4 Network Working Group O. Gsenger
5 Internet-Draft June 21, 2007
6 Expires: December 23, 2007
9 secure anycast tunneling protocol (SATP)
10 draft-gsenger-secure-anycast-tunneling-protocol-00
14 By submitting this Internet-Draft, each author represents that any
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35 This Internet-Draft will expire on December 23, 2007.
39 Copyright (C) The IETF Trust (2007).
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62 The secure anycast tunneling protocol (SATP) defines a protocol used
63 for communication between any combination of unicast and anycast
64 tunnel endpoints. It allows tunneling of every ETHER TYPE protocol
65 (ethernet, ip ...). SATP directly includes cryptography and message
66 authentication based on the methodes used by SRTP. It can be used as
67 an encrypted alternative to IP Encapsulation within IP [3] and
68 Generic Routing Encapsulation (GRE) [4]. It supports both anycast
69 receivers and senders.
74 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
75 1.1. Notational Conventions . . . . . . . . . . . . . . . . . . 3
76 2. Motivation and usage scenarios . . . . . . . . . . . . . . . . 4
77 2.1. Usage scenarions . . . . . . . . . . . . . . . . . . . . . 4
78 2.1.1. Tunneling from unicast hosts over anycast routers
79 to other unicast hosts . . . . . . . . . . . . . . . . 4
80 2.1.2. Tunneling from unicast hosts to anycast networks . . . 5
81 2.1.3. Redundant tunnel connection of 2 networks . . . . . . 5
82 2.2. Encapsulation . . . . . . . . . . . . . . . . . . . . . . 6
83 3. Using SATP on top of IP . . . . . . . . . . . . . . . . . . . 8
84 3.1. Fragmentation . . . . . . . . . . . . . . . . . . . . . . 8
85 3.2. ICMP messages . . . . . . . . . . . . . . . . . . . . . . 8
86 4. Protocol specification . . . . . . . . . . . . . . . . . . . . 9
87 4.1. Header format . . . . . . . . . . . . . . . . . . . . . . 9
88 4.2. sender ID . . . . . . . . . . . . . . . . . . . . . . . . 9
89 4.3. sequence number . . . . . . . . . . . . . . . . . . . . . 9
90 4.4. payload . . . . . . . . . . . . . . . . . . . . . . . . . 9
91 4.5. padding (OPTIONAL) . . . . . . . . . . . . . . . . . . . . 9
92 4.6. padding count (OPTIONAL) . . . . . . . . . . . . . . . . . 10
93 4.7. payload type field . . . . . . . . . . . . . . . . . . . . 10
94 4.7.1. MKI (OPTIONAL) . . . . . . . . . . . . . . . . . . . . 10
95 4.7.2. authentication tag (RECOMMENDED) . . . . . . . . . . . 10
96 4.8. Encryption . . . . . . . . . . . . . . . . . . . . . . . . 10
97 5. Security Considerations . . . . . . . . . . . . . . . . . . . 12
98 5.1. Replay protection . . . . . . . . . . . . . . . . . . . . 12
99 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
100 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
101 7.1. Normative References . . . . . . . . . . . . . . . . . . . 14
102 7.2. Informational References . . . . . . . . . . . . . . . . . 14
103 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 16
104 Intellectual Property and Copyright Statements . . . . . . . . . . 17
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118 SATP is a mixture of a generic encapsulation protocol like GRE [4]
119 and a secure tunneling protocol as IPsec [5] in tunnel mode. It can
120 be used to build redundant virtual private network (VPN) connections.
121 It supports peer to peer tunnels, where tunnel endpoints can be any
122 combination of unicast, multicast or anycast hosts, so it defines a
123 Host Anycast Service [6]. Encryption is done per packet, so the
124 protocol is robust against packet loss and routing changes. To save
125 some header overhead it uses the encryption techniques of SRTP [1].
127 1.1. Notational Conventions
129 The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
130 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
131 document are to be interpreted as described in RFC2119 [2].
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172 2. Motivation and usage scenarios
174 This section gives an overview of possible usage scenarios. Please
175 note, that the protocols used in the figures are only examples and
176 that SATP itself does not care about either transport protocols or
177 encapsulated protocols. Routing is not done by SATP and each
178 implemetation MAY choose it's own way of doing this task (e.g. using
179 functions provided by the operating system). SATP is used only to
180 encapsulate and encrypt data.
182 2.1. Usage scenarions
184 2.1.1. Tunneling from unicast hosts over anycast routers to other
187 An example of SATP used to tunnel in a unicast client - anycast
190 --------- router -----------
192 unicast ------+---------- router ------------+------ unicast
194 --------- router -----------
196 unicast | encrypted | anycast | encrypted | unicast
197 tunnel | communication | tunnel | communication | tunnel
198 endpoint | using SATP | endpoint | using SATP | endpoint
202 In this scenario the payload gets encapsuleted into a SATP packet by
203 a unicast host and gets transmitted to one of the anycast routers.
