Which routing protocol does Tinc use in router mode?

[marek22k]

Which routing protocol does Tinc use in router mode?

[gsliepen]

Because tinc doesn't know how your network interfaces are configured. This is done on purpose: it simplifies the code, and it actually makes tinc much more flexible. The Subnet statements indicate which subnets belong to which nodes. That information is exchanged between nodes, so that if one node receives a packet from its local tun/tap interface, it can look at the desination IP address, and find out which node owns the Subnet that best matches that address, and then send the packet to it. Note also that you can have multiple Subnet statements in a given host configuration file.

[gsliepen]

There might be some confusion here; "router mode" has nothing to do with the routing protocol that tinc uses internally to route packets between nodes. The same routing protocol is also used in switch and hub modes. What Mode does is change the way how tinc decides the destination node based in the header of the packet received from the tun/tap device. In router mode, it uses a routing table, the same as you see when you type ip route show or netstat -r. You can see this routing table by giving the command tinc -n $NETNAME dump subnets.

Tinc tries to send packets directly to the destination node. Only if that is not possible will it try to route it via intermediate nodes. The routing protocol used for that is a link-state routing protocol. From the link state it derives the shortest paths using Dijkstra's algorithm, and a minimum spanning tree using Kruskal's algorithm. The latter is used to handle broadcast packets.

[marek22k]

Many thanks for the answer!

I have one more question (I hope it's not too stupid): If a routing protocol is used, why is it necessary to specify Subnet = in the host configuration files?

[marek22k]

Thanks for the further answer! I took another look at Tinc today and apparently had a misunderstanding. I thought each node had to manually configure the subnets from every other node it is connected to. However, you only have to configure the subnet for your own node.

[marek22k]

Hi, I still have a question regarding the 'switch' mode:
The documentation states that Tinc can be bridged with other Ethernet segments, i.e. that Tinc can dynamically learn MAC addresses.
Does this not contradict the fact that these are specified via subnet?
How does Tinc learn these MAC addresses dynamically? I guess whenever a node sends out an Ethernet frame from itself, it sends the source address in an ADD_SUBNET message?!
Where are the first packets sent (if the destination is not known)? I guess a broadcast to all nodes?!
If there is MACExpire: Is the MAC address deleted at each node individually on or does the node with the ADD_SUBNET message send a DEL_SUBNET message when its MACExpire timer expires?