Configure Networking

This page will assist you in setting up networking on Alpine Linux.

Note: You must be logged in as root in order to perform the actions on this page.

Setting System Hostname

To set the system hostname:

# echo "shortname" > /etc/hostname

Then, to activate the change:

# hostname -F /etc/hostname

If you're using IPv6, you should also add the following special IPv6 addresses to your /etc/hosts file:

Contents of /etc/hosts

... ::1 localhost ipv6-localhost ipv6-loopback fe00::0 ipv6-localnet ff00::0 ipv6-mcastprefix ff02::1 ipv6-allnodes ff02::2 ipv6-allrouters ff02::3 ipv6-allhosts

Tip: If you're going to use automatic IP configuration, such as IPv4 DHCP or IPv6 Stateless Autoconfiguration, you can skip ahead to Configuring DNS. Otherwise, if you're going to use a static IPv4 or IPv6 address, continue below.

For a static IP configuration, it's common to also add the machine's hostname you just set (above) to the /etc/hosts file.

Here's an IPv4 example:

Contents of /etc/hosts

... 192.168.1.150 shortname.domain.com ...

And here's an IPv6 example:

Contents of /etc/hosts

... 2001:470:ffff:ff::2 shortname.domain.com ...

Configuring DNS

Tip: For users of IPv4 DHCP: Please note that /etc/resolv.conf will be completely overwritten with any nameservers provided by DHCP. If DHCP does not provide any nameservers, then /etc/resolv.conf will still be overwritten, but will not contain any nameservers!

For a static IP address and static nameservers, use one of the following examples.

For IPv4 nameservers, edit your /etc/resolv.conf file to look like this:
The following example uses Google's Public DNS servers.

Contents of /etc/resolv.conf

nameserver 8.8.8.8 nameserver 8.8.4.4

For IPv6 nameservers, edit your /etc/resolv.conf file to look like this:
The following example uses Hurricane Electric's public DNS server.

Contents of /etc/resolv.conf

nameserver 2001:470:20::2

You can also use Hurricane Electric's public IPv4 DNS server:

Contents of /etc/resolv.conf

nameserver 74.82.42.42

Tip: If you decide to use Hurricane Electric's nameserver, be aware that it is 'Google-whitelisted'. What does this mean? It allows you access to many of Google's services via IPv6. (Just don't add other, non-whitelisted, nameservers to /etc/resolv.conf — ironically, such as Google's Public DNS Servers.) Read here for more information.

Interface Configuration

Loopback Configuration (Required)

Note: The loopback configuration must appear first in /etc/network/interfaces to prevent networking issues.

To configure loopback, add the following to a new file /etc/network/interfaces:

Contents of /etc/network/interfaces

... auto lo iface lo inet loopback

The above works to set up the IPv4 loopback address (127.0.0.1), and the IPv6 loopback address (::1) — if you enabled IPv6.

Wireless Configuration

See Connecting to a wireless access point.

Ethernet Configuration

For the following Ethernet configuration examples, we will assume that you are using Ethernet device eth0.

Initial Configuration

Add the following to the file /etc/network/interfaces, above any IP configuration for eth0:

Contents of /etc/network/interfaces

... auto eth0 ...

IPv4 DHCP Configuration

Add the following to the file /etc/network/interfaces, below the auto eth0 definition:

Contents of /etc/network/interfaces

... iface eth0 inet dhcp ...

By default, the busybox DHCP client (udhcpc) requests a static set of options from the DHCP server. If you need to extend this set, you can do so by setting some additional command line options for the DHCP client, via the udhcpc_opts in your interface configuration. The following example requests domain-search option:

Contents of /etc/network/interfaces

... iface eth0 inet dhcp udhcpc_opts -O search ...

For a complete list of command line options for udhcpc, see this document.

IPv4 Static Address Configuration

Add the following to the file /etc/network/interfaces, below the auto eth0 definition:

Contents of /etc/network/interfaces

... iface eth0 inet static address 192.168.1.150 netmask 255.255.255.0 gateway 192.168.1.1 ...

Since Alpine 3.13 (and only if you have ifupdown-ng installed) must be:

Contents of /etc/network/interfaces

... iface eth0 inet static address 192.168.1.150/24 gateway 192.168.1.1 ...

Additional IP addresses

Contents of /etc/network/interfaces

... iface eth0 inet static address 192.168.1.150 netmask 255.255.255.0 iface eth0 inet static address 192.168.1.151/24 ...

Since Alpine 3.13 (and only if you have ifupdown-ng installed) must be:

Contents of /etc/network/interfaces

... iface eth0 inet static address 192.168.1.150/24 gateway 192.168.1.1 iface eth0 inet static address 192.168.1.151/24 ...

IPv6 DHCP Configuration

Alpine's use of ifupdown-ng supports three DHCP clients: udhcpc, dhclient, and dhcpcd. Of these, only dhcpcd can interact with both DHCP and DHCPv6 from the same process, which ifupdown-ng requires. Thus the IPv4 DHCP configuration given above will also result in the use of DHCPv6, but only if you install the dhcpcd package. (The ifupdown-ng scripts prioritize dhclient over udhcpc, and they prioritize dhcpcd over dhclient; see /usr/libexec/ifupdown-ng/dhcp.)

IPv6 Stateless Autoconfiguration

Add the following to the file /etc/network/interfaces, below the auto eth0 definition:

Contents of /etc/network/interfaces

... iface eth0 inet6 auto ...

