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 141 </head>
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 143 <table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
 144 <table summary="layout" width="66%" border="0" cellpadding="0" cellspacing="0"><tr><td><table summary="layout" width="100%" border="0" cellpadding="2" cellspacing="1">
 145 <tr><td class="header">Network Working Group</td><td class="header">O. Gsenger</td></tr>
 146 <tr><td class="header">Internet-Draft</td><td class="header">April 27, 2007</td></tr>
 147 <tr><td class="header">Expires: October 29, 2007</td><td class="header">&nbsp;</td></tr>
 148 </table></td></tr></table>
 149 <h1><br />secure anycast tunneling protocol (SATP)<br />draft-gsenger-secure-anycast-tunneling-protocol-00</h1>
 150
 151 <h3>Status of this Memo</h3>
 152 <p>
 153 By submitting this Internet-Draft,
 154 each author represents that any applicable patent or other IPR claims of which
 155 he or she is aware have been or will be disclosed,
 156 and any of which he or she becomes aware will be disclosed,
 157 in accordance with Section&nbsp;6 of BCP&nbsp;79.</p>
 158 <p>
 159 Internet-Drafts are working documents of the Internet Engineering
 160 Task Force (IETF), its areas, and its working groups.
 161 Note that other groups may also distribute working documents as
 162 Internet-Drafts.</p>
 163 <p>
 164 Internet-Drafts are draft documents valid for a maximum of six months
 165 and may be updated, replaced, or obsoleted by other documents at any time.
 166 It is inappropriate to use Internet-Drafts as reference material or to cite
 167 them other than as &ldquo;work in progress.&rdquo;</p>
 168 <p>
 169 The list of current Internet-Drafts can be accessed at
 170 <a href='http://www.ietf.org/ietf/1id-abstracts.txt'>http://www.ietf.org/ietf/1id-abstracts.txt</a>.</p>
 171 <p>
 172 The list of Internet-Draft Shadow Directories can be accessed at
 173 <a href='http://www.ietf.org/shadow.html'>http://www.ietf.org/shadow.html</a>.</p>
 174 <p>
 175 This Internet-Draft will expire on October 29, 2007.</p>
 176
 177 <h3>Copyright Notice</h3>
 178 <p>
 179 Copyright &copy; The IETF Trust (2007).</p>
 180
 181 <h3>Abstract</h3>
 182
 183 <p>The secure anycast tunneling protocol (SATP) defines a protocol used for communication between any combination of unicast and anycast tunnel endpoints. It allows tunneling of every ETHER TYPE protocol (e.g. ethernet, ip, arp ...). SATP directly includes cryptography and message authentication based on the methodes used by SRTP. It is intended to deliver a generic, scaleable and secure solution for tunneling and relaying of packets of any protocol.
 184
 185 </p><a name="toc"></a><br /><hr />
 186 <h3>Table of Contents</h3>
 187 <p class="toc">
 188 <a href="#anchor1">1.</a>&nbsp;
 189 Introduction<br />
 190 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#anchor2">1.1.</a>&nbsp;
 191 Notational Conventions<br />
 192 <a href="#anchor3">2.</a>&nbsp;
 193 Motivation and usage scenarios<br />
 194 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#anchor4">2.1.</a>&nbsp;
 195 Usage scenarions<br />
 196 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#anchor5">2.1.1.</a>&nbsp;
 197 Tunneling from unicast hosts over anycast routers to other unicast hosts<br />
 198 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#anchor6">2.1.2.</a>&nbsp;
 199 Tunneling from unicast hosts to anycast networks<br />
 200 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#anchor7">2.1.3.</a>&nbsp;
 201 Redundant tunnel connection of 2 networks<br />
 202 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#anchor8">2.2.</a>&nbsp;
 203 Encapsulation<br />
 204 <a href="#anchor9">3.</a>&nbsp;
 205 Using SATP on top of IP<br />
 206 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#anchor10">3.1.</a>&nbsp;
 207 Fragmentation<br />
 208 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#anchor11">3.2.</a>&nbsp;
 209 ICMP messages<br />
 210 <a href="#anchor12">4.</a>&nbsp;
 211 Protocol specification<br />
 212 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#anchor13">4.1.</a>&nbsp;
 213 Header format<br />
 214 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#anchor14">4.2.</a>&nbsp;
