https://wiki.archlinux.org/api.php?action=feedcontributions&user=Octagonal&feedformat=atomArchWiki - User contributions [en]2024-03-29T05:19:41ZUser contributionsMediaWiki 1.41.0https://wiki.archlinux.org/index.php?title=Network_configuration&diff=311601Network configuration2014-04-23T20:05:01Z<p>Octagonal: /* Promiscuous mode */</p>
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<div>[[Category:Networking]]<br />
[[Category:Getting and installing Arch]]<br />
[[cs:Configuring Network]]<br />
[[el:Configuring Network]]<br />
[[es:Configuring Network]]<br />
[[fr:Connexions reseau]]<br />
[[it:Configuring Network]]<br />
[[ja:Network Configuration]]<br />
[[nl:Configuring Network]]<br />
[[pt:Configuring Network]]<br />
[[ro:Configurare retea]]<br />
[[ru:Configuring Network]]<br />
[[sk:Configuring Network]]<br />
[[tr:Ağ_Yapılandırması]]<br />
[[zh-CN:Network Configuration]]<br />
[[zh-TW:Network Configuration]]<br />
{{Related articles start}}<br />
{{Related|Jumbo Frames}}<br />
{{Related|Firewalls}}<br />
{{Related|Wireless network configuration}}<br />
{{Related|List of applications#Network managers}}<br />
{{Related articles end}}<br />
<br />
This page explains how to set up a '''wired''' connection to a network. If you need to set up '''wireless''' networking see the [[Wireless network configuration]] page.<br />
<br />
== Check the connection ==<br />
<br />
{{Note|If you receive an error like {{ic|ping: icmp open socket: Operation not permitted}} when executing ping, try to re-install the {{ic|iputils}} package.}} <br />
<br />
Many times, the basic installation procedure has created a working network configuration. To check if this is so, use the following command:<br />
<br />
{{Note|The {{ic|-c 3}} option calls it three times. See {{ic|man ping}} for more information.}}<br />
<br />
{{hc|$ ping -c 3 www.google.com|<nowiki><br />
PING www.l.google.com (74.125.224.146) 56(84) bytes of data.<br />
64 bytes from 74.125.224.146: icmp_req=1 ttl=50 time=437 ms<br />
64 bytes from 74.125.224.146: icmp_req=2 ttl=50 time=385 ms<br />
64 bytes from 74.125.224.146: icmp_req=3 ttl=50 time=298 ms<br />
<br />
--- www.l.google.com ping statistics ---<br />
3 packets transmitted, 3 received, 0% packet loss, time 1999ms<br />
rtt min/avg/max/mdev = 298.107/373.642/437.202/57.415 ms<br />
</nowiki>}}<br />
<br />
If it works, then you may only wish to personalize your settings from the options below.<br />
<br />
If the previous command complains about unknown hosts, it means that your machine was unable to resolve this domain name. It might be related to your service provider or your router/gateway. You can try pinging a static IP address to prove that your machine has access to the Internet.<br />
<br />
{{hc|$ ping -c 3 8.8.8.8|<nowiki><br />
PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.<br />
64 bytes from 8.8.8.8: icmp_req=1 ttl=53 time=52.9 ms<br />
64 bytes from 8.8.8.8: icmp_req=2 ttl=53 time=72.5 ms<br />
64 bytes from 8.8.8.8: icmp_req=3 ttl=53 time=70.6 ms<br />
<br />
--- 8.8.8.8 ping statistics ---<br />
3 packets transmitted, 3 received, 0% packet loss, time 2002ms<br />
rtt min/avg/max/mdev = 52.975/65.375/72.543/8.803 ms<br />
</nowiki>}}<br />
<br />
{{Note|{{ic|8.8.8.8}} is a static address that is easy to remember. It is the address of Google's primary DNS server, therefore it can be considered reliable, and is generally not blocked by content filtering systems and proxies.}}<br />
<br />
If you are able to ping {{ic|8.8.8.8}} but not {{ic|www.google.com}}, check your DNS configuration. See [[resolv.conf]] for details.<br />
<br />
== Set the hostname ==<br />
<br />
A [[Wikipedia:Hostname|hostname]] is a unique name created to identify a machine on a network: it is configured in {{ic|/etc/hostname}}. The file can contain the system's domain name, if any. To set the hostname, do:<br />
<br />
# hostnamectl set-hostname ''myhostname''<br />
<br />
This will put {{ic|''myhostname''}} into {{ic|/etc/hostname}}.<br />
<br />
See {{ic|man 5 hostname}} and {{ic|man 1 hostnamectl}} for details.<br />
<br />
Add the same hostname to {{ic|/etc/hosts}}:<br />
<br />
{{hc|/etc/hosts|<br />
#<ip-address> <hostname.domain.org> <hostname><br />
127.0.0.1 localhost.localdomain localhost ''myhostname''<br />
::1 localhost.localdomain localhost<br />
}}<br />
<br />
To set the hostname temporarily (until a reboot), use ''hostname'' from {{Pkg|inetutils}}:<br />
<br />
# hostname ''myhostname''<br />
<br />
== Device Driver ==<br />
<br />
=== Check the driver status ===<br />
<br />
[[udev]] should detect your network interface card ([[Wikipedia:Network_interface_controller|NIC]]) and automatically load the necessary module at start up. 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:<br />
<br />
{{hc|$ lspci -v|<br />
02:00.0 Ethernet controller: Attansic Technology Corp. L1 Gigabit Ethernet Adapter (rev b0)<br />
...<br />
Kernel driver in use: atl1<br />
Kernel modules: atl1<br />
}}<br />
<br />
Next, check that the driver was loaded via {{ic|dmesg <nowiki>|</nowiki> grep ''module_name''}}. For example:<br />
<br />
$ dmesg | grep atl1<br />
...<br />
atl1 0000:02:00.0: eth0 link is up 100 Mbps full duplex<br />
<br />
Skip the next section if the driver was loaded successfully. Otherwise, you will need to know which module is needed for your particular model.<br />
<br />
=== Load the device module ===<br />
<br />
Google 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's possible that the driver is not included in Arch kernel. You may search the [[AUR]] for the module name.<br />
