ifconfig
configure a network interface
see also :
route - netstat - arp - rarp - iptables - ifup
Synopsis
ifconfig
[-v] [-a] [-s] [interface]
ifconfig [-v] interface [aftype] options | address
...
add an example, a script, a trick and tips
examples
source
How to detect VPN disconnection with vpnc?
Typically the VPN connection should not break so frequently. In
your case, you can first try to diagnose the real connectivity
issue instead of writing scripts to automatically connect to the
vpn when disconnected.
source
ip versus ifconfig
Simple answer: On Linux ifconfig is obsolete.
From man ifconfig:
This program is obsolete! For replacement check ip
addr and ip link. For statistics use
ip -s link.
source
Three computers accessing internet but only two network interfaces showing in ´ifconfig´, why?
I am not sure if I understand correctly. But you have 1 Wireless
gateway and 3 Devices connected to it?
So doing ifconfig only shows PHYSICAL hardware/connections
on the PC that ran the command - not the connections available or
other device.
ifconfig stands for interface configuration
-
An interface if a virtual or physical layer on the computer
that enables it to communicate with other devices using a
standard, for example in your case TCP/IP
-
eth0 could be your Wired Network card running at
10/100/1000
-
eth1 is possibly your wirless interface running at
a/b/g/n speeds.
-
lo is a virtual interface and is called a loopback
and bind to your computer using home (127.0.0.1) or (localhost)
or whatever your computers name is(because it loops back to it
self)
To see other computers you need to use something like ARP and to find other computers or devices within
your network range.
Also as suggested you can use a wireless tool iwconfig to scan for access points (an access
point is not an interface- but the access point it self uses an
interface to communicates with other devices found in ARP)
And you only have 1 internet connection, not 3.
In total you should have 5 ARP entries - 2 PC's,
1Notebook, 1Switch and 1 Modem
So as you can see in the illustration, each host has an interface
of eth0, the gateway has eth0 and the ISP on the other side has
eth0. the more interfaces a device has the higher the number.
source
Is `ip` to supersede `ifconfig`
IP is a newer subset of commands that is meant to take the place
of ifconfig, some examples:
ip link show List network interfaces
ip link set dev eth0 name wan Rename interface eth0 to wan
ip link set dev eth0 up Bring interface eth0 up (or down)
ip addr show List addresses for interfaces
ip addr add 1.2.3.4/24 brd + dev eth0 Add (or del) ip and mask (255.255.255.0)
ip route show List routing table
ip route add default via 1.2.3.254 Set default gateway to 1.2.3.254
source
How to restore MAC address in Linux?
Maybe try removing then installing the module again?
sudo rmmod <NICmodule>
sudo insmod <NICmodule>
Or maybe dropping the interface and bringing it back up?
sudo ifdown <interface> && sudo ifup <interface>
source
`ifconfig` isn't showing stats for an alx gigabit card
I could not find a way to fix ifconfig, but I used nstat and some
clever awk computations in my conky script to achieve the same
thing. So, instead of using "${downspeed eth0}/s" to obtain your
download speed for eth0, you could use the following one-liner:
${execi 1 /sbin/nstat | grep -i IpExtInOctets | awk '{if($2>1024*1024){mb=$2/1024/1024;printf "%.2F MB", mb} else if($2>1024){kb=$2/1024;printf "%.2F KB", kb} else {printf "%d B", $2}}' }/s
You have to use execi with 1 second intervals. nstat shows the
difference in bytes from its previous run. If you want to run it
in longer than 1 sec intervals you may want to divide your result
in awk to that number of seconds so you have an average.
For upload, use the IpExtOutOctets line from nstat. You can adapt
this to your needs. Please remember that it will show all traffic
in and out, not just for a specific interface. But I presume you
only have one network interface, I have only one on my desktop
PC. For multiple interfaces a different solution may be required.
UPDATE: however, be careful, running the command once for
incoming then for outgoing immediately after the first one will
show you zero for outgoing. Maybe some "sleep" commands
here-and-there will fix this.