 215 sender ID<br />
 216 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#anchor15">4.3.</a>&nbsp;
 217 sequence number<br />
 218 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#anchor16">4.4.</a>&nbsp;
 219 payload<br />
 220 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#anchor17">4.5.</a>&nbsp;
 221 padding (OPTIONAL)<br />
 222 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#anchor18">4.6.</a>&nbsp;
 223 padding count<br />
 224 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#anchor19">4.7.</a>&nbsp;
 225 payload type field<br />
 226 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#anchor20">4.7.1.</a>&nbsp;
 227 MKI<br />
 228 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="#anchor21">4.7.2.</a>&nbsp;
 229 authentication tag<br />
 230 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#anchor22">4.8.</a>&nbsp;
 231 Encryption<br />
 232 <a href="#anchor23">5.</a>&nbsp;
 233 Security Considerations<br />
 234 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#anchor24">5.1.</a>&nbsp;
 235 Replay protection<br />
 236 <a href="#anchor25">6.</a>&nbsp;
 237 IANA Considerations<br />
 238 <a href="#rfc.references1">7.</a>&nbsp;
 239 References<br />
 240 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#rfc.references1">7.1.</a>&nbsp;
 241 Normative References<br />
 242 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#rfc.references2">7.2.</a>&nbsp;
 243 Informational References<br />
 244 <a href="#rfc.authors">&#167;</a>&nbsp;
 245 Author's Address<br />
 246 <a href="#rfc.copyright">&#167;</a>&nbsp;
 247 Intellectual Property and Copyright Statements<br />
 248 </p>
 249 <br clear="all" />
 250
 251 <a name="anchor1"></a><br /><hr />
 252 <table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
 253 <a name="rfc.section.1"></a><h3>1.&nbsp;
 254 Introduction</h3>
 255
 256 <p>SATP is somehow a mixture of a generic encapsulation protocol like <a class='info' href='#RFC2784'>GRE<span> (</span><span class='info'>Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. Traina, &ldquo;Generic Routing Encapsulation (GRE),&rdquo; March&nbsp;2000.</span><span>)</span></a> [4] and a secure tunneling protocol as <a class='info' href='#RFC2401'>IPsec<span> (</span><span class='info'>Kent, S. and R. Atkinson, &ldquo;Security Architecture for the Internet Protocol,&rdquo; November&nbsp;1998.</span><span>)</span></a> [5] in tunnel mode. To save some header overhead it uses the encryption technices of <a class='info' href='#RFC3711'>SRTP<span> (</span><span class='info'>Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman, &ldquo;The Secure Real-time Transport Protocol (SRTP),&rdquo; March&nbsp;2004.</span><span>)</span></a> [1]. It supports peer to peer tunnels, where tunnel endpoints can be any combination of unicast, multicast or anycast hosts, so it defines a <a class='info' href='#RFC1546'>Host Anycast Service<span> (</span><span class='info'>Partridge, C., Mendez, T., and W. Milliken, &ldquo;Host Anycasting Service,&rdquo; November&nbsp;1993.</span><span>)</span></a> [6]
 257 </p>
 258 <a name="anchor2"></a><br /><hr />
 259 <table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
 260 <a name="rfc.section.1.1"></a><h3>1.1.&nbsp;
 261 Notational Conventions</h3>
 262
 263 <p>The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in  <a class='info' href='#RFC2119'>RFC2119<span> (</span><span class='info'>Bradner, S., &ldquo;Key words for use in RFCs to Indicate Requirement Levels,&rdquo; March&nbsp;1997.</span><span>)</span></a> [2].
 264 </p>
 265 <a name="anchor3"></a><br /><hr />
 266 <table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
 267 <a name="rfc.section.2"></a><h3>2.&nbsp;
 268 Motivation and usage scenarios</h3>
 269
 270 <p>This section gives an overview of possible usage scenarios. Please note, that the protocols used in the figures are only examples and that SATP itself does not care about either transport protocols or encapsulated protocols. Routing is not done by SATP and each implemetation MAY choose it's own way of doing this task (e.g. using functions provided by the operating system). SATP is used only to encapsulate and encrypt data.
