path: root/internet-draft-anycast-tcp-stream-relay.txt

Network Working Group                                         O. Gsenger
Internet-Draft                                                March 2007
Expires: September 2, 2007


                      Anycast TCP stream relaying
               draft-gsenger-anycast-tcp-stream-relay-00

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Copyright Notice

   Copyright (C) The IETF Trust (2007).















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Abstract

   The anycast tunneling (anytun) protocol defines a protocol used for
   communication between unicast clients and anycast servers.  It can be
   used for tunneling information between 2 clients over the servers or
   in relay mode to transmit data form the client over the servers to a
   third party not using the protocol and vice versa.












































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1.  full anycast tcp

1.1.  Introduction

   TCP is statefull, this is a big problem, because every anycast server
   has to know the tcp state.  The TCP state has to be synced between
   the servers, that meens a lot of overhead.  To keep this amount small
   and therefor make anycast TCP connections efficient some tricks MUST
   be used.  This is considered to be a real hack, so it is not
   recommendid to use this mode unless it is really necessary.  It might
   for instance be necessary to build connection trough special kind of
   NAT routers or firewalls.

1.2.  Reducing syncronisaton overhead

1.2.1.  Fragmentation

   The only way of fully supporting fragmentation would be to syncronise
   fragments between all anycast servers.  This is considered to be to
   much overhead, so there are two non perfect solutions for this
   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 ip datagram will get retransmitted by TCP and all
   fragments will arrive at the new server.

1.2.2.  sequence number

   It is nessarary to send tcp segments with a correct sequence number,
   that appear to come from the same host, in order to get a valid
   connecton to the client.  Syncronisation of sequence numbers would
   mean to much overhead, so it hast to be provided by the relayed data.
   The relayed data from the anycast serveres point of view, consits of
   multible datastream, each directed from one client to anotherIn
   tunneling mode all anytun packets from the client

1.3.  keep alive message request

   Most NAT routers need a tcp connection to transmit some packets once
   in while to stay open.  In full anycast tcp mode anytun hast to
   predict the tcp state including the sequence number.  Synconisation
   of the sequence number would be to much overhead, so a keep alive
   intervall is agreed.  This interval is used to calculate the sequemce
   number.







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Appendix A.  The appan


















































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2.  References

   [1]  Huitema, C., "An Anycast Prefix for 6to4 Relay Routers",
        RFC 3068, June 2001.















































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Author's Address

   Othmar Gsenger
   Sporgasse 6
   Graz  8010
   AT

   Phone:
   Email: otti@wirdorange.org
   URI:   http://anytun.org/









































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Full Copyright Statement

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