Network Working GroupO. Gsenger
Internet-DraftMarch 2007
Expires: September 2, 2007 


secure anycast tunneling protocol (satp)
draft-gsenger-secure-anycast-tunneling-protocol-00

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Copyright © The IETF Trust (2007).

Abstract

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.



1.  Introduction

SATP is somehow a mixture of a generic encapsulation protocol like GRE (Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. Traina, “Generic Routing Encapsulation (GRE),” March 2000.) [1] and a secure tunneling protocol as IPsec (Kent, S. and R. Atkinson, “Security Architecture for the Internet Protocol,” November 1998.) [2] in tunnel mode. To save some header overhead it uses the encryption technices of SRTP (Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman, “The Secure Real-time Transport Protocol (SRTP),” March 2004.) [3]. It supports peer to peer tunnels, where tunnel endpoints can be any combination of unicast, multicast or anycast hosts, so it defines a Host Anycast Service (Partridge, C., Mendez, T., and W. Milliken, “Host Anycasting Service,” November 1993.) [4]



2.  Motivation and usage scenarios

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.



2.1.  Usage scenarions



2.1.1.  tunneling from unicast hosts over anycast routers to other unicast hosts



An example of SATP used to tunnel in a unicast client - anycast server model

                    --------- router -----------
                   /                            \
    unicast ------+---------- router ------------+------ unicast
    host           \                            /        host
                    --------- router -----------

  unicast  | encrypted     |  anycast  | encrypted     |  unicast
  tunnel   | communication |  tunnel   | communication |  tunnel
  endpoint | using SATP    |  endpoint | using SATP    |  endpoint
 Figure 1 

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.



2.1.2.  tunneling from unicast hosts to anycast networks



An example of SATP used to encrypt data between a unicast host and anycast networks

                       -------Router -+---- DNS Server
                      /                \
                     /                  --- 6to4 Router
                    /
    unicast -------+----------Router --+--- DNS Server
    host            \                   \
                     \                   --- 6to4 Router
                      \
                       -------Router -+---- DNS Server
                                       \
                                        --- 6to4 Router

  unicast  | encrypted     |  anycast  | plaintext
  tunnel   | communication |  tunnel   | anycast
  endpoint | using SATP    |  endpoint | services

 Figure 2 



2.1.3.  redundant tunnel connection of 2 networks



An example of SATP used to connect 2 networks

              Router -----------   ---------------Router
            /                   \ /                     \
    Network - Router ------------x                       Network
       A    \                   / \                     /   B
              Router -----------   ---------------Router

            | packets       |  packets  |  packets      |
 plaintext  | get           |  take a   |  get          | plaintext
 packets    | de/encrypted  |  random   |  de/encrypted | packets
            |de/encapsulated|   path    |de/encapsulated|

 Figure 3 

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.



2.2.  Encapsulation

SATP does not depend on which lower layer protocols is used, but it's most likely used on top of IP or UDP. This section should only discuss some issues on IP and UDP in combination with anycasting and tunnels.



Examples of SATP used with different lower layer and payload protocols

    +------+-----+-------------------------------+
    |      |     |      + ---------------+------ |
    | IPv6 | UDP | SATP | Ethernet 802.3 | ... | |
    |      |     |      +----------------+-----+ |
    +------+-----+-------------------------------+

Tunneling of Ethernet over UDP/IPv6

    +------+-----+---------------------------+
    |      |     |      +------+-----+-----+ |
    | IPv4 | UDP | SATP | IPv6 | UDP | RTP | |
    |      |     |      +------+-----+-----+ |
    +------+-----+---------------------------+

Tunneling of IPv6 over UDP/IPv4 with RTP payload

    +------+-------------------------------+
    |      |      + ---------------+------ |
    | IPv6 | SATP | Ethernet 802.3 | ... | |
    |      |      +----------------+-----+ |
    +------+-------------------------------+

Tunneling of Ethernet over IPv6

    +------+---------------------------+
    |      |      +------+-----+-----+ |
    | IPv4 | SATP | IPv6 | UDP | RTP | |
    |      |      +------+-----+-----+ |
    +------+---------------------------+

Tunneling of IPv6 over IPv4 with RTP payload
 Figure 4 

When using UDP no flow control or retransmission is done, neither by UDP nor anytun. The encapsulated protocol HAS TO take care of this tasks if needed. UDP however has a checksum of the complete UDP datagram, so a packet gets discarded if there is a biterror in the payload



2.3.  Fragmentation

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.



3.  Protocol specification



3.1.  Header format



Protocol Format

        0                   1                   2                   3
      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         sequence number                       | |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+ |
     |           sender ID           #                               | |
   +#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+                               + |
   | |              ....        payload        ...                   | |
   | |-------------------------------+-------------------------------+ |
   | | padding (OPT) | pad count(OPT)|         payload type          | |
   +#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+#+-+
   | ~                          MKI (OPTIONAL)                       ~ |
   | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
   | :                 authentication tag (RECOMMENDED)              : |
   | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
   |                                                                   |
   +- Encrypted Portion*                      Authenticated Portion ---+
 Figure 5 



3.2.  sender ID

The sender ID is a 16bit unsigned integer. It HAS TO be unique for every sender sharing the same anycast address



3.3.  sequence number

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.



3.4.  payload

A packet of the type payload type (e.g. an IP packet).



3.5.  padding (OPTIONAL)

Padding of max 255 octets. None of the pre-defined encryption transforms uses any padding; for 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.



3.6.  padding count

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.



3.7.  payload type field

The payload type field defines the payload protocol. ETHER TYPE protocol numbers are used. See IANA assigned ethernet numbers . The values 0000-05DC are reserverd and MUST NOT be used.


Some examples for protocol types

HEX
0000 Reserved
.... Reserved
05DC Reserved
0800 Internet IP (IPv4)
6558 transparent ethernet bridging
86DD IPv6
 Figure 6 



3.8.  Encryption

Encryption is done in the same way as for SRTP (Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman, “The Secure Real-time Transport Protocol (SRTP),” March 2004.) [3]. This section will only discuss some small changes that HAVE TO be made.



4. References

[1] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. Traina, “Generic Routing Encapsulation (GRE),” RFC 2784, March 2000.
[2] Kent, S. and R. Atkinson, “Security Architecture for the Internet Protocol,” RFC 2401, November 1998 (TXT, HTML, XML).
[3] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman, “The Secure Real-time Transport Protocol (SRTP),” RFC 3711, March 2004.
[4] Partridge, C., Mendez, T., and W. Milliken, “Host Anycasting Service,” RFC 1546, November 1993.


Author's Address

  Othmar Gsenger
  Puerstingerstr 32/7
  Saalfelden 5760
  AT
Phone: 
Email:  satp@gsenger.com
URI:  http://www.gsenger.com/satp/


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