 271 </p>
 272 <a name="anchor4"></a><br /><hr />
 273 <table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
 274 <a name="rfc.section.2.1"></a><h3>2.1.&nbsp;
 275 Usage scenarions</h3>
 276
 277 <a name="anchor5"></a><br /><hr />
 278 <table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
 279 <a name="rfc.section.2.1.1"></a><h3>2.1.1.&nbsp;
 280 Tunneling from unicast hosts over anycast routers to other unicast hosts</h3>
 281 <br /><hr class="insert" />
 282 <a name="tunnel_mode"></a>
 283
 284 <p>An example of SATP used to tunnel in a unicast client - anycast server model
 285 </p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
 286                     --------- router -----------
 287                    /                            \
 288     unicast ------+---------- router ------------+------ unicast
 289     host           \                            /        host
 290                     --------- router -----------
 291
 292   unicast  | encrypted     |  anycast  | encrypted     |  unicast
 293   tunnel   | communication |  tunnel   | communication |  tunnel
 294   endpoint | using SATP    |  endpoint | using SATP    |  endpoint
 295 </pre></div><table border="0" cellpadding="0" cellspacing="2" align="center"><tr><td align="center"><font face="monaco, MS Sans Serif" size="1"><b>&nbsp;Figure&nbsp;1&nbsp;</b></font><br /></td></tr></table><hr class="insert" />
 296
 297 <p>In this scenario the payload gets encapsuleted into a SATP packet by a unicast host and gets transmitted to one of the anycast routers. It than gets decapsulated by the router. This router makes a routing descision based on the underlying protocol and transmits a new SATP package to one or more unicast hosts depending on the routing descition.
 298 </p>
 299 <a name="anchor6"></a><br /><hr />
 300 <table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
 301 <a name="rfc.section.2.1.2"></a><h3>2.1.2.&nbsp;
 302 Tunneling from unicast hosts to anycast networks</h3>
 303 <br /><hr class="insert" />
 304 <a name="open_tunnel_mode"></a>
 305
 306 <p>An example of SATP used to encrypt data between a unicast host and anycast networks
 307 </p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
 308                        -------Router -+---- DNS Server
 309                       /                \
 310                      /                  --- 6to4 Router
 311                     /
 312     unicast -------+----------Router --+--- DNS Server
 313     host            \                   \
 314                      \                   --- 6to4 Router
 315                       \
 316                        -------Router -+---- DNS Server
 317                                        \
 318                                         --- 6to4 Router
 319
 320   unicast  | encrypted     |  anycast  | plaintext
 321   tunnel   | communication |  tunnel   | anycast
 322   endpoint | using SATP    |  endpoint | services
 323
 324 </pre></div><table border="0" cellpadding="0" cellspacing="2" align="center"><tr><td align="center"><font face="monaco, MS Sans Serif" size="1"><b>&nbsp;Figure&nbsp;2&nbsp;</b></font><br /></td></tr></table><hr class="insert" />
 325
 326 <p>When the unicast hosts wants to transmit data to one of the anycast DNS servers, it encapsulates the data and sends a SATP packet to the anycast address of the routers. The packet arrives at one of the routers, gets decapsulated and routed to the DNS server. This method can be used to tunnel between a clients and networks providing anycast services. It can also be used the other way to virtually locate a unicast service within anycasted networks.
 327 </p>
 328 <a name="anchor7"></a><br /><hr />
 329 <table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
 330 <a name="rfc.section.2.1.3"></a><h3>2.1.3.&nbsp;
 331 Redundant tunnel connection of 2 networks</h3>
 332 <br /><hr class="insert" />
 333 <a name="connect_networks"></a>
 334
 335 <p>An example of SATP used to connect 2 networks
 336 </p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
 337               Router -----------   ---------------Router
 338             /                   \ /                     \
 339     Network - Router ------------x                       Network
 340        A    \                   / \                     /   B
 341               Router -----------   ---------------Router
 342
 343             | packets       |  packets  |  packets      |
 344  plaintext  | get           |  take a   |  get          | plaintext
 345  packets    | de/encrypted  |  random   |  de/encrypted | packets
 346             |de/encapsulated|   path    |de/encapsulated|
 347
 348 </pre></div><table border="0" cellpadding="0" cellspacing="2" align="center"><tr><td align="center"><font face="monaco, MS Sans Serif" size="1"><b>&nbsp;Figure&nbsp;3&nbsp;</b></font><br /></td></tr></table><hr class="insert" />
 349
 350 <p>Network A has multiple routers, that act as gateway/tunnel endpoints to another network B. This is done to build a redundant encrypted tunnel connection between the two networks. All tunnel endpoints of network A share the same anycast address and all tunnel endpoints of network B share another anycast address. When a packet from network A gets transmitted to network B, it first arrives on one of network A's border routers. Which router is used is determined by network A's internal routing. This router encapsulates the package and sends it to the anycast address of the network B routers. The SATP packet arrives at one of network B's routers and gets decapsulated and routed to it's destination within network B.
