This guide describes a simple configuration for OpenBGPD running on OpenBSD. The portable version should run with little to no configuration changes on other operating systems as well.

Other than the bgpd.conf(5) and bgpd(8) man pages and the OpenBSD /etc/examples/bgpd.conf, you might also find useful reference or ideas in the Bird2 page (even if you don't use Bird), as it likely presents the most widespread dn42 router setup.

Example configuration

When copying from the below configuration, be sure to at least replace the various <PLACEHOLDER>s with your own numbers.

Concrete configuration examples can also be found elsewhere, e.g.:

https://smrk.net/text/openbsd-dn42-setup.txt

https://kaizo.org/2024/01/03/openbsd-bgpd/

Given OpenBGPD's limited support for multiprotocol sessions (no extended next hop (RFC8950)) and some issues with IPv6 link-local nexthops, we configure separate IPv4 and IPv6 sessions for each peer, and for IPv6 we adjust nexthop to a "global" address (i.e., one from our dn42 IPv6 allocation) assigned to each peering (Wireguard) interface (each interface gets its own).

To avoid burning a dn42 IPv4 address for each peering, we'll put the router's dn42 IPv4 address on the loopback interface and peer using an RFC1918 subnet (192.168.42/24) NATed to the loopback address (the NAT is only used in case of actively opening an IPv4 BGP session, it does not affect routing or incoming connections).

/etc/hostname.lo0

inet alias <YOUR-ROUTER-DN42-IPv4>

/etc/hostname.wg1234

(one example; similar for each peer)

inet 192.168.42.1/32
inet6 fe80::1 64 # this is the address your peer will want to know
# (and connect to); the following address is only really needed
# to provide a non-link-local IPv6 address for the nexthop setting;
# you can pick it "arbitrarily" from your dn42 IPv6 allocation
inet6 <YOUR-DN42-IPv6-OF-PEER1-INTERFACE> 64
group my_dn
wgport 21234 wgkey <PRIVKEY-BASE64>
wgpeer <PEER1-PUBKEY-BASE64> \
  wgdescr "dn42 peer1" \
  wgaip fe80::/64 wgaip fd00::/8 wgaip 10.0.0.0/8 wgaip 172.20.0.0/14 \
  wgendpoint <PEER1-HOSTNAME-OR-IP> 24321
up
# add a static IPv4 route to the peer
!route -nq add <PEER1-IPv4> 192.168.42.1

/etc/pf.conf

(only the dn42-related snippet)

pass in quick proto {icmp icmp6} max-pkt-rate 30/3
dn42_self = <YOUR-ROUTER-DN42-IPv4>
table <dn42etc> const {172.20/14 172.31/16 10/8 fd00::/8 fe80::/64}
table <dn42peers> const {<PEER1-IPv4> fe80::/64}
pass in quick on egress proto udp to port 21234
pass in quick on my_dn proto tcp from <dn42peers> \
  to {$dn42_self (my_dn)} port bgp
# block everything (except for ICMP above) destined to the
# router itself; only dn42 transit and BGP sessions are allowed
block in log quick on my_dn to {$dn42_self (my_dn)}
pass out on my_dn from 192.168.42/24 nat-to $dn42_self
# 'no state' as we might not see both directions of transit traffic
pass on my_dn from <dn42etc> to <dn42etc> no state

/etc/bgpd.conf

ASN = "<YOUR-AS-NUMBER>"

AS $ASN
router-id <YOUR-ROUTER-DN42-IPv4>

# list of networks that may be originated by our ASN
prefix-set mydn42 {
	<YOUR-DN42-IPv4-PREFIX>
	<YOUR-DN42-IPv6-PREFIX>
}

# https://dn42.eu/howto/Bird2#example-configuration
prefix-set dn42etc {
	172.20.0.0/14 prefixlen 21 - 29	# dn42
	172.20.0.0/24 prefixlen 28 - 32	# dn42 Anycast
	172.21.0.0/24 prefixlen 28 - 32	# dn42 Anycast
	172.22.0.0/24 prefixlen 28 - 32	# dn42 Anycast
	172.23.0.0/24 prefixlen 28 - 32	# dn42 Anycast
	172.31.0.0/16 or-longer		# ChaosVPN
	10.100.0.0/14 or-longer		# ChaosVPN
	10.127.0.0/16 prefixlen 16 - 32	# neonetwork
	10.0.0.0/8    prefixlen 15 - 24	# Freifunk.net
	fd00::/8      prefixlen 44 - 64	# dn42
}

