Network configuration

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Set the hostname

A hostname is a unique name created to identify a machine on a network. With Arch Linux, a machine's hostname is set in Template:Filename or until a restart using the hostname command. Hostnames are restricted to alphanumeric characters. The dash (Template:Codeline) can be used but a hostname cannot start or end with it. Length is restricted to 63 characters.

Edit Template:Filename and set HOSTNAME (archlinux in this example):


After setting a hostname, it is also a good idea to include the same name in Template:Filename. This will help processes that refer to the computer by its hostname to find its IP.

Edit Template:Filename and add the same HOSTNAME you entered in Template:Filename:   localhost.localdomain      localhost    archlinux

To set the hostname temporarily (until the next reboot) use the hostname command as root:

# hostname archlinux

Load the device module

Udev should detect your network card (NIC) module and load it automatically at startup. Otherwise, you will need to know which module is needed for your particular model:

hwdetect --show-net

Once you recognize which module to use, you can load it with:

# modprobe <modulename>

If udev is not detecting and loading the proper module automatically during bootup, you can add it into the MODULES= array in /etc/rc.conf, so you do not need to "modprobe" it everytime you boot. For example, if tg3 is the network module:

MODULES=(!usbserial tg3 snd-cmipci)

Other common modules are 8139too for cards with the Realtek chipset or sis900 for SiS cards.

Configure IP

It is important to realize that you may have a dynamically-assigned address using DHCP, or an unchanging and set "static" address.

Note: For motherboards that have integrated NICs it is important to know which one is considered the primary (i.e. eth0) and which is considered the secondary (i.e. eth1) NIC. Many configuration issues are caused by users incorrectly configuring eth0 in their /etc/rc.conf when in fact, they have their eth1 plugged into the LAN!


For this option, you need the dhcpcd package (already available on most installations). To make use of it, edit /etc/rc.conf like this:


If you use DHCP and you do not want your DNS servers automatically assigned every time you start your network, be sure to add the following to the last section of /etc/dhcpcd.conf:

nohook resolv.conf

Then add your own DNS nameserver to /etc/resolv.conf.

Make sure to test your new settings by stopping and starting the /etc/rc.d/network daemon, as opposed to bringing down your interface and starting dhcp manually. To restart the network daemon:

# /etc/rc.d/network restart

You may use openresolv package from AUR if several different processes want to control resolv.conf (i.e. dhcpcd and VPN client). No additional configuration for dhcpcd is needed to use openresolv.

Note: It is possible to have a static ip using dhcpcd. Simply edit your /etc/conf.d/dhcpcd file to look something like this (where x.x.x.x is your desired ip):

DHCPCD_ARGS="-q -s x.x.x.x"

For Static IP

There are various reasons why you may wish to assign static IP addresses on your network. For instance, one may gain a certain degree of predictability, and a particular type of security benefit. Also, if you share your internet connection from a Windows box without a router, be sure to use static IPs on both computers. Otherwise you will have LAN issues.

You need:

  • Your static IP address,
  • The netmask,
  • The broadcast address,
  • Your gateway,
  • Your nameservers' IP addresses,
  • Your domain name.

If you are running a private network, it is safe to use IP addresses in 192.168.*.'* for your IPs, with a netmask of and broadcast address of 192.168.*.255. Unless your network has a router, the gateway address does not matter. Edit /etc/rc.conf like this, substituting your own values for the IP, netmask, broadcast, and gateway:

eth0="eth0 netmask broadcast"
gateway="default gw"

To add additional static routes, use the normal syntax for the 'route add' command such as:

static_route1="-net gw"

Then add static_route1 to your ROUTES array. Note that a route name can not begin with a number, static_route1 is ok, 1static_route is not. You should probably avoid using hyphens too.

Edit your /etc/resolv.conf like this, substituting your nameservers' IPs and your domain name:

nameserver 61.95.849.8

You may include as many nameserver lines as you wish.