<br />
If udev is not detecting and loading the proper module automatically during bootup, see [[Kernel modules#Loading]].<br />
<br />
== Network Interfaces ==<br />
<br />
=== Device names ===<br />
<br />
For computers with multiple NICs, it is important to have fixed device name. Many configuration problems are caused by interface name changing.<br />
<br />
[[udev]] is responsible for which device gets which name. Systemd v197 introduced [http://www.freedesktop.org/wiki/Software/systemd/PredictableNetworkInterfaceNames Predictable Network Interface Names], which automatically assigns static names to network devices. Interfaces are now prefixed with {{ic|en}} (ethernet), {{ic|wl}} (WLAN), or {{ic|ww}} (WWAN) followed by an automatically generated identifier, creating an entry such as {{ic|enp0s25}}. <br />
<br />
This behavior may be disabled by adding {{ic|1=net.ifnames=0}} in your kernel command line.<br />
<br />
{{Tip|You can run {{ic|ip link}} or {{ic|ls /sys/class/net}} to list all available interfaces.}}<br />
<br />
{{Note|When changing the interface naming scheme, do not forget to update all network-related configuration files and custom systemd unit files to reflect the change. Specifically, if you have [[netctl#Basic method|netctl static profiles]] enabled, run {{ic|netctl reenable ''profile''}} to update the generated service file.}}<br />
<br />
==== Change device name ====<br />
<br />
You can change the device name by defining the name manually with an udev-rule. For example:<br />
<br />
{{hc|/etc/udev/rules.d/10-network.rules|<nowiki><br />
SUBSYSTEM=="net", ACTION=="add", ATTR{address}=="aa:bb:cc:dd:ee:ff", NAME="net1"<br />
SUBSYSTEM=="net", ACTION=="add", ATTR{address}=="ff:ee:dd:cc:bb:aa", NAME="net0"<br />
</nowiki>}}<br />
<br />
A couple of things to note:<br />
<br />
* To get the MAC address of each card, use this command: {{ic|cat /sys/class/net/''device_name''/address}}<br />
* Make sure to use the lower-case hex values in your udev rules. It doesn't like upper-case.<br />
<br />
If the network card has a dynamic MAC, you can use DEVPATH, for example:<br />
<br />
{{hc|/etc/udev/rules.d/10-network.rules|<nowiki><br />
SUBSYSTEM=="net", DEVPATH=="/devices/platform/wemac.*", NAME="int"<br />
</nowiki>}}<br />
<br />
{{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.}}<br />
<br />
=== Set device MTU and queue Length ===<br />
<br />
You can change the device MTU and queue length by defining manually with an udev-rule. For example:<br />
<br />
{{hc|/etc/udev/rules.d/10-network.rules|<nowiki><br />
ACTION=="add", SUBSYSTEM=="net", KERNEL=="wl*", ATTR{mtu}="1480", ATTR{tx_queue_len}="2000"<br />
</nowiki>}}<br />
<br />
=== Get current device names ===<br />
<br />
Current NIC names can be found via sysfs<br />
<br />
{{hc|$ ls /sys/class/net|<br />
lo eth0 eth1 firewire0<br />
}}<br />
<br />
=== Enabling and disabling network interfaces ===<br />
<br />
You can activate or deactivate network interfaces using:<br />
<br />
# ip link set eth0 up<br />
# ip link set eth0 down<br />
<br />
To check the result:<br />
<br />
{{hc|$ ip link show dev eth0|<br />
2: eth0: <BROADCAST,MULTICAST,PROMISC,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master br0 state UP mode DEFAULT qlen 1000<br />
...<br />
}}<br />
<br />
== Configure the IP address ==<br />
<br />
You have two options: a dynamically assigned address using [[Wikipedia:Dynamic Host Configuration Protocol|DHCP]], or an unchanging "static" address.<br />
<br />
=== Dynamic IP address ===<br />
<br />
==== dhcpcd ====<br />
The easiest is to use [[dhcpcd]], which is included in the {{Grp|base}} group. Either use the provided service file {{ic|dhcpcd@.service}}, passing the interface name as an argument, or start it manually by running {{ic|dhcpcd ''interface''}}.<br />
<br />
=== Static IP address ===<br />
<br />
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.<br />
<br />
{{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.}}<br />
<br />
You need:<br />
<br />
* Static IP address<br />
* [[Wikipedia:Subnetwork|Subnet mask]]<br />
* [[Wikipedia:Broadcast_address|Broadcast address]]<br />
* [[Wikipedia:Default_gateway|Gateway]]'s IP address<br />
<br />
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.<br />
<br />
{{Tip|You may need to manually set the DNS servers, see [[resolv.conf]] for details.}}<br />
<br />
==== Manual assignment ====<br />
<br />
You can assign a static IP address in the console:<br />
<br />
# ip addr add ''IP_address''/''subnet_mask'' broadcast ''broadcast_address'' dev ''interface''<br />
<br />
For example:<br />
<br />
# ip addr add 192.168.1.2/24 broadcast 192.168.1.255 dev eth0<br />
<br />
{{Note|The subnet mask was specified using [[Wikipedia:CIDR_notation|CIDR notation]].}}<br />
<br />
For more options, see {{ic|man ip}}.<br />
<br />
Add your gateway IP address like so:<br />
<br />
# ip route add default via ''default_gateway''<br />
<br />
For example:<br />
<br />
# ip route add default via 192.168.1.1<br />
<br />
If you the get the error "No such process", it means you have to run {{ic|ip link set dev eth0 up}} as root.<br />
<br />
==== Persistent configuration on boot using systemd and udev rules ====<br />
<br />
First create a configuration file for the [[systemd]] service, replace {{ic|''interface''}} with the proper network interface name:<br />
<br />
{{hc|/etc/conf.d/network@''interface''|<nowiki><br />
address=192.168.0.15<br />
netmask=24<br />
broadcast=192.168.0.255<br />