UPDATE2: here is how I solved the problem of showing both
download and upload spedd in two differen commands and still
about right. Adaptations to graphs and charts are needed, but for
text only you can try this:
${goto 630}${font sansation:size=10,weight:bold}${color5} \
${texeci 2 /sbin/nstat | grep -i IpExtInOctets | awk '{if($2>1024*1024){mb=$2/1024/1024;printf "%.2F MB", mb} else if($2>1024){kb=$2/1024;printf "%.2F KB", kb} else {printf "%d B", $2}}' }/s \
${alignr 1}${color6} \
${texeci 2 sleep 1 && /sbin/nstat | grep -i IpExtOutOctets | awk '{if($2>1024*1024){mb=$2/1024/1024;printf "%.2F MB", mb} else if($2>1024){kb=$2/1024;printf "%.2F KB", kb} else {printf "%d B", $2}}' }/s
UPDATE: Or you could take both values at once and format them
with awk for output.
U/D: ${execi 1 /sbin/nstat | grep -A1 -i IpExtInOctets | awk '{if($2>1024*1024){mb=$2/1024/1024;printf "%.2F MB/s ", mb} else if($2>1024){kb=$2/1024;printf "%.2F KB/s ", kb} else {printf "%d B/s ", $2}}'}
source
What is the real capacity of a network device (ethtool - MiB or MB?)
Ethernet speeds are in base 10 units (10000000, 100000000,
100000000, etc) so that correct unit would be based on SI
prefixes. For some time the IT industry has been moving to using
SI prefixes. The notable (and logical) exception is computer
memory / cache which is based in binary.
source
ppp0 strange default router address
The destination isn't the default gateway. PPP stands for
'point-to-point protocol' and this is exactly what you're seeing:
the near-end point is 10.223.229.136, and the far
end is 10.64.64.64.
Check your routing table (route -n): this will
display the default gateway.
The 'all 1s' netmask means that there is in effect no subnet
associated with the local address. Don't bother with classes of
subnet: they haven't had any real-world meaning for many years.
source
What does eth0:cp1 refer to in ifconfig on CentOS?
These are subinterfaces and a method of adding additional IP
addresses along with their subnets to an interface. The part
after the colon is arbitrary.
iptables cannot reference subinterfaces, so any rules required
would be based on IP addresses, but bound to the physical
interface if required.
source
ifupdown: interface does not get properly configured
Check your scripts in dirs:
if-down.d
if-post-down.d
if-pre-up.d
if-up.d
interfaces.d
source
Network conf - ever time must set ifconfig
(This assumes that you are running Mint, and that Mint didn't
change anything from Debian on this matter)
You need an auto line:
auto eth1
Otherwise, the interface will not be handled by the
init.d/networking script.
This way, the interface is started when networking
is started, reconfigured if networking is
reloaded/restarted and stopped when networking is
stopped.
Alternatively, for hotplugged devices, you can use :
allow-hotplug eth1
This way, the device will be configured when it is plugged and
unconfigured when unplugged. If the device is already plugged at
boot, networking will start it, but will not touch
it when networking is stopped/restarted/reloaded
Oh, and by the way, ifconfig is deprecated. I hope
that your ìfupdown package is recent enough to use
ip (from the iproute2 package) instead.
source
Linux: Any distro-independent way to change and persist IP settings?
Perhaps the most direct way would be to put your configuration in
a bash script, then run the script at login.
How you have the script run will be distro-dependent but the
script itself can be used on any Linux distro.
source
What does the field `Memory` mean in `ifconfig`?
Yes. The network card's onboard memory buffers are mapped into
memory so the CPU can copy data into and out of them as the card
sends and receives packets.
description
Ifconfig
is used to configure the kernel-resident network interfaces.
It is used at boot time to set up interfaces as necessary.
After that, it is usually only needed when debugging or when
system tuning is needed.
If no arguments
are given, ifconfig displays the status of the
currently active interfaces. If a single interface
argument is given, it displays the status of the given
interface only; if a single -a argument is
given, it displays the status of all interfaces, even those
that are down. Otherwise, it configures an interface.
options
-a
display all interfaces which are
currently available, even if down
-s
display a short list (like netstat -i)
-v
be more verbose for some error conditions
interface
The name of the interface. This
is usually a driver name followed by a unit number, for
example eth0 for the first Ethernet interface. If
your kernel supports alias interfaces, you can specify them
with eth0:0 for the first alias of eth0. You can use
them to assign a second address. To delete an alias
interface use ifconfig eth0:0 down. Note: for every
scope (i.e. same net with address/netmask combination) all
aliases are deleted, if you delete the first (primary).
up
This flag causes the interface to be activated. It is
implicitly specified if an address is assigned to the
interface.
down
This flag causes the driver for this interface to be
shut down.
[-]arp
Enable or disable the use of the ARP protocol on this
interface.