 351 </p>
 352 <a name="anchor8"></a><br /><hr />
 353 <table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
 354 <a name="rfc.section.2.2"></a><h3>2.2.&nbsp;
 355 Encapsulation</h3>
 356
 357 <p>SATP does not depend on which lower layer protocols is used, but this section gives an example of how packets could look like.
 358
 359 </p><br /><hr class="insert" />
 360 <a name="transport_udp"></a>
 361
 362 <p>Examples of SATP used with different lower layer and payload protocols
 363 </p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
 364     +------+-----+-------------------------------+
 365     |      |     |      + ---------------+------ |
 366     | IPv6 | UDP | SATP | Ethernet 802.3 | ... | |
 367     |      |     |      +----------------+-----+ |
 368     +------+-----+-------------------------------+
 369
 370 Tunneling of Ethernet over UDP/IPv6
 371
 372     +------+-----+---------------------------+
 373     |      |     |      +------+-----+-----+ |
 374     | IPv4 | UDP | SATP | IPv6 | UDP | RTP | |
 375     |      |     |      +------+-----+-----+ |
 376     +------+-----+---------------------------+
 377
 378 Tunneling of IPv6 over UDP/IPv4 with RTP payload
 379
 380     +------+-------------------------------+
 381     |      |      + ---------------+------ |
 382     | IPv6 | SATP | Ethernet 802.3 | ... | |
 383     |      |      +----------------+-----+ |
 384     +------+-------------------------------+
 385
 386 Tunneling of Ethernet over IPv6
 387
 388     +------+---------------------------+
 389     |      |      +------+-----+-----+ |
 390     | IPv4 | SATP | IPv6 | UDP | RTP | |
 391     |      |      +------+-----+-----+ |
 392     +------+---------------------------+
 393
 394 Tunneling of IPv6 over IPv4 with RTP payload
 395 </pre></div><table border="0" cellpadding="0" cellspacing="2" align="center"><tr><td align="center"><font face="monaco, MS Sans Serif" size="1"><b>&nbsp;Figure&nbsp;4&nbsp;</b></font><br /></td></tr></table><hr class="insert" />
 396
 397 <a name="anchor9"></a><br /><hr />
 398 <table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
 399 <a name="rfc.section.3"></a><h3>3.&nbsp;
 400 Using SATP on top of IP</h3>
 401
 402 <a name="anchor10"></a><br /><hr />
 403 <table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
 404 <a name="rfc.section.3.1"></a><h3>3.1.&nbsp;
 405 Fragmentation</h3>
 406
 407 <p>
 408            The only way of fully supporting fragmentation would be to synchronise fragments between all anycast servers. This is considered to be too much overhead, so there are two non perfect solutions for these problems. Either fragmentation HAS TO be disabled or if not all fragments arrive at the same server the ip datagramm HAS TO be discarded. As routing changes are not expected to occure very frequently, the encapsulated protocol can do a retransmission and all fragments will arrive at the new server.
 409
 410 </p>
 411 <p>If the payload ip headers's Don't Fragment (DF) bit is set, than the DF bit of the outer ip header HAS TO be set as well.
 412 </p>
 413 <a name="anchor11"></a><br /><hr />
 414 <table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
 415 <a name="rfc.section.3.2"></a><h3>3.2.&nbsp;
 416 ICMP messages</h3>
 417
 418 <p>ICMP messages MUST be relayed according to <a class='info' href='#RFC2003'>rfc2003 section 4<span> (</span><span class='info'>Perkins, C., &ldquo;IP Encapsulation within IP,&rdquo; October&nbsp;1996.</span><span>)</span></a> [3]. This is needed for path MTU detection.
