Anycast stream relaying

This section gives an overview of possible operation modes und usage scenarios. Please note, that the protocols used in the figures are only examples and that anytun itself does not care about either transport protocols or encapsulated protocols. Routing and network address translation is not done by anytun. Each implemetation MAY choose it's own way of doing this task (e.g. using functions provided by the operating system). Anytun is used to establish and controll tunnnels, to encapsulate and encrypt data.

An example of anytun used in tunnel mode ----------- ----------- | RTP | ---------- | RTP | ----------- -> |server 1| -> ----------- | UDP | ---------- | UDP | ----------- ----------- ----- | IPv6 | ---------- | IPv6 | ----- | | -> ----------- -> |server 2| -> ----------- -> | | ----- | anytun | ---------- | anytun | ----- ##### ----------- ----------- ##### | UDP | ---------- | UDP | client 1 ----------- -> |server 3| -> ----------- client 2 | IPv4 | ---------- | IPv4 | ----------- ----------- | ... | anycast | ... | In tunneling mode the payload of the anytun packet is transmitted from one unicast host to the anycast server. This server makes a routing descision based on the underlying protocol and transmits a new anytun package to one or more clients depending on the routing descition. The server MAY also route the packet to a directly connected network or a service running on the server, but please note, that this is only usefull for anycast host services like DNS and that the services HAVE TO be running on all servers in order to work.

An example of anytun used in open tunnel mode ----------- | RTP | ---------- ----------- -> |server 1| -> | UDP | ---------- ----------- ----------- | RTP | ----- | IPv6 | ---------- ----------- ----- | | -> ----------- -> |server 2| -> | UDP* | -> | | ----- | anytun | ---------- ----------- ----- ##### ----------- | IPv6* | ##### | UDP | ---------- ----------- client 1 ----------- -> |server 3| -> | ... | host | IPv4 | ---------- not using ----------- anytun | ... | anycast *changed source address or port In open tunnel mode only one of two clients talking to each other over the servers MUST use the anytun protocol. When a client using the anytun protocol wants to tunnel data, it is building a connection to the anycast servers using the anytun protocol. The anycast servers relay the encapsulated packages directly to the destination without using the anytun protocol. The source address of the datagramm HAS TO be changed to the anycast address of the server. The anytun servers act like a source NAT router, therefor for the destination it saems that it is talking to the client directly.

An example of anytun used in relay mode ----------- ----- | RTP | ---------- | | -> ----------- -> |server 1| -> ----- | UDP** | ---------- ----------- ##### ----------- | RTP | | IPv6**| ---------- ----------- ----- host ----------- -> |server 2| -> | UDP* | -> | | not using | ... | ---------- ----------- ----- anytun | IPv6* | ##### ---------- ----------- ----------- -> |server 3| | ... | host ----- | anytun | ---------- not using | | -> ----------- anytun ----- | IPv4 | anycast ##### ----------- connection| ... | controller *changed source address or port **changed destination address or port In relay mode the anycast serveres directly repaet the packetes of clients, only the source and destination addresses are changed. The anytun protocol is only used for controll messages, but not fr encapsulation.

An example of anytun used with udp transport ----------- ----------- | RTP | ---------- | RTP | ----------- -> |server 1| -> ----------- | UDP | ---------- | UDP | ----------- ----------- ----- | IPv6 | ---------- | IPv6 | ----- | | -> ----------- -> |server 2| -> ----------- -> | | ----- | anytun | ---------- | anytun | ----- ##### ----------- ----------- ##### | UDP | ---------- | UDP | client 1 ----------- -> |server 3| -> ----------- client 2 | IPv4 | ---------- | IPv4 | ----------- ----------- | ... | anycast | ... | In anycast udp mode the data between clients and anycast serveres is carried by udp packets. Packets are routed by the serveres from one client to another. Because udp is stateless no inforamtion has to be syncronised

An example of anytun used with udp transport ----------- ----------- | RTP | ---------- | RTP | ----------- -> |server 1| -> ----------- | UDP | ---------- | UDP | ----------- ----------- ----- | IPv6 | ---------- | IPv6 | ----- | | -> ----------- -> |server 2| -> ----------- -> | | ----- | anytun | ---------- | anytun | ----- ##### ----------- ----------- ##### |lightUDP | ---------- |lightUDP | client 1 ----------- -> |server 3| -> ----------- client 2 | IPv4 | ---------- | IPv4 | ----------- ----------- | ... | anycast | ... | The light UDP mode is neerly the same as the normal UDP mode, the only difference is, that the udp size is set to the udp header lenght and not to the length of the full packet and therefor the checksum is only calculated for the udp header itself. So there is no error correction or detection done on the payload. This can be usefull if realtime data is beeing transimittet or the tunneled protocol does error correction/detection by itself.

TCP is statefull, this is a big problem, because everey anycast server hast 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 SHOULD be used.

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.