Difference between revisions of "Network configuration"
(→systemd-networkd: Add example about symlink /etc/resolv.conf - otherwise user can't resolve DNS) |
m (→systemd-networkd: style) |
||
Line 188: | Line 188: | ||
==== systemd-networkd ==== | ==== systemd-networkd ==== | ||
− | With [[systemd]] version >= 209, it's possible to manage network connections with | + | With [[systemd]] version >= 209, it's possible to manage network connections with ''systemd-networkd''. With this approach, only a single configuration file per interface is needed, for example: |
{{hc|/etc/systemd/network/20-dhcp.network|<nowiki> | {{hc|/etc/systemd/network/20-dhcp.network|<nowiki> | ||
Line 198: | Line 198: | ||
</nowiki>}} | </nowiki>}} | ||
''Name = *'' matches all available network interfaces, and e.g. ''Name = en*'' would only match ethernet interfaces. See [[Network configuration#Device names]] for the naming scheme and {{ic|ip link}} for a list of available interfaces. | ''Name = *'' matches all available network interfaces, and e.g. ''Name = en*'' would only match ethernet interfaces. See [[Network configuration#Device names]] for the naming scheme and {{ic|ip link}} for a list of available interfaces. | ||
+ | |||
+ | systemd doesn't update {{ic|/etc/resolv.conf}} - instead it updates {{ic|/run/systemd/network/resolv.conf}}. A quick fix is to symlink the two, ie: | ||
+ | # ln -sf /run/systemd/network/resolv.conf /etc/resolv.conf | ||
Then start/enable {{ic|systemd-networkd.service}}. | Then start/enable {{ic|systemd-networkd.service}}. | ||
− | |||
− | |||
− | |||
− | |||
Further examples: https://coreos.com/blog/intro-to-systemd-networkd/ | Further examples: https://coreos.com/blog/intro-to-systemd-networkd/ |
Revision as of 22:11, 9 March 2014
zh-CN:Network Configuration zh-TW:Network Configuration
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.
Contents
- 1 Check the connection
- 2 Set the hostname
- 3 Device Driver
- 4 Network Interfaces
- 5 Configure the IP address
- 6 Load configuration
- 7 Additional settings
- 8 Troubleshooting
Check the connection
ping: icmp open socket: Operation not permitted
when executing ping, try to re-install the iputils
package.Many times, the basic installation procedure has created a working network configuration. To check if this is so, use the following command:
-c 3
option calls it three times. See man ping
for more information.$ ping -c 3 www.google.com
PING www.l.google.com (74.125.224.146) 56(84) bytes of data. 64 bytes from 74.125.224.146: icmp_req=1 ttl=50 time=437 ms 64 bytes from 74.125.224.146: icmp_req=2 ttl=50 time=385 ms 64 bytes from 74.125.224.146: icmp_req=3 ttl=50 time=298 ms --- www.l.google.com ping statistics --- 3 packets transmitted, 3 received, 0% packet loss, time 1999ms rtt min/avg/max/mdev = 298.107/373.642/437.202/57.415 ms
If it works, then you may only wish to personalize your settings from the options below.
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.
$ ping -c 3 8.8.8.8
PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data. 64 bytes from 8.8.8.8: icmp_req=1 ttl=53 time=52.9 ms 64 bytes from 8.8.8.8: icmp_req=2 ttl=53 time=72.5 ms 64 bytes from 8.8.8.8: icmp_req=3 ttl=53 time=70.6 ms --- 8.8.8.8 ping statistics --- 3 packets transmitted, 3 received, 0% packet loss, time 2002ms rtt min/avg/max/mdev = 52.975/65.375/72.543/8.803 ms
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.If you are able to ping 8.8.8.8
but not www.google.com
, check your DNS configuration. See resolv.conf for details.
Set the hostname
A hostname is a unique name created to identify a machine on a network: it is configured in /etc/hostname
. The file can contain the system's domain name, if any. To set the hostname, do:
# hostnamectl set-hostname myhostname
This will put myhostname
into /etc/hostname
.
