Difference between revisions of "Network configuration"

From ArchWiki
Jump to navigation Jump to search
m (fix broken section links)
m (update links)
 
(134 intermediate revisions by 19 users not shown)
Line 8: Line 8:
 
[[nl:Network configuration]]
 
[[nl:Network configuration]]
 
[[pt:Network configuration]]
 
[[pt:Network configuration]]
[[ro:Configurare retea]]
 
 
[[ru:Network configuration]]
 
[[ru:Network configuration]]
 
[[sk:Network configuration]]
 
[[sk:Network configuration]]
Line 20: Line 19:
 
{{Related|Router}}
 
{{Related|Router}}
 
{{Related articles end}}
 
{{Related articles end}}
This article explains how to manually set up a network connection. For automatic network configuration see [[Network manager]].
 
  
To set up or troubleshoot a network connection, go through the following conditions and ensure that you meet them:
+
This article describes how to configure network connections on [[Wikipedia:OSI layer 3|OSI layer 3]] and above. Medium-specifics are handled in the [[/Ethernet]] and [[/Wireless]] subpages.
  
# Your network interface is listed, see [[#Listing network interfaces]].
+
== Check the connection ==
# Your network interface is enabled, see [[#Enabling and disabling network interfaces]].
 
# If its a Wi-Fi connection, you must be connected to your Wireless LAN, see [[Wireless network configuration]].
 
# Your network interface has an IP address, see [[#IP addresses]].
 
# Your routing table is correctly set up, see [[#Routing table]].
 
# You can [[#Ping|ping]] your default gateway.
 
# You can [[#Ping|ping]] a public IP address.
 
# You can resolve domain names, see [[#Resolving domain names]].
 
  
== Device driver ==
+
To troubleshoot a network connection, go through the following conditions and ensure that you meet them:
  
=== Check the status ===
+
# Your [[#Network interfaces|network interface]] is listed and enabled. Otherwise, check the device driver – see [[/Ethernet#Device driver]] or [[/Wireless#Device driver]].
 +
# You are connected to the network. The cable is plugged in or you are [[/Wireless|connected to the wireless LAN]].
 +
# Your network interface has an [[#IP addresses|IP address]].
 +
# Your [[#Routing table|routing table]] is correctly set up.
 +
# You can [[#Ping|ping]] a local IP address (e.g. your default gateway).
 +
# You can [[#Ping|ping]] a public IP address (e.g. {{ic|8.8.8.8}}, which is a Google DNS server and is a convenient address to test with).
 +
# [[Check if you can resolve domain names]] (e.g. {{ic|archlinux.org}}).
  
[[udev]] should detect your [[Wikipedia:Network interface controller|network interface controller]] (NIC) and automatically load the necessary [[kernel module]] at startup. Check the "Ethernet controller" entry (or similar) from the {{ic|lspci -v}} output. It should tell you which kernel module contains the driver for your network device. For example:
+
=== Ping ===
  
{{hc|$ lspci -v|
+
{{Expansion|Add or link explanation of common ping errors like Unknown hosts / Network is unreachable.}}
02:00.0 Ethernet controller: Attansic Technology Corp. L1 Gigabit Ethernet Adapter (rev b0)
 
...
 
Kernel driver in use: atl1
 
Kernel modules: atl1
 
}}
 
  
Next, check that the driver was loaded via {{ic|dmesg {{!}} grep ''module_name''}}. For example:
+
[[Wikipedia:Ping (networking utility)|ping]] is used to test if you can reach a host.
  
{{hc|$ dmesg {{!}} grep atl1|
+
{{hc|$ ping www.example.com|2=
 +
PING www.example.com (93.184.216.34): 56(84) data bytes
 +
64 bytes from 93.184.216.34: icmp_seq=0 ttl=56 time=11.632 ms
 +
64 bytes from 93.184.216.34: icmp_seq=1 ttl=56 time=11.726 ms
 +
64 bytes from 93.184.216.34: icmp_seq=2 ttl=56 time=10.683 ms
 
...
 
...
atl1 0000:02:00.0: eth0 link is up 100 Mbps full duplex
 
 
}}
 
}}
  
Skip the next section if the driver was loaded successfully. Otherwise, you will need to know which module is needed for your particular model.
+
For every reply you receive, the ping utility will print a line like the above. For more information see the {{man|8|ping}} manual. Note that computers can be configured not to respond to ICMP echo requests. [https://unix.stackexchange.com/questions/412446/how-to-disable-ping-response-icmp-echo-in-linux-all-the-time]
 +
 
 +
If you receive no reply, this may be related to your default gateway or your Internet Service Provider (ISP). You can run a [[traceroute]] to further diagnose the route to the host.
 +
 
 +
{{Note|If you receive an error like {{ic|ping: icmp open socket: Operation not permitted}} when executing ''ping'', try to re-install the {{Pkg|iputils}} package.}}
 +
 
 +
== Network management ==
 +
 
 +
To set up a network connection, go through the following steps:
 +
 
 +
# Ensure your [[#Network interfaces|network interface]] is listed and enabled.
 +
# Connect to the network. Plug in the Ethernet cable or [[/Wireless|connect to the wireless LAN]].
 +
# Configure your network connection:
 +
#* [[#Static IP address|static IP address]]
 +
#* dynamic IP address: use [[#DHCP|DHCP]]
 +
 
 +
{{Note|The installation image enables [[dhcpcd]] ({{ic|dhcpcd@''interface''.service}}) for [https://git.archlinux.org/archiso.git/tree/configs/releng/airootfs/etc/udev/rules.d/81-dhcpcd.rules wired network devices] on boot.}}
 +
 
 +
=== net-tools ===
  
=== Load the module ===
+
Arch Linux has deprecated {{Pkg|net-tools}} in favor of {{Pkg|iproute2}}.[https://www.archlinux.org/news/deprecation-of-net-tools/]
  
Search in the Internet for the right module/driver for the chipset. Some common modules are {{ic|8139too}} for cards with a Realtek chipset, or {{ic|sis900}} for cards with a SiS chipset. Once you know which module to use, try to [[Kernel modules#Manual module handling|load it manually]]. If you get an error saying that the module was not found, it is possible that the driver is not included in Arch kernel. You may search the [[AUR]] for the module name.
+
{| class="wikitable"
 +
! Deprecated command !! Replacement commands
 +
|-
 +
| arp || ip neighbor
 +
|-
 +
| [[Wikipedia:ifconfig|ifconfig]] || ip address, ip link
 +
|-
 +
| netstat || [[#Investigate sockets|ss]]
 +
|-
 +
| route || ip route
 +
|}
  
If udev is not detecting and loading the proper module automatically during bootup, see [[Kernel module#Automatic module handling]].
+
For a more complete rundown, see [https://dougvitale.wordpress.com/2011/12/21/deprecated-linux-networking-commands-and-their-replacements/ this blog post].
  