[-]promisc
Enable or disable the
promiscuous mode of the interface. If selected, all
packets on the network will be received by the
interface.
[-]allmulti
Enable or disable
all-multicast mode. If selected, all multicast
packets on the network will be received by the
interface.
metric N
This parameter sets the
interface metric.
mtu N
This parameter sets the Maximum Transfer Unit (MTU) of
an interface.
dstaddr addr
Set the remote IP address for a
point-to-point link (such as PPP). This keyword is now
obsolete; use the pointopoint keyword instead.
netmask addr
Set the IP network mask for
this interface. This value defaults to the usual class A, B
or C network mask (as derived from the interface IP
address), but it can be set to any value.
add addr/prefixlen
Add an IPv6 address to an
interface.
del addr/prefixlen
Remove an IPv6 address from an
interface.
tunnel aa.bb.cc.dd
Create a new SIT (IPv6-in-IPv4)
device, tunnelling to the given destination.
irq addr
Set the interrupt line used by
this device. Not all devices can dynamically change their
IRQ setting.
io_addr addr
Set the start address in I/O
space for this device.
mem_start addr
Set the start address for
shared memory used by this device. Only a few devices need
this.
media type
Set the physical port or medium
type to be used by the device. Not all devices can change
this setting, and those that can vary in what values they
support. Typical values for type are 10base2
(thin Ethernet), 10baseT (twisted-pair 10Mbps
Ethernet), AUI (external transceiver) and so on. The
special medium type of auto can be used to tell the
driver to auto-sense the media. Again, not all drivers can
do this.
[-]broadcast
[addr]
If the address argument is
given, set the protocol broadcast address for this
interface. Otherwise, set (or clear) the
IFF_BROADCAST flag for the interface.
[-]pointopoint
[addr]
This keyword enables the
point-to-point mode of an interface, meaning that it
is a direct link between two machines with nobody else
listening on it.
If the address argument is also given, set the protocol
address of the other side of the link, just like the
obsolete dstaddr keyword does. Otherwise, set or
clear the IFF_POINTOPOINT flag for the interface.
hw class address
Set the hardware address of
this interface, if the device driver supports this
operation. The keyword must be followed by the name of the
hardware class and the printable ASCII equivalent of the
hardware address. Hardware classes currently supported
include ether (Ethernet), ax25 (AMPR AX.25),
ARCnet and netrom (AMPR NET/ROM).
multicast
Set the multicast flag on the
interface. This should not normally be needed as the drivers
set the flag correctly themselves.
address
The IP address to be assigned
to this interface.
txqueuelen length
Set the length of the transmit
queue of the device. It is useful to set this to small
values for slower devices with a high latency (modem links,
ISDN) to prevent fast bulk transfers from disturbing
interactive traffic like telnet too much.
address families
If the first argument after the interface name is recognized as
the name of a supported address family, that address family is
used for decoding and displaying all protocol addresses.
Currently supported address families include inet (TCP/IP,
default), inet6 (IPv6), ax25 (AMPR Packet Radio),
ddp (Appletalk Phase 2), ipx (Novell IPX) and
netrom (AMPR Packet radio).
files
/proc/net/socket
/proc/net/dev
/proc/net/if_inet6
notes
Since kernel release 2.2 there are no explicit interface
statistics for alias interfaces anymore. The statistics printed
for the original address are shared with all alias addresses on
the same device. If you want per-address statistics you should
add explicit accounting rules for the address using the
ipchains(8) or iptables(8) command.
Interrupt problems with Ethernet device drivers fail with EAGAIN
(SIOCSIIFLAGS: Resource temporarily unavailable) it is
most likely a interrupt conflict. See
http://www.scyld.com/expert/irq-conflict.html for more
information.
bugs
While appletalk
DDP and IPX addresses will be displayed they cannot be
altered by this command.
see also
route ,
netstat , arp , rarp , ipchains, iptables ,
ifup , interfaces.
http://physics.nist.gov/cuu/Units/binary.html - Prefixes for
binary multiples
authors
Fred N. van
Kempen, <waltje[:at:]uwalt.nl.mugnet[:dot:]org>
Alan Cox, <Alan.Cox[:at:]linux[:dot:]org>
Phil Blundell, <Philip.Blundell[:at:]pobox[:dot:]com>
Andi Kleen
Bernd Eckenfels, <net-tools[:at:]lina.inka[:dot:]de>