See man 5 hostname
and man 1 hostnamectl
for details.
-
hostnamectl
supports FQDNs - You no longer need to edit
/etc/hosts
, systemd will provide host name resolution, and is installed on all systems by default.
To set the hostname temporarily (until a reboot), use hostname from inetutils:
# hostname myhostname
Device Driver
Check the driver status
udev should detect your network interface card (NIC) and automatically load the necessary module at start up. Check the "Ethernet controller" entry (or similar) from the lspci -v
output. It should tell you which kernel module contains the driver for your network device. For example:
$ lspci -v
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 dmesg | grep module_name
. For example:
$ dmesg | grep atl1 ... 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.
Load the device module
Google for the right module/driver for the chipset. Some common modules are 8139too
for cards with a Realtek chipset, or sis900
for cards with a SiS chipset. Once you know which module to use, try to 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.
If udev is not detecting and loading the proper module automatically during bootup, see Kernel modules#Loading.
Network Interfaces
Device names
For computers with multiple NICs, it is important to have fixed device name. Many configuration problems are caused by interface name changing.
udev is responsible for which device gets which name. Systemd v197 introduced Predictable Network Interface Names, which automatically assigns static names to network devices. Interfaces are now prefixed with en
(ethernet), wl
(WLAN), or ww
(WWAN) followed by an automatically generated identifier, creating an entry such as enp0s25
.
This behavior may be disabled by adding a symlink:
# ln -s /dev/null /etc/udev/rules.d/80-net-setup-link.rules
Users upgrading from an earlier systemd version will have a blank rules file created automatically. So if you want to use persistent device names, just delete the file.
ip link
or ls /sys/class/net
to list all available interfaces.netctl reenable profile
to update the generated service file.Change device name
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"
A couple 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 doesn't 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"
net0
, net1
, wifi0
, wifi1
. For further details please see the systemd documentation.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}="1480", ATTR{tx_queue_len}="2000"
Get current device names
Current NIC names can be found via sysfs
$ ls /sys/class/net
lo eth0 eth1 firewire0
Enabling and disabling network interfaces
You can activate or deactivate network interfaces using:
# ip link set eth0 up # ip link set eth0 down
To check the result:
$ ip link show dev eth0
2: eth0: <BROADCAST,MULTICAST,PROMISC,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master br0 state UP mode DEFAULT qlen 1000 ...
Configure the IP address
You have two options: a dynamically assigned address using DHCP, or an unchanging "static" address.
Dynamic IP address
dhcpcd
The easiest is to use dhcpcd, which is included in the base group. Either use the provided service file dhcpcd@.service
, passing the interface name as an argument, or start it manually by running dhcpcd interface
.
systemd-networkd
With systemd version >= 209, it's possible to manage network connections with systemd-networkd. With this approach, only a single configuration file per interface is needed, for example:
/etc/systemd/network/20-dhcp.network
[Match] Name=* [Network] DHCP=yes
Name = * matches all available network interfaces, and e.g. Name = en* would only match ethernet interfaces. See Network configuration#Device names for the naming scheme and ip link
for a list of available interfaces.
systemd doesn't update /etc/resolv.conf
- instead it updates /run/systemd/network/resolv.conf
. A quick fix is to symlink the two, ie:
# ln -sf /run/systemd/network/resolv.conf /etc/resolv.conf
Then start/enable systemd-networkd.service
.
Further examples: https://coreos.com/blog/intro-to-systemd-networkd/
Static IP address
There are various reasons why you may wish to assign static IP addresses on your network. For instance, one may gain a certain degree of predictability with unchanging addresses, or you may not have a DHCP server available.
You need:
- Static IP address
- Subnet mask
- Broadcast address
- Gateway's IP address
If you are running a private network, it is safe to use IP addresses in 192.168.*.* for your IP addresses, with a subnet mask of 255.255.255.0 and a broadcast address of 192.168.*.255. The gateway is usually 192.168.*.1 or 192.168.*.254.