204 It than gets decapsulated by the router. This router makes a routing
205 descision based on the underlying protocol and transmits a new SATP
206 package to one or more unicast hosts depending on the routing
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228 2.1.2. Tunneling from unicast hosts to anycast networks
230 An example of SATP used to encrypt data between a unicast host and
233 -------Router -+---- DNS Server
237 unicast -------+----------Router --+--- DNS Server
241 -------Router -+---- DNS Server
245 unicast | encrypted | anycast | plaintext
246 tunnel | communication | tunnel | anycast
247 endpoint | using SATP | endpoint | services
252 When the unicast hosts wants to transmit data to one of the anycast
253 DNS servers, it encapsulates the data and sends a SATP packet to the
254 anycast address of the routers. The packet arrives at one of the
255 routers, gets decapsulated and routed to the DNS server. This method
256 can be used to tunnel between a clients and networks providing
257 anycast services. It can also be used the other way to virtually
258 locate a unicast service within anycasted networks.
260 2.1.3. Redundant tunnel connection of 2 networks
262 An example of SATP used to connect 2 networks
264 Router ----------- ---------------Router
266 Network - Router ------------x Network
268 Router ----------- ---------------Router
270 | packets | packets | packets |
271 plaintext | get | take a | get | plaintext
272 packets | de/encrypted | random | de/encrypted | packets
273 |de/encapsulated| path |de/encapsulated|
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286 Network A has multiple routers, that act as gateway/tunnel endpoints
287 to another network B. This is done to build a redundant encrypted
288 tunnel connection between the two networks. All tunnel endpoints of
289 network A share the same anycast address and all tunnel endpoints of
290 network B share another anycast address. When a packet from network
291 A gets transmitted to network B, it first arrives on one of network
292 A's border routers. Which router is used is determined by network
293 A's internal routing. This router encapsulates the package and sends
294 it to the anycast address of the network B routers. The SATP packet
295 arrives at one of network B's routers and gets decapsulated and
296 routed to it's destination within network B.
300 SATP does not depend on which lower layer protocols is used, but this
301 section gives an example of how packets could look like.
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340 Examples of SATP used with different lower layer and payload
343 +------+-----+-------------------------------+
344 | | | + ---------------+------ |
345 | IPv6 | UDP | SATP | Ethernet 802.3 | ... | |
346 | | | +----------------+-----+ |
347 +------+-----+-------------------------------+
349 Tunneling of Ethernet over UDP/IPv6
351 +------+-----+---------------------------+
352 | | | +------+-----+-----+ |
353 | IPv4 | UDP | SATP | IPv6 | UDP | RTP | |
354 | | | +------+-----+-----+ |
355 +------+-----+---------------------------+
357 Tunneling of IPv6 over UDP/IPv4 with RTP payload
359 +------+-------------------------------+
360 | | + ---------------+------ |
361 | IPv6 | SATP | Ethernet 802.3 | ... | |
362 | | +----------------+-----+ |
363 +------+-------------------------------+
365 Tunneling of Ethernet over IPv6
367 +------+---------------------------+
368 | | +------+-----+-----+ |
369 | IPv4 | SATP | IPv6 | UDP | RTP | |
370 | | +------+-----+-----+ |
371 +------+---------------------------+
373 Tunneling of IPv6 over IPv4 with RTP payload
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396 3. Using SATP on top of IP
400 The only way of fully supporting fragmentation would be to
401 synchronise fragments between all anycast servers. This is
402 considered to be too much overhead, so there are two non perfect
403 solutions for these problems. Either fragmentation HAS TO be
404 disabled or if not all fragments arrive at the same server the ip
405 datagramm HAS TO be discarded. As routing changes are not expected
406 to occure very frequently, the encapsulated protocol can do a
407 retransmission and all fragments will arrive at the new server.
409 If the payload type is IP and the ip headers's Don't Fragment (DF)
410 bit is set, than the DF bit of the outer IP header HAS TO be set as
415 ICMP messages MUST be relayed according to rfc2003 section 4 [3].
416 This is needed for path MTU detection.
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452 4. Protocol specification
459 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
460 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
461 | sequence number | |
462 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+ |
464 +#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+ + |
465 | | .... payload ... | |
466 | |-------------------------------+-------------------------------+ |
467 | | padding (OPT) | pad count(OPT)| payload type | |
468 +#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+-+
469 | ~ MKI (OPTIONAL) ~ |
470 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
471 | : authentication tag (RECOMMENDED) : |
472 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
474 +- Encrypted Portion Authenticated Portion ---+
480 The sender ID is a 16 bit unsigned integer. It HAS TO be unique for
481 every sender sharing the same anycast address
485 The sequence number is a 32 bit unsigned integer in network byte
486 order. It starts with a random value and is increased by 1 for every
487 sent packet. After the maximum value, it starts over from 0. This
488 overrun causes the ROC to be increased.
