Posts Tagged ‘ifconfig eth0’

Create local network between virtual machines in Virtualbox VM – Add local LAN between Linux Virtual Machines

Wednesday, June 11th, 2014


I want to do test MySQL Cluster following MySQL Cluster Install Guide for that purpose, I've installed 2 version of CentOS 6.5 inside Virtualbox and I wanted to make the 2 Linux hosts reachable inside a local LAN network, I consulted some colleagues who adviced me to configure two Linux hosts to use Bridget Adapter Virtualbox networking (Network configuration in Virtualbox is done on a Virtual Machine basis from):

Devices -> Network Settings

(Attached to: Bridged Adapter)

Note!: that by default Cable Connected (tick) is not selected so when imposing changes on Network – tick should be set)
After Specifying Attached to be Bridged Adapter to make CentOS linux refresh network settings run in gnome-terminal:

[root@centos ~]# dhclient eth0

However CentOS failed to grab itself DHCP IP address.
Thus I tried to assign manually IP addresses with ifconfig, hoping that at least this would work, e.g.:

on CentOS VM 1:

/sbin/ifconfig eth0 netmask

on CentOS VM 2:

/sbin/ifconfig eth1 netmask

To test whether there is connection between the 2 VM hosts tried ping-ing (from and tested with telnet if I can access remotely SSH (protocol), from CentOS VM2 1 to CentOS VM2 and vice versa, i.e.:

[root@centos ~]# telnet 22


telnet: connect to address No route to host

Then after checking other options and already knowing by using VBox NAT network option I had access to the internet, I tried to attach a standard local IP addresses to both Linux-es as Virtual interfaces (e.g eth0:1), .e.g:

On Linux VM 1:

/sbin/ifconfig eth0:0 netmask

On Linux VM 2:

/sbin/ifconfig eth1:0 netmask

Then to test again used telnet

[root@centos ~]# telnet 22

Then I found Virtualbox has a special Internal Networking support

to choose in Attached to drop down menu. According to Internal Networking Virtualbox instructions to put two Virtual Machine hosts inside an Internal network they should be both set in Internal network with identical name.
P. S. It is explicitly stated that using Internal Network will enable access between Guest Virtual Machines OS, but hosts will not have access to the Internet (which in my case doesn't really mattered as I needed the two Linux VMs just as a testbed)


I tried this option but it doesn't work for me for some reason, after some time of research online on how to create local LAN network between 2 Virtual Machines luckily I decided to test all available Virtualbox Networking choices and noticed Host-only adapter.

Selecting Host-only Adapter and using terminal to re-fetch IP address over dhcp:


On CentOS VM1

dhclient eht0

On CentOS VM2

dhclient eth1

assigned me two adjoining IPs – ( and

Connection between the 2 IPs and on TCP and UDP and ICMP protocol works, now all left is to install MySQL cluster on both nodes.


Boost local network performance (Increase network thoroughput) by enabling Jumbo Frames on GNU / Linux

Saturday, March 10th, 2012

Jumbo Frames boost local network performance in GNU / Linux

So what is Jumbo Frames? and why, when and how it can increase the network thoroughput on Linux?

Jumbo Frames are Ethernet frames with more than 1500 bytes of payload. They can carry up to 9000 bytes of payload. Many Gigabit switches and network cards supports them.
Jumbo frames is a networking standard for many educational networks like AARNET. Unfortunately most commercial ISPs doesn't support them and therefore enabling Jumbo frames will rarely increase bandwidth thoroughput for information transfers over the internet.
Hopefully in the years to come with the constant increase of bandwidths and betterment of connectivity, jumbo frames package transfers will be supported by most ISPs as well.
Jumbo frames network support is just great for is small local – home networks and company / corporation office intranets.

Thus enabling Jumbo Frame is absolutely essential for "local" ethernet networks, where large file transfers occur frequently. Such networks are networks where, there is often a Video or Audio streaming with high quality like HD quality on servers running File Sharing services like Samba, local FTP sites,Webservers etc.

One other advantage of enabling jumbo frames is reduce of general server overhead and decrease in CPU load / (CPU usage), when transferring large or enormous sized files.Therefore having jumbo frames enabled on office network routers with GNU / Linux or any other *nix OS is vital.