# https://dn42.burble.com/services/public/#roa-data
# https://dn42.burble.com/roa/dn42_roa_obgpd_46.conf
# see the crontab snippet and an update script further below
include "/var/db/openbgpd/dn42_roa_obgpd_46.conf"

network prefix-set mydn42 set {
	# https://dn42.dev/howto/BGP-communities
	# e.g., for Germany this could read
	# community 64511:41
	# community 64511:1276
	community 64511:<READ-THE-LINK-ABOVE>
	community 64511:<READ-THE-LINK-ABOVE>
	large-community $ASN:1:1
}

listen on <YOUR-ROUTER-DN42-IPv4>
listen on <PEER1-IPv6-LOCAL> # e.g. fe80::1%wg1234

group dn42peers {
	# RFC7454 sec. 8
	# (currently no peer sends more than 800 prefixes for
	# a single address family; increase this if using
	# multi-protocol BGP (or when the network grows)!)
	max-prefix 1000 restart 60
	neighbor <PEER1-IPv4> {
		descr peer1_4
		remote-as <PEER1-ASN>
	}
	neighbor <PEER1-IPv6-REMOTE> { # e.g. fe80::2%wg1234
		descr peer1_6
		remote-as <PEER1-ASN>
		set nexthop <YOUR-DN42-IPv6-OF-PEER1-INTERFACE>
	}
}

# deny EBGP UPDATEs to our own originated prefixes
deny quick from ebgp prefix-set mydn42 or-longer
# filter out overlong paths
deny quick from any max-as-len 10

allow from group dn42peers prefix-set dn42etc ovs valid
allow to group dn42peers prefix-set dn42etc

# scrub communities relevant to our ASN from EBGP neighbors
# (RFC7454 sec. 11)
# match from ebgp set { community delete $ASN:* }
match from ebgp set { large-community delete $ASN:*:* }

# honor requests to gracefully shutdown BGP sessions (RFC8326)
match from any community GRACEFUL_SHUTDOWN set { localpref 0 }

ROA

The roa-set for route origin validation (ovs valid in the config above) can be generated from the dn42 registry; here we use data conveniently provided by BURBLE-MNT.

If using the update script below, don't forget to create the /var/db/openbgpd/ directory first.

/root/openbgpd-roa-update.sh

#!/bin/sh

die() {
  >&2 printf '%s: %s\n' "${0##*/}" "$*"
  exit 1
}

# Unfortunately, burble regenerates the ROA files (hourly?)
# even when nothing changed, so If-Modified-Since doesn't
# help (similar story for .meta).

metafile=/var/db/openbgpd/registry.meta
err=$(ftp -o "$metafile" \
  https://explorer.burble.com/api/registry/.meta 2>&1 >/dev/null) ||
  die "/api/registry/.meta download failed: $err"

if ! cmp -s "$metafile" "$metafile".old >/dev/null 2>&1; then
  mv "$metafile" "$metafile".old
  roafile=/var/db/openbgpd/dn42_roa_obgpd_46.conf
  if err=$(ftp -To "$roafile".new \
    https://dn42.burble.com/roa/dn42_roa_obgpd_46.conf \
    2>&1 >/dev/null); then
    mv "$roafile".new "$roafile"
    bgpctl reload
  else
    die "ROA download failed: $err"
  fi
else
  logger -cisp user.info "${0##*/}: registry unchanged, not reloading"
fi

/var/cron/tabs/root

~       *       *       *       *       -ns /root/openbgpd-roa-update.sh

Looking glass

This is mostly OpenBSD specific since bgplg(8) and httpd(8) ship as part of the operating system. The bgplg manual contains the steps and example httpd.conf(5) required to enable the looking glass.

See https://lg-dn42.vinishor.xyz/bgplg (IPv6) for a running instance operating within DN42.