gateway=192.168.0.1<br />
</nowiki>}}<br />
<br />
Create a systemd unit file:<br />
<br />
{{hc|/etc/systemd/system/network@.service|<nowiki><br />
[Unit]<br />
Description=Network connectivity (%i)<br />
Wants=network.target<br />
Before=network.target<br />
BindsTo=sys-subsystem-net-devices-%i.device<br />
After=sys-subsystem-net-devices-%i.device<br />
<br />
[Service]<br />
Type=oneshot<br />
RemainAfterExit=yes<br />
EnvironmentFile=/etc/conf.d/network@%i<br />
<br />
ExecStart=/usr/bin/ip link set dev %i up<br />
ExecStart=/usr/bin/ip addr add ${address}/${netmask} broadcast ${broadcast} dev %i<br />
ExecStart=/usr/bin/sh -c 'test -n ${gateway} && /usr/bin/ip route add default via ${gateway}'<br />
<br />
ExecStop=/usr/bin/ip addr flush dev %i<br />
ExecStop=/usr/bin/ip link set dev %i down<br />
<br />
[Install]<br />
WantedBy=multi-user.target<br />
</nowiki>}}<br />
<br />
Enable the unit and start it, passing the name of the interface:<br />
<br />
# systemctl enable network@''interface''.service<br />
# systemctl start network@''interface''.service<br />
<br />
==== Calculating addresses ====<br />
<br />
You can use {{ic|ipcalc}} provided by the {{Pkg|ipcalc}} package to calculate IP broadcast, network, netmask, and host ranges for more advanced configurations. For example, I use ethernet over firewire to connect a windows machine to arch. For security and network organization, I placed them on their own network and configured the netmask and broadcast so that they are the only 2 machines on it. To figure out the netmask and broadcast addresses for this, I used ipcalc, providing it with the IP of the arch firewire nic 10.66.66.1, and specifying ipcalc should create a network of only 2 hosts.<br />
<br />
{{hc|$ ipcalc -nb 10.66.66.1 -s 1|<nowiki><br />
Address: 10.66.66.1<br />
<br />
Netmask: 255.255.255.252 = 30<br />
Network: 10.66.66.0/30<br />
HostMin: 10.66.66.1<br />
HostMax: 10.66.66.2<br />
Broadcast: 10.66.66.3<br />
Hosts/Net: 2 Class A, Private Internet<br />
</nowiki>}}<br />
<br />
=== systemd-networkd ===<br />
<br />
With [[systemd]] version >= 209, it is possible to manage network connections with [[systemd-networkd]], which is intended to easily set up network on containers and virtual machines. It can manage both dynamic and static IP addresses.<br />
<br />
== Load configuration ==<br />
<br />
To test your settings either reboot the computer or reload the relevant systemd services. Then 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:<br />
<br />
$ ping -c 3 www.google.com<br />
<br />
== Additional settings ==<br />
<br />
=== ifplugd for laptops ===<br />
<br />
{{Tip|[[dhcpcd]] provides the same feature out of the box.}}<br />
<br />
{{Pkg|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.<br />
<br />
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}}.<br />
<br />
{{Note|[[Netctl]] package includes {{ic|netctl-ifplugd@.service}}, otherwise you can use {{ic|ifplugd@.service}} from {{Pkg|ifplugd}} package. Use for example {{ic|systemctl enable ifplugd@eth0.service}}.}}<br />
<br />
=== Bonding or LAG ===<br />
<br />
See [[netctl#Bonding]].<br />
<br />
=== IP address aliasing ===<br />
<br />
{{Expansion|Manual method using [[Core utilities#ip|ip]] should be added; then move current example using ''netctl'' into [[netctl]].}}<br />
<br />
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).<br />
<br />
==== Example ====<br />
<br />
You will need {{Pkg|netctl}} from the [[official repositories]].<br />
<br />
Prepare the configuration:<br />
<br />
{{hc|/etc/netctl/mynetwork|<nowiki><br />
Connection='ethernet'<br />
Description='Five different addresses on the same NIC.'<br />
Interface='eth0'<br />
IP='static'<br />
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')<br />
Gateway='192.168.1.1'<br />
DNS=('192.168.1.1')<br />
</nowiki>}}<br />
<br />
Then simply execute: <br />
<br />
$ netctl start mynetwork<br />
<br />
=== Change MAC/hardware address ===<br />
<br />
See [[MAC Address Spoofing]].<br />
<br />
=== Internet Sharing ===<br />
<br />
See [[Internet sharing]].<br />
<br />
=== Router Configuration ===<br />
<br />
See [[Router]].<br />
<br />
=== Local network hostname resolution ===<br />
<br />
The pre-requisite is to [[#Set the hostname]] after which hostname resolution works on the local system itself {{hc|$ ping hostname|<br />
PING hostname <nowiki>(192.168.1.2) 56(84) bytes of data.<br />
64 bytes from hostname (192.168.1.2): icmp_seq=1 ttl=64 time=0.043 ms</nowiki>}}<br />
To enable other machines to address the host by name, either a manual configuration of the respective {{ic|/etc/hosts}} files or a service to propagate/resolve the name is required. <br />
<br />
When setting up a DNS server such as [[BIND]] or [[Unbound]] is overkill, manually editing your {{ic|/etc/hosts}} is too cumbersome, or when you want more flexibility with dynamic leaving and joining of hosts to the network, it is possible to handle hostname resolution on your local network using zero-configuration networking. There are two options available:<br />
<br />
*[[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, OS X, or Linux with {{ic|nmbd}} running, will be able to find your machine.<br />
<br />
*[[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 OS X, 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.<br />
<br />
=== Promiscuous mode ===<br />
<br />
Toggling [https://en.wikipedia.org/wiki/Promiscuous_mode 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 [https://en.wikipedia.org/wiki/Packet_sniffing packet sniffing].<br />