== Network management ==
+
=== iproute2 ===
  
{{Pkg|iproute2}} provides the major network configuration utilities, many of which are accessible via the {{man|8|ip}} command-line interface. Be aware that configuration made using {{ic|ip}} will be lost after a reboot. You can automate these commands using scripts and [[systemd#Writing unit files|systemd units]]. Also note that {{ic|ip}} commands can generally be abbreviated, for clarity they are however spelled out in this article.
+
[[Wikipedia:iproute2|iproute2]] is a dependency of the {{Pkg|base}} [[meta package]] and provides the {{man|8|ip}} command-line interface, used to manage [[#Network interfaces|network interfaces]], [[#IP addresses|IP addresses]] and the [[#Routing table|routing table]]. Be aware that configuration made using {{ic|ip}} will be lost after a reboot. For persistent configuration, you can use a [[network manager]] or automate ''ip'' commands using scripts and [[systemd#Writing unit files|systemd units]]. Also note that {{ic|ip}} commands can generally be abbreviated, for clarity they are however spelled out in this article.
  
 
=== Network interfaces ===
 
=== Network interfaces ===
  
By default [[udev]] assigns names to your network interfaces using [http://www.freedesktop.org/wiki/Software/systemd/PredictableNetworkInterfaceNames Predictable Network Interface Names], which prefixes interfaces names with {{ic|en}} (wired/[[w:Ethernet|Ethernet]]), {{ic|wl}} (wireless/WLAN), or {{ic|ww}} ([[w:Wireless WAN|WWAN]]).
+
By default [[udev]] assigns names to your network interfaces using [http://www.freedesktop.org/wiki/Software/systemd/PredictableNetworkInterfaceNames Predictable Network Interface Names], which prefixes interfaces names with {{ic|en}} (wired/[[Wikipedia:Ethernet|Ethernet]]), {{ic|wl}} (wireless/WLAN), or {{ic|ww}} ([[Wikipedia:Wireless WAN|WWAN]]).
  
 
{{Tip|To change interface names, see [[#Change interface name]] and [[#Revert to traditional interface names]].}}
 
{{Tip|To change interface names, see [[#Change interface name]] and [[#Revert to traditional interface names]].}}
Line 73: Line 96:
 
==== Listing network interfaces ====
 
==== Listing network interfaces ====
  
Both wired and wireless interface names can be found via {{ic|ls /sys/class/net}} or {{ic|ip link}}. Note that {{ic|lo}} is the [[w:loop device|loop device]] and not used in making network connections.
+
Both wired and wireless interface names can be found via {{ic|ls /sys/class/net}} or {{ic|ip link}}. Note that {{ic|lo}} is the [[Wikipedia:loop device|loop device]] and not used in making network connections.
  
Wireless device names can also be retrieved using {{ic|iw dev}}. See also [[Wireless network configuration#Get the name of the interface]].
+
Wireless device names can also be retrieved using {{ic|iw dev}}. See also [[/Wireless#Get the name of the interface]].
  
If your network interface is not listed, make sure your [[#Device driver]] was loaded successfully.
+
If your network interface is not listed, make sure your [[#Device driver|device driver]] was loaded successfully.
  
 
==== Enabling and disabling network interfaces ====
 
==== Enabling and disabling network interfaces ====
  
Network interfaces can be enabled / disabled using {{ic|# ip link set ''interface'' up{{!}}down}}, see {{man|8|ip-link}}.
+
Network interfaces can be enabled / disabled using {{ic|ip link set ''interface'' up{{!}}down}}, see {{man|8|ip-link}}.
  
 
To check the status of the interface {{ic|eth0}}:
 
To check the status of the interface {{ic|eth0}}:
Line 92: Line 115:
 
The {{ic|UP}} in {{ic|<BROADCAST,MULTICAST,UP,LOWER_UP>}} is what indicates the interface is up, not the later {{ic|state DOWN}}.
 
The {{ic|UP}} in {{ic|<BROADCAST,MULTICAST,UP,LOWER_UP>}} is what indicates the interface is up, not the later {{ic|state DOWN}}.
  
{{Note|If your default route is through interface {{ic|eth0}}, taking it down will also remove the route, and bringing it back up will not automatically reestablish the default route.  See [[#Routing table]] for reestablishing it.}}
+
{{Note|If your default route is through interface {{ic|eth0}}, taking it down will also remove the route, and bringing it back up will not automatically re-establish the default route.  See [[#Routing table]] for re-establishing it.}}
  
=== IP addresses ===
+
=== Static IP address ===
 +
 
 +
A static IP address can be configured with most standard [[#Network managers|network managers]] and also [[dhcpcd]].
  
An [[Wikipedia:IP address|IP address]] can either be assigned manually (called static IP address), described in [[#Manual IP address management]], or assigned dynamically using [[#DHCP]].
+
To manually configure a static IP address, add an IP address as described in [[#IP addresses]], set up your [[#Routing table|routing table]] and [[Domain name resolution|configure your DNS servers]].
If you use a static IP address, you will also need to manually configure your default gateway in the [[#Routing table]].
 
  
==== Manual IP address management ====
+
=== IP addresses ===
  
 
[[Wikipedia:IP address|IP addresses]] are managed using {{man|8|ip-address}}.
 