Manual assignment
You can assign a static IP address in the console:
# ip addr add IP_address/subnet_mask broadcast broadcast_address dev interface
For example:
# ip addr add 192.168.1.2/24 broadcast 192.168.1.255 dev eth0
For more options, see man ip
.
Add your gateway IP address like so:
# ip route add default via default_gateway
For example:
# ip route add default via 192.168.1.1
If you the get the error "No such process", it means you have to run ip link set dev eth0 up
as root.
Persistent configuration on boot using systemd and udev rules
First create a configuration file for the systemd service, replace interface
with the proper network interface name:
/etc/conf.d/network@interface
address=192.168.0.15 netmask=24 broadcast=192.168.0.255 gateway=192.168.0.1
Create a systemd unit file:
/etc/systemd/system/network@.service
[Unit] Description=Network connectivity (%i) Wants=network.target Before=network.target BindsTo=sys-subsystem-net-devices-%i.device After=sys-subsystem-net-devices-%i.device [Service] Type=oneshot RemainAfterExit=yes EnvironmentFile=/etc/conf.d/network@%i ExecStart=/usr/bin/ip link set dev %i up ExecStart=/usr/bin/ip addr add ${address}/${netmask} broadcast ${broadcast} dev %i ExecStart=/usr/bin/sh -c 'test -n ${gateway} && /usr/bin/ip route add default via ${gateway}' ExecStop=/usr/bin/ip addr flush dev %i ExecStop=/usr/bin/ip link set dev %i down [Install] WantedBy=multi-user.target
Enable the unit and start it, passing the name of the interface:
# systemctl enable network@interface.service # systemctl start network@interface.service
Persistent configuration on boot using systemd-networkd
With systemd version >= 209, it's possible to manage network connections with the integrated systemd-networkd service (which is disabled by default with version 210). With this approach, only a single configuration file per interface is needed, for example:
/etc/systemd/network/10-static-ethernet.network
[Match] Name=enp0s25 [Network] Address=192.168.0.15/24 Gateway=192.168.0.1
Name has to be the name of the interface you want to configure, see ip link
for the names of available interfaces.
Then start/enable systemd-networkd.service
.
Further examples: https://coreos.com/blog/intro-to-systemd-networkd/
Calculating addresses
You can use ipcalc
provided by the ipcalc package to calculate IP broadcast, network, netmask, and host ranges for more advanced configurations. For example, I use ethernet over firewire to connect a windows machine to arch. For security and network organization, I placed them on their own network and configured the netmask and broadcast so that they are the only 2 machines on it. To figure out the netmask and broadcast addresses for this, I used ipcalc, providing it with the IP of the arch firewire nic 10.66.66.1, and specifying ipcalc should create a network of only 2 hosts.
$ ipcalc -nb 10.66.66.1 -s 1
Address: 10.66.66.1 Netmask: 255.255.255.252 = 30 Network: 10.66.66.0/30 HostMin: 10.66.66.1 HostMax: 10.66.66.2 Broadcast: 10.66.66.3 Hosts/Net: 2 Class A, Private Internet
Load configuration
To test your settings either reboot the computer or reload the relevant systemd services. 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:
$ ping -c 3 www.google.com
Additional settings
ifplugd for laptops
ifplugd in official repositories is a daemon which will automatically configure your Ethernet device when a cable is plugged in and automatically unconfigure it if the cable is pulled. This is useful on laptops with onboard network adapters, since it will only configure the interface when a cable is really connected. Another use is when you just need to restart the network but do not want to restart the computer or do it from the shell.
By default it is configured to work for the eth0
device. This and other settings like delays can be configured in /etc/ifplugd/ifplugd.conf
.
netctl-ifplugd@.service
, otherwise you can use ifplugd@.service
from ifplugd package. Use for example systemctl enable ifplugd@eth0.service
.Bonding or LAG
See netctl#Bonding.