<br />
{{hc|/etc/systemd/system/promiscuous@.service|<nowiki><br />
[Unit]<br />
Description=Set %i interface in promiscuous mode<br />
After=network.target<br />
<br />
[Service]<br />
Type=oneshot<br />
ExecStart=/usr/bin/ip link set dev %i promisc on<br />
RemainAfterExit=yes<br />
<br />
[Install]<br />
WantedBy=multi-user.target<br />
</nowiki>}}<br />
<br />
If you want to enable promiscuous mode on interface {{ic|eth0}} run:<br />
<br />
# systemctl enable promiscuous@eth0.service<br />
<br />
== Troubleshooting ==<br />
<br />
=== Swapping computers on the cable modem ===<br />
<br />
Some 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.<br />
<br />
If this method does not work, you will need to clone the MAC address of the original machine. See also [[Configuring Network#Change MAC/hardware address|Change MAC/hardware address]].<br />
<br />
=== The TCP window scaling problem ===<br />
<br />
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.<br />
<br />
Back in 1992, as more and more memory became available, [http://www.faqs.org/rfcs/rfc1323.html 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.<br />
<br />
That 8-bit Scale Factor allows the Window to be up to 32 times higher than the initial 64Kb.<br />
<br />
It appears that some broken routers and firewalls on the Internet are rewriting the Scale Factor to 0 which causes misunderstandings between hosts.<br />
<br />
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.<br />
<br />
The resulting connection is at best very slow or broken.<br />
<br />
==== How to diagnose the problem ====<br />
<br />
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).<br />
<br />
When you have this problem, the {{ic|dmesg}}'s output is OK, logs are clean and {{ic|ip addr}} will report normal status... and actually everything appears normal.<br />
<br />
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.<br />
<br />
You can try to use Wireshark. You might see successful UDP and ICMP communications but unsuccessful TCP communications (only to foreign hosts).<br />
<br />
==== How to fix it (The bad way) ====<br />
<br />
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.<br />
<br />
# echo "4096 87380 174760" > /proc/sys/net/ipv4/tcp_rmem<br />
<br />
==== How to fix it (The good way) ====<br />
<br />
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 {{ic|/etc/sysctl.d/99-disable_window_scaling.conf}} (see also [[sysctl]])<br />
<br />
net.ipv4.tcp_window_scaling = 0<br />
<br />
==== How to fix it (The best way) ====<br />
<br />
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.<br />
<br />
==== More about it ====<br />
<br />
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].<br />
<br />
There are also several relevant threads on the LKML.<br />
<br />
=== Realtek no link / WOL problem ===<br />
<br />
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:<br />
<br />
==== Method 1 - Enable the NIC directly in Linux ====<br />
<br />
Get the ethernet NIC name from the output of<br />
<br />
$ ip a<br />
<br />
Bring up the device as root using the NIC name:<br />
<br />
# ip link set dev <NIC_name> up<br />
<br />
For ex, if <NIC_name> is enp7s0<br />
<br />
# ip link set dev enp7s0 up<br />
<br />
If it worked and the card is powered on, you should see {{ic|state UP}} for the given interface in the output of {{ic|ip link}}.<br />
<br />
==== Method 2 - Rollback/change Windows driver ====<br />
<br />
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).<br />
<br />
==== Method 3 - Enable WOL in Windows driver ====<br />
<br />
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.<br />
<br />
In Windows XP (example)<br />
Right click my computer<br />
--> Hardware tab<br />
--> Device Manager<br />
--> Network Adapters<br />
--> "double click" Realtek ...<br />
--> Advanced tab<br />
--> Wake-On-Lan After Shutdown<br />
--> Enable<br />
<br />
{{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.}}<br />
<br />
==== Method 4 - Newer Realtek Linux driver ====<br />
<br />
Any newer driver for these Realtek cards can be found for Linux on the realtek site. (untested but believed to also solve the problem).<br />
<br />
==== Method 5 - Enable ''LAN Boot ROM'' in BIOS/CMOS ====<br />
<br />
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.<br />
<br />
{{Note|This was tested successfully multiple times with GIGABYTE system board GA-G31M-ES2L with BIOS version F8 released on 2009/02/05. YMMV.}}<br />
<br />
=== No interface with Atheros chipsets ===<br />
<br />
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 the package {{AUR|backports-patched}} from AUR.<br />
<br />
=== Broadcom BCM57780 ===<br />
<br />
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.<br />
<br />
These steps should help if your computer has this chipset:<br />
$ lspci | grep Ethernet<br />
02:00.0 Ethernet controller: Broadcom Corporation NetLink BCM57780 Gigabit Ethernet PCIe (rev 01)<br />
<br />
If your wired networking is not functioning in some way or another, try unplugging your cable then doing the following (as root):<br />
# modprobe -r tg3<br />
# modprobe broadcom<br />
# modprobe tg3<br />
<br />
Now plug you network cable in. If this solves your problems you can make this permanent by adding {{ic|broadcom}} and {{ic|tg3}} (in this order) to the {{ic|MODULES}} array in {{ic|/etc/mkinitcpio.conf}}:<br />
<br />
MODULES=".. broadcom tg3 .."<br />
<br />
Then rebuild the initramfs:<br />
<br />
# mkinitcpio -p linux<br />
<br />