 419 </p>
 420 <a name="anchor12"></a><br /><hr />
 421 <table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
 422 <a name="rfc.section.4"></a><h3>4.&nbsp;
 423 Protocol specification</h3>
 424
 425 <a name="anchor13"></a><br /><hr />
 426 <table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
 427 <a name="rfc.section.4.1"></a><h3>4.1.&nbsp;
 428 Header format</h3>
 429 <br /><hr class="insert" />
 430 <a name="prot_header_table"></a>
 431
 432 <p>Protocol Format
 433 </p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
 434         0                   1                   2                   3
 435       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 436      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 437      |                         sequence number                       | |
 438      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+ |
 439      |           sender ID           #                               | |
 440    +#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+                               + |
 441    | |              ....        payload        ...                   | |
 442    | |-------------------------------+-------------------------------+ |
 443    | | padding (OPT) | pad count(OPT)|         payload type          | |
 444    +#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+-+
 445    | ~                          MKI (OPTIONAL)                       ~ |
 446    | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
 447    | :                 authentication tag (RECOMMENDED)              : |
 448    | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
 449    |                                                                   |
 450    +- Encrypted Portion                       Authenticated Portion ---+
 451 </pre></div><table border="0" cellpadding="0" cellspacing="2" align="center"><tr><td align="center"><font face="monaco, MS Sans Serif" size="1"><b>&nbsp;Figure&nbsp;5&nbsp;</b></font><br /></td></tr></table><hr class="insert" />
 452
 453 <p>
 454 </p>
 455 <a name="anchor14"></a><br /><hr />
 456 <table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
 457 <a name="rfc.section.4.2"></a><h3>4.2.&nbsp;
 458 sender ID</h3>
 459
 460 <p>The sender ID is a 16 bit unsigned integer. It HAS TO be unique for every sender sharing the same anycast address
 461 </p>
 462 <a name="anchor15"></a><br /><hr />
 463 <table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
 464 <a name="rfc.section.4.3"></a><h3>4.3.&nbsp;
 465 sequence number</h3>
 466
 467 <p>The sequence number is a 32 bit unsigned integer in network byte order. It starts with a random value and is increased by 1 for every sent packet. After the maximum value, it starts over from 0. This overrun causes the ROC to be increased.
 468 </p>
 469 <a name="anchor16"></a><br /><hr />
 470 <table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
 471 <a name="rfc.section.4.4"></a><h3>4.4.&nbsp;
 472 payload</h3>
 473
 474 <p>A packet of the type payload type (e.g. an IP packet).
 475 </p>
 476 <a name="anchor17"></a><br /><hr />
 477 <table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
 478 <a name="rfc.section.4.5"></a><h3>4.5.&nbsp;
 479 padding (OPTIONAL)</h3>
 480
 481 <p>Padding of max 255 octets.
 482 None of the pre-defined encryption transforms uses any padding; for
 483    these, the plaintext and encrypted payload sizes match exactly. Transforms are based on transforms of the SRTP protocol and these transforms might use the RTP padding format, so a RTP like padding is supported. If padding field is present, than the padding count field MUST be set to the padding lenght.
 484 </p>
 485 <a name="anchor18"></a><br /><hr />
 486 <table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
 487 <a name="rfc.section.4.6"></a><h3>4.6.&nbsp;
 488 padding count</h3>
 489
 490 <p>The number of octets of the padding field. This field is optional. It's presence is signaled by the key management and not by this protocol. If this field isn't present, the padding field MUST NOT be present as well.
 491 </p>
 492 <a name="anchor19"></a><br /><hr />
 493 <table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
 494 <a name="rfc.section.4.7"></a><h3>4.7.&nbsp;
 495 payload type field</h3>
 496
 497 <p>The payload type field defines the payload protocol. ETHER TYPE protocol numbers are used. <a href='http://www.iana.org/assignments/ethernet-numbers'>See IANA assigned ethernet numbers</a> . The values 0000-05DC are reserverd and MUST NOT be used.
 498         <br /><hr class="insert" />
 499 <a name="prot_type_table"></a>
 500
 501 <p>Some examples for protocol types
 502 </p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
 503 HEX
 504 0000 Reserved
 505 .... Reserved
 506 05DC Reserved
 507 0800 Internet IP (IPv4)
 508 6558 transparent ethernet bridging
 509 86DD IPv6
 510 </pre></div><table border="0" cellpadding="0" cellspacing="2" align="center"><tr><td align="center"><font face="monaco, MS Sans Serif" size="1"><b>&nbsp;Figure&nbsp;6&nbsp;</b></font><br /></td></tr></table><hr class="insert" />
 511
 512
 513 <a name="anchor20"></a><br /><hr />
 514 <table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
 515 <a name="rfc.section.4.7.1"></a><h3>4.7.1.&nbsp;
 516 MKI</h3>
 517
 518 <p>The MKI (Master Key Identifier) is OPTIONAL and of configurable length. See <a class='info' href='#RFC3711'>SRTP Section 3.1<span> (</span><span class='info'>Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman, &ldquo;The Secure Real-time Transport Protocol (SRTP),&rdquo; March&nbsp;2004.</span><span>)</span></a> [1] for details
 519 </p>
 520
 521 <a name="anchor21"></a><br /><hr />
 522 <table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
 523 <a name="rfc.section.4.7.2"></a><h3>4.7.2.&nbsp;
 524 authentication tag</h3>
 525
 526 <p>The authentication tag is RECOMMENDED and of configurable length. It contains a cryptographic checksum of the sender ID, sequence number and the encrypted portion, but not of the MKI. On sender side encryption HAS TO be done before calculating the authentication tag. A receiver HAS TO calculate the authentication tag before decrypting the encrypted portion.