IP address aliasing
IP aliasing is the process of adding more than one IP address to a network interface. With this, one node on a network can have multiple connections to a network, each serving a different purpose. Typical uses are virtual hosting of Web and FTP servers, or reorganizing servers without having to update any other machines (this is especially useful for nameservers).
Example
You will need netctl from the official repositories.
Prepare the configuration:
/etc/netctl/mynetwork
Connection='ethernet' Description='Five different addresses on the same NIC.' Interface='eth0' IP='static' Address=('192.168.1.10' '192.168.178.11' '192.168.1.12' '192.168.1.13' '192.168.1.14' '192.168.1.15') Gateway='192.168.1.1' DNS=('192.168.1.1')
Then simply execute:
$ netctl start mynetwork
Change MAC/hardware address
See MAC Address Spoofing.
Internet Sharing
See Internet sharing.
Router Configuration
See Router.
Local network hostname resolution
The pre-requisite is to #Set the hostname after which hostname resolution works on the local system itself$ ping hostname
PING hostname (192.168.1.2) 56(84) bytes of data. 64 bytes from hostname (192.168.1.2): icmp_seq=1 ttl=64 time=0.043 ms
To enable other machines to address the host by name, either a manual configuration of the respective /etc/hosts
files or a service to propagate/resolve the name is required.
When setting up a DNS server such as BIND or Unbound is overkill, manually editing your /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:
- Samba provides hostname resolution via Microsoft's NetBIOS. It only requires installation of samba and enabling of the
nmbd.service
service. Computers running Windows, OS X, or Linux withnmbd
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 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.
Troubleshooting
Swapping computers on the cable modem
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.
If this method does not work, you will need to clone the MAC address of the original machine. See also Change MAC/hardware address.
The TCP window scaling problem
TCP packets contain a "window" value in their headers indicating how much data the other host may send in return. This value is represented with only 16 bits, hence the window size is at most 64Kb. TCP packets are cached for a while (they have to be reordered), and as memory is (or used to be) limited, one host could easily run out of it.
Back in 1992, as more and more memory became available, RFC 1323 was written to improve the situation: Window Scaling. The "window" value, provided in all packets, will be modified by a Scale Factor defined once, at the very beginning of the connection.
That 8-bit Scale Factor allows the Window to be up to 32 times higher than the initial 64Kb.
It appears that some broken routers and firewalls on the Internet are rewriting the Scale Factor to 0 which causes misunderstandings between hosts.
The Linux kernel 2.6.17 introduced a new calculation scheme generating higher Scale Factors, virtually making the aftermaths of the broken routers and firewalls more visible.
The resulting connection is at best very slow or broken.
How to diagnose the problem
First of all, let's make it clear: this problem is odd. In some cases, you will not be able to use TCP connections (HTTP, FTP, ...) at all and in others, you will be able to communicate with some hosts (very few).
When you have this problem, the dmesg
's output is OK, logs are clean and ip addr
will report normal status... and actually everything appears normal.
If you cannot browse any website, but you can ping some random hosts, chances are great that you're experiencing this problem: ping uses ICMP and is not affected by TCP problems.
You can try to use Wireshark. You might see successful UDP and ICMP communications but unsuccessful TCP communications (only to foreign hosts).
How to fix it (The bad way)
To fix it the bad way, you can change the tcp_rmem value, on which Scale Factor calculation is based. Although it should work for most hosts, it is not guaranteed, especially for very distant ones.
# echo "4096 87380 174760" > /proc/sys/net/ipv4/tcp_rmem
How to fix it (The good way)
Simply disable Window Scaling. Since Window Scaling is a nice TCP feature, it may be uncomfortable to disable it, especially if you cannot fix the broken router. There are several ways to disable Window Scaling, and it seems that the most bulletproof way (which will work with most kernels) is to add the following line to /etc/sysctl.d/99-disable_window_scaling.conf
(see also sysctl)
net.ipv4.tcp_window_scaling = 0
How to fix it (The best way)
This problem is caused by broken routers/firewalls, so let's change them. Some users have reported that the broken router was their very own DSL router.