{{Note|These methods may work for other chipsets, such as BCM57760.}}</div>Octagonalhttps://wiki.archlinux.org/index.php?title=Network_configuration&diff=311600Network configuration2014-04-23T20:04:34Z<p>Octagonal: Added a short explanation about what promisc mode is</p>
<hr />
<div>[[Category:Networking]]<br />
[[Category:Getting and installing Arch]]<br />
[[cs:Configuring Network]]<br />
[[el:Configuring Network]]<br />
[[es:Configuring Network]]<br />
[[fr:Connexions reseau]]<br />
[[it:Configuring Network]]<br />
[[ja:Network Configuration]]<br />
[[nl:Configuring Network]]<br />
[[pt:Configuring Network]]<br />
[[ro:Configurare retea]]<br />
[[ru:Configuring Network]]<br />
[[sk:Configuring Network]]<br />
[[tr:Ağ_Yapılandırması]]<br />
[[zh-CN:Network Configuration]]<br />
[[zh-TW:Network Configuration]]<br />
{{Related articles start}}<br />
{{Related|Jumbo Frames}}<br />
{{Related|Firewalls}}<br />
{{Related|Wireless network configuration}}<br />
{{Related|List of applications#Network managers}}<br />
{{Related articles end}}<br />
<br />
This page explains how to set up a '''wired''' connection to a network. If you need to set up '''wireless''' networking see the [[Wireless network configuration]] page.<br />
<br />
== Check the connection ==<br />
<br />
{{Note|If you receive an error like {{ic|ping: icmp open socket: Operation not permitted}} when executing ping, try to re-install the {{ic|iputils}} package.}} <br />
<br />
Many times, the basic installation procedure has created a working network configuration. To check if this is so, use the following command:<br />
<br />
{{Note|The {{ic|-c 3}} option calls it three times. See {{ic|man ping}} for more information.}}<br />
<br />
{{hc|$ ping -c 3 www.google.com|<nowiki><br />
PING www.l.google.com (74.125.224.146) 56(84) bytes of data.<br />
64 bytes from 74.125.224.146: icmp_req=1 ttl=50 time=437 ms<br />
64 bytes from 74.125.224.146: icmp_req=2 ttl=50 time=385 ms<br />
64 bytes from 74.125.224.146: icmp_req=3 ttl=50 time=298 ms<br />
<br />
--- www.l.google.com ping statistics ---<br />
3 packets transmitted, 3 received, 0% packet loss, time 1999ms<br />
rtt min/avg/max/mdev = 298.107/373.642/437.202/57.415 ms<br />
</nowiki>}}<br />
<br />
If it works, then you may only wish to personalize your settings from the options below.<br />
<br />
If the previous command complains about unknown hosts, it means that your machine was unable to resolve this domain name. It might be related to your service provider or your router/gateway. You can try pinging a static IP address to prove that your machine has access to the Internet.<br />
<br />
{{hc|$ ping -c 3 8.8.8.8|<nowiki><br />
PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.<br />
64 bytes from 8.8.8.8: icmp_req=1 ttl=53 time=52.9 ms<br />
64 bytes from 8.8.8.8: icmp_req=2 ttl=53 time=72.5 ms<br />
64 bytes from 8.8.8.8: icmp_req=3 ttl=53 time=70.6 ms<br />
<br />
--- 8.8.8.8 ping statistics ---<br />
3 packets transmitted, 3 received, 0% packet loss, time 2002ms<br />
rtt min/avg/max/mdev = 52.975/65.375/72.543/8.803 ms<br />
</nowiki>}}<br />
<br />
{{Note|{{ic|8.8.8.8}} is a static address that is easy to remember. It is the address of Google's primary DNS server, therefore it can be considered reliable, and is generally not blocked by content filtering systems and proxies.}}<br />
<br />
If you are able to ping {{ic|8.8.8.8}} but not {{ic|www.google.com}}, check your DNS configuration. See [[resolv.conf]] for details.<br />
<br />
== Set the hostname ==<br />
<br />
A [[Wikipedia:Hostname|hostname]] is a unique name created to identify a machine on a network: it is configured in {{ic|/etc/hostname}}. The file can contain the system's domain name, if any. To set the hostname, do:<br />
<br />
# hostnamectl set-hostname ''myhostname''<br />
<br />
This will put {{ic|''myhostname''}} into {{ic|/etc/hostname}}.<br />
<br />
See {{ic|man 5 hostname}} and {{ic|man 1 hostnamectl}} for details.<br />
<br />
Add the same hostname to {{ic|/etc/hosts}}:<br />
<br />
{{hc|/etc/hosts|<br />
#<ip-address> <hostname.domain.org> <hostname><br />
127.0.0.1 localhost.localdomain localhost ''myhostname''<br />
::1 localhost.localdomain localhost<br />
}}<br />
<br />
To set the hostname temporarily (until a reboot), use ''hostname'' from {{Pkg|inetutils}}:<br />
<br />
# hostname ''myhostname''<br />
<br />
== Device Driver ==<br />
<br />
=== Check the driver status ===<br />
<br />
[[udev]] should detect your network interface card ([[Wikipedia:Network_interface_controller|NIC]]) and automatically load the necessary module at start up. 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:<br />
<br />
{{hc|$ lspci -v|<br />
02:00.0 Ethernet controller: Attansic Technology Corp. L1 Gigabit Ethernet Adapter (rev b0)<br />
...<br />
Kernel driver in use: atl1<br />
Kernel modules: atl1<br />
}}<br />
<br />
Next, check that the driver was loaded via {{ic|dmesg <nowiki>|</nowiki> grep ''module_name''}}. For example:<br />
<br />
$ dmesg | grep atl1<br />
...<br />
atl1 0000:02:00.0: eth0 link is up 100 Mbps full duplex<br />
<br />
Skip the next section if the driver was loaded successfully. Otherwise, you will need to know which module is needed for your particular model.<br />
<br />
=== Load the device module ===<br />
<br />
Google 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's possible that the driver is not included in Arch kernel. You may search the [[AUR]] for the module name.<br />
<br />
If udev is not detecting and loading the proper module automatically during bootup, see [[Kernel modules#Loading]].<br />
