Posts Tagged ‘etc network’

How to configure manually static IP address on Debian GNU/Linux / How to fix eth0 interface not brought up with error (networking restart is deprecated)

Friday, July 29th, 2011

Reading Time: 2 minutes
I’ve recently had to manually assign a static IP address on one of the servers I manage, here is how I did it:             

debian:~# vim /etc/network/interfaces

Inside the file I placed:

# The primary network interface
allow-hotplug eth0
auto eth0
iface eth0 inet static address 192.168.0.2 netmask 255.255.255.0 broadcast 192.168.0.0 gateway 192.168.0.1 dns-nameservers 8.8.8.8 8.8.4.4 208.67.222.222 208.67.220.220

The broadcast and gateway configuration lines are not obligitory.
dns-nameservers would re-create /etc/resolv.conf file with the nameserver values specified which in these case are Google Public DNS servers and OpenDNS servers.

Very important variable is allow-hotplug eth0
If these variable with eth0 lan interface is omitted or missing (due to some some weird reason), the result would be the output you see from the command below:

debian:~# /etc/init.d/networking restart
Running /etc/init.d/networking restart is deprecated because it may not enable again some interfaces ... (warning).
Reconfiguring network interfaces...

Besides the /etc/init.d/networking restart is deprecated because it may not enable again some interfaces … (warning). , if the allow-hotplug eth0 variable is omitted the eth0 interface would not be brough up on next server boot or via the networking start/stop/restart init script.

My first reaction when I saw the message was that probably I’ll have to use invoke-rc.d, e.g.:
debian:~# invoke-rc.d networking restart
Running invoke-rc.d networking restart is deprecated because it may not enable again some interfaces ... (warning).

However as you see from above’s command output, running invoke-rc.d helped neither.

I was quite surprised with the inability to bring my network up for a while with the networking init script.
Interestingly using the command:

debian:~# ifup eth0

was able to succesfully bring up the network interface, whether still invoke-rc.d networking start failed.

After some wondering I finally figured out that the eth0 was not brought up by networking init script, because auto eth0 or allow-hotplug eth0 (which by the way are completely interchangable variables) were missing.

I added allow-hotplug eth0 and afterwards the networking script worked like a charm 😉


How to configure networking in CentOS, Fedora and other Redhat based distros

Wednesday, June 1st, 2011

Reading Time: 3 minutes
On Debian Linux I’m used to configure the networking via /etc/network/interfaces , however on Redhat based distributions to do a manual configuration of network interfaces is a bit different.

In order to configure networking in CentOS there is a special file for each interface and some values one needs to fill in to enable networking.

These network adapters configuration files for Redhat based distributions are located in the files:

/etc/sysconfig/network-scripts/ifcfg-*

Just to give you and idea on the content of this network configuration file, here is how it looks like:

[root@centos:~ ]# cat /etc/sysconfig/network-scripts/ifcfg-eth0
# Broadcom Corporation NetLink BCM57780 Gigabit Ethernet PCIe
DEVICE=eth0
BOOTPROTO=static
DHCPCLASS=
HWADDR=00:19:99:9C:08:3A
IPADDR=192.168.0.1
NETMASK=255.255.252.0
ONBOOT=yes

This configuration is of course just for eth0 for other network card names and devices, one needs to look up for the proper file name which corresponds to the network interface visible with the ifconfig command.
For instance to list all network interfaces via ifconfig use:

[root@centos:~ ]# /sbin/ifconfig |grep -i 'Link encap'|awk '{ print $1 }'
eth0
eth1
lo

In this case there are only two network cards on my host.
The configuration files for the ethernet network devices eth0 and eth1 from below example are located in files /etc/sysconfig/network-scripts/ifcfg-eth{1,2}

/etc/sysconfig/network-scripts/ directory contains plenty of shell scripts related to Fedora networking.
This directory contains actually the networking boot time load up rules for fedora and CentOS hosts.

The complete list of options available which can be used in /etc/sysconfig/network-scripts/ifcfg-ethx is located in:
/usr/share/doc/initscripts-*/sysconfig.txt

, to quickly observe the documentation:

[root@centos:~ ]# less /usr/share/doc/initscripts-*/sysconfig.txt

One typical example of configuring a CentOS based host to possess a static IP address (192.168.1.5) and a gateway (192.168.1.1), which will be assigned in boot time during the /etc/init.d/network is loaded is:

[root@centos:~ ]# cat /etc/sysconfig/network-scripts/ifcfg-eth0
# Broadcom Corporation NetLink BCM57780 Gigabit Ethernet PCIe
IPV6INIT=no
BOOTPROTO=static
ONBOOT=yes
USERCTL=yes
TYPE=Ethernet
DEVICE=eth0
IPADDR=192.168.1.5
NETWORK=192.168.1.0
GATEWAY=192.168.1.1
BROADCAST=192.168.1.255
NETMASK=255.255.255.0

After some changes to the network configuration files are made, to load up the new rules a /etc/init.d/network script restart is necessery with the command:

[root@centos:~ ]# /etc/init.d/network restart

Of course one can always use /etc/rc.local script as universal way to configure network rules on a Redhat based host, however using methods like rc.local to load up, ifconfig or route rules in a Fedora would break the distribution logic and therefore is not recommended.

