IFSYSCTL(5) Network configuration IFSYSCTL(5)NAME
ifsysctl[-<interface name>] - per network interface sysctl settings
SYNOPSIS
/etc/sysconfig/network/ifsysctl
/etc/sysconfig/network/ifsysctl-<interface name>
DESCRIPTION
These files are intended to contain sysctl settings, that should be applied when a network interface is created. This are usually interface
specific settings, like:
net.ipv6.conf.eth0.use_tempaddr = 1
or
net.ipv4.conf.eth0.rp_filter = 0
The settings are applied by the /etc/sysconfig/network/scripts/ifup-sysctl script executed via /etc/udev/rules.d/77-network.rules rule (see
udev(7)), after the creation and after the rename of the interface name to its persistent name (when applicable), but before the ifup
<interface name> -o hotplug may be executed to configure the interface.
The settings are not applied by default when the NetworkManager is active (NETWORKMANAGER=yes), except when the IFSYSCTL_NETWORKMANAGER=yes
variable is set in the /etc/sysconfig/network/config file.
Settings from the ifsysctl- file are applied every time an interface has been created.
Settings from the ifsysctl-interface name file are applied when the interface with the corresponding interface name has been created.
SYNTAX
The sysctl(8) utility is required to apply the settings. It supports two separator characters for sysctl keywords: a "." in default format
and a "/" in the alternate format. Therefore the syntax is basically same to the /etc/sysctl.conf file.
Interface names may contain a ".". In the default sysctl format using a "." as separator, that is any "." in the interface name of the key-
word, has to be replaced with a "/". In the alternate sysctl format with "/" as separator, normal interface names can be used.
Optionally, the ifsysctl files may contain also the $INTERFACE and the $SYSCTL_IF variables, that are automatically replaced with the cur-
rent interface name usable in the alternate format and with the sysctl-quoted interface name for the default format, before the settings
are passed to the sysctl utility.
Note also, that settings with variables in the ifsysctl (without the -<interface name> suffix), will be applied for every interface!
Further, files with variables are not compatible to the /etc/sysctl.conf file.
EXAMPLES
Settings for "eth0" and "eth0.1" interfaces
# using "." as separator:
net.ipv6.conf.eth0.use_tempaddr = 1
net.ipv6.conf.eth0/1.use_tempaddr = 1
# using "/" as separator:
net/ipv6/conf/eth0/use_tempaddr = 1
net/ipv6/conf/eth0.0/use_tempaddr = 1
Settings with variables:
# using "." as separator:
net.ipv6.conf.$SYSCTL_IF.use_tempaddr = 1
# using "/" as separator:
net/ipv6/conf/$INTERFACE/use_tempaddr = 1
To test your ifsysctl-eth0 or ifsysctl file, use:
/etc/sysconfig/network/scripts/ifup-sysctl eth0 -o debug
BUGS
Please report bugs at <https://bugzilla.novell.com/>
AUTHOR
Marius Tomaschewski <mt@suse.de>
SEE ALSO ifup(8)ifcfg(5)sysctl(8)sysconfig December 2009 IFSYSCTL(5)
Check Out this Related Man Page
SYSCTL.D(5) sysctl.d SYSCTL.D(5)NAME
sysctl.d - Configure kernel parameters at boot
SYNOPSIS
/etc/sysctl.d/*.conf
/run/sysctl.d/*.conf
/usr/lib/sysctl.d/*.conf
DESCRIPTION
At boot, systemd-sysctl.service(8) reads configuration files from the above directories to configure sysctl(8) kernel parameters.
CONFIGURATION FORMAT
The configuration files contain a list of variable assignments, separated by newlines. Empty lines and lines whose first non-whitespace
character is "#" or ";" are ignored.
Note that either "/" or "." may be used as separators within sysctl variable names. If the first separator is a slash, remaining slashes
and dots are left intact. If the first separator is a dot, dots and slashes are interchanged. "kernel.domainname=foo" and
"kernel/domainname=foo" are equivalent and will cause "foo" to be written to /proc/sys/kernel/domainname. Either
"net.ipv4.conf.enp3s0/200.forwarding" or "net/ipv4/conf/enp3s0.200/forwarding" may be used to refer to
/proc/sys/net/ipv4/conf/enp3s0.200/forwarding.
The settings configured with sysctl.d files will be applied early on boot. The network interface-specific options will also be applied
individually for each network interface as it shows up in the system. (More specifically, net.ipv4.conf.*, net.ipv6.conf.*,
net.ipv4.neigh.* and net.ipv6.neigh.*).
Many sysctl parameters only become available when certain kernel modules are loaded. Modules are usually loaded on demand, e.g. when
certain hardware is plugged in or network brought up. This means that systemd-sysctl.service(8) which runs during early boot will not
configure such parameters if they become available after it has run. To set such parameters, it is recommended to add an udev(7) rule to
set those parameters when they become available. Alternatively, a slightly simpler and less efficient option is to add the module to
modules-load.d(5), causing it to be loaded statically before sysctl settings are applied (see example below).
CONFIGURATION DIRECTORIES AND PRECEDENCE
Configuration files are read from directories in /etc/, /run/, and /lib/, in order of precedence. Each configuration file in these
configuration directories shall be named in the style of filename.conf. Files in /etc/ override files with the same name in /run/ and
/lib/. Files in /run/ override files with the same name in /lib/.
Packages should install their configuration files in /lib/. Files in /etc/ are reserved for the local administrator, who may use this logic
to override the configuration files installed by vendor packages. All configuration files are sorted by their filename in lexicographic
order, regardless of which of the directories they reside in. If multiple files specify the same option, the entry in the file with the
lexicographically latest name will take precedence. It is recommended to prefix all filenames with a two-digit number and a dash, to
simplify the ordering of the files.
If the administrator wants to disable a configuration file supplied by the vendor, the recommended way is to place a symlink to /dev/null
in the configuration directory in /etc/, with the same filename as the vendor configuration file. If the vendor configuration file is
included in the initrd image, the image has to be regenerated.
EXAMPLES
Example 1. Set kernel YP domain name
/etc/sysctl.d/domain-name.conf:
kernel.domainname=example.com
Example 2. Apply settings available only when a certain module is loaded (method one)
/etc/udev/rules.d/99-bridge.rules:
ACTION=="add", SUBSYSTEM=="module", KERNEL=="br_netfilter",
RUN+="/lib/systemd/systemd-sysctl --prefix=/net/bridge"
/etc/sysctl.d/bridge.conf:
net.bridge.bridge-nf-call-ip6tables = 0
net.bridge.bridge-nf-call-iptables = 0
net.bridge.bridge-nf-call-arptables = 0
This method applies settings when the module is loaded. Please note that, unless the br_netfilter module is loaded, bridged packets will
not be filtered by Netfilter (starting with kernel 3.18), so simply not loading the module is sufficient to avoid filtering.
Example 3. Apply settings available only when a certain module is loaded (method two)
/etc/modules-load.d/bridge.conf:
br_netfilter
/etc/sysctl.d/bridge.conf:
net.bridge.bridge-nf-call-ip6tables = 0
net.bridge.bridge-nf-call-iptables = 0
net.bridge.bridge-nf-call-arptables = 0
This method forces the module to be always loaded. Please note that, unless the br_netfilter module is loaded, bridged packets will not be
filtered with Netfilter (starting with kernel 3.18), so simply not loading the module is sufficient to avoid filtering.
SEE ALSO systemd(1), systemd-sysctl.service(8), systemd-delta(1), sysctl(8), sysctl.conf(5), modprobe(8)systemd 237SYSCTL.D(5)