPN Domain..(Intranet)..... 402 . . . . 403 . +----+ . +----+ +-------+ +-------+ . 404 . |MNs | . | VPN| | Router| | VPN/HA| . 405 . |away| .<=========>| | | 1..n | | 1..n | . 406 . +----+ . | GW | +-------+ +-------+ . 407 . . +----+ . 408 ................... . +-------+ +-------+ . 409 . | CN | | MNs | . 410 . | 1..n | | home | . 411 . +-------+ +-------+ . 412 . . 413 ................................ 415 Figure 6: Intranet protected by a VPN Gateway 417 The Intranet, depicted in Figure 6, may include both wired (IEEE 418 802.3) and IEEE 802.11 wireless LAN deployments. However, it is also 419 possible to see IEEE 802.11 deployments outside the Intranet due to 420 the perceived lack of current 802.11 security, as depicted in Figure 421 7. 423 ....Internet....... .....VPN Domain..(Intranet)..... 424 . . . . 425 . +----+ . +----+ +-------+ +-------+ . 426 . |MNs | . | VPN| | Router| | VPN/HA| . 427 . |away| .<=========>| | | 1..n | | 1..n | . 428 . +----+ . | GW | +-------+ +-------+ . 429 . . | | . 430 ................... | | +-------+ +-------+ . 431 | | | CN | | MNs | . 432 ..802.11 Wireless.. <====>| | | 1..n | | home | . 433 . Network . +----+ +-------+ +-------+ . 434 . . . . 435 ................... ................................ 437 Figure 7: IEEE 802.11 Wireless deployment outside the home network 439 4.1 Registering in co-located mode 441 In co-located mode, the IPsec tunnel endpoints would be at the MN and 442 the VPN gateway, which (supposing we have the scenario described in 443 Section 2.1) results in the mobile-ip tunnel from MN to HA being 444 encapsulated inside the IPsec tunnel. See Figure 8 below. This 445 scenario is still possible, but has some major drawbacks. 447 ....Internet....... .....VPN Domain..(Intranet)..... 448 . . . . 449 . +----+ . +----+ +-------+ +-------+ . 450 . |MNs | . | VPN| | Router| | VPN/HA| . 451 . |away|<###################>| |-----| 1..n |->| 1..n | . 452 . +----+ . \ | GW | +-------+ +-------+ . 453 . . \ +----+ . 454 ................... mip . +-------+ +-------+ . 455 inside . | CN | | MNs | . 456 IPsec . | 1..n | | home | . 457 . +-------+ +-------+ . 458 . . 459 ................................ 461 Figure 8 463 The MN obtains an address at its point of attachment (via DHCP[7] or 464 some other means), and then first sets up an IPsec tunnel to the VPN 465 gateway, after which it can successfully register with its HA through 466 the IPsec tunnel. The problem is that in an end-to-end security 467 model, an IPsec tunnel that terminates at the VPN gateway must 468 protect the IP traffic originating at the MN. As the MN's IPsec 469 tunnel address is the address obtained at the point of attachment, it 470 will change during movement, and the VPN tunnel security association 471 must be refreshed after each IP subnet handoff. This could have 472 noticeable performance implications on real-time applications. In 473 effect, we don't have mobility support for the tunnel endpoint 474 changes associated with MN movements. 476 4.2 Registering via an FA 478 In the case where a mobile node is in a network where mobility 479 support is provided through the use of an FA, and no dhcpd allocated 480 address and co-located mode is possible, we run into severe trouble. 481 Figure 9 below illustrates this: 483 ..Foreign Network.. .....VPN Domain..(Intranet)..... 484 . . . . 485 . +----+ +----+ . +----+ +-------+ +-------+ . 486 . |MNs | | FA | . | VPN| | Router| | VPN/HA| . 487 . |away|| |-----| 1..n |->| 1..n | . 488 . +----+ \ +----+ . \ | GW | +-------+ +-------+ . 489 . \ . \ +----+ . 490 ...........\....... mip . +-------+ +-------+ . 491 \ inside . | CN | | MNs | . 492 MN expects IPsec . | 1..n | | home | . 493 IPsec traffic . +-------+ +-------+ . 494 . . 495 ................................ 497 Figure 9 499 The mobile node, when arriving at this network, may have a IPsec 500 session going with its VPN gateway. This session will not be passed 501 through the FA as long as the MN has not registered and a mip tunnel 502 has been set up. But the MN, which is secure inside the IPsec based 503 VPN, will not even hear the FA advertisements. And any IPsec traffic 504 from the intranet (via the VPN gateway and IPsec tunnel) will not be 505 understood by the FA. Simply put, you could say that the FA needs to 506 see the mip tunnel outermost, while the VPN-GW needs to see the IPsec 507 tunnel outermost. Or in more details: 509 Firstly, the MN must have a IPsec tunnel established with the VPN-GW 510 in order to reach the HA, which places the IPsec tunnel outside the 511 mip traffic between MN and HA. The FA (which is likely in a 512 different administrative domain) cannot decrypt MIPv4 packets between 513 the MN and the VPN gateway, and will consequently be not able to 514 relay the MIPv4 packets. This is because the MIPv4 headers (which 515 the FA should be able to interpret) will be encrypted and protected 516 by IPSec. 