IPv6 Static Address Configuration

Add the following to the file /etc/network/interfaces, below the auto eth0 definition:

Contents of /etc/network/interfaces

... iface eth0 inet6 static address 2001:470:ffff:ff::2 netmask 64 gateway 2001:470:ffff:ff::1 pre-up echo 0 > /proc/sys/net/ipv6/conf/eth0/accept_ra ...

Since Alpine Linux 3.13 (and only if you have ifupdown-ng installed) must be as:

Contents of /etc/network/interfaces

... iface eth0 inet6 static address 2001:470:ffff:ff::2/64 gateway 2001:470:ffff:ff::1 pre-up echo 0 > /proc/sys/net/ipv6/conf/eth0/accept_ra ...

Example: Dual-Stack Configuration

This example shows a dual-stack configuration.

Contents of /etc/network/interfaces

auto lo iface lo inet loopback auto eth0 iface eth0 inet static address 192.168.1.150 netmask 255.255.255.0 gateway 192.168.1.1 iface eth0 inet6 static address 2001:470:ffff:ff::2 netmask 64 gateway 2001:470:ffff:ff::1 pre-up echo 0 > /proc/sys/net/ipv6/conf/eth0/accept_ra

Take care since Alpine 3.13 (and only if you have ifupdown-ng installed) must be as:

Contents of /etc/network/interfaces

auto lo iface lo inet loopback auto eth0 iface eth0 inet static address 192.168.1.150/24 gateway 192.168.1.1 iface eth0 inet6 static address 2001:470:ffff:ff::2/64 gateway 2001:470:ffff:ff::1 pre-up echo 0 > /proc/sys/net/ipv6/conf/eth0/accept_ra

Firewalling with iptables and ip6tables

See also: Alpine Wall - How-To Alpine Wall - Alpine Wall User's Guide.

Install iptables/ip6tables

• To install iptables (includes ip6tables in alpine 3.19 and up):

# apk add iptables

• To install ip6tables (Alpine older than 3.19 only):

# apk add ip6tables

• To install the man pages for iptables and ip6tables:

# apk add iptables-doc

Save Firewall Rules

For iptables

1. Set iptables to start on reboot

   • # rc-update add iptables

2. Write the firewall rules to disk

   • # rc-service iptables save

3. If you use Alpine Local Backup:
   1. Save the configuration

      • # lbu ci

For ip6tables

1. Set ip6tables to start on reboot

   • # rc-update add ip6tables

2. Write the firewall rules to disk

   • # rc-service ip6tables save

3. If you use Alpine Local Backup:
   1. Save the configuration

      • # lbu ci

Activating Changes and Testing Connectivity

Changes made to /etc/network/interfaces can be activated by running:

# rc-service networking restart

If you did not get any errors, you can now test that networking is configured properly by attempting to ping out:

$ ping www.google.com PING www.l.google.com (74.125.47.103) 56(84) bytes of data. 64 bytes from yw-in-f103.1e100.net (74.125.47.103): icmp_seq=1 ttl=48 time=58.5 ms 64 bytes from yw-in-f103.1e100.net (74.125.47.103): icmp_seq=2 ttl=48 time=56.4 ms 64 bytes from yw-in-f103.1e100.net (74.125.47.103): icmp_seq=3 ttl=48 time=57.0 ms 64 bytes from yw-in-f103.1e100.net (74.125.47.103): icmp_seq=4 ttl=48 time=60.2 ms ^C --- www.l.google.com ping statistics --- 4 packets transmitted, 4 received, 0% packet loss, time 3007ms rtt min/avg/max/mdev = 56.411/58.069/60.256/1.501 ms

For an IPv6 traceroute run traceroute6:

$ traceroute6 ipv6.google.com traceroute to ipv6.l.google.com (2001:4860:8009::67) from 2001:470:ffff:ff::2, 30 hops max, 16 byte packets 1 2001:470:ffff:ff::1 (2001:470:ffff:ff::1) 3.49 ms 0.62 ms 0.607 ms 2 * * * 3 * * * 4 pr61.iad07.net.google.com (2001:504:0:2:0:1:5169:1) 134.313 ms 95.342 ms 88.425 ms 5 2001:4860::1:0:9ff (2001:4860::1:0:9ff) 100.759 ms 100.537 ms 89.907 ms 6 2001:4860::1:0:5db (2001:4860::1:0:5db) 115.563 ms 102.946 ms 106.191 ms 7 2001:4860::2:0:a7 (2001:4860::2:0:a7) 101.754 ms 100.475 ms 100.512 ms 8 2001:4860:0:1::c3 (2001:4860:0:1::c3) 99.272 ms 111.989 ms 99.835 ms 9 yw-in-x67.1e100.net (2001:4860:8009::67) 101.545 ms 109.675 ms 99.431 ms

Additional Utilities

iproute2

You may wish to install the 'iproute2' package (note that this will also install iptables if not yet installed)

# apk add iproute2

This provides the 'ss' command which is IMHO a 'better' version of netstat.

Show listening tcp ports:

$ ss -tl

Show listening tcp ports and associated processes:

$ ss -ptl

Show listening and established tcp connections:

$ ss -ta

Show socket usage summary:

$ ss -s

Show more options:

$ ss -h

drill

You may also wish to install 'drill' (it will also install the 'ldns' package) which is a superior (IMHO) replacement for nslookup and dig etc:

# apk add drill

Then use it as you would for dig:

$ drill alpinelinux.org @8.8.8.8

To perform a reverse lookup (get a name from an IP) use the following syntax:

$ drill -x 8.8.8.8 @208.67.222.222

Related articles

You may also wish to review the following network related articles:

VLAN setup

Bonding setup

Network bridge setup

udhcpc configuration