Merge pull request 'add docs for babeld' (#23) from mark22k/docs:babeld into master

Reviewed-on: https://codeberg.org/CRXN/docs/pulls/23

docs/routing/babeld/babeld.md

@@ -0,0 +1,148 @@
+
+# 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 `redistribute local` filter filters routes that are imported from the kernel and bound locally to an interface.
+The `install` filter filters routes that are installed into the kernel.
+
+By default, all filters are set to `allow`. So all routes are accepted.
+
+### Setting up the static routes
+
+In order for babeld to know and propagate your own prefix, it must be statically defined. In bird you can do this with the `protocol static`. babeld takes its routing information from the kernel routing table. Therefore there must be a static route to its own prefix in the kernel routing table.
+This can be created with the following command:
+```
+ip route add unreachable <OWNNET> proto static
+```
+This route does not survive a reboot (volatile). The protocol `proto static` is necessary, because babeld ignores the default protocol. 
+
+You can delete it with the following command:
+```
+ip route del <OWNNET>
+```
+
+## Start babeld
+
+If you use a system with Systemd, you can use it to start:
+```
+sudo systemctl start babeld
+```
+
+Alternatively, you can start babel with the following command:
+```
+babeld -c <config>
+```
+`<config>` will be replaced with the path to the configuration file.
+
+## Kernel parameters
+
+Once babeld is started, forwarding is enabled in the kernel for IPv4 and IPv6. As soon as babeld is stopped, forwarding is deactivated again. A separate enabling like with bird is not necessary. So if you use babeld, you can ignore the steps of [IPv6 forwarding](../forwarding).
+
+## Further links
+
+- [babeld homepage](https://www.irif.fr/~jch/software/babel/)
+- [babeld MAC authentication](https://alioth-lists.debian.net/pipermail/babel-users/2021-June/003827.html)
+- [babeld manuel](https://www.irif.fr/~jch/software/babel/babeld.html)
+- [babeld FAQ](https://www.irif.fr/~jch/software/babel/faq.html)
+- [babeld mailling list](https://alioth-lists.debian.net/pipermail/babel-users/)
+- [babeld source code](https://github.com/jech/babeld)

docs/routing/forwarding.md

@@ -1,3 +1,4 @@
+
 # IPv6 forwarding
 
 ## Enabling forwarding

docs/routing/index.md

@@ -1,7 +1,12 @@
 
 # Routing
 
-- [Forwarding](forwarding)
+- [IPv6 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)