[[Wikipedia:IP address|IP addresses]] are managed using {{man|8|ip-address}}.
Line 114: Line 138:
  
 
:* the address is given in [[Wikipedia:Classless Inter-Domain Routing#CIDR notation|CIDR notation]] to also supply a [[Wikipedia:Subnetwork|subnet mask]]
 
:* the address is given in [[Wikipedia:Classless Inter-Domain Routing#CIDR notation|CIDR notation]] to also supply a [[Wikipedia:Subnetwork|subnet mask]]
:* {{ic|+}} is a special symbol that makes ''ip'' derive the broadcast address from the address prefix
+
:* {{ic|+}} is a special symbol that makes {{ic|ip}} derive the [[Wikipedia:Broadcast address|broadcast address]] from the IP address and the subnet mask
  
:{{Note|Make sure manually assigned IP addresses do not conflict with DHCP assigned ones. See [http://www.raspberrypi.org/forums/viewtopic.php?f&#61;28&t&#61;16797 this forum thread].
+
:{{Note|Make sure manually assigned IP addresses do not conflict with DHCP assigned ones.}}
}}
 
  
 
Delete an IP address from an interface:
 
Delete an IP address from an interface:
Line 127: Line 150:
 
  $ ip address flush dev ''interface''
 
  $ ip address flush dev ''interface''
  
{{Tip|IP addresses can be calculated using [http://jodies.de/ipcalc ipcalc] ({{Pkg|ipcalc}}).}}
+
{{Tip|IP addresses can be calculated with [http://jodies.de/ipcalc ipcalc] ({{Pkg|ipcalc}}).}}
  
==== Routing table ====
+
=== Routing table ===
  
 
The [[Wikipedia:Routing table|routing table]] is used to determine if you can reach an IP address directly or what gateway (router) you should use. If no other route matches the IP address, the [[Wikipedia:Default gateway|default gateway]] is used.
 
The [[Wikipedia:Routing table|routing table]] is used to determine if you can reach an IP address directly or what gateway (router) you should use. If no other route matches the IP address, the [[Wikipedia:Default gateway|default gateway]] is used.
Line 137: Line 160:
 
''PREFIX'' is either a CIDR notation or {{ic|default}} for the default gateway.
 
''PREFIX'' is either a CIDR notation or {{ic|default}} for the default gateway.
  
List routes:
+
List IPv4 routes:
  
 
  $ ip route show
 
  $ ip route show
 +
 +
List IPv6 routes:
 +
 +
$ ip -6 route
  
 
Add a route:
 
Add a route:
Line 149: Line 176:
 
  # ip route del ''PREFIX'' via ''address'' dev ''interface''
 
  # ip route del ''PREFIX'' via ''address'' dev ''interface''
  
==== DHCP ====
+
=== DHCP ===
  
A [[Wikipedia:DHCP|DHCP]] server provides clients with a dynamic IP address, the subnet mask, the default gateway IP address and optionally also with DNS name servers.
+
A [[Wikipedia:Dynamic Host Configuration Protocol|Dynamic Host Configuration Protocol]] (DHCP) server provides clients with a dynamic IP address, the subnet mask, the default gateway IP address and optionally also with DNS name servers.
 +
 
 +
{{Note|You should not run two DHCP clients simultaneously.}}
  
 
To use DHCP you need a DHCP server in your network and a DHCP client:
 
To use DHCP you need a DHCP server in your network and a DHCP client:
  
* [[dhcpcd]] DHCP, DHCPv6 and ZeroConf client daemon.
+
{| class="wikitable"
* ISC DHCP ({{Pkg|dhclient}})
+
! Client !! Package !! [[Archiso]] !! Note !! Systemd units
* {{AUR|pump}}
+
|-
 +
| [[dhcpcd]] || {{Pkg|dhcpcd}} || {{Yes}} || DHCP, DHCPv6, ZeroConf, static IP || {{ic|dhcpcd.service}}, {{ic|dhcpcd@''interface''.service}}
 +
|-
 +
| [https://www.isc.org/downloads/dhcp/ ISC dhclient] || {{Pkg|dhclient}} || {{Yes}} || DHCP, DHCPv6, BOOTP, static IP || {{ic|dhclient@''interface''.service}}
 +
|}
  
Note that instead of directly using a DHCP client you can also use a [[network manager]].
+
Note that instead of directly using a DHCP client you can also use a [[#Network managers|network manager]].
  
== Ping ==
+
{{Tip|You can check if a DHCP server is running with {{Pkg|dhcping}}.}}
  
[[Wikipedia:Ping (networking utility)|ping]] is used to test if you can reach a host. See the {{man|8|ping}} manual. Note that computers can be configured not to respond to ICMP echo requests.[https://unix.stackexchange.com/questions/412446/how-to-disable-ping-response-icmp-echo-in-linux-all-the-time]
+
=== Network managers ===
  
When you receive no reply, you can use a [[Wikipedia:Traceroute|traceroute]] ({{man|8|traceroute}} or {{man|8|tracepath}}) to further diagnose the route to the host.
+
A network manager lets you manage network connection settings in so called network profiles to facilitate switching networks.
  
{{Note|If you receive an error like {{ic|ping: icmp open socket: Operation not permitted}} when executing ''ping'', try to re-install the {{Pkg|iputils}} package.}}
+
{{Note|There are many solutions to choose from, but remember that all of them are mutually exclusive; you should not run two daemons simultaneously.}}
  
== Resolving domain names ==
+
{| class="wikitable"
 +
! Network manager || GUI || [[Archiso]] [https://git.archlinux.org/archiso.git/tree/configs/releng/packages.x86_64] || CLI tools || [[Wikipedia:Point-to-Point Protocol|PPP]] support <br>(e.g. 3G modem) || [[#DHCP|DHCP client]] || Systemd units
 +
|-
 +
! [[ConnMan]]
 +
| {{Y|8 unofficial}} || {{No}} || {{man|1|connmanctl}} || {{Yes}} (with {{aur|ofono}}) || internal || {{ic|connman.service}}
 +
|-
 +
! [[netctl]]
 +
| {{Y|2 unofficial}} || {{Yes}} || {{man|1|netctl}}, wifi-menu || {{Yes}} || [[dhcpcd]] or {{Pkg|dhclient}} || {{ic|netctl-ifplugd@''interface''.service}}, {{ic|netctl-auto@''interface''.service}}
 +
|-
 +
! [[NetworkManager]]
 +
| {{Yes}} || {{No}} || {{man|1|nmcli}}, {{man|1|nmtui}} || {{Yes}} || internal, [[dhcpcd]] or {{Pkg|dhclient}} || {{ic|NetworkManager.service}}
 +
|-
 +
! [[systemd-networkd]]
 +
| {{No}} || {{Yes}} ({{Pkg|base}}) || {{man|1|networkctl}} || {{No|https://github.com/systemd/systemd/issues/481}} || internal || {{ic|systemd-networkd.service}}, {{ic|systemd-resolved.service}}
 +
|-
 +
! [[Wicd]]
 +
| {{Yes}} || {{No}} || {{man|8|wicd-cli}}, {{man|8|wicd-curses}} || {{No}} || [[dhcpcd]] || {{ic|wicd.service}}
 +
|}
  
To resolve a [[Wikipedia:Domain name|domain name]] using your system configuration, run:
+
There also is [[Wifi Radar]], a GUI application to manage WiFi networks with {{Pkg|wireless_tools}}, it however does not handle wired connections.
  
