BIRD 2: BGPv4 + BGPv6 sessions to VeryCloud (AS198825)

Introduction

BIRD (BIRD Internet Routing Daemon) is one of the two reference open-source routing daemons in the operator world (FRR being the other). BIRD 2.x unifies IPv4 and IPv6 in a single daemon with clean syntax, and runs single-threaded very efficiently — it powers many Looking Glasses and IXP route-servers (FranceIX included).

This tutorial shows how to bring up a dual-stack BGP session to VeryCloud (AS198825) once your GRE/VXLAN/WireGuard tunnel is up.

Prerequisites

• A Linux server with an up tunnel to VeryCloud (see transport tutorials)
• VeryCloud's technical email with: 169.254.X.1 (v4 peer), 2a0e:XXXX:XXXX::0 (v6 peer), MD5 password if chosen
• Your ASN (public e.g. AS65000 or private 64512-65534)
• Your IPv4 and IPv6 prefixes to announce
• BIRD 2.x installed

Step 1: Install BIRD 2

# Debian / Ubuntu
sudo apt install -y bird2

# RHEL / Rocky / Alma
sudo dnf install -y bird

bird --version

💡 BIRD 1.x (legacy) had separate v4/v6 daemons (bird and bird6). BIRD 2 unifies. If you still have BIRD 1, migrate now.

Step 2: Config structure

/etc/bird/bird.conf follows this logical structure:

1. Variables and global router-id
2. Base protocols (device, kernel, direct, static)
3. BGP templates (optional but clean)
4. Filters (in/out)
5. BGP sessions (one per peer)

BIRD works with routing tables (master4 and master6 by default) and each protocol imports/exports routes from/to these tables with filters.

Step 3: Variables and prefixes

At the top of /etc/bird/bird.conf:

log syslog all;
log "/var/log/bird.log" all;

router id 192.0.2.1;

define MY_PREFIXES_V4 = [
    192.0.2.0/24,
    198.51.100.0/24
];

define MY_PREFIXES_V6 = [
    2001:db8::/32
];

define VC_ASN = 198825;

⚠️ router id must be a unique IPv4 on your machine. If you only have IPv6, use an arbitrary internal /32 (e.g. 0.0.0.1).

Step 4: Base protocols

protocol device {
    scan time 10;
}

protocol kernel {
    ipv4 {
        export all;
        import none;
    };
    merge paths on;
}

protocol kernel {
    ipv6 {
        export all;
        import none;
    };
    merge paths on;
}

protocol direct {
    ipv4;
    ipv6;
    interface "lo", "eth0", "wg-vc", "gre-vc", "vxlan-vc";
}

protocol static static_v4 {
    ipv4;
    route 192.0.2.0/24 blackhole;
    route 198.51.100.0/24 blackhole;
}

protocol static static_v6 {
    ipv6;
    route 2001:db8::/32 blackhole;
}

blackhole routes are perfect for "anchor" prefixes: they exist in BIRD's table, announced via BGP, traffic without a more specific route goes to null.

Step 5: Filters

filter bgp_in_v4 {
    if net = 0.0.0.0/0 then accept;
    if net.len > 24 then reject;
    if net.len < 8 then reject;
    accept;
}

filter bgp_in_v6 {
    if net = ::/0 then accept;
    if net.len > 48 then reject;
    if net.len < 16 then reject;
    accept;
}

filter bgp_out_v4 {
    if net ~ MY_PREFIXES_V4 then accept;
    reject;
}

filter bgp_out_v6 {
    if net ~ MY_PREFIXES_V6 then accept;
    reject;
}

💡 Always filter out. Without it, you risk announcing prefixes you don't own — major BGP incident.

Step 6: BGP template

template bgp vc_peers {
    local as 65000;
    multihop 2;
    password "MD5_SECRET";
    hold time 90;
    keepalive time 30;
    graceful restart on;
}

Step 7: BGP sessions

protocol bgp verycloud_v4 from vc_peers {
    description "VeryCloud Transit v4";
    neighbor 169.254.X.1 as VC_ASN;

    ipv4 {
        import filter bgp_in_v4;
        export filter bgp_out_v4;
        next hop self;
        import limit 5000 action restart;
    };
}

protocol bgp verycloud_v6 from vc_peers {
    description "VeryCloud Transit v6";
    neighbor 2a0e:XXXX:XXXX::0 as VC_ASN;

    ipv6 {
        import filter bgp_in_v6;
        export filter bgp_out_v6;
        next hop self;
        import limit 1000 action restart;
    };
}

Step 8: Start BIRD

sudo bird -p -c /etc/bird/bird.conf
sudo systemctl enable --now bird
sudo systemctl status bird

Step 9: Verify sessions

sudo birdc show protocols

Expected state:

Name         Proto  Table  State  Since         Info
verycloud_v4 BGP    ---    up     16:45:12      Established
verycloud_v6 BGP    ---    up     16:45:12      Established

Details:

sudo birdc show protocols all verycloud_v4

Step 10: Verify routes

sudo birdc show route protocol verycloud_v4
sudo birdc show route protocol verycloud_v6
sudo birdc show route export verycloud_v4
sudo birdc show route export verycloud_v6
sudo birdc show route

Validate default route in kernel:

ip route show default
ip -6 route show default

Troubleshooting

Session stays Active or Connect

• Tunnel issue (see transport tutorials)
• TCP/179 firewalled
• MD5 password mismatch

Session Established but no routes received

• Filters too restrictive: birdc show route filter bgp_in_v4
• VeryCloud hasn't activated route sending

Your prefixes not announced

• birdc show route export verycloud_v4 empty
• Static/direct doesn't include your prefixes

Route limit exceeded

• More routes than expected — switch to full table or increase import limit

Useful commands

sudo birdc configure                  # reload config without disruption
sudo birdc restart verycloud_v4       # restart a session
sudo birdc disable verycloud_v4
sudo birdc enable verycloud_v4
sudo birdc                            # interactive CLI
sudo journalctl -u bird -f

Conclusion

BIRD 2 = clean declarative config, powerful filters, single binary v4+v6. Once you understand the file structure (protocols, filters, tables), you set up BGP sessions in minutes. This tutorial's skeleton covers 95% of VeryCloud Remote Transit IP cases.

Going further: RPKI validation with routinator + RPKI protocol, BFD for fast failover, BGP communities for traffic engineering, multipath ECMP across multiple tunnels.

Resources

• BIRD — Official
• BIRD 2 — User's Guide
• RFC 4271 — BGP-4
• RFC 4760 — Multiprotocol Extensions for BGP-4