<br />
== Network Interfaces ==<br />
<br />
=== Device names ===<br />
<br />
For computers with multiple NICs, it is important to have fixed device name. Many configuration problems are caused by interface name changing.<br />
<br />
[[udev]] is responsible for which device gets which name. Systemd v197 introduced [http://www.freedesktop.org/wiki/Software/systemd/PredictableNetworkInterfaceNames Predictable Network Interface Names], which automatically assigns static names to network devices. Interfaces are now prefixed with {{ic|en}} (ethernet), {{ic|wl}} (WLAN), or {{ic|ww}} (WWAN) followed by an automatically generated identifier, creating an entry such as {{ic|enp0s25}}. <br />
<br />
This behavior may be disabled by adding {{ic|1=net.ifnames=0}} in your kernel command line.<br />
<br />
{{Tip|You can run {{ic|ip link}} or {{ic|ls /sys/class/net}} to list all available interfaces.}}<br />
<br />
{{Note|When changing the interface naming scheme, do not forget to update all network-related configuration files and custom systemd unit files to reflect the change. Specifically, if you have [[netctl#Basic method|netctl static profiles]] enabled, run {{ic|netctl reenable ''profile''}} to update the generated service file.}}<br />
<br />
==== Change device name ====<br />
<br />
You can change the device name by defining the name manually with an udev-rule. For example:<br />
<br />
{{hc|/etc/udev/rules.d/10-network.rules|<nowiki><br />
SUBSYSTEM=="net", ACTION=="add", ATTR{address}=="aa:bb:cc:dd:ee:ff", NAME="net1"<br />
SUBSYSTEM=="net", ACTION=="add", ATTR{address}=="ff:ee:dd:cc:bb:aa", NAME="net0"<br />
</nowiki>}}<br />
<br />
A couple of things to note:<br />
<br />
* To get the MAC address of each card, use this command: {{ic|cat /sys/class/net/''device_name''/address}}<br />
* Make sure to use the lower-case hex values in your udev rules. It doesn't like upper-case.<br />
<br />
If the network card has a dynamic MAC, you can use DEVPATH, for example:<br />
<br />
{{hc|/etc/udev/rules.d/10-network.rules|<nowiki><br />
SUBSYSTEM=="net", DEVPATH=="/devices/platform/wemac.*", NAME="int"<br />
</nowiki>}}<br />
<br />
{{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.}}<br />
<br />
=== Set device MTU and queue Length ===<br />
<br />
You can change the device MTU and queue length by defining manually with an udev-rule. For example:<br />
<br />
{{hc|/etc/udev/rules.d/10-network.rules|<nowiki><br />
ACTION=="add", SUBSYSTEM=="net", KERNEL=="wl*", ATTR{mtu}="1480", ATTR{tx_queue_len}="2000"<br />
</nowiki>}}<br />
<br />
=== Get current device names ===<br />
<br />
Current NIC names can be found via sysfs<br />
<br />
{{hc|$ ls /sys/class/net|<br />
lo eth0 eth1 firewire0<br />
}}<br />
<br />
=== Enabling and disabling network interfaces ===<br />
<br />
You can activate or deactivate network interfaces using:<br />
<br />
# ip link set eth0 up<br />
# ip link set eth0 down<br />
<br />
To check the result:<br />
<br />
{{hc|$ ip link show dev eth0|<br />
2: eth0: <BROADCAST,MULTICAST,PROMISC,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master br0 state UP mode DEFAULT qlen 1000<br />
...<br />
}}<br />
<br />
== Configure the IP address ==<br />
<br />
You have two options: a dynamically assigned address using [[Wikipedia:Dynamic Host Configuration Protocol|DHCP]], or an unchanging "static" address.<br />
<br />
=== Dynamic IP address ===<br />
<br />
==== dhcpcd ====<br />
The easiest is to use [[dhcpcd]], which is included in the {{Grp|base}} group. Either use the provided service file {{ic|dhcpcd@.service}}, passing the interface name as an argument, or start it manually by running {{ic|dhcpcd ''interface''}}.<br />
<br />
=== Static IP address ===<br />
<br />
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.<br />
<br />
{{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.}}<br />
<br />
You need:<br />
<br />
* Static IP address<br />
* [[Wikipedia:Subnetwork|Subnet mask]]<br />
* [[Wikipedia:Broadcast_address|Broadcast address]]<br />
* [[Wikipedia:Default_gateway|Gateway]]'s IP address<br />
<br />
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.<br />
<br />
{{Tip|You may need to manually set the DNS servers, see [[resolv.conf]] for details.}}<br />
<br />
==== Manual assignment ====<br />
<br />
You can assign a static IP address in the console:<br />
<br />
# ip addr add ''IP_address''/''subnet_mask'' broadcast ''broadcast_address'' dev ''interface''<br />
<br />
For example:<br />
<br />
# ip addr add 192.168.1.2/24 broadcast 192.168.1.255 dev eth0<br />
<br />
{{Note|The subnet mask was specified using [[Wikipedia:CIDR_notation|CIDR notation]].}}<br />
<br />
For more options, see {{ic|man ip}}.<br />
<br />
Add your gateway IP address like so:<br />
<br />
# ip route add default via ''default_gateway''<br />
<br />
For example:<br />
<br />
# ip route add default via 192.168.1.1<br />
<br />
If you the get the error "No such process", it means you have to run {{ic|ip link set dev eth0 up}} as root.<br />
<br />
==== Persistent configuration on boot using systemd and udev rules ====<br />
<br />
First create a configuration file for the [[systemd]] service, replace {{ic|''interface''}} with the proper network interface name:<br />
<br />
{{hc|/etc/conf.d/network@''interface''|<nowiki><br />
address=192.168.0.15<br />
netmask=24<br />
broadcast=192.168.0.255<br />
gateway=192.168.0.1<br />
</nowiki>}}<br />
<br />
Create a systemd unit file:<br />
<br />
{{hc|/etc/systemd/system/network@.service|<nowiki><br />