$ getent hosts ''domain_name''
+
See also [[List of applications#Network managers]].
 
 
For more fine-grained DNS queries use a dedicated DNS lookup utility, like {{man|1|dig}} (provided by {{Pkg|bind-tools}}) or {{man|1|drill}} (provided by {{Pkg|ldns}}).
 
 
 
If you cannot resolve domain names but you are connected to the internet, see [[resolv.conf]] and check the {{ic|hosts}} line in {{man|5|nsswitch.conf}}.
 
  
 
== Set the hostname ==
 
== Set the hostname ==
Line 199: Line 245:
 
To set the "pretty" hostname and other machine metadata, see {{man|5|machine-info|https://www.freedesktop.org/software/systemd/man/machine-info.html}}.
 
To set the "pretty" hostname and other machine metadata, see {{man|5|machine-info|https://www.freedesktop.org/software/systemd/man/machine-info.html}}.
  
=== Local network hostname resolution ===
+
=== Local hostname resolution ===
  
The pre-requisite is to [[#Set the hostname]], after which hostname resolution works on the local system itself:
+
{{Expansion|Explain why you want a resolvable hostname, why {{ic|127.0.1.1}} is used (and why a static IP address should be preferred over it).}}
  
{{hc|$ ping ''myhostname''|2=
+
The {{ic|myhostname}} [[Name Service Switch]] (NSS) module of [[systemd]] provides local hostname resolution without having to edit {{ic|/etc/hosts}} ({{man|5|hosts}}). It is enabled by default.
PING ''myhostname'' (192.168.1.2) 56(84) bytes of data.
 
64 bytes from ''myhostname'' (192.168.1.2): icmp_seq=1 ttl=64 time=0.043 ms
 
}}
 
  
To allow other machines to address the host by name, it is necessary to either:
+
Some clients may however still rely on {{ic|/etc/hosts}}, see [https://lists.debian.org/debian-devel/2013/07/msg00809.html] [https://bugzilla.mozilla.org/show_bug.cgi?id=87717#c55] for examples.
  
* Configure the {{man|5|hosts}} file, or
+
To configure the hosts file, add the following lines to {{ic|/etc/hosts}}:
* Enable a service which resolves the hostname.
 
  
{{Note|1={{Pkg|systemd}} provides hostname resolution via the {{ic|myhostname}} nss module, enabled by default in {{ic|/etc/nsswitch.conf}}. However, clients may still rely on {{ic|/etc/hosts}}, see [https://lists.debian.org/debian-devel/2013/07/msg00809.html] [https://bugzilla.mozilla.org/show_bug.cgi?id=87717#c55] for examples.}}
+
127.0.0.1        localhost
 
+
::1              localhost
To configure the hosts file, add the following line to {{ic|/etc/hosts}}:
+
  127.0.1.1       ''myhostname''.localdomain       ''myhostname''
 
 
  127.0.1.1 ''myhostname''.localdomain ''myhostname''
 
  
 
{{Note|The order of hostnames/aliases that follow the IP address in {{ic|/etc/hosts}} is significant. The first string is considered the canonical hostname and may be appended with parent domains, where domain components are separated by a dot (ie. {{ic|.localdomain}} above). All following strings on the same line are considered aliases. See {{man|5|hosts}} for more info.}}
 
{{Note|The order of hostnames/aliases that follow the IP address in {{ic|/etc/hosts}} is significant. The first string is considered the canonical hostname and may be appended with parent domains, where domain components are separated by a dot (ie. {{ic|.localdomain}} above). All following strings on the same line are considered aliases. See {{man|5|hosts}} for more info.}}
Line 225: Line 265:
 
{{hc|$ getent hosts|
 
{{hc|$ getent hosts|
 
127.0.0.1      localhost
 
127.0.0.1      localhost
127.0.1.1      ''myhostname''.localdomain ''myhostname''
+
127.0.0.1      localhost
 +
127.0.1.1      ''myhostname''.localdomain ''myhostname''
 
}}
 
}}
  
For a system with a permanent IP address, that permanent IP address should be used instead of {{ic|127.0.1.1}}.  
+
For a system with a permanent IP address, that permanent IP address should be used instead of {{ic|127.0.1.1}}.
 +
 
 +
=== Local network hostname resolution ===
  
{{Note|1=Another option is to set up a full DNS server such as [[BIND]] or [[Unbound]], but that is overkill and too complex for most systems. For small networks and dynamic flexibility with hosts joining and leaving the network [[Wikipedia:Zero-configuration networking|zero-configuration networking]] services may be more applicable:
+
To make your machine accessible in your LAN via its hostname you can:
* [[Samba]] provides hostname resolution via Microsoft's '''NetBIOS'''. It only requires installation of {{Pkg|samba}} and enabling of the {{ic|nmbd.service}} service. Computers running Windows, macOS, or Linux with {{ic|nmbd}} running, will be able to find your machine.
+
 
* [[Avahi]] provides hostname resolution via '''zeroconf''', also known as Avahi or Bonjour. It requires slightly more complex configuration than Samba: see [[Avahi#Hostname resolution]] for details. Computers running macOS, or Linux with an Avahi daemon running, will be able to find your machine. Windows does not have an built-in Avahi client or daemon.
+
* edit the {{ic|/etc/hosts}} file for every device in your LAN, see {{man|5|hosts}}
}}
+
* set up a [[DNS server]] to resolve your hostname and make the LAN devices use it (e.g. via [[#DHCP]])
 +
* or the easy way: use a [[Wikipedia:Zero-configuration networking|Zero-configuration networking]] service:
 +
** Hostname resolution via Microsoft's [[Wikipedia:NetBIOS#Name service|NetBIOS]]. Provided by [[Samba]] on Linux. It only requires the {{ic|nmb.service}}. Computers running Windows, macOS, or Linux with {{ic|nmb}} running, will be able to find your machine.
 +
** Hostname resolution via [[Wikipedia:Multicast DNS|mDNS]]. Provided by either {{ic|nss_mdns}} with [[Avahi]] (see [[Avahi#Hostname resolution]] for setup details) or [[systemd-resolved]]. Computers running macOS, or Linux with Avahi or systemd-resolved running, will be able to find your machine. Windows does not have a built-in mDNS client or daemon.
  