There is also a serious additional reason against using /etc/rc.local post init commands load up script.
If one uses rc.local to load up and configure the networing, the network will get initialized only after all the other scripts in /etc/init.d/ gets started.

Therefore using /etc/rc.local might also be DANGEROUS!, if used remotely via (ssh), supposedly it might completely fail to load the networking, if all bringing the server interfaces relies on it.

Here is an example, imagine that some of the script set in to load up during a CentOS boot up hangs and does continue to load forever (for example after some crucial software upate), as a consequence the /etc/rc.local script will never get executed as it only starts up after all the rest init scripts had succesfully completed execution.

A network eth1 interface configuration for a Fedora host which has to fetch it’s network settings automatically via DHCP is as follows:

[root@fedora:/etc/network:]# cat /etc/sysconfig/network-scripts/ifcfg-eth1
# Intel Corporation 82557/8/9 [Ethernet Pro 100]DEVICE=eth1
BOOTPROTO=dhcp
HWADDR=00:0A:E4:C9:7B:51
ONBOOT=yes

To sum it up I think Fedora’s /etc/sysconfig/network-scripts methodology to configure ethernet devices is a way inferior if compared to Debian.

In GNU/Debian Linux configuration of all networking is (simpler)!, everything related to networking is in one single file ( /etc/network/interfaces ), moreover getting all the thorough documentation for the network configurations options for the interfaces is available as a system wide manual (e.g. man interfaces).

Partially Debian interfaces configuration is a bit more complicated in terms of syntax if matched against Redhat’s network-scripts/ifcfg-*, lest that generally I still find Debian’s manual network configuration interface to be easier to configure networking manually vicommand line.


How to configure static IP address on Lan card eth0 on Ubuntu and Debian Linux

Wednesday, April 27th, 2011

Reading Time: 2 minutes
Does your provider provides you with a connection to the internet via a static IP address? Are you an Ubuntu or Debian user like me? Are you looking for a way to configure your eth0 Linux network card with the static ISP provided IP address? That was the scenario with me and in this article I will explain, how you can configure your Home internet access with your Ubuntu/Debian based Linux.

Both Ubuntu and Debian does have a graphic tools, which also can be used to set a static IP address to your network interface, however I find it easier to do it straight from the command line.

To configure your internet static IP via a command line, what you will need to modify is the file:

/etc/network/interfaces

In order to configure a static IP address, your provider should have equipped you with few IP addresses like let’s say the example values below:

Host IP Address: 192.168.0.5
Netmask Address: 255.255.255.0
Gateway: 192.168.0.1
Primary DNS Server: 192.168.0.1
Secondary DNS Server: 192.168.0.2

Now edit with vim, nano or mcedit /etc/network/interfaces e.g.:

root@ubuntu:~# mcedit /etc/network/interfaces

A plain /etc/network/interfaces file should contain something similar to:

auto lo
iface lo inet loopback

In order to be able to set your static IP address, Netmask, Gateway and DNS servers you will have to append in the interfaces file, the settings:

iface eth0 inet static
address 192.168.0.1
netmask 255.255.255.0
network 192.168.0.0
gateway 192.168.0.1

The eth0 sets the lan card on which the values will be assigned, address variable is the IP address assigned by your ISP, netmask is logically the netmask, network should always be configured same as the value set for address but the last ip block should be always .0 , gateway as you already know is the gateway (the ISP router).

One more thing you need to do is to configure your DNS servers by including the DNS ip addresses to /etc/resolv.conf , just issue something like:

root@ubuntu:~# echo 'nameserver 192.168.0.1' >> /etc/resolv.conf
root@ubuntu:~# echo 'nameserver 192.168.0.2' >> /etc/resolv.conf

To test that your new Linux static ip configuration is correct exec:

root@ubuntu:~# /etc/init.d/networking restart

Next use ping or (if ping is disabled by ISP), use matt’s traceroute (mtr) or a browser to test if the Linux is connected to the net.

ubuntu:~# ping google.com
...
ubuntu:~# mtr google.com

If none of the two are not able to show either ping requests flowing around, or routes to google, then something is either wrong with your internet configuration or you forgot to pay your internet bill 😉