Manual assignment

You can assign a static IP in console:

# ifconfig <interface> <ip> netmask <netmask>

For example: ifconfig eth0 netmask For more options, see: man ifconfig

Load configuration

To test your settings either reboot the computer, or as root, run /etc/rc.d/network restart. Try pinging your gateway, DNS server, ISP provider and other Internet sites, in that order, to detect any connection problems along the way, as in this example:

$ ping

Additional settings

Enable/disable interface

You can activate or deactivate net interface:

# ifconfig <interface> up/down


You can install and configure a firewall to feel more secure.

Wireless Setup

See the Wireless Setup article for more information.

Laptops, 'ifplugd'

You can install a daemon which will automatically configure your Ethernet device when a cable is plugged in and automatically unconfigure it if the cable is pulled. This is useful on laptops with onboard network adapters, since it will only configure the interface when a cable is really connected. Another use is when you just need to restart the network but do not want to restart the computer or do it from the shell.

Installation is very simple since it is in [extra]:

# pacman -S ifplugd

By default it is configured to work for eth0 device. This and other settings like delays can be configured in /etc/ifplugd/ifplugd.conf.

Start it with:

# /etc/rc.d/ifplugd start

or add it into DAEMONS array in /etc/rc.conf.

Jumbo Frames

See the Jumbo Frames article for more information.


You can install the ifenslave package to bind two real Ethernet cables with one IP address. After installation, you will need to edit each of the following files:


bond_bond0="eth0 eth1"


Note: The new module-init-tools 3.8 package changes the location of the configuration file: /etc/modprobe.conf is no longer read, instead /etc/modprobe.d/modprobe.conf is used. link
options bonding miimon=100


MODULES=(... bonding ...)
bond0="bond0 netmask broadcast"

To activate the new bonded ports, restart your network by:

/etc/rc.d/network restart

IP aliasing

One IP on one card:

# nano /etc/rc.conf
eth0="eth0 netmask broadcast"
INTERFACES=(lo eth0)

Two IPs on one card: (BUG:/etc/rc.d/network stop)

# nano /etc/rc.conf
eth0="eth0 netmask broadcast"
eth0_0="eth0:0 netmask broadcast"
INTERFACES=(lo eth0 eth0_0)

One IP on two cards:

# pacman -S ifenslave
# nano /etc/rc.conf
 bond0="bond0 netmask broadcast"
 INTERFACES=(lo bond0)
 MODULES=(... bonding ...)

Two IPs on two cards: (BUG:/etc/rc.d/network stop)

# pacman -S ifenslave
# nano /etc/rc.conf
bond0="bond0 netmask broadcast"
bond01="bond0:1 netmask broadcast"
INTERFACES=(lo bond0 bond01)
MODULES=(... bonding ...)
Note: After setting these options (bonding, etc.), adjust firewall settings so that they are in-tune with the changes, else the network will not work properly.

Change MAC/hardware address

Useful in some situations, for example when your ISP binds the access to one of your computers to identify you, but you need to use the connection on more than one computer without running ifconfig every time. Add the usual ifconfig option to your card configuration.

For a ethernet card:

 eth0="eth0 netmask broadcast hw ether

This won't work if you acquire IP address from the DCHP server. Instead, you can create new "daemon" which sets the MAC address and run it prior to network daemon. Create file Template:Filename with the following content:

 . /etc/rc.conf                                                                  
 . /etc/rc.d/functions
case "$1" in start) stat_busy 'Setting MAC address' if ifconfig eth0 hw ether 01:23:45:67:89:ab # your new MAC address then stat_done else stat_fail fi  ;; stop) stat_busy 'Restoring original MAC address' if ifconfig eth0 hw ether 00:11:22:33:44:55 # your old MAC address then stat_done else stat_fail fi  ;; restart) $0 stop $0 start  ;; *) echo "Usage: $0 {start|stop|restart}" esac

and ensure it is run prior to network, so in Template:Filename, change DAEMONS to:

DAEMONS=(... set-hw-addr network ...)