 
== Tips and tricks ==
 
== Tips and tricks ==
Line 260: Line 306:
 
SUBSYSTEM=="net", DEVPATH=="/devices/platform/wemac.*", NAME="int"
 
SUBSYSTEM=="net", DEVPATH=="/devices/platform/wemac.*", NAME="int"
 
SUBSYSTEM=="net", DEVPATH=="/devices/pci*/*1c.0/*/net/*", NAME="en"
 
SUBSYSTEM=="net", DEVPATH=="/devices/pci*/*1c.0/*/net/*", NAME="en"
 +
}}
 +
 +
To get the {{ic|DEVPATH}} of all currently-connected devices, see where the symlinks in {{ic|/sys/class/net/}} lead. For example:
 +
 +
{{hc|file /sys/class/net/*|
 +
/sys/class/net/enp0s20f0u4u1: symbolic link to ../../devices/pci0000:00/0000:00:14.0/usb2/2-4/2-4.1/2-4.1:1.0/net/enp0s20f0u4u1
 +
/sys/class/net/enp0s31f6:    symbolic link to ../../devices/pci0000:00/0000:00:1f.6/net/enp0s31f6
 +
/sys/class/net/lo:            symbolic link to ../../devices/virtual/net/lo
 +
/sys/class/net/wlp4s0:        symbolic link to ../../devices/pci0000:00/0000:00:1c.6/0000:04:00.0/net/wlp4s0
 
}}
 
}}
  
 
The device path should match both the new and old device name, since the rule may be executed more than once on bootup. For example, in the second rule, {{ic|"/devices/pci*/*1c.0/*/net/enp*"}} would be wrong since it will stop matching once the name is changed to {{ic|en}}. Only the system-default rule will fire the second time around, causing the name to be changed back to e.g. {{ic|enp1s0}}.
 
The device path should match both the new and old device name, since the rule may be executed more than once on bootup. For example, in the second rule, {{ic|"/devices/pci*/*1c.0/*/net/enp*"}} would be wrong since it will stop matching once the name is changed to {{ic|en}}. Only the system-default rule will fire the second time around, causing the name to be changed back to e.g. {{ic|enp1s0}}.
  
To [[udev#Testing rules before loading|test]] your rules, they can be triggered directly from userspace, e.g. with {{ic|udevadm --debug test /sys/''DEVPATH''}}. Remember to first take down the interface you are trying to rename (e.g. {{ic|ip link set enp1s0 down}}).
+
If you are using a USB network device (e.g. Android phone tethering) that has a dynamic MAC address and you want to be able to use different USB ports, you could use a rule that matched depending on vendor and product ID instead:
 +
 
 +
{{hc|/etc/udev/rules.d/10-network.rules|2=
 +
SUBSYSTEM=="net", ACTION=="add", ATTRS{idVendor}=="12ab", ATTRS{idProduct}=="3cd4", NAME="net2"
 +
}}
 +
 
 +
To [[udev#Testing rules before loading|test]] your rules, they can be triggered directly from userspace, e.g. with {{ic|udevadm --debug test /sys/class/net/*}}. Remember to first take down the interface you are trying to rename (e.g. {{ic|ip link set enp1s0 down}}).
  
 
{{Note|When choosing the static names '''it should be avoided to use names in the format of "eth''X''" and "wlan''X''"''', because this may lead to race conditions between the kernel and udev during boot. Instead, it is better to use interface names that are not used by the kernel as default, e.g.: {{ic|net0}}, {{ic|net1}}, {{ic|wifi0}}, {{ic|wifi1}}. For further details please see the [http://www.freedesktop.org/wiki/Software/systemd/PredictableNetworkInterfaceNames systemd] documentation.}}
 
{{Note|When choosing the static names '''it should be avoided to use names in the format of "eth''X''" and "wlan''X''"''', because this may lead to race conditions between the kernel and udev during boot. Instead, it is better to use interface names that are not used by the kernel as default, e.g.: {{ic|net0}}, {{ic|net1}}, {{ic|wifi0}}, {{ic|wifi1}}. For further details please see the [http://www.freedesktop.org/wiki/Software/systemd/PredictableNetworkInterfaceNames systemd] documentation.}}
Line 288: Line 349:
 
* {{ic|tx_queue_len}}: Small value for slower devices with a high latency like modem links and ISDN. High value is recommend for server connected over the high-speed Internet connections that perform large data transfers.
 
* {{ic|tx_queue_len}}: Small value for slower devices with a high latency like modem links and ISDN. High value is recommend for server connected over the high-speed Internet connections that perform large data transfers.
 
}}
 
}}
 
=== ifplugd for laptops ===
 
 
{{Tip|[[dhcpcd]] provides the same feature out of the box.}}
 
 
{{Pkg|ifplugd}} 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 {{ic|eth0}} device. This and other settings like delays can be configured in {{ic|/etc/ifplugd/ifplugd.conf}}.
 
 
{{Note|[[netctl]] package includes {{ic|netctl-ifplugd@.service}}, otherwise you can use {{ic|ifplugd@.service}} from {{Pkg|ifplugd}} package. For example, [[enable]] {{ic|ifplugd@eth0.service}}.}}
 
  
 
=== Bonding or LAG ===
 
=== Bonding or LAG ===
Line 339: Line 390:
 
If you want to enable promiscuous mode on interface {{ic|eth0}} run [[enable]] {{ic|promiscuous@eth0.service}}.
 
If you want to enable promiscuous mode on interface {{ic|eth0}} run [[enable]] {{ic|promiscuous@eth0.service}}.
  
== Troubleshooting ==
+
=== Investigate sockets ===
 +
 
 +
''ss'' is a utility to investigate network ports and is part of the {{Pkg|iproute2}} package. It has a similar functionality to the [https://www.archlinux.org/news/deprecation-of-net-tools/ deprecated] netstat utility.
 +
 
 +
Common usage includes:
 +
 
 +
Display all TCP Sockets with service names:
 +
$ ss -at
 +
 
 +
Display all TCP Sockets with port numbers:
 +
$ ss -atn
  
=== Swapping computers on the cable modem ===
+
Display all UDP Sockets:
 +
$ ss -au
  
Some cable ISPs (Vidéotron 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.
+
For more information see {{man|8|ss}}.
  
