Network configuration (Português)

Esta página explica como configurar uma conexão cabeada. Se você deseja configurar uma rede wireless/sem fio veja a página Configuração de Redes Sem Fio.

Verificando a conexão

Note: Se você receber algum erro como ping: icmp open socket: Operation not permitted quando executar o comando ping, tente reinstalar o pacote iputils.

Muitas vezes, o procedimento básico de instalação cria uma configuração de rede cabeada. Para verificar se há configuração, utilize o seguinte comando:

Note: A opção -c 3 chama 3 vezes a ação de envio de pacotes icmp. Veja man ping para maiores informações.

$ ping -c 3 www.google.com

PING www.l.google.com (74.125.224.146) 56(84) bytes of data.
64 bytes from 74.125.224.146: icmp_req=1 ttl=50 time=437 ms
64 bytes from 74.125.224.146: icmp_req=2 ttl=50 time=385 ms
64 bytes from 74.125.224.146: icmp_req=3 ttl=50 time=298 ms

--- www.l.google.com ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 1999ms
rtt min/avg/max/mdev = 298.107/373.642/437.202/57.415 ms

Caso funcione, você precisará apenas personalizar algumas das opções abaixo.

Se o comando acima reclamar de unknown hosts(host desconhecido), significa que seu computador não pôde resolver nomes de domínios. Pode ser relacionado ao seu provedor de internet ou gateway/roteador. Tente pingar um endereço IP para provar que sua máquina possui acesso a internet.

$ ping -c 3 8.8.8.8

PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.
64 bytes from 8.8.8.8: icmp_req=1 ttl=53 time=52.9 ms
64 bytes from 8.8.8.8: icmp_req=2 ttl=53 time=72.5 ms
64 bytes from 8.8.8.8: icmp_req=3 ttl=53 time=70.6 ms

--- 8.8.8.8 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2002ms
rtt min/avg/max/mdev = 52.975/65.375/72.543/8.803 ms

Note: 8.8.8.8 é um endereço ip estático de fácil memorização. É o endereço do DNS primário do Google, considerado uma fonte confiável para testes e geralmente não bloqueado por sistemas de filtro de conteúdo ou proxies.

Caso você consiga pingar este endereço, pode adicioná-lo ao arquivo /etc/resolv.conf com a palavra nameserver na frente como solução de dns.

Configurando um hostname

Um A hostname é um endereço único criado para identificar um computador em uma rede. É configurado no arquivo /etc/hostname. Este arquivo pode conter o domínio do sistema, se houver. Para configurar um hostname, execute:

# hostnamectl set-hostname meunome

Este comando colocará a informação meunome no arquivo /etc/hostname.

Veja man 5 hostname e man 1 hostnamectl para maiores detalhes.

Note:

• hostnamectl suporta FQDNs
• Você não precisa mais editar o arquivo /etc/hosts, pois o systemd proverá a resolução de nomes, e é instalado por padrão no sistema.

Para alterar o hostname temporariamente(até o próximo restart), utilize o comando hostname do pacote inetutils:

# hostname meunome

Drivers de dispositivos

Verifique o estado do seu driver

O udev deverá detectar sua interface de rede(NIC) e carregará automaticamente o módulo necessário. Busque pela entrada "Ethernet controller"(ou similar) no resultado do comando lspci -v. Este comando dirá qual módulo do kernel é necessário para o funcionamento do dispositivo. Por exemplo:

$ lspci -v

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

Após, veja se o driver foi carregado através de um dmesg | grep module_name. Exemplo:

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

Pule para a próxima sessão caso o driver tenha sido carregado com sucesso. Caso contrário, você precisará descobrir qual é o módulo necessário para o seu modelo de interface de rede em específico.

Carregando o driver do dispositivo

Busque na internet(google) pelo modelo de sua placa e descubra qual o chipset. Algumas placas mais comuns utilizam o chipset da Realtek 8139too, ou sis900 da SiS. Assim que descobrir qual módulo deve usar, tente carregar o módulo manualmente. Caso você esbarre com algum erro dizendo que o módulo não foi encontrado, é possível que o driver não foi incluído no kernel do Arch Linux. Tente procurar no AUR pelo nome do módulo.

Caso o udev não detecte ou não carregue o módulo de forma apropriada e automaticamente durante o boot, veja a página Kernel modules#Loading.