[Unit]<br />
Description=Network connectivity (%i)<br />
Wants=network.target<br />
Before=network.target<br />
BindsTo=sys-subsystem-net-devices-%i.device<br />
After=sys-subsystem-net-devices-%i.device<br />
<br />
[Service]<br />
Type=oneshot<br />
RemainAfterExit=yes<br />
EnvironmentFile=/etc/conf.d/network@%i<br />
<br />
ExecStart=/usr/bin/ip link set dev %i up<br />
ExecStart=/usr/bin/ip addr add ${address}/${netmask} broadcast ${broadcast} dev %i<br />
ExecStart=/usr/bin/sh -c 'test -n ${gateway} && /usr/bin/ip route add default via ${gateway}'<br />
<br />
ExecStop=/usr/bin/ip addr flush dev %i<br />
ExecStop=/usr/bin/ip link set dev %i down<br />
<br />
[Install]<br />
WantedBy=multi-user.target<br />
</nowiki>}}<br />
<br />
Enable the unit and start it, passing the name of the interface:<br />
<br />
# systemctl enable network@''interface''.service<br />
# systemctl start network@''interface''.service<br />
<br />
==== Calculating addresses ====<br />
<br />
You can use {{ic|ipcalc}} provided by the {{Pkg|ipcalc}} package to calculate IP broadcast, network, netmask, and host ranges for more advanced configurations. For example, I use ethernet over firewire to connect a windows machine to arch. For security and network organization, I placed them on their own network and configured the netmask and broadcast so that they are the only 2 machines on it. To figure out the netmask and broadcast addresses for this, I used ipcalc, providing it with the IP of the arch firewire nic 10.66.66.1, and specifying ipcalc should create a network of only 2 hosts.<br />
<br />
{{hc|$ ipcalc -nb 10.66.66.1 -s 1|<nowiki><br />
Address: 10.66.66.1<br />
<br />
Netmask: 255.255.255.252 = 30<br />
Network: 10.66.66.0/30<br />
HostMin: 10.66.66.1<br />
HostMax: 10.66.66.2<br />
Broadcast: 10.66.66.3<br />
Hosts/Net: 2 Class A, Private Internet<br />
</nowiki>}}<br />
<br />
=== systemd-networkd ===<br />
<br />
With [[systemd]] version >= 209, it is possible to manage network connections with [[systemd-networkd]], which is intended to easily set up network on containers and virtual machines. It can manage both dynamic and static IP addresses.<br />
<br />
== Load configuration ==<br />
<br />
To test your settings either reboot the computer or reload the relevant systemd services. Then 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:<br />
<br />
$ ping -c 3 www.google.com<br />
<br />
== Additional settings ==<br />
<br />
=== ifplugd for laptops ===<br />
<br />
{{Tip|[[dhcpcd]] provides the same feature out of the box.}}<br />
<br />
{{Pkg|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.<br />
<br />
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}}.<br />
<br />
{{Note|[[Netctl]] package includes {{ic|netctl-ifplugd@.service}}, otherwise you can use {{ic|ifplugd@.service}} from {{Pkg|ifplugd}} package. Use for example {{ic|systemctl enable ifplugd@eth0.service}}.}}<br />
<br />
=== Bonding or LAG ===<br />
<br />
See [[netctl#Bonding]].<br />
<br />
=== IP address aliasing ===<br />
<br />
{{Expansion|Manual method using [[Core utilities#ip|ip]] should be added; then move current example using ''netctl'' into [[netctl]].}}<br />
<br />
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).<br />
<br />
==== Example ====<br />
<br />
You will need {{Pkg|netctl}} from the [[official repositories]].<br />
<br />
Prepare the configuration:<br />
<br />
{{hc|/etc/netctl/mynetwork|<nowiki><br />
Connection='ethernet'<br />
Description='Five different addresses on the same NIC.'<br />
Interface='eth0'<br />
IP='static'<br />
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')<br />
Gateway='192.168.1.1'<br />
DNS=('192.168.1.1')<br />
</nowiki>}}<br />
<br />
Then simply execute: <br />
<br />
$ netctl start mynetwork<br />
<br />
=== Change MAC/hardware address ===<br />
<br />
See [[MAC Address Spoofing]].<br />
<br />
=== Internet Sharing ===<br />
<br />
See [[Internet sharing]].<br />
<br />
=== Router Configuration ===<br />
<br />
See [[Router]].<br />
<br />
=== Local network hostname resolution ===<br />
<br />
The pre-requisite is to [[#Set the hostname]] after which hostname resolution works on the local system itself {{hc|$ ping hostname|<br />
PING hostname <nowiki>(192.168.1.2) 56(84) bytes of data.<br />
64 bytes from hostname (192.168.1.2): icmp_seq=1 ttl=64 time=0.043 ms</nowiki>}}<br />
To enable other machines to address the host by name, either a manual configuration of the respective {{ic|/etc/hosts}} files or a service to propagate/resolve the name is required. <br />
<br />
When setting up a DNS server such as [[BIND]] or [[Unbound]] is overkill, manually editing your {{ic|/etc/hosts}} is too cumbersome, or when you want more flexibility with dynamic leaving and joining of hosts to the network, it is possible to handle hostname resolution on your local network using zero-configuration networking. There are two options available:<br />
<br />
*[[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, OS X, or Linux with {{ic|nmbd}} running, will be able to find your machine.<br />
<br />
*[[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 OS X, 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.<br />
<br />
=== Promiscuous mode ===<br />
<br />
Toggling [https://en.wikipedia.org/wiki/Promiscuous_mode 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 [https://en.wikipedia.org/wiki/Packet_sniffing packet sniffing].<br />
<br />
{{Expansion|Explain what is promiscuous mode, provide some reference links}}<br />
<br />