If this method does not work, you will need to clone the MAC address of the original machine. See also [[MAC address spoofing]].
+
== Troubleshooting ==
  
 
=== The TCP window scaling problem ===
 
=== The TCP window scaling problem ===
Line 387: Line 449:
 
==== More about it ====
 
==== More about it ====
  
This section is based on the LWN article [http://lwn.net/Articles/92727/ TCP window scaling and broken routers] and a Kernel Trap article: [http://kerneltrap.org/node/6723 Window Scaling on the Internet].
+
This section is based on the LWN article [http://lwn.net/Articles/92727/ TCP window scaling and broken routers] and an archived Kernel Trap article: [https://web.archive.org/web/20120426135627/http://kerneltrap.org:80/node/6723 Window Scaling on the Internet].
  
 
There are also several relevant threads on the LKML.
 
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 official 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 operating systems without newer drivers (eg. Live CDs). Here are a few fixes for this problem.
 
 
==== Enable the NIC directly in Linux ====
 
 
Follow [[#Enabling and disabling network interfaces]] to enable the interface.
 
 
==== 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).
 
 
==== 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 operating 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 and choose "Properties"
 
--> "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 {{ic|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.}}
 
 
==== 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).
 
 
==== 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.
 
 
{{Note|This was tested several times on a GIGABYTE GA-G31M-ES2L motherboard, BIOS version F8 released on 2009/02/05.}}
 
 
=== No interface with Atheros chipsets ===
 
 
Users of some Atheros ethernet chips are reporting it does not work out-of-the-box (with installation media of February 2014). The working solution for this is to install {{AUR|backports-patched}}.
 
 
=== Broadcom BCM57780 ===
 
 
This Broadcom chipset sometimes does not behave well unless you specify the order of the modules to be loaded. The modules are {{ic|broadcom}} and {{ic|tg3}}, the former needing to be loaded first.
 
 
These steps should help if your computer has this chipset:
 
 
* Find your NIC in ''lspci'' output:
 
 
{{hc|$ 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, unplug your cable then do the following:
 
 
# modprobe -r tg3
 
# modprobe broadcom
 
# modprobe tg3
 
 
* Plug your network cable back in and check whether the module succeeded with:
 
 
$ dmesg | greg tg3
 
 
* If this procedure solved the issue you can make it permanent by adding {{ic|broadcom}} and {{ic|tg3}} (in this order) to the {{ic|MODULES}} array:
 
{{hc|/etc/mkinitcpio.conf|2=MODULES=(.. broadcom tg3 ..)}}
 
 
* [[Regenerate the initramfs]]
 
* Alternatively, you can create an {{ic|/etc/modprobe.d/broadcom.conf}}:
 
 
softdep tg3 pre: broadcom
 
 
{{Note|These methods may work for other chipsets, such as BCM57760.}}
 
 
=== Realtek RTL8111/8168B ===
 
 
{{hc|# lspci {{!}} grep Ethernet|
 
03:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168B PCI Express Gigabit Ethernet controller (rev 02)
 
}}
 
 
The adapter should be recognized by the {{ic|r8169}} module. However, with some chip revisions the connection may go off and on all the time. The alternative {{Pkg|r8168}} should be used for a reliable connection in this case. [[Blacklist]] {{ic|r8169}}, if {{Pkg|r8168}} is not automatically loaded by [[udev]], see [[Kernel modules#Automatic module handling]].
 
 
{{Accuracy|"some revisions", no proof the driver is the cause, and not e.g poorly configured DNS servers}}
 
 
Another fault in the drivers for some revisions of this adapter is poor IPv6 support. [[IPv6#Disable functionality]] can be helpful if you encounter issues such as hanging webpages and slow speeds.
 
 
=== Gigabyte Motherboard with Realtek 8111/8168/8411 ===
 
 
With motherboards such as the ''Gigabyte GA-990FXA-UD3'', booting with [[PCI passthrough via OVMF#Setting up IOMMU|IOMMU]] off (which can be the default) will cause the network interface to be unreliable, often failing to connect or connecting but allowing no throughput. This will apply to the onboard NIC and to any other pci-NIC in the box because the IOMMU setting affects the entire network interface on the board. Enabling IOMMU and booting with the install media will throw AMD I-10/xhci page faults for a second, but then boots normally, resulting in a fully functional onboard NIC (even with the r8169 module).
 
 
When configuring the boot process for your installation, add {{ic|1=iommu=soft}} as a [[kernel parameter]] to eliminate the error messages on boot and restore USB3.0 functionality.
 
  
 
== See also ==
 
== See also ==
  
 +
* [https://www.tldp.org/LDP/nag2/index.html Linux Network Administrators Guide]
 
* [https://www.debian.org/doc/manuals/debian-reference/ch05.en.html Debian Reference: Network setup]
 
* [https://www.debian.org/doc/manuals/debian-reference/ch05.en.html Debian Reference: Network setup]
 
* [https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/Networking_Guide/ RHEL7: Networking Guide]
 
* [https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/Networking_Guide/ RHEL7: Networking Guide]

Latest revision as of 06:58, 14 October 2019

This article describes how to configure network connections on OSI layer 3 and above. Medium-specifics are handled in the /Ethernet and /Wireless subpages.

Check the connection

To troubleshoot a network connection, go through the following conditions and ensure that you meet them:

  1. Your network interface is listed and enabled. Otherwise, check the device driver – see /Ethernet#Device driver or /Wireless#Device driver.
  2. You are connected to the network. The cable is plugged in or you are connected to the wireless LAN.
  3. Your network interface has an IP address.
  4. Your routing table is correctly set up.
  5. You can ping a local IP address (e.g. your default gateway).
  6. You can ping a public IP address (e.g. 8.8.8.8, which is a Google DNS server and is a convenient address to test with).
  7. Check if you can resolve domain names (e.g. archlinux.org).

Ping

Tango-view-fullscreen.pngThis article or section needs expansion.Tango-view-fullscreen.png

Reason: Add or link explanation of common ping errors like Unknown hosts / Network is unreachable. (Discuss in Talk:Network configuration#)

ping is used to test if you can reach a host.

$ ping www.example.com
PING www.example.com (93.184.216.34): 56(84) data bytes
64 bytes from 93.184.216.34: icmp_seq=0 ttl=56 time=11.632 ms
64 bytes from 93.184.216.34: icmp_seq=1 ttl=56 time=11.726 ms
64 bytes from 93.184.216.34: icmp_seq=2 ttl=56 time=10.683 ms
...

For every reply you receive, the ping utility will print a line like the above. For more information see the ping(8) manual. Note that computers can be configured not to respond to ICMP echo requests. [1]

If you receive no reply, this may be related to your default gateway or your Internet Service Provider (ISP). You can run a traceroute to further diagnose the route to the host.