DHCP fails at boot

First, check all the steps that the computer normally executes at boot in order to find out which one failed. These steps are: 1. detect the network device and load its driver, 2. bring up the interface and 3. call dhcp

For step 1 check the "Ethernet controller" entry in the output of lspci -v. It should tell you which kernel module contains the driver of your network device. For example:

02:00.0 Ethernet controller: Attansic Technology Corp. L1 Gigabit Ethernet Adapter (rev b0)
	Kernel driver in use: atl1
	Kernel modules: atl1

Next, check the the driver was loaded via dmesg | grep <module name> . For example:

$ dmesg |grep atl1
atl1 0000:02:00.0: eth0 link is up 100 Mbps full duplex

For step 2, check the output of dmesg for the interface associated with your network device and bring it up via (as root) ifconfig <interface> up. Check the result with ifconfig -a. For example:

$ ifconfig -a
eth0      Link encap:Ethernet  ...
          inet6 addr: f.../64 Scope:Link

What you probably will not see here is an inet address. You need to get that from your router in step 3:

To be on the safe side, start by releasing the lease of your interface with dhcpcd --release, then try to get a lease with dhcpcd. As always, the man page is your friend. If all goes well it will look like this:

$ dhcpcd --release eth0
dhcpcd: dhcpcd not running
$ dhcpcd eth0
dhcpcd: version 5.1.1 starting
dhcpcd: eth0: broadcasting for a lease
dhcpcd: eth0: leased for 86400 seconds

And now ifconfig <interface> should show your inet address. Probably things will not work as described somewhere along these steps, or else the network would have started automatically at boot.

If dhcp works using the steps above but not at boot, add the following to /etc/rc.local

dhcpcd -k eth0 
dhcpcd -nd eth0

See for more information.

For some people, the dhclient package (available in [extra]) works where dhcpcd fails.

Swapping computers on the cable modem

Most domestic cable ISPs (videotron for example) have the cable modem configured to recognise only one client PC, by the MAC address of its network interface. Once the cable modem has learnt the MAC address of the first PC or equipment that talks to it, it will not respond to another MAC address in any way. Thus if you swap one PC for another (or for a router), the new PC (or router) will not work with the cable modem, because the new PC (or router) has a different MAC address to the old one. To reset the cable modem so that it will recognise the new PC, you must power the cable modem off and on again. Once the cable modem has rebooted and gone fully online again (indicator lights settled down), reboot the newly connected PC so that it makes a DHCP request, or manually make it request a new DHCP lease.

If this method does not work, you will need to clone the MAC address of the original machine. See also Change MAC/hardware address.

The TCP window scaling issue

TCP packets contain a "window" value in their headers indicating how much data the other host may send in return. This value is represented with only 16 bits, hence the window size is at most 64Kb. TCP packets are cached for a while (they have to be reordered), and as memory is (or used to be) limited, one host could easily run out of it.

Back in 1992, as more and more memory became available, RFC 1323 was written to improve the situation: Window Scaling. The "window" value, provided in all packets, will be modified by a Scale Factor defined once, at the very beginning of the connection.

That 8-bit Scale Factor allows the Window to be up to 32 times higher than the initial 64Kb.

It appears that some broken routers and firewalls on the Internet are rewriting the Scale Factor to 0 which causes misunderstandings between hosts.

The Linux kernel 2.6.17 introduced a new calculation scheme generating higher Scale Factors, virtually making the aftermaths of the broken routers and firewalls more visible.

The resulting connection is at best very slow or broken.

How to diagnose the problem

First of all, lets make it clear: this problem is odd. In some cases, you will not be able to use TCP connections (HTTP, FTP, ...) at all and in others, you will be able to communicate with some hosts (very few).

When you have this problem, the dmesg's output is OK, logs are clean and ifconfig will report normal status — and actually everything appears normal.

