From f4887b981f109fc4264f50170b2d12c4033bf5e9 Mon Sep 17 00:00:00 2001 From: Guus Sliepen Date: Sun, 4 Mar 2001 14:00:24 +0000 Subject: [PATCH] Added a description of what is going on in net.c and route.c, and how packets flow through tinc. --- doc/NETWORKING | 83 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 83 insertions(+) create mode 100644 doc/NETWORKING diff --git a/doc/NETWORKING b/doc/NETWORKING new file mode 100644 index 00000000..66b03eda --- /dev/null +++ b/doc/NETWORKING @@ -0,0 +1,83 @@ +This is the network infrastructure documentation for tinc, a Virtual Private +Network daemon. + + Copyright 2001 Guus Sliepen + + Permission is granted to make and distribute verbatim copies of + this documentation provided the copyright notice and this + permission notice are preserved on all copies. + + Permission is granted to copy and distribute modified versions of + this documentation under the conditions for verbatim copying, + provided that the entire resulting derived work is distributed + under the terms of a permission notice identical to this one. + + $Id: NETWORKING,v 1.1.2.1 2001/03/04 14:00:24 guus Exp $ + +1. Packet flow +============== + +There are two directions for packets. There are packets received from the tap +device that have to be sent out to other tinc daemon, and there are packets +that are received from other tinc daemons which have to be send to the tap +device. The first direction will be called the outgoing direction, while the +latter will be called the incoming direction. + +1.1 Outgoing flow +----------------- + + handle_tap_input() + | + | + V + route_outgoing() + | + | + V + send_packet() ---- + / \ / \ + / \ | queue + V V V / +send_tcppacket() send_udppacket()-- + +Packets are read from the tap device by handle_tap_input(). The packets will be +marked as coming from ourself, and are then handled by route_outgoing(). This +function will determine the destination tinc daemon this packet has to be sent +to, and in the future it may also determine if this packet has to be broadcast +or multicast. route_outgoing() will call send_packet() (in case of +broad/multicast several times). send_packet() will check the destination +connection_t entry to see if it is a valid destination, and whether it has to +be sent via TCP or UDP. It will then either call send_tcppacket() or +send_udppacket(). Since a different key is used for UDP packets, which might +not be available at that time, send_udppacket() might put the packet in a queue +and send a REQ_KEY to the destination tinc daemon. If the key has been retrieved, +the packet will be fed to send_udppacket() again. + +1.2 Incoming flow +----------------- + + handle_vpn_input() + | + | + V +tcppacket_h() receive_udppacket() + \ / + \ / + V V + receive_packet() + | + | + V + route_incoming() + | + | + V + accept_packet() + +Packets from other tinc daemons can be received by tcppacket_h(), for TCP +packets, and receive_udppacket() via handle_vpn_input() for UDP packets. +receive_packet() actually does not have to do much, except logging and calling +route_incoming(), but it's there for symmetry with the scheme for the outgoing +flow. route_incoming() will change the MAC header of the packet if necessary to +let the kernel accept the packet after it has been sent to the tap device by +accept_packet(). -- 2.20.1