Note: If you receive an error like ping: icmp open socket: Operation not permitted when executing ping, try to re-install the iputils package.

Network management

To set up a network connection, go through the following steps:

  1. Ensure your network interface is listed and enabled.
  2. Connect to the network. Plug in the Ethernet cable or connect to the wireless LAN.
  3. Configure your network connection:
Note: The installation image enables dhcpcd (dhcpcd@interface.service) for wired network devices on boot.

net-tools

Arch Linux has deprecated net-tools in favor of iproute2.[2]

Deprecated command Replacement commands
arp ip neighbor
ifconfig ip address, ip link
netstat ss
route ip route

For a more complete rundown, see this blog post.

iproute2

iproute2 is a dependency of the base meta package and provides the ip(8) command-line interface, used to manage network interfaces, IP addresses and the routing table. Be aware that configuration made using ip will be lost after a reboot. For persistent configuration, you can use a network manager or automate ip commands using scripts and systemd units. Also note that ip commands can generally be abbreviated, for clarity they are however spelled out in this article.

Network interfaces

By default udev assigns names to your network interfaces using Predictable Network Interface Names, which prefixes interfaces names with en (wired/Ethernet), wl (wireless/WLAN), or ww (WWAN).

Tip: To change interface names, see #Change interface name and #Revert to traditional interface names.

Listing network interfaces

Both wired and wireless interface names can be found via ls /sys/class/net or ip link. Note that lo is the loop device and not used in making network connections.

Wireless device names can also be retrieved using iw dev. See also /Wireless#Get the name of the interface.

If your network interface is not listed, make sure your device driver was loaded successfully.

Enabling and disabling network interfaces

Network interfaces can be enabled / disabled using ip link set interface up|down, see ip-link(8).

To check the status of the interface eth0:

$ ip link show dev eth0
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master br0 state DOWN mode DEFAULT qlen 1000
...

The UP in <BROADCAST,MULTICAST,UP,LOWER_UP> is what indicates the interface is up, not the later state DOWN.

Note: If your default route is through interface eth0, taking it down will also remove the route, and bringing it back up will not automatically re-establish the default route. See #Routing table for re-establishing it.

Static IP address

A static IP address can be configured with most standard network managers and also dhcpcd.

To manually configure a static IP address, add an IP address as described in #IP addresses, set up your routing table and configure your DNS servers.

IP addresses

IP addresses are managed using ip-address(8).

List IP addresses:

$ ip address show

Add an IP address to an interface:

# ip address add address/prefix_len broadcast + dev interface
Note that:
Note: Make sure manually assigned IP addresses do not conflict with DHCP assigned ones.

Delete an IP address from an interface:

$ ip address del address/prefix_len dev interface

Delete all addresses matching a criteria, e.g. of a specific interface:

$ ip address flush dev interface
Tip: IP addresses can be calculated with ipcalc (ipcalc).

Routing table

The routing table is used to determine if you can reach an IP address directly or what gateway (router) you should use. If no other route matches the IP address, the default gateway is used.

The routing table is managed using ip-route(8).

PREFIX is either a CIDR notation or default for the default gateway.

List IPv4 routes:

$ ip route show

List IPv6 routes:

$ ip -6 route

Add a route:

# ip route add PREFIX via address dev interface

Delete a route:

# ip route del PREFIX via address dev interface

DHCP

A Dynamic Host Configuration Protocol (DHCP) server provides clients with a dynamic IP address, the subnet mask, the default gateway IP address and optionally also with DNS name servers.

Note: You should not run two DHCP clients simultaneously.

To use DHCP you need a DHCP server in your network and a DHCP client:

Client Package Archiso Note Systemd units
dhcpcd dhcpcd Yes DHCP, DHCPv6, ZeroConf, static IP dhcpcd.service, dhcpcd@interface.service
ISC dhclient dhclient Yes DHCP, DHCPv6, BOOTP, static IP dhclient@interface.service

Note that instead of directly using a DHCP client you can also use a network manager.

Tip: You can check if a DHCP server is running with dhcping.

Network managers

A network manager lets you manage network connection settings in so called network profiles to facilitate switching networks.

Note: There are many solutions to choose from, but remember that all of them are mutually exclusive; you should not run two daemons simultaneously.
Network manager GUI Archiso [3] CLI tools PPP support
(e.g. 3G modem)
DHCP client Systemd units
ConnMan 8 unofficial No connmanctl(1) Yes (with ofonoAUR) internal connman.service
netctl 2 unofficial Yes netctl(1), wifi-menu Yes dhcpcd or dhclient netctl-ifplugd@interface.service, netctl-auto@interface.service
NetworkManager Yes No nmcli(1), nmtui(1) Yes internal, dhcpcd or dhclient NetworkManager.service
systemd-networkd No Yes (base) networkctl(1) No internal systemd-networkd.service, systemd-resolved.service
Wicd Yes No wicd-cli(8), wicd-curses(8) No dhcpcd wicd.service

There also is Wifi Radar, a GUI application to manage WiFi networks with wireless_tools, it however does not handle wired connections.

See also List of applications#Network managers.

Set the hostname

A hostname is a unique name created to identify a machine on a network, configured in /etc/hostname—see hostname(5) and hostname(7) for details. The file can contain the system's domain name, if any. To set the hostname, edit /etc/hostname to include a single line with myhostname:

/etc/hostname
myhostname
Tip: For advice on choosing a hostname, see RFC 1178.

Alternatively, using hostnamectl(1):

# hostnamectl set-hostname myhostname

To temporarily set the hostname (until reboot), use hostname(1) from inetutils:

# hostname myhostname

To set the "pretty" hostname and other machine metadata, see machine-info(5).

Local hostname resolution

Tango-view-fullscreen.pngThis article or section needs expansion.Tango-view-fullscreen.png

Reason: Explain why you want a resolvable hostname, why 127.0.1.1 is used (and why a static IP address should be preferred over it). (Discuss in Talk:Network configuration#)

The myhostname Name Service Switch (NSS) module of systemd provides local hostname resolution without having to edit /etc/hosts (hosts(5)). It is enabled by default.

Some clients may however still rely on /etc/hosts, see [4] [5] for examples.

To configure the hosts file, add the following lines to /etc/hosts:

127.0.0.1        localhost
::1              localhost
127.0.1.1        myhostname.localdomain        myhostname
Note: The order of hostnames/aliases that follow the IP address in /etc/hosts is significant. The first string is considered the canonical hostname and may be appended with parent domains, where domain components are separated by a dot (ie. .localdomain above). All following strings on the same line are considered aliases. See hosts(5) for more info.