 527 </p>
 528
 529
 530 <a name="anchor22"></a><br /><hr />
 531 <table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
 532 <a name="rfc.section.4.8"></a><h3>4.8.&nbsp;
 533 Encryption</h3>
 534
 535 <p>Encryption is done in the same way as for <a class='info' href='#RFC3711'>SRTP<span> (</span><span class='info'>Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman, &ldquo;The Secure Real-time Transport Protocol (SRTP),&rdquo; March&nbsp;2004.</span><span>)</span></a> [1]. This section will only discuss some small changes that HAVE TO be made. Please read  <a class='info' href='#RFC3711'>SRTP RFC3711 section 3-9<span> (</span><span class='info'>Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman, &ldquo;The Secure Real-time Transport Protocol (SRTP),&rdquo; March&nbsp;2004.</span><span>)</span></a> [1] for details.
 536 </p>
 537 <p>The least significant bits of SSRC are replaced by the sender ID and the rest is filled with zeros. For the SRTP SEQ the 16 least significant bits of the SATP sequence number are used and the 16 most significant bits of the sequence number replace the 16 least significant bits of the SRTP ROC.
 538 </p><br /><hr class="insert" />
 539 <a name="srtp_vs_satp"></a>
 540
 541 <p>Difference between SRTP and SATP
 542 </p><div style='display: table; width: 0; margin-left: 3em; margin-right: auto'><pre>
 543         0                   1                   2                   3
 544       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 545      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 546      |                     SATP    sequence number                   |
 547      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 548                                     =
 549      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 550      | SRTP ROC least significant   |         SRTP SEQ               |
 551      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 552
 553
 554         0                   1                   2                   3
 555       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 556      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 557      |0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0|       SATP sender ID          |
 558      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 559                                     =
 560      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 561      |                           SRTP SSRC                           |
 562      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 563 </pre></div><table border="0" cellpadding="0" cellspacing="2" align="center"><tr><td align="center"><font face="monaco, MS Sans Serif" size="1"><b>&nbsp;Figure&nbsp;7&nbsp;</b></font><br /></td></tr></table><hr class="insert" />
 564
 565 <a name="anchor23"></a><br /><hr />
 566 <table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
 567 <a name="rfc.section.5"></a><h3>5.&nbsp;
 568 Security Considerations</h3>
 569
 570 <p>As SATP uses the same encrytion technics as <a class='info' href='#RFC3711'>SRTP<span> (</span><span class='info'>Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman, &ldquo;The Secure Real-time Transport Protocol (SRTP),&rdquo; March&nbsp;2004.</span><span>)</span></a> [1], it shares the same security issues. This section will only discuss some small changes. Please read  <a class='info' href='#RFC3711'>SRTP RFC3711 section 9<span> (</span><span class='info'>Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman, &ldquo;The Secure Real-time Transport Protocol (SRTP),&rdquo; March&nbsp;2004.</span><span>)</span></a> [1] for details.
 571 </p>
 572 <a name="anchor24"></a><br /><hr />
 573 <table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
 574 <a name="rfc.section.5.1"></a><h3>5.1.&nbsp;
 575 Replay protection</h3>
 576
 577 <p>Replay protection is done by a replay list. Every anycast receiver has it's own replay list, which SHOULDN'T be syncronised, because of massive overhead. This leads to an additional possible attack. A attacker is able to replay a captured packet once to every anycast reciever. This attack is considered of be very unlikely, because multiple attack hosts in different loactions are needed to reach the seperate anycast receivers and the number of replays is limited to the count of receivers - 1. Such replays might also happen because of routing problems, so a payload protocol HAS TO be robust against a small number of duplicated packages. The window size and position HAS TO be syncronised between multible anycast receivers to limit this attack.