Interfaces de Rede

Nomes de dispositivos

Para placas-mãe que possuem interfaces de rede embutidas, é importante ter um nome de dispositivo fixo. Grande parte dos problemas são causados por nomes de dispositivos que mudam.

O Udev é o responsavel por qual nome um dispositivo deve receber. O systemd v197 introduziu os nomes de interface previsíveis, que automaticamente atribuem nomes estáticos a dispositivos de rede. Interfaces são prefixadas como en (ethernet), wl (WLAN), ou ww (WWAN) seguido por um identificados, criando uma entrada similar a enp0s25.

Este comportamento pode ser desabilitado com o segunite link simbólico:

# ln -s /dev/null /etc/udev/rules.d/80-net-name-slot.rules

Usuários atualizando de uma versão mais antiga do systemd terão arquivos de regras criados automaticamente em branco. Caso você queira usar os nomes persistentes, apenas delete tal arquivo.

Tip: Você pode rodar um ip link ou ls /sys/class/net para listar todas as interfaces.

Alterando o nome de um dispositivo

Você pode alterar o nome de um dispositivo definindo o nome em uma regra do udev. Exemplo:

/etc/udev/rules.d/10-network.rules

SUBSYSTEM=="net", ACTION=="add", ATTR{address}=="aa:bb:cc:dd:ee:ff", NAME="net1"
SUBSYSTEM=="net", ACTION=="add", ATTR{address}=="ff:ee:dd:cc:bb:aa", NAME="net0"

Alguns detalhes devem ser ressaltados:

• Para obter o endereço MAC de cada interface, utilize o comando cat /sys/class/net/device-name/address
• Certifique-se de utilizar valores em caixa baixa para valores hexadecimais em regras do udev. Ele não gosta de caixa alta.

Note: Quando escolher nomes estáticos nomes no formato "ethX" and "wlanX" devem ser evitados, pois podem causar race conditions entre o kernel e o udev durante o boot. É melhor utilizar nomes que não são os padrões do kernel como: net0, net1, wifi0, wifi1. Para maiores detalhes, veja a documentação do systemd.

Alterando MTU e tamanho da fila

Você pode alterar o MTU de um dispositivo através de uma regra do udev. Exemplo:

/etc/udev/rules.d/10-network.rules

ACTION=="add", SUBSYSTEM=="net", KERNEL=="wl*", ATTR{mtu}="1480", ATTR{tx_queue_len}="2000"

Descobrir nome dos dispositivos atuais

Os nomes dos dispositivos em execução podem ser obtidos através do sysfs

$ ls /sys/class/net

lo eth0 eth1 firewire0

Ativando e desabilitando interfaces de rede

Você pode ativar e desabilitar interfaces de rede através dos comandos:

# ip link set eth0 up
# ip link set eth0 down

Prova real:

$ ip link show dev eth0

2: eth0: <BROADCAST,MULTICAST,PROMISC,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master br0 state UP mode DEFAULT qlen 1000
[...]

Configurando endereços IP

Você possui duas opções: Endereços dinâmicos através de DHCP ou um endereço "estático".

Endereço IP dinâmico

Execução manual do serviço(daemon) DHCP

Note que dhcpcd não é dhcpd.

# dhcpcd eth0

 dhcpcd: version 5.1.1 starting
 dhcpcd: eth0: broadcasting for a lease
 ...
 dhcpcd: eth0: leased 192.168.1.70 for 86400 seconds

Através do comando, ip addr show dev eth0 você verificará o endereço obtido.

Em alguns cenários, o comando dhclient do pacote dhclient funcionará e o dhcpcd falhará.

DHCP durante o boot

Se você deseja apenas usar o DHCP em sua coenxão cabeada, você pode usar o serviço dhcpcd@.service provido pelo pacote {Pkg|dhcpcd}},

Para iniciar o DHCP na interface eth0:

# systemctl start dhcpcd@eth0

Você pode habilitar o serviço para iniciar no boot do sistema com o comando:

# systemctl enable dhcpcd@eth0

Caso o serviço dhcpd inicie antes do módulo da interface de rede ser carregado(FS#30235), adicione sua interface de rede ao arquivo /etc/modules-load.d/*.conf. Por exemplo, se o módulo da Realtek r8169 precisa ser carregado crie o arquivo:

/etc/modules-load.d/realtek.conf

r8169

Tip: Para descobrir quais módulos são utilizados por uma placa de rede, utilize o comando lspci -k.