As a result the system resolves to both entries:

$ getent hosts
127.0.0.1       localhost
127.0.0.1       localhost
127.0.1.1       myhostname.localdomain myhostname

For a system with a permanent IP address, that permanent IP address should be used instead of 127.0.1.1.

Local network hostname resolution

To make your machine accessible in your LAN via its hostname you can:

  • edit the /etc/hosts file for every device in your LAN, see hosts(5)
  • set up a DNS server to resolve your hostname and make the LAN devices use it (e.g. via #DHCP)
  • or the easy way: use a Zero-configuration networking service:
    • Hostname resolution via Microsoft's NetBIOS. Provided by Samba on Linux. It only requires the nmb.service. Computers running Windows, macOS, or Linux with nmb running, will be able to find your machine.
    • Hostname resolution via mDNS. Provided by either nss_mdns with Avahi (see Avahi#Hostname resolution for setup details) or systemd-resolved. Computers running macOS, or Linux with Avahi or systemd-resolved running, will be able to find your machine. Windows does not have a built-in mDNS client or daemon.

Tips and tricks

Change interface name

Note: When changing the naming scheme, do not forget to update all network-related configuration files and custom systemd unit files to reflect the change.

You can change the device name by defining the name manually with an udev-rule. For example:

/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"

These rules will be applied automatically at boot.

A couple of things to note:

  • To get the MAC address of each card, use this command: cat /sys/class/net/device_name/address
  • Make sure to use the lower-case hex values in your udev rules. It does not like upper-case.

If the network card has a dynamic MAC, you can use DEVPATH, for example:

/etc/udev/rules.d/10-network.rules
SUBSYSTEM=="net", DEVPATH=="/devices/platform/wemac.*", NAME="int"
SUBSYSTEM=="net", DEVPATH=="/devices/pci*/*1c.0/*/net/*", NAME="en"

To get the DEVPATH of all currently-connected devices, see where the symlinks in /sys/class/net/ lead. For example:

file /sys/class/net/*
/sys/class/net/enp0s20f0u4u1: symbolic link to ../../devices/pci0000:00/0000:00:14.0/usb2/2-4/2-4.1/2-4.1:1.0/net/enp0s20f0u4u1
/sys/class/net/enp0s31f6:     symbolic link to ../../devices/pci0000:00/0000:00:1f.6/net/enp0s31f6
/sys/class/net/lo:            symbolic link to ../../devices/virtual/net/lo
/sys/class/net/wlp4s0:        symbolic link to ../../devices/pci0000:00/0000:00:1c.6/0000:04:00.0/net/wlp4s0

The device path should match both the new and old device name, since the rule may be executed more than once on bootup. For example, in the second rule, "/devices/pci*/*1c.0/*/net/enp*" would be wrong since it will stop matching once the name is changed to en. Only the system-default rule will fire the second time around, causing the name to be changed back to e.g. enp1s0.

If you are using a USB network device (e.g. Android phone tethering) that has a dynamic MAC address and you want to be able to use different USB ports, you could use a rule that matched depending on vendor and product ID instead:

/etc/udev/rules.d/10-network.rules
SUBSYSTEM=="net", ACTION=="add", ATTRS{idVendor}=="12ab", ATTRS{idProduct}=="3cd4", NAME="net2"

To test your rules, they can be triggered directly from userspace, e.g. with udevadm --debug test /sys/class/net/*. Remember to first take down the interface you are trying to rename (e.g. ip link set enp1s0 down).

Note: When choosing the static names it should be avoided to use names in the format of "ethX" and "wlanX", because this may lead to race conditions between the kernel and udev during boot. Instead, it is better to use interface names that are not used by the kernel as default, e.g.: net0, net1, wifi0, wifi1. For further details please see the systemd documentation.

Revert to traditional interface names

If you would prefer to retain traditional interface names such as eth0, Predictable Network Interface Names can be disabled by masking the udev rule:

# ln -s /dev/null /etc/udev/rules.d/80-net-setup-link.rules

Alternatively, add net.ifnames=0 to the kernel parameters.

Set device MTU and queue length

You can change the device MTU and queue length by defining manually with an udev-rule. For example:

/etc/udev/rules.d/10-network.rules
ACTION=="add", SUBSYSTEM=="net", KERNEL=="wl*", ATTR{mtu}="1500", ATTR{tx_queue_len}="2000"
Note:
  • mtu: For PPPoE, the MTU should be no larger than 1492. You can also set MTU via systemd.netdev(5).
  • tx_queue_len: Small value for slower devices with a high latency like modem links and ISDN. High value is recommend for server connected over the high-speed Internet connections that perform large data transfers.

Bonding or LAG

See netctl#Bonding or Wireless 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

To manually set an alias, for some NIC, use iproute2 to execute

# ip addr add 192.168.2.101/24 dev eth0 label eth0:1

To remove a given alias execute

# ip addr del 192.168.2.101/24 dev eth0:1

Packets destined for a subnet will use the primary alias by default. If the destination IP is within a subnet of a secondary alias, then the source IP is set respectively. Consider the case where there is more than one NIC, the default routes can be listed with ip route.

Promiscuous mode

Toggling promiscuous mode will make a (wireless) NIC forward all traffic it receives to the OS for further processing. This is opposite to "normal mode" where a NIC will drop frames it is not intended to receive. It is most often used for advanced network troubleshooting and packet sniffing.

/etc/systemd/system/promiscuous@.service
[Unit]
Description=Set %i interface in promiscuous mode
After=network.target

[Service]
Type=oneshot
ExecStart=/usr/bin/ip link set dev %i promisc on
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target

If you want to enable promiscuous mode on interface eth0 run enable promiscuous@eth0.service.

Investigate sockets

ss is a utility to investigate network ports and is part of the iproute2 package. It has a similar functionality to the deprecated netstat utility.

Common usage includes:

Display all TCP Sockets with service names:

$ ss -at

Display all TCP Sockets with port numbers:

$ ss -atn

Display all UDP Sockets:

$ ss -au

For more information see ss(8).

Troubleshooting

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 us 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 are 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).

Ways of fixing it

Bad

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
Good

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.d/99-disable_window_scaling.conf (see also sysctl):

net.ipv4.tcp_window_scaling = 0
Best

This problem is caused by broken routers/firewalls, so let us 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 an archived Kernel Trap article: Window Scaling on the Internet.

There are also several relevant threads on the LKML.

See also