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Configuring Bird2

We now need to configure the routing daemon for your router which will allow you to exchange routes with other routers over the tunnels you will setup later. This is at the core of what makes CRXN an inter-network.

The software we use for this procedure is known as BIRD or BIRD Internet Routing Daemon, of which there are two versions:

  1. Bird 1.6
  2. Bird 2

You can use Bird 1.6 but you are on your own then in terms of configuration, the syntax differs slightly but we recommend (and for the rest of this document we will be) using Bird 2 as it comes with many bug fixes and improvements and most distributions (including Debian) now have support for it.

Installation

In order to install the BIRD daemon on your machine you should look for a package named bird2 or something similar (some repositories name it slightly differently - such as just bird). On a Debian-based system you can use:

sudo apt install bird2 -y

You can confirm that the version of BIRD you installed is version 2 with the command bird -v. If that shows the correct version number then continue to the next step:

sudo systemctl enable --now bird

This will ensure that the routing daemon starts on boot.

Configuration

In this section we will be configuring two files:

  1. bird.conf
    • For general BIRD configuration e.g. router IDs, device protocol and includes
  2. crxn.conf
    • For CRXN-specific details

Basics

There are some basic definition that we are required to add to our configuration file. BIRD is normally configured to use the base configuration stored at something like /etc/bird/bird.conf or /etc/bird.conf, so open that file up and add the following to it.

Router ID

Every BIRD daemon is required to have what is known as a router ID which is written in the form of an IPv4 address. Now this does not actually need to be a valid IPv4 address in the sense of one you actually use but rather it just needs to follow the format, hence a router ID such as 1.1.1.1 is fine, despite you not "owning it".

Define the router ID as the first line in the configuration file like so:

router id 1.1.1.1;

TODO: These need to be unique - check how much this applies etc

These router IDs are required to be unique as they are used in the various protocols that BIRD supports in order to determine where a route advertisement came from - see them as a unique identifier of your BIRD router. Failing to do so will cause issues when routing on CRXN and a banning (TODO: see how we can enforce this).

Device protocol

BIRD supports many protocols which are used to import routing data from and export routing data to. However, the most basic of protocols which BIRD supports is known as the device protocol. The job of this protocol is just to provide basic device information to BIRD over time, it is required but luckily does not require much setup.

All that is required for this protocol to work is the following:

protocol device
{
    # Optional parameters go here
}

You can adjust scan times and such but the kernel normally will signal any changes to BIRD.

Includes

BIRD allows one to source configuration file contents from other files. Seeing that we will configure the CRXN-specific parts next we will want to include that file in the main entry file (bird.conf), this can be accomplished by placing this line at the bottom of said file:

include "/etc/crxn.conf";

CRXN-specific setup

The below sections all apply to the CRXN-specific configuration and are to be placed in the file /etc/crxn.conf.

Tables

We need to define the routing tables that BIRD will use in its process to store the routes that we want to learn from other routers and also advertise. Such a definition looks as follows:

# Define the IPv6 BIRD table
ipv6 table crxn;

You can choose any name for the table you want but you will just need to remember it such that you can refer to it later when it is needed.

Filters

We need to define a filter which will be used to filter out any incorrect routes we want to advertise to the network but also prevents any incorrect routes that are being propagated from any misconfigured BIRD instances on the network:

filter crxnFilter
{
    if (net ~ fd00::/8) then accept;
    reject;
}

TODO: Add a check about not installing RTD_UNREACHABLEs which babel will generate sometimes and which BIRD reportedly has undefined behavior with

Direct protocol

TODO: fix/finish this section

This provides BIRD with a manner of picking up the subnet/prefix pair that is assigned to local interfaces such that these can be imported into BIRD and later advertised.

protocol direct crxnDirect
{
    ipv6
    {
        table crxn;
        import filter crxnFilter;
    };
    # Interfaces to find neighbours on
    interface "eth*";
}

Old stuff below WIP):

TODO: Re-do this sections

The configuration template is constructed out of the following files:

  1. filters.conf
    • Filter functions and the filter itself
  2. networks.conf
    • Advertisement of ULA
  3. tables.conf
    • The table definitions
  4. router.conf
    • This contains the needed protocol definition for discovering your interface's prefixes and generating routes form them
    • It also contains the needed protocol definitions to sync bird routes into the Linux kernel's routing table (so you cna forward packets based on the routes from Bird)
  5. protocols.conf
    • Depending on what protocol you want to use this will contains configurations for each

All of these will be included in a file saved at /etc/bird/bird.conf like so:

router id <ipv4>;

include "/etc/bird/crxn/tables.conf";
include "/etc/bird/crxn/filters.conf";
include "/etc/bird/crxn/router.conf";
include "/etc/bird/crxn/networks.conf";

Additionally, add the files for the route distribution protocol which we configure in the next steps.

include "/etc/bird/crxn/babel.conf"; # For babel routing
include "/etc/bird/crxn/ospfv3.conf"; # For OSPFv3 routing

Remember to set a unique router ID in <ipv4>, make it anything - it doesn't have to even be an address you own.

filters.conf

This file holds all the required functions for subnet matching and also filters that match to the specific prefix aggregates (regional subnets) that CRXN uses.

filter crxnFilter
{
    if (net ~ fd00::/8) then accept;
    reject;
}

tables.conf

This file holds all table definitions. There are only two actually. The table crxn is the one we actually use, master is optional and is only present because if one uses bird-lg-go (the looking glass we use) then it, by default, only shows routes in the master table. It is meant to have the same routes as the crxn table.

# CRXN table
ipv6 table crxn;

router.conf

This contains an instance of the direct protocol which reads the address and prefix assigned to your AF_INET6 interfaces and generates routes from those that represent routes to directly atrtached networks those interfaces are on. The reason for this is that the kernel protocol never learns routes in the Linux kernel's routing table that have the kernel protocol which is what you get when you assign interfaces addresses and prefixes. This doesn't even need those, it gets them from the interface.

# The kernel protocol doesn't grab kernel routes that are added by you when you assign an
# address and prefix. So instead of reading this from all routes with `proto kernel` this just
# yeets the routes off of the interface structure itself (even if you didn't have a route for your
# directly attached networks - i.e. nexthop = 0.0.0.0)
protocol direct crxnDirect
{
    ipv6
    {
        table crxn;
        import filter crxnFilter;
    };
    # Interfaces to find neighbours on
    interface "eth*";
}

protocol device {
}

The second part is for syncing routes from Bird to the Linux kernel's routing table such that you can forward traffic based on the routes in Bird.

TODO: Check, defualt learn should learn non kernel and non-bird routes

# CRXN Kernel protocol
# We import any routes from the kernel table other than `proto bird` and `proto kernel`,
# could be `proto static` for example. By default it will learn these.
# Of course we also then export all routes from our Bird tables into the kernel so you can actually forward packets
protocol kernel crxnKernel
{
    ipv6 {
        # bird's crxn table -> kernel
        table crxn;
        export filter crxnFilter;
    };
}

networks.conf

This is just something we normally add. Usually you would assign a /64 within your ULA /48 but you also want to claim the whole /48 by advertising a blackhole for it. Here our /48/ULA is fd40:ec65:5b4c::/48.

protocol static crxnStatic
{
        # Advertise your /48 with a blackhole
        route fd40:ec65:5b4c::/48 blackhole;

        ipv6 {
                import filter crxn6;
                table crxn;
        }
}