If you can not browse any website, but you can ping some rare hosts, chances are great that you're experiencing this issue: ping uses the ICMP protocol and is not affected by TCP issues.

You can try to use WireShark. You might see successful UDP and ICMP communications but unsuccessful TCP communications (only to foreign hosts).

How to fix it (The bad way)

To fix it the bad way, you can change the tcp_rmem value, on which Scale Factor calculation is based. Although it should work for most hosts, it is not guaranteed, especially for very distant ones.

echo "4096 87380 174760" > /proc/sys/net/ipv4/tcp_rmem

Or you can try to remove one of your RAM sticks (yes, sir).

How to fix it (The good way)

Simply disable Window Scaling. Since Window Scaling is a nice TCP feature, it may be uncomfortable to disable it, especially if you can not fix the broken router. There are several ways to disable Window Scaling, and it seems that the most bulletproof (which will work with most kernels) is to add the following lines to your /etc/rc.local:

echo 0 > /proc/sys/net/ipv4/tcp_window_scaling

How to fix it (The best way)

This issue is caused by broken routers/firewalls, so lets change them. Some users have reported that the broken router was their very own DSL router.

More about it

This section is based on the LWN article TCP window scaling and broken routers and a Kernel Trap article: Window Scaling on the Internet.

And more recently, some Archers have been hit by this issue:

There are also several relevant threads on the LKML.

Interface names varying

Your network cards are sometimes named differently between two reboot. Configuring your network connection is hard if you don't know if you card will be called eth0 or eth1.

A file /etc/udev/rules.d/75-persistent-net-generator.rules.optional can be used to tell udev to generate persistent network rules.

mv /etc/udev/rules.d/75-persistent-net-generator.rules.optional /etc/udev/rules.d/75-persistent-net-generator.rules

Reboot your system. A /etc/udev/rules.d/70-persistent-net.rules file has been generated. Now you can disable the generator:

mv /etc/udev/rules.d/75-persistent-net-generator.rules /etc/udev/rules.d/75-persistent-net-generator.rules.optional

Realtek no link / WOL issue

Users with Realtek 8168 8169 8101 8111(C) based NICs (cards / and on-board) may notice an issue where the NIC seems to be disabled on boot and has no Link light. This can usually be found on a dual boot system where Windows is also installed. It seems that using the offical Realtek drivers (dated anything after May 2007) under Windows is the cause. These newer drivers disable the Wake-On-LAN feature by disabling the NIC at Windows shutdown time, where it will remain disabled until the next time Windows boots. You will be able to notice if this issue is affecting you if the Link light remains off until Windows boots up; during Windows shutdown the Link light will switch off. Normal operation should be that the link light is always on as long as the system is on, even during POST. This issue will also affect other operative systems without newer drivers (eg. Live CDs). Here are a few fixes for this issue:

Method 1 - Rollback/change Windows driver

You can roll back your Windows NIC driver to the Microsoft provided one (if available), or roll back/install an official Realtek driver pre-dating May 2007 (may be on the CD that came with your hardware).

Method 2 - Enable WOL in Windows driver

Probably the best and the fastest fix is to change this setting in the Windows driver. This way it should be fixed system-wide and not only under Arch (eg. live CDs, other operative systems). In Windows, under Device Manager, find your Realtek network adapter and double-click it. Under the Advanced tab, change "Wake-on-LAN after shutdown" to Enable.

In Windows XP (example)
Right click my computer
--> Hardware tab
  --> Device Manager
    --> Network Adapters
      --> "double click" Realtek ...
        --> Advanced tab
          --> Wake-On-Lan After Shutdown
            --> Enable
  • Note: newer Realtek Windows drivers (tested with Realtek 8111/8169 LAN Driver v5.708.1030.2008, dated 2009/01/22, available from GIGABYTE) may refer to this option slightly differently, like Shutdown Wake-On-LAN --> Enable. It seems that switching it to Disable has no effect (you will notice the Link light still turns off upon Windows shutdown). One rather dirty workaround is to boot to Windows and just reset the system (perform an ungraceful restart/shutdown) thus not giving the Windows driver a chance to disable LAN. The Link light will remain on and the LAN adapter will remain accessible after POST - that is until you boot back to Windows and shut it down properly again.