More about it
This section is based on the LWN article TCP window scaling and broken routers and a Kernel Trap article: Window Scaling on the Internet.
There are also several relevant threads on the LKML.
Realtek no link / WOL problem
Users with Realtek 8168 8169 8101 8111(C) based NICs (cards / and on-board) may notice a problem where the NIC seems to be disabled on boot and has no Link light. This can usually be found on a dual boot system where Windows is also installed. It seems that using the offical Realtek drivers (dated anything after May 2007) under Windows is the cause. These newer drivers disable the Wake-On-LAN feature by disabling the NIC at Windows shutdown time, where it will remain disabled until the next time Windows boots. You will be able to notice if this problem is affecting you if the Link light remains off until Windows boots up; during Windows shutdown the Link light will switch off. Normal operation should be that the link light is always on as long as the system is on, even during POST. This problem will also affect other operative systems without newer drivers (eg. Live CDs). Here are a few fixes for this problem:
Method 1 - Enable the NIC directly in Linux
Get the ethernet NIC name from the output of
$ ip a
Bring up the device as root using the NIC name:
# ip link set dev <NIC_name> up
For ex, if <NIC_name> is enp7s0
# ip link set dev enp7s0 up
If it worked and the card is powered on, a new interface should appear in the output of ifconfig
Method 2 - Rollback/change Windows driver
You can roll back your Windows NIC driver to the Microsoft provided one (if available), or roll back/install an official Realtek driver pre-dating May 2007 (may be on the CD that came with your hardware).
Method 3 - Enable WOL in Windows driver
Probably the best and the fastest fix is to change this setting in the Windows driver. This way it should be fixed system-wide and not only under Arch (eg. live CDs, other operative systems). In Windows, under Device Manager, find your Realtek network adapter and double-click it. Under the Advanced tab, change "Wake-on-LAN after shutdown" to Enable.
In Windows XP (example) Right click my computer --> Hardware tab --> Device Manager --> Network Adapters --> "double click" Realtek ... --> Advanced tab --> Wake-On-Lan After Shutdown --> Enable
Disable
has no effect (you will notice the Link light still turns off upon Windows shutdown). One rather dirty workaround is to boot to Windows and just reset the system (perform an ungraceful restart/shutdown) thus not giving the Windows driver a chance to disable LAN. The Link light will remain on and the LAN adapter will remain accessible after POST - that is until you boot back to Windows and shut it down properly again.Method 4 - Newer Realtek Linux driver
Any newer driver for these Realtek cards can be found for Linux on the realtek site. (untested but believed to also solve the problem).
Method 5 - 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.
No eth0 with Atheros AR9485
The ethernet (eth0) for Atheros AR9485 are not working out-of-the-box (with installation media of February 2014). The working solution for this is to install the package backports-patchedAUR from AUR.
Broadcom BCM57780
This Broadcom chipset sometimes does not behave well unless you specify the order of the modules to be loaded. The modules are broadcom
and tg3
, the former needing to be loaded first.
These steps should help if your computer has this chipset:
$ lspci | grep Ethernet 02:00.0 Ethernet controller: Broadcom Corporation NetLink BCM57780 Gigabit Ethernet PCIe (rev 01)
If your wired networking is not functioning in some way or another, try unplugging your cable then doing the following (as root):
# modprobe -r tg3 # modprobe broadcom # modprobe tg3
Now plug you network cable in. If this solves your problems you can make this permanent by adding broadcom
and tg3
(in this order) to the MODULES
array in /etc/mkinitcpio.conf
:
MODULES=".. broadcom tg3 .."
Then rebuild the initramfs:
# mkinitcpio -p linux