{{hc|/etc/systemd/system/promiscuous@.service|<nowiki><br />
[Unit]<br />
Description=Set %i interface in promiscuous mode<br />
After=network.target<br />
<br />
[Service]<br />
Type=oneshot<br />
ExecStart=/usr/bin/ip link set dev %i promisc on<br />
RemainAfterExit=yes<br />
<br />
[Install]<br />
WantedBy=multi-user.target<br />
</nowiki>}}<br />
<br />
If you want to enable promiscuous mode on interface {{ic|eth0}} run:<br />
<br />
# systemctl enable promiscuous@eth0.service<br />
<br />
== Troubleshooting ==<br />
<br />
=== Swapping computers on the cable modem ===<br />
<br />
Some 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.<br />
<br />
If this method does not work, you will need to clone the MAC address of the original machine. See also [[Configuring Network#Change MAC/hardware address|Change MAC/hardware address]].<br />
<br />
=== The TCP window scaling problem ===<br />
<br />
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.<br />
<br />
Back in 1992, as more and more memory became available, [http://www.faqs.org/rfcs/rfc1323.html 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.<br />
<br />
That 8-bit Scale Factor allows the Window to be up to 32 times higher than the initial 64Kb.<br />
<br />
It appears that some broken routers and firewalls on the Internet are rewriting the Scale Factor to 0 which causes misunderstandings between hosts.<br />
<br />
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.<br />
<br />
The resulting connection is at best very slow or broken.<br />
<br />
==== How to diagnose the problem ====<br />
<br />
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).<br />
<br />
When you have this problem, the {{ic|dmesg}}'s output is OK, logs are clean and {{ic|ip addr}} will report normal status... and actually everything appears normal.<br />
<br />
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.<br />
<br />
You can try to use Wireshark. You might see successful UDP and ICMP communications but unsuccessful TCP communications (only to foreign hosts).<br />
<br />
==== How to fix it (The bad way) ====<br />
<br />
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.<br />
<br />
# echo "4096 87380 174760" > /proc/sys/net/ipv4/tcp_rmem<br />
<br />
==== How to fix it (The good way) ====<br />
<br />
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 {{ic|/etc/sysctl.d/99-disable_window_scaling.conf}} (see also [[sysctl]])<br />
<br />
net.ipv4.tcp_window_scaling = 0<br />
<br />
==== How to fix it (The best way) ====<br />
<br />
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.<br />
<br />
==== More about it ====<br />
<br />
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].<br />
<br />
There are also several relevant threads on the LKML.<br />
<br />
=== Realtek no link / WOL problem ===<br />
<br />
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:<br />
<br />
==== Method 1 - Enable the NIC directly in Linux ====<br />
<br />
Get the ethernet NIC name from the output of<br />
<br />
$ ip a<br />
<br />
Bring up the device as root using the NIC name:<br />
<br />
# ip link set dev <NIC_name> up<br />
<br />
For ex, if <NIC_name> is enp7s0<br />
<br />
# ip link set dev enp7s0 up<br />
<br />
If it worked and the card is powered on, you should see {{ic|state UP}} for the given interface in the output of {{ic|ip link}}.<br />
<br />
==== Method 2 - Rollback/change Windows driver ====<br />
<br />
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).<br />
<br />
==== Method 3 - Enable WOL in Windows driver ====<br />
<br />
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.<br />
<br />
In Windows XP (example)<br />
Right click my computer<br />
--> Hardware tab<br />
--> Device Manager<br />
--> Network Adapters<br />
--> "double click" Realtek ...<br />
--> Advanced tab<br />
--> Wake-On-Lan After Shutdown<br />
--> Enable<br />
<br />
{{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.}}<br />
<br />
==== Method 4 - Newer Realtek Linux driver ====<br />
<br />
Any newer driver for these Realtek cards can be found for Linux on the realtek site. (untested but believed to also solve the problem).<br />
<br />
==== Method 5 - Enable ''LAN Boot ROM'' in BIOS/CMOS ====<br />
<br />
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.<br />
<br />
{{Note|This was tested successfully multiple times with GIGABYTE system board GA-G31M-ES2L with BIOS version F8 released on 2009/02/05. YMMV.}}<br />
<br />
=== No interface with Atheros chipsets ===<br />
<br />
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 the package {{AUR|backports-patched}} from AUR.<br />
<br />
=== Broadcom BCM57780 ===<br />
<br />
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.<br />
<br />
These steps should help if your computer has this chipset:<br />
$ lspci | grep Ethernet<br />
02:00.0 Ethernet controller: Broadcom Corporation NetLink BCM57780 Gigabit Ethernet PCIe (rev 01)<br />
<br />
If your wired networking is not functioning in some way or another, try unplugging your cable then doing the following (as root):<br />
# modprobe -r tg3<br />
# modprobe broadcom<br />
# modprobe tg3<br />
<br />
Now plug you network cable in. If this solves your problems you can make this permanent by adding {{ic|broadcom}} and {{ic|tg3}} (in this order) to the {{ic|MODULES}} array in {{ic|/etc/mkinitcpio.conf}}:<br />
<br />
MODULES=".. broadcom tg3 .."<br />
<br />
Then rebuild the initramfs:<br />
<br />
# mkinitcpio -p linux<br />
<br />
{{Note|These methods may work for other chipsets, such as BCM57760.}}</div>Octagonal