Method 3 - Newer Realtek Linux driver

Any newer driver for these Realtek cards can be found for Linux on the realtek site. (untested but believed to also solve the problem).

Method 4 - Enable LAN Boot ROM in BIOS/CMOS

It appears that setting Integrated Peripherals --> Onboard LAN Boot ROM --> Enabled in BIOS/CMOS reactivates the Realtek LAN chip on system boot-up, despite the Windows driver disabling it on OS shutdown.
This was tested successfully multiple times with GIGABYTE system board GA-G31M-ES2L with BIOS version F8 released on 2009/02/05. YMMV.

DLink G604T/DLink G502T DNS issue

Users with a DLink G604T/DLink G502T router, using DHCP and have firmware v2.00+ (typically users with AUS firmware) may have issues with certain programs not resolving the DNS. One of these programs are unfortunatley pacman. The problem is basically the router in certain situations is not sending the DNS properly to DHCP, which causes programs to try and connect to servers with an IP of and fail with a connection timed out error

How to diagnose the problem

The best way to diagnose the problem is to use a firefox/konqueror/links/seamonkey and to enable wget for pacman. If this is a fresh install of Arch Linux, then you may want to consider installing links through the live CD.

Firstly enable wget for pacman (since it gives us info about pacman when its downloading packages) Open /etc/pacman.conf with your favourite editor and uncomment the following line (remove the # if its there)

XferCommand=/usr/bin/wget --passive-ftp -c -O %o %u

While your in pacman.conf, check the default mirror that pacman uses to download packages.

Now open up the default mirror in an internet browser to see if the mirror actually works. If it does work then do pacman -Syy (otherwise pick another working mirror and set it to the pacman default), if you get something similar to the following (notice the                                                            
           => `/var/lib/pacman/community.db.tar.gz.part'

then you most likely have this problem. The means its unable to resolve the DNS, so we must add it to resolv.conf.

How to fix It

Basically what we need to do is to manually add the DNS to our /etc/resolv.conf file, The problem is that DHCP automatically deletes and replaces this file on boot, so we need to edit /etc/conf.d/dhcpcd and change the flags to stop DHCP doing this

When you open up /etc/conf.d/dhcpcd, you should see something close to the following


add the -R flag to the arguments, i.e.


NOTE: If you are using dhcpcd >=4.0.2 the -R flag has been deprecated, please look here on ([1]) section how to use a custom resolv.conf file

Save and close, now open /etc/resolv.conf. You should see a single namespace (most likely, this is the gateway to your router, which we need to connect to in order to get the DNS of your ISP. Paste the IP into your browser and login to your router. Go to the DNS section and you should see an IP in the Preferred DNS Server, copy it and paste it as a namespace ABOVE the current gateway one.

i.e. a resolv.conf should look something along the lines of


If my Primary DNS Server is then chance resolv.conf to


Now restart the network daemon by doing /etc/rc.d/network restart and do pacman -Syy, if it syncs fine with the server then problem solved

More about it

This is the whirlpool forum (Australian ISP community) which talks about and gives the same solution to the problem

Get an IP from the wrong DHCP in linked (by VPN) router cases

In my case, I have a network where two routers are tied together through VPN. I have one router at my home, and one at a completely different place in the world. In some rare cases, it it appears that the router that is connected to me by VPN is assigning me an IP address. I don't know a way to prevent that process, but I do know a way to fix it. On a console, as root, try this:

dhcpcd -k

The first line releases your IP and the next line requests a new one. I had to run those two commands three times till my issue was fixed, so don't expect it to work after just one try. If that also fails you might need to disconnect the VPN connection and try it again with the commands above.

This even works when NetworkManager is installed.