 578 </p>
 579 <a name="anchor25"></a><br /><hr />
 580 <table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
 581 <a name="rfc.section.6"></a><h3>6.&nbsp;
 582 IANA Considerations</h3>
 583
 584 <p>To use the protocol on top of UDP and IP protocol numberes have to be assiged by IANA.
 585 </p>
 586 <a name="rfc.references"></a><br /><hr />
 587 <table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
 588 <a name="rfc.section.7"></a><h3>7.&nbsp;
 589 References</h3>
 590
 591 <a name="rfc.references1"></a><br /><hr />
 592 <table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
 593 <h3>7.1.&nbsp;Normative References</h3>
 594 <table width="99%" border="0">
 595 <tr><td class="author-text" valign="top"><a name="RFC3711">[1]</a></td>
 596 <td class="author-text">Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman, &ldquo;<a href="ftp://ftp.isi.edu/in-notes/rfc3711.txt">The Secure Real-time Transport Protocol (SRTP)</a>,&rdquo; RFC&nbsp;3711, March&nbsp;2004.</td></tr>
 597 <tr><td class="author-text" valign="top"><a name="RFC2119">[2]</a></td>
 598 <td class="author-text"><a href="mailto:sob@harvard.edu">Bradner, S.</a>, &ldquo;<a href="ftp://ftp.isi.edu/in-notes/rfc2119.txt">Key words for use in RFCs to Indicate Requirement Levels</a>,&rdquo; BCP&nbsp;14, RFC&nbsp;2119, March&nbsp;1997 (<a href="ftp://ftp.isi.edu/in-notes/rfc2119.txt">TXT</a>, <a href="http://xml.resource.org/public/rfc/html/rfc2119.html">HTML</a>, <a href="http://xml.resource.org/public/rfc/xml/rfc2119.xml">XML</a>).</td></tr>
 599 <tr><td class="author-text" valign="top"><a name="RFC2003">[3]</a></td>
 600 <td class="author-text"><a href="mailto:perk@watson.ibm.com">Perkins, C.</a>, &ldquo;<a href="ftp://ftp.isi.edu/in-notes/rfc2003.txt">IP Encapsulation within IP</a>,&rdquo; RFC&nbsp;2003, October&nbsp;1996 (<a href="ftp://ftp.isi.edu/in-notes/rfc2003.txt">TXT</a>, <a href="http://xml.resource.org/public/rfc/html/rfc2003.html">HTML</a>, <a href="http://xml.resource.org/public/rfc/xml/rfc2003.xml">XML</a>).</td></tr>
 601 </table>
 602
 603 <a name="rfc.references2"></a><br /><hr />
 604 <table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
 605 <h3>7.2.&nbsp;Informational References</h3>
 606 <table width="99%" border="0">
 607 <tr><td class="author-text" valign="top"><a name="RFC2784">[4]</a></td>
 608 <td class="author-text"><a href="mailto:dino@procket.com">Farinacci, D.</a>, <a href="mailto:tony1@home.net">Li, T.</a>, <a href="mailto:stan_hanks@enron.net">Hanks, S.</a>, <a href="mailto:dmm@cisco.com">Meyer, D.</a>, and <a href="mailto:pst@juniper.net">P. Traina</a>, &ldquo;<a href="ftp://ftp.isi.edu/in-notes/rfc2784.txt">Generic Routing Encapsulation (GRE)</a>,&rdquo; RFC&nbsp;2784, March&nbsp;2000.</td></tr>
 609 <tr><td class="author-text" valign="top"><a name="RFC2401">[5]</a></td>
 610 <td class="author-text"><a href="mailto:kent@bbn.com">Kent, S.</a> and <a href="mailto:rja@corp.home.net">R. Atkinson</a>, &ldquo;<a href="ftp://ftp.isi.edu/in-notes/rfc2401.txt">Security Architecture for the Internet Protocol</a>,&rdquo; RFC&nbsp;2401, November&nbsp;1998 (<a href="ftp://ftp.isi.edu/in-notes/rfc2401.txt">TXT</a>, <a href="http://xml.resource.org/public/rfc/html/rfc2401.html">HTML</a>, <a href="http://xml.resource.org/public/rfc/xml/rfc2401.xml">XML</a>).</td></tr>
 611 <tr><td class="author-text" valign="top"><a name="RFC1546">[6]</a></td>
 612 <td class="author-text"><a href="mailto:craig@bbn.com">Partridge, C.</a>, <a href="mailto:tmendez@bbn.com">Mendez, T.</a>, and <a href="mailto:milliken@bbn.com">W. Milliken</a>, &ldquo;<a href="ftp://ftp.isi.edu/in-notes/rfc1546.txt">Host Anycasting Service</a>,&rdquo; RFC&nbsp;1546, November&nbsp;1993.</td></tr>
 613 </table>
 614