492 A packet of the type payload type (e.g. an IP packet).
494 4.5. padding (OPTIONAL)
496 Padding of max 255 octets. None of the pre-defined encryption
497 transforms uses any padding; for these, the plaintext and encrypted
498 payload sizes match exactly. Transforms are based on transforms of
499 the SRTP protocol and these transforms might use the RTP padding
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508 format, so a RTP like padding is supported. If the padding count
509 field is present, than the padding count field MUST be set to the
512 4.6. padding count (OPTIONAL)
514 The number of octets of the padding field. This field is optional.
515 It's presence is signaled by the key management and not by this
516 protocol. If this field isn't present, the padding field MUST NOT be
519 4.7. payload type field
521 The payload type field defines the payload protocol. ETHER TYPE
522 protocol numbers are used. See IANA assigned ethernet numbers [7] .
523 The values 0000-05DC are reserverd and MUST NOT be used.
525 Some examples for protocol types
531 0800 Internet IP (IPv4)
532 6558 transparent ethernet bridging
537 4.7.1. MKI (OPTIONAL)
539 The MKI (Master Key Identifier) is OPTIONAL and of configurable
540 length. See SRTP Section 3.1 [1] for details
542 4.7.2. authentication tag (RECOMMENDED)
544 The authentication tag is RECOMMENDED and of configurable length. It
545 contains a cryptographic checksum of the sender ID, sequence number
546 and the encrypted portion, but not of the MKI. On sender side
547 encryption HAS TO be done before calculating the authentication tag.
548 A receiver HAS TO calculate the authentication tag before decrypting
549 the encrypted portion.
553 Encryption is done in the same way as for SRTP [1]. This section
554 will only discuss some small changes that HAVE TO be made. Please
555 read SRTP RFC3711 section 3-9 [1] for details.
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564 The least significant bits of SSRC are replaced by the sender ID and
565 the rest is filled with zeros. For the SRTP SEQ the 16 least
566 significant bits of the SATP sequence number are used and the 16 most
567 significant bits of the sequence number replace the 16 least
568 significant bits of the SRTP ROC.
570 Difference between SRTP and SATP
573 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
574 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
575 | SATP sequence number |
576 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
578 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
579 | SRTP ROC least significant | SRTP SEQ |
580 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
584 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
585 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
586 |0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0| SATP sender ID |
587 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
589 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
591 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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620 5. Security Considerations
622 As SATP uses the same encrytion technics as SRTP [1], it shares the
623 same security issues. This section will only discuss some small
624 changes. Please read SRTP RFC3711 section 9 [1] for details.
626 5.1. Replay protection
628 Replay protection is done by a replay list. Every anycast receiver
629 has it's own replay list, which SHOULDN'T be syncronised, because of
630 massive overhead. This leads to an additional possible attack. A
631 attacker is able to replay a captured packet once to every anycast
632 receiver. This attack is considered of be very unlikely, because
633 multiple attack hosts in different loactions are needed to reach the
634 seperate anycast receivers and the number of replays is limited to
635 the count of receivers - 1. Such replays might also happen because
636 of routing problems, so a payload protocol HAS TO be robust against a
637 small number of duplicated packages. The window size and position
638 HAS TO be syncronised between multible anycast receivers to limit
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676 6. IANA Considerations
678 The protocol is intended to be used on top of IP or on top of UDP (to
679 be compatible with NAT routers), so UDP and IP protocol numbers have
680 to be assiged by IANA.
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734 7.1. Normative References
736 [1] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
737 Norrman, "The Secure Real-time Transport Protocol (SRTP)",
738 RFC 3711, March 2004.
740 [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
741 Levels", BCP 14, RFC 2119, March 1997.
743 [3] Perkins, C., "IP Encapsulation within IP", RFC 2003,
746 7.2. Informational References
748 [4] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. Traina,
749 "Generic Routing Encapsulation (GRE)", RFC 2784, March 2000.
751 [5] Kent, S. and R. Atkinson, "Security Architecture for the
752 Internet Protocol", RFC 2401, November 1998.
754 [6] Partridge, C., Mendez, T., and W. Milliken, "Host Anycasting
755 Service", RFC 1546, November 1993.
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790 [7] <http://www.iana.org/assignments/ethernet-numbers>
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852 Email: satp@gsenger.com
853 URI: http://www.gsenger.com/satp/
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900 Full Copyright Statement
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