Tip: To find out which modules are used by your network card, use lspci -k.

Se você utiliza DHCP e não deseja ter o DNS configurado automaticamente cada vez que a rede for iniciada, adicione o seguinte conteúdo na última sessão do arquivo dhcpcd.conf:

/etc/dhcpcd.conf

nohook resolv.conf

Para previnir que o dhcpcd adicione nomes de domínio ao /etc/resolv.conf, use a opção nooption:

/etc/dhcpcd.conf

nooption domain_name_servers

Assim, você poderá editar o arquivo /etc/resolv.conf com suas próprias configurações de DNS.

Você pode usar o pacote openresolv caso diferentes processos desejam controlar o arquivo /etc/resolv.conf (por exemplo, dhcpcd e um cliente de VPN). Nenhuma configuração adicional para o dhcpcd é necessária para se adequar ao openresolv.

Static IP address

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 with unchanging addresses, or you may not have a DHCP server available.

Note: If you share your Internet connection from a Windows machine without a router, be sure to use static IP addresses on both computers to avoid LAN problems.

You need:

• Static IP address
• Subnet mask
• Broadcast address
• Gateway's IP address

If you are running a private network, it is safe to use IP addresses in 192.168.*.* for your IP addresses, with a subnet mask of 255.255.255.0 and a broadcast address of 192.168.*.255. The gateway is usually 192.168.*.1 or 192.168.*.254.

Manual assignment

You can assign a static IP address in the console:

# ip addr add <IP address>/<subnet mask> dev <interface>

For example:

# ip addr add 192.168.1.2/24 dev eth0

Note: The subnet mask was specified using CIDR notation.

For more options, see man ip.

Add your gateway like so:

# ip route add default via <default gateway IP address>

For example:

# ip route add default via 192.168.1.1

If you the get the error "No such process", it means you have to run ip link set dev eth0 up as root.

Manual connection at boot using systemd

First create configuration file for the systemd service, replace <interface> with proper interface name:

/etc/conf.d/network@<interface>

address=192.168.0.15
netmask=24
broadcast=192.168.0.255
gateway=192.168.0.1

Create a systemd unit file:

/etc/systemd/system/network@.service

[Unit]
Description=Network connectivity (%i)
Wants=network.target
Before=network.target
BindsTo=sys-subsystem-net-devices-%i.device
After=sys-subsystem-net-devices-%i.device

[Service]
Type=oneshot
RemainAfterExit=yes
EnvironmentFile=/etc/conf.d/network@%i
ExecStart=/usr/bin/ip link set dev %i up
ExecStart=/usr/bin/ip addr add ${address}/${netmask} broadcast ${broadcast} dev %i
ExecStart=/usr/bin/ip route add default via ${gateway}

ExecStop=/usr/bin/ip addr flush dev %i
ExecStop=/usr/bin/ip link set dev %i down

[Install]
WantedBy=multi-user.target

Enable the unit and start it, passing the name of the interface:

# systemctl enable network@eth0.service
# systemctl start network@eth0.service

Calculating addresses

You can use ipcalc provided by the ipcalc package to calculate IP broadcast, network, netmask, and host ranges for more advanced configurations. For example, I use ethernet over firewire to connect a windows machine to arch. For security and network organization, I placed them on their own network and configured the netmask and broadcast so that they are the only 2 machines on it. To figure out the netmask and broadcast addresses for this, I used ipcalc, providing it with the IP of the arch firewire nic 10.66.66.1, and specifying ipcalc should create a network of only 2 hosts.

$ ipcalc -nb 10.66.66.1 -s 1

Address:   10.66.66.1

Netmask:   255.255.255.252 = 30
Network:   10.66.66.0/30
HostMin:   10.66.66.1
HostMax:   10.66.66.2
Broadcast: 10.66.66.3
Hosts/Net: 2                     Class A, Private Internet

Load configuration

To test your settings either reboot the computer or reload the relevant systemd services:

# systemctl restart dhcpcd@eth0

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 -c 3 www.google.com

Additional settings

ifplugd for laptops

ifplugd in Official Repositories is 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.