 615 <a name="rfc.authors"></a><br /><hr />
 616 <table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
 617 <h3>Author's Address</h3>
 618 <table width="99%" border="0" cellpadding="0" cellspacing="0">
 619 <tr><td class="author-text">&nbsp;</td>
 620 <td class="author-text">Othmar Gsenger</td></tr>
 621 <tr><td class="author-text">&nbsp;</td>
 622 <td class="author-text">Puerstingerstr 32</td></tr>
 623 <tr><td class="author-text">&nbsp;</td>
 624 <td class="author-text">Saalfelden  5760</td></tr>
 625 <tr><td class="author-text">&nbsp;</td>
 626 <td class="author-text">AT</td></tr>
 627 <tr><td class="author" align="right">Phone:&nbsp;</td>
 628 <td class="author-text"></td></tr>
 629 <tr><td class="author" align="right">Email:&nbsp;</td>
 630 <td class="author-text"><a href="mailto:satp@gsenger.com">satp@gsenger.com</a></td></tr>
 631 <tr><td class="author" align="right">URI:&nbsp;</td>
 632 <td class="author-text"><a href="http://www.gsenger.com/satp/">http://www.gsenger.com/satp/</a></td></tr>
 633 </table>
 634 <a name="rfc.copyright"></a><br /><hr />
 635 <table summary="layout" cellpadding="0" cellspacing="2" class="TOCbug" align="right"><tr><td class="TOCbug"><a href="#toc">&nbsp;TOC&nbsp;</a></td></tr></table>
 636 <h3>Full Copyright Statement</h3>
 637 <p class='copyright'>
 638 Copyright &copy; The IETF Trust (2007).</p>
 639 <p class='copyright'>
 640 This document is subject to the rights,
 641 licenses and restrictions contained in BCP&nbsp;78,
 642 and except as set forth therein,
 643 the authors retain all their rights.</p>
 644 <p class='copyright'>
 645 This document and the information contained herein are provided
 646 on an &ldquo;AS IS&rdquo; basis and THE CONTRIBUTOR,
 647 THE ORGANIZATION HE/SHE REPRESENTS
 648 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST
 649 AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES,
 650 EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT
 651 THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY
 652 IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR
 653 PURPOSE.</p>
 654 <h3>Intellectual Property</h3>
 655 <p class='copyright'>
 656 The IETF takes no position regarding the validity or scope of any
 657 Intellectual Property Rights or other rights that might be claimed
 658 to pertain to the implementation or use of the technology
 659 described in this document or the extent to which any license
 660 under such rights might or might not be available; nor does it
 661 represent that it has made any independent effort to identify any
 662 such rights.
 663 Information on the procedures with respect to
 664 rights in RFC documents can be found in BCP&nbsp;78 and BCP&nbsp;79.</p>
 665 <p class='copyright'>
 666 Copies of IPR disclosures made to the IETF Secretariat and any
 667 assurances of licenses to be made available,
 668 or the result of an attempt made to obtain a general license or
 669 permission for the use of such proprietary rights by implementers or
 670 users of this specification can be obtained from the IETF on-line IPR
 671 repository at <a href='http://www.ietf.org/ipr'>http://www.ietf.org/ipr</a>.</p>
 672 <p class='copyright'>
 673 The IETF invites any interested party to bring to its attention
 674 any copyrights,
 675 patents or patent applications,
 676 or other
 677 proprietary rights that may cover technology that may be required
 678 to implement this standard.
 679 Please address the information to the IETF at <a href='mailto:ietf-ipr@ietf.org'>ietf-ipr@ietf.org</a>.</p>
 680 <h3>Acknowledgment</h3>
 681 <p class='copyright'>
 682 Funding for the RFC Editor function is provided by
 683 the IETF Administrative Support Activity (IASA).</p>
 684 </body></html>