518 Secondly, when the MN is communicating with the VPN-GW, an explicit 519 bypass policy for MIP packets is required, so that the MN can hear FA 520 advertisments and send and receive MIP registration packets. 521 Although not a problem in principle, there may be practical problems 522 when VPN and MIP clients from different vendors are used. 524 The use of a 'trusted FA' has been suggested in this scenario; 525 meaning an FA which is actually a combined VPN GW and FA. The 526 scenario will work fine in this case; effectively we are then 527 operating within the VPN established between the two VPN gateways, 528 and the case is analogous to deploying mobile-ip within a corporate 529 intranet which is not physically disjoint. See Figure 10 below. 530 However, we cannot expect that e.g. wireless hot-spots or CDMA 2000 531 FAs will have VPN gateways with security associations with any given 532 corporate network, so this is not particularly realistic in the 533 general mobility case. 535 ..Foreign Network.. .....VPN Domain..(Intranet)..... 536 . . . . 537 . +----+ +----+ . +----+ +-------+ +-------+ . 538 . | FA | | VPN| . | VPN| | Router| | VPN/HA| . 539 . | |<--| GW |<###########>| |-----| 1..n |->| 1..n | . 540 . +----+ +----+ . \ | GW | +-------+ +-------+ . 541 . | . \ +----+ . 542 . +----+ . mip . +-------+ +-------+ . 543 . |MNs | . inside . | CN | | MNs | . 544 . |away| . IPsec . | 1..n | | home | . 545 . +----+ . . +-------+ +-------+ . 546 ................... . . 547 ................................ 549 Figure 10 551 Furthermore, this solution would leave the traffic between FA and MN 552 unprotected, and as this link in particular may be a wireless link, 553 this is clearly undesireable. 555 4.3 Summary: MIP Incompatibilities with IPsec-based VPN Gateways 557 An MN roaming outside the Intranet has to establish an IPsec tunnel 558 to its home VPN gateway first, in order to be able to register with 559 its home agent. This is because the MN cannot reach its HA (inside 560 the private protected network) directly from the outside. This 561 implies that the MIPv4 traffic from the MN to a node inside the 562 Intranet is forced to run inside an IPsec tunnel, and hence will not 563 be in the clear. This in turn leads to two distinct problems 564 depending on whether the MN uses co-located or non co-located modes 565 to register with its HA. 567 5. Solution Guidelines 569 This section describes guidelines for a solution to MIPv4 traversal 570 across VPN gateways. The subsections discuss the guidelines in a 571 decreasing order of importance. 573 5.1 Preservation of Existing VPN Infrastructure 575 o The solution MUST preserve the investment in existing VPN 576 gateways. 578 o The solution MUST provide security which is not inferior to what 579 is already provided to existing "nomadic computing" remote access 580 users, i.e. for confidentiality, authentication, message 581 integrity, protection against replay attacks and related security 582 services. 584 5.2 Software Upgrades to Existing VPN Client and Gateways 586 o The solution SHOULD minimize changes to existing VPN client/ 587 gateway software. 589 5.3 IPsec Protocol 591 o The solution SHOULD NOT require any changes to existing IPsec or 592 key exchange standard protocols implemented by VPN gateways. 594 o The solution SHOULD NOT require that the VPN gateway or the VPN 595 client implement any new protocols in addition to the existing 596 standard protocols. 598 5.4 Multi-Vendor Interoperability 600 o The solution MUST provide multi-vendor interoperability, where 601 MIPv4 mobility agents, mobility clients (MN), VPN server, and VPN 602 client solutions may come from four different vendors. This is 603 typical for medium and large enterprises which purchase and deploy 604 best-of-breed multi-vendor solutions for IP routing, VPNs, 605 firewalls etc. 607 5.5 MIPv4 Protocol 609 o The solution MUST adhere to MIPv4 protocol [1]. That is, the 610 solution MUST NOT impose any changes that violates MIPv4 protocol. 