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

Note: Netctl package includes netctl-ifplugd@.service, otherwise you can use ifplugd@.service from ifplugd package. Use for example systemctl enable ifplugd@eth0.service.

Bonding or LAG

See netctl#Bonding.

IP address aliasing

IP aliasing is the process of adding more than one IP address to a network interface. With this, one node on a network can have multiple connections to a network, each serving a different purpose. Typical uses are virtual hosting of Web and FTP servers, or reorganizing servers without having to update any other machines (this is especially useful for nameservers).

Example

You will need netctl from the Official Repositories.

Prepare the configuration:

/etc/netctl/mynetwork

Connection='ethernet'
Description='Five different addresses on the same NIC.'
Interface='eth0'
IP='static'
Address=('192.168.1.10' '192.168.178.11' '192.168.1.12' '192.168.1.13' '192.168.1.14' '192.168.1.15')
Gateway='192.168.1.1'
DNS=('192.168.1.1')

Then simply execute:

$ netctl start mynetwork

Change MAC/hardware address

See MAC Address Spoofing.

Internet Share

See Internet Share.

Router Configuration

See Router.

Troubleshooting

Swapping computers on the cable modem

Most domestic cable ISPs (videotron for example) have the cable modem configured to recognize only one client PC, by the MAC address of its network interface. Once the cable modem has learned 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 MAC address different from 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 problem

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, let's 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 ip addr will report normal status... and actually everything appears normal.

If you cannot browse any website, but you can ping some random hosts, chances are great that you're experiencing this problem: ping uses ICMP and is not affected by TCP problems.

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

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 cannot fix the broken router. There are several ways to disable Window Scaling, and it seems that the most bulletproof way (which will work with most kernels) is to add the following line to /etc/sysctl.conf (see also sysctl)

net.ipv4.tcp_window_scaling = 0

How to fix it (The best way)

This problem is caused by broken routers/firewalls, so let's 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.

There are also several relevant threads on the LKML.

Realtek no link / WOL problem

Users with Realtek 8168 8169 8101 8111(C) based NICs (cards / and on-board) may notice a problem 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 problem 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 problem will also affect other operative systems without newer drivers (eg. Live CDs). Here are a few fixes for this problem:

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 problem

Users with a DLink G604T/DLink G502T router, using DHCP and have firmware v2.00+ (typically users with AUS firmware) may have problems 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 address of 1.0.0.0 and fail with a connection timed out error

How to diagnose the problem

The best way to diagnose the problem is to use 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 it is downloading packages) Open /etc/pacman.conf with your favourite editor and uncomment the following line (remove the # if it is there)

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

While you are editing /etc/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 1.0.0.0),

ftp://mirror.pacific.net.au/linux/archlinux/extra/os/i686/extra.db.tar.gz
           => '/var/lib/pacman/community.db.tar.gz.part'
Resolving mirror.pacific.net.au... 1.0.0.0

then you most likely have this problem. The 1.0.0.0 means it is unable to resolve DNS, so we must add it to /etc/resolv.conf.

How to fix it

Basically what we need to do is to manually add the DNS servers 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 from doing this.

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

DHCPCD_ARGS="-t 30 -h $HOSTNAME"

Add the -R flag to the arguments, e.g.,

DHCPCD_ARGS="-R -t 30 -h $HOSTNAME"

Note: If you are using dhcpcd >= 4.0.2, the -R flag has been deprecated. Please see the #For DHCP assigned IP address section for information on how to use a custom /etc/resolv.conf file.

Save and close the file; now open /etc/resolv.conf. You should see a single nameserver (most likely 10.1.1.1). This is the gateway to your router, which we need to connect to in order to get the DNS servers of your ISP. Paste the IP address into your browser and log in to your router. Go to the DNS section, and you should see an IP address in the Primary DNS Server field; copy it and paste it as a nameserver ABOVE the current gateway one.

For example, /etc/resolv.conf should look something along the lines of:

nameserver 10.1.1.1

If my primary DNS server is 211.29.132.12, then change /etc/resolv.conf to:

nameserver 211.29.132.12
nameserver 10.1.1.1

Now restart the network daemon by running systemctl restart dhcpcd@<interface> and do pacman -Syy. If it syncs correctly with the server, then the problem is solved.

