Learn NetBSD - Networking & Network Configuration

#Introduction

In episode 7 we understood filesystems and disks — where NetBSD data rests. But a server is meaningless without connectivity. In this episode we'll connect the system to the outside world: networking and network configuration on NetBSD — configuring interfaces with ifconfig, building routes with route, setting up the resolver with /etc/resolv.conf, and exploring advanced features like interface aliases, VLAN, bonding, and bridges.

#Finding Interfaces

Viewing all interfaces

ifconfig -a

Example ifconfig -a output

wm0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
        address: 52:54:00:12:34:56
        inet 192.168.1.50 netmask 0xffffff00 broadcast 192.168.1.255
lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 33624
        inet 127.0.0.1 netmask 0xff000000

NetBSD interface names follow a pattern: wm0 for Intel PRO/1000, re0 for Realtek, virtio0 for KVM/QEMU VMs, and lo0 for loopback. For a concise list of all active interfaces:

Concise list of active interfaces

ifconfig -l

Example output

lo0 wm0

#Configuring Interfaces in /etc/rc.conf

Permanent interface configuration is written in /etc/rc.conf — remember the pattern from episode 6. Here are the two most common scenarios:

#Static IP

Static IP configuration in rc.conf

hostname="nbsd11"
ifconfig_wm0="inet 192.168.1.50 netmask 255.255.255.0"
defaultroute="192.168.1.1"

#DHCP

DHCP configuration in rc.conf

ifconfig_wm0="DHCP"

#Setting an IP Live

Changes to rc.conf only take effect at boot. To apply them immediately without rebooting, use ifconfig on the command line:

Setting an IP live

ifconfig wm0 inet 192.168.1.50 netmask 255.255.255.0

Bringing the interface up

ifconfig wm0 up

To reset to DHCP:

Enabling DHCP live

dhcpcd wm0

Warning

ifconfig changes on the command line are lost at reboot. If you want them permanent, always write them in /etc/rc.conf. Rule of thumb: live for testing, rc.conf for permanent.

#Routing

#Viewing the Route Table

Viewing the routing table

route show

Example output

Routing tables
 
Internet:
Destination        Gateway            Flags     Use    Mtu    Interface
default            192.168.1.1        UGS         12      -        wm0
loopback           localhost          UH          -  33624        lo0
192.168.1.0/24     link#1             U           5      -        wm0

#Adding and Removing Routes

Adding a static route manually:

Adding a static route

route add 10.10.10.0/24 192.168.1.254

Removing a route:

Removing a route

route delete 10.10.10.0/24

To enable forwarding (so NetBSD acts as a router), set a sysctl:

Enabling IP forwarding

sysctl -w net.inet.ip.forwarding=1

#/etc/resolv.conf: Pointing at DNS

Name resolution is configured in /etc/resolv.conf:

Contents of /etc/resolv.conf

nameserver 8.8.8.8
nameserver 1.1.1.1
domain example.com

Test name resolution with nslookup or dig:

Testing DNS resolution

nslookup netbsd.org

Example output

Server:  8.8.8.8
Address: 8.8.8.8#53
 
Non-authoritative answer:
Name: netbsd.org
Address: 156.146.41.125

#Advanced Features

#Interface Aliases

A single physical interface can hold multiple IPs:

Adding an alias IP

ifconfig wm0 alias 192.168.1.51

Checking the alias result

ifconfig wm0

For permanence, write it in rc.conf as two lines:

Permanent alias in rc.conf

ifconfig_wm0="inet 192.168.1.50 netmask 255.255.255.0"
ifconfig_wm0_alias0="inet 192.168.1.51 netmask 255.255.255.255"

#VLAN

VLANs split one physical network into multiple logical networks (802.1Q). First make sure VLAN support exists, then create a VLAN interface:

Creating a VLAN interface

ifconfig vlan0 create
ifconfig vlan0 vlan 10 vlanif wm0
ifconfig vlan0 inet 10.0.10.1/24

#Bonding (lagg)

lagg combines multiple interfaces for redundancy or bandwidth. Creating a lagg with two ports:

Creating a lagg from two interfaces

ifconfig lagg0 create
ifconfig lagg0 laggproto failover laggport wm0 laggport re0
ifconfig lagg0 inet 192.168.1.60/24 up

#Bridge

A bridge connects multiple interfaces at layer 2 — the basis of a virtual switch:

Creating a bridge from several interfaces

ifconfig bridge0 create
ifconfig bridge0 add wm0 add re0
ifconfig bridge0 up

#Debugging the Network

When networking is broken, follow a systematic approach:

Step	Command	What to Check
1	`ifconfig -a`	Does the interface exist and is it UP?
2	`route show`	Does the default route exist?
3	`ping 192.168.1.1`	Is the gateway reachable?
4	`nslookup netbsd.org`	Does DNS work?
5	`ping netbsd.org`	Is the internet reachable?

Testing basic connectivity

ping -c 3 8.8.8.8

#Closing

In this episode 8, you've mastered NetBSD networking: finding and configuring interfaces with ifconfig, static IP and DHCP configuration in /etc/rc.conf, routing with route, DNS resolution with /etc/resolv.conf, and advanced features like aliases, VLAN, bonding (lagg), and bridges.

Key takeaways:

Permanent configuration goes in /etc/rc.conf; live ifconfig changes vanish on reboot.
Static IP: ifconfig_wm0="inet 192.168.1.50 netmask 255.255.255.0" + defaultroute.
DNS is configured in /etc/resolv.conf; test with nslookup.
Advanced features: alias (multiple IPs), vlan (802.1Q), lagg (bonding), bridge (layer 2).
Debug systematically: interface → route → gateway → DNS → internet.

In the next episode, episode 9, we'll go deeper into the machine: kernel modules and kernel configuration — loading modules with modload, assembling your own kernel with config, and building the kernel with build.sh. See you in episode 9!