612 o The solution MAY introduce new extensions to MIPv4 nodes per 613 guidelines specified in the MIPv4 protocol [1]. However, it is 614 highly desirable to avoid any changes to MIPv4 mobility agents 615 such as the FA and HA in order to overcome barriers to 616 deployment. 618 o The solution MAY require more than one instance of MIPv4 running 619 in parallel (multiple encapsulation). 621 5.6 Handoff Overhead 623 o It is imperative to keep the key management overhead down to a 624 minimum, in order to support fast handoffs across IP subnets. 625 Hence, the solution MUST propose a mechanism to avoid or minimize 626 IPsec tunnel SA renegotiation and IKE renegotiation as the MN 627 changes its current point of network attachment. 629 5.7 Scalability, Availability, Reliability, and Performance 631 o The solution complexity MUST increase at most linearly with the 632 number of MNs registered and accessing resources inside the 633 Intranet. 635 o The solution MAY introduce additional header or tunnelling 636 overhead if needed. 638 5.8 Functional Entities 640 o The solution MAY introduce new MIPv4 compliant functional 641 entities. 643 5.9 Implications of Intervening NAT Gateways 645 o The solution MUST be able to leverage the existing MIPv4 and IPsec 646 NAT traversal solutions [9][10][11]. 648 5.10 Security Implications 650 o The solution MUST NOT introduce any new vulnerabilities to the 651 MIPv4 or IPsec as specified in related RFCs. 653 6. Acknowledgements 655 The authors who contributed text to this document were in no 656 particular order: Farid Adrangi, Milind Kulkarni, Gopal Dommety, Eli 657 Gelasco, Qiang Zhang, Sami Vaarala, Dorothy Gellert, Nitsan Baider 658 and Henrik Levkowetz. 660 The authors would like to thank other contributors, especially 661 Prakash Iyer, Mike Andrews, Ranjit Narjala, Joe Lau, Kent Leung, 662 Alpesh Patel, Phil Roberts, Hans Sjostrand, Serge Tessier, Antti 663 Nuopponen, Alan O'neill, Gaetan Feige, Brijesh Kumar for their 664 continuous feedback and helping us improve this draft. 666 Normative References 668 [1] Perkins, C., "IP Mobility Support for IPv4", RFC 3344, August 669 2002. 671 Informative References 673 [2] Hanks, S., Li, T., Farinacci, D. and P. Traina, "Generic 674 Routing Encapsulation (GRE)", RFC 1701, October 1994. 676 [3] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G. and E. 677 Lear, "Address Allocation for Private Internets", BCP 5, RFC 678 1918, February 1996. 680 [4] Perkins, C., "Minimal Encapsulation within IP", RFC 2004, 681 October 1996. 683 [5] Bradner, S., "Key words for use in RFCs to Indicate Requirement 684 Levels", BCP 14, RFC 2119, March 1997. 686 [6] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, 687 March 1997. 689 [7] Srisuresh, P. and M. Holdrege, "IP Network Address Translator 690 (NAT) Terminology and Considerations", RFC 2663, August 1999. 692 [8] Montenegro, G., "Reverse Tunneling for Mobile IP, revised", RFC 693 3024, January 2001. 695 [9] Vaarala, S. and O. Levkowetz, "Mobile IP NAT/NAPT Traversal 696 using UDP Tunnelling", draft-ietf-mobileip-nat-traversal-07 697 (work in progress), November 2002. 699 [10] Aboba, B. and W. Dixon, "IPsec-NAT Compatibility Requirements", 700 draft-ietf-ipsec-nat-reqts-04 (work in progress), March 2003. 702 [11] Kivinen, T., "Negotiation of NAT-Traversal in the IKE", 703 draft-ietf-ipsec-nat-t-ike-05 (work in progress), January 2003. 705 Authors' Addresses 707 Farid Adrangi 708 Intel Corporation 709 2111 N.E. 25th Avenue 710 Hillsboro OR 711 USA 713 Phone: +1 503-712-1791 714 EMail: farid.adrangi@intel.com 716 Henrik Levkowetz 717 ipUnplugged AB 718 Arenavagen 33 719 Stockholm S-121 28 720 SWEDEN 722 Phone: +46 8 725 9513 723 EMail: henrik@levkowetz.com 725 Intellectual Property Statement 727 The IETF takes no position regarding the validity or scope of any 728 intellectual property or other rights that might be claimed to 729 pertain to the implementation or use of the technology described in 730 this document or the extent to which any license under such rights 731 might or might not be available; neither does it represent that it 732 has made any effort to identify any such rights. 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