add docs for babeld

Signed-off-by: Marek Küthe <m.k@mk16.de>

docs/routing/babeld/babeld.md

@@ -0,0 +1,108 @@
+
+# Configuring babeld
+
+babeld is the reference implementation of the babel protocol. One difference to the bird implementation is that babeld can calculate the cost based on latency.
+
+## Installation
+
+In order to install the babeld on your machine you should look for a package named `babeld`. On a Debian-based system you can use:
+
+```bash
+sudo apt install babeld -y
+```
+
+To see if you have installed babeld correctly, you can view the babeld version:
+```bash
+babeld -V
+```
+
+If you are using a system with Systemd, you can enable babeld in the autostart:
+```bash
+sudo systemctl enable babeld
+```
+
+## Configuration
+
+The babeld configuration file is normally located at `/etc/babeld.conf`.
+
+### Full example
+
+```
+random-id true
+
+link-detect true
+
+default hello-interval 4
+default type tunnel rtt-min 1 rtt-max 1001 max-rtt-penalty 1000 enable-timestamps true
+
+interface <PEER> type tunnel
+
+redistribute ip <OWNNET> eq <OWN LENGTH> allow
+redistribute local deny
+redistribute deny
+
+in ip <OWNNET> deny
+in ip fd00::/8 le 64 ge 44 allow
+in deny
+```
+
+Replace `<OWNNET>` with your prefix and `<OWN LENGTH>` with your prefix length.
+
+```
+random-id true
+```
+No explicit router ID is set by this instruction. Instead, a new random ID is generated at each startup. This allows the router to integrate itself into the network more quickly after a reboot.
+
+```
+link-detect true
+```
+When you peer with a peer, you do so through an interface. With this instruction babeld fetches information from the operating system. If the operating system tells babeld that the interface is down, the peer on this interface is considered down.
+
+```
+default hello-interval 4
+```
+Here you can set the default interval in which babeld Hello should send packets to its neighbors. As with bird, 4 seconds are set here.
+
+```
+default type tunnel rtt-min 1 rtt-max 1001 max-rtt-penalty 1000 enable-timestamps true
+```
+This statement specifies that if a peer interface has type tunnel, the cost is equal to the latency. This only works if the peer also uses babeld.
+
+```
+interface <PEER> type tunnel
+```
+The individual peers are configured here. You can use `tunnel`, `wired` or `wireless` as type. Other parameters are adjusted accordingly. If you want to adjust the cost manually, you can write `rxcost <cost>`, replacing `<cost>` with the cost.
+
+```
+redistribute ip <OWNNET> eq <OWN LENGTH> allow
+redistribute local deny
+redistribute deny
+```
+Here the filters are defined, which come from the kernel into the babeld Routing Table. Only the own prefix is imported.
+
+```
+in ip <OWNNET> deny
+in ip fd00::/8 le 64 ge 44 allow
+in deny
+```
+Here the filters are defined, which routes are filtered from neighbors.
+The own route is not accepted. Only ULA addresses are accepted. All other routes are filtered.
+
+The `out` and `install` filters are omitted. The babeld routing table contains only CRXN routes. Therefore no filtering must be made with the export into the kernel or to neighbors.
+
+### Filter
+
+babeld has a total of five filters:
+- `in`
+- `out`
+- `redistribute`
+- `redistribute local`
+- `install`
+
+The filter `in` filters routes coming from neighbors.
+The filter `out` filters routes which are sent to neighbors.
+The filter `redistribute` filters routes which are imported by the kernel.
+The filter `redistribute local` filters routes which are imported by the kernel and have length 128.
+The `install` filter filters routes that are installed into the kernel.
+
+By default, all filters are set to `allow`. So all routes are accepted.

docs/routing/index.md

@@ -2,6 +2,11 @@
 # Routing
 
 - [Forwarding](forwarding)
+- [Create a dummy interface](create-dummy-interface)
+
+## bird
 - [Setting up Bird](bird/bird)
 - [max-len filter in bird](bird/maxlen-filter)
-- [Create a dummy interface](create-dummy-interface)
+
+## babeld
+- [Setting up Babeld](babeld/babeld)