More about it

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

http://forums.whirlpool.net.au/forum-replies-archive.cfm/461625.html

Check DHCP problem by releasing IP first

Problem may occur when DHCP get wrong IP assignment. For example when two routers are tied together through VPN. The router that is connected to me by VPN may assigning IP address. To fix it. On a console, as root, release IP address:

# dhcpcd -k

Then request a new one:

# dhcpcd

Maybe you had to run those two commands many times.

No eth0 with Atheros AR8161

Note: With the 3.10.2-1-ARCH kernel update, the alx ethernet driver module is included in the package.

With the Atheros AR8161 Gigabit Ethernet card, the ethernet connection is not working out-of-the-box (with the installation media of March 2013). The module "alx" needs to be loaded but is not present.

The driver from compat-wireless (that has become compat-drives since linux 3.7) need to be installed. The "-u" postfix annotates that Qualcomm have applied a driver under a unified driver.

 $ wget https://www.kernel.org/pub/linux/kernel/projects/backports/2013/03/28/compat-drivers-2013-03-28-5-u.tar.bz2
 $ tar xjf compat*
 $ cd compat*
 $ ./scripts/driver-select alx
 $ make
 $ sudo make install
 $ sudo modprobe alx

The alx driver has not been added to Linux kernel due to various problems. Compatibility between the different kernel versions has been spotty. For better support follow the mailing listand alx pagefor latest working solution for alx.

The driver must be built and installed after every kernel change.

Alternatively you can use the AUR package for compat drivers, which installs many other drivers.

No eth0 with Atheros AR9485

The ethernet (eth0) for Atheros AR9485 are not working out-of-the-box (with installation media of March 2013). The working solution for this is to install the package compat-drivers-patched from AUR.

No carrier / no connection after suspend

After suspend to RAM no connection is found although the network cable is plugged in. This may be caused by PCI power management. What is the output of

# ip link show eth0

If the line contains "NO-CARRIER" even though there's a cable connected to your eth0 port, it is possible that the device was auto-suspended and the media sense feature doesn't work. To solve this, first you need to find your ethernet controllers PCI address by

# lspci

This should look similar to this:

...
00:19.0 Ethernet controller: Intel Corporation 82577LM Gigabit Network Connection (rev 06)
...

So the address is 00:19.0. Now check the PM status of the device by issuing

# cat "/sys/bus/pci/devices/0000:00:19.0/power/control"

substituting 00:19.0 with the address obtained from lspci. If the output reads "auto", you can try to bring the device out of suspend by

# echo on > "/sys/bus/pci/devices/0000:00:19.0/power/control"

Don't forget to substitute the address again.

Note: This appears to be a bug in kernel 3.8.4.1- (3.8.8.1 is still affected): Forum discussion. It also appears a fix is on the way. (It will be likely fixed in 3.9.) In the meantime, the above is a suitable workaround.

PC Pingable by IP but not by hostname?

This issue hunted me for months! Turns out to be a very simple fix IF you are using samba as well. Usually people only start smbd which is enough for network access to work, but does not advocate the pc's name to the router. nmbd is doing that so you should always have:

systemctl enable smbd.service
systemctl enable nmbd.service

Which makes them run at startup. If you don't want to restart then you can start then right away with:

systemctl start smbd.service
systemctl start nmbd.service

And that makes the computer available by name on the network.

Broadcom BCM57780

This Broadcom chipset sometimes does not behave well unless you specify the order of the modules to be loaded. The modules are broadcom and tg3, the former needing to be loaded first.

These steps should help if your computer has this chipset:

$ lspci | grep Ethernet
02:00.0 Ethernet controller: Broadcom Corporation NetLink BCM57780 Gigabit Ethernet PCIe (rev 01)

If your wired networking is not functioning in some way or another, try unplugging your cable then doing the following (as root):

# modprobe -r tg3
# modprobe broadcom
# modprobe tg3

Now plug you network cable in. If this solves your problems you can make this permanent by adding broadcom and tg3 (in this order) to the MODULES array in /etc/mkinitcpio.conf:

MODULES=".. broadcom tg3 .."

Then rebuild the initramfs:

# mkinitcpio -p linux

Note: These methods may work for other chipsets, such as BCM57760.