Configuring network interfaces in OpenBSD

Last updated: Nov 1, 2024

Intro

I'm going to gather here my notes on setting up network interfaces under OpenBSD.

Network Configuration

Preamble

Get interface name:

openbsd# ifconfig

we need to create a /etc/hostname."interface_name" file for each interface, containing this information:
- dhcp: sets interface to dhcp mode
- address_family: inet for IPv4
- address: IP address
- netmask: network mask
- NONE: no broadcast address

address_family address netmask broadcast [other options]

Here with static addressing:

openbsd# ifconfig
lo0: flags=2008049<UP,LOOPBACK,RUNNING,MULTICAST,LRO> mtu 32768
	index 5 priority 0 llprio 3
	groups: lo
	inet6 ::1 prefixlen 128
	inet6 fe80::1%lo0 prefixlen 64 scopeid 0x5
	inet 127.0.0.1 netmask 0xff000000
vmx0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
	lladdr 00:50:56:1a:b0:11
	index 1 priority 0 llprio 3
	groups: egress
	media: Ethernet autoselect (10GbaseT)
	status: active
	inet 192.168.1.10 netmask 0xffffff00 broadcast 192.168.1.255

openbsd# cat /etc/hostname.vmx0
inet 192.168.1.10 255.255.255.0 NONE

Some examples of configurations

Set the gateway:

openbsd# echo "192.168.1.1" > /etc/mygate

Set the em0 interface to dhcp:

openbsd# echo "dhcp" > /etc/hostname.em0

Set the em1 interface with a static address (/etc/hostname.em1 file):

inet 192.168.1.2 255.255.255.0 NONE

Set up a vlan10 interface on the em1 interface (/etc/hostname.vlan10 file):

inet 172.21.0.31 255.255.255.0 NONE vlan 10 vlandev em1

Set host name:

openbsd# echo "gateway.std.rocks" > /etc/myname

Set DNS:

openbsd# echo "nameserver 192.168.1.254" > /etc/resolv.conf

Complete DNS configuration (edit /etc/resolv.conf):

search example.com
nameserver 125.2.3.4
nameserver 125.2.3.5
#file will look for entries in /etc/hosts
#bind will request them from the name servers.
#In this case, the order would be: search in /etc/hosts, then request to DNS servers.
lookup file bind

To take these changes into account, we need to run the following command:

openbsd# sh /etc/netstart

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Misc

Configuring network interfaces in OpenBSD

Intro

Network Configuration

Preamble

Some examples of configurations