Jumbo Frames traffic is supported in GNU / Linux kernel since version 2.6.17+ in earlier 2.4.x it was possible through external third party kernel patches.

1. Manually increase MTU to 9000 with ifconfig to enable Jumbo frames

debian:~# /sbin/ifconfig eth0 mtu 9000

The default MTU on most GNU / Linux (if not all) is 1500, to check the default set MTU with ifconfig:

linux:~# /sbin/ifconfig eth0|grep -i mtu

To take advantage of Jumbo Frames, all that has to be done is increase the default Maximum Transmission Unit from 1500 to 9000

For those who don't know MTU is the largest physical packet size that can be transferred over the network. MTU is measured by default in bytes. If a information has to be transferred over the network which exceeds the lets say 1500 MTU (bytes), it will be chopped and transferred in few packs each of 1500 size.

MTUs differ on different netework topologies. Just for info here are the few main MTUs for main network types existing today:

  • 16 MBit/Sec Token Ring – default MTU (17914)
  • 4 Mbits/Sec Token Ring – default MTU (4464)
  • FDDI – default MTU (4352)
  • Ethernet – def MTU (1500)
  • IEEE 802.3/802.2 standard – def MTU (1492)
  • X.25 (dial up etc.) – def MTU (576)
  • Jumbo Frames – def max MTU (9000)

Setting the MTU packet frames to 9000 to enable Jumbo Frames is done with:

linux:~# /sbin/ifconfig eth0 mtu 9000

If the command returns nothing, this most likely means now the server can communicate on eth0 with MTUs of each 9000 and therefore the network thoroughput will be better. In other case, if the network card driver or card is not a gigabit one the cmd will return error:

SIOCSIFMTU: Invalid argument

2. Enabling Jumbo Frames on Debian / Ubuntu etc. "the Debian way"

a.) Jumbo Frames on ethernet interfaces with static IP address assigned Edit /etc/network/interfaces and you should have for each of the interfaces you would like to set the Jumbo Frames, records similar to:

Raising the MTU to 9000 if for one time can be done again manually with ifconfig

debian:~# /sbin/ifconfig eth0 mtu 9000

iface eth0 inet static
mtu 9000

For each of the interfaces (eth1, eth2 etc.), add a chunk similar to one above changing the changing the IPs, Gateway and Netmask.

If the server is with two gigabit cards (eth0, eth1) supporting Jumbo frames add to /etc/network/interfaces :

iface eth0 inet static
mtu 9000

iface eth1 inet static
mtu 9000

b.) Jumbo Frames on ethernet interfaces with dynamic IP obtained via DHCP

Again in /etc/network/interfaces put:

auto eth0
iface eth0 inet dhcp
post-up /sbin/ifconfig eth0 mtu 9000

3. Setting Jumbo Frames on Fedora / CentOS / RHEL "the Redhat way"

Enabling jumbo frames on all Gigabit lan interfaces (eth0, eth1, eth2 …) in Fedora / CentOS / RHEL is done through files:

  • /etc/sysconfig/network-script/ifcfg-eth0
  • /etc/sysconfig/network-script/ifcfg-eth1

etc. …
append in each one at the end of the respective config:


[root@fedora ~]# echo 'MTU=9000' >> /etc/sysconfig/network-scripts/ifcfg-eth

a quick way to set Maximum Transmission Unit to 9000 for all network interfaces on on Redhat based distros is by executing the following loop:

[root@centos ~]# for i in $(echo /etc/sysconfig/network-scripts/ifcfg-eth*); do \echo 'MTU=9000' >> $i

P.S.: Be sure that all your interfaces are supporting MTU=9000, otherwise increase while the MTU setting is set will return SIOCSIFMTU: Invalid argument err.
The above loop is to be used only, in case you have a group of identical machines with Lan Cards supporting Gigabit networks and loaded kernel drivers supporting MTU up to 9000.

Some Intel and Realtek Gigabit cards supports only a maximum MTU of 7000, 7500 etc., so if you own a card like this check what is the max MTU the card supports and set it in the lan device configuration.
If increasing the MTU is done on remote server through SSH connection, be extremely cautious as restarting the network might leave your server inaccessible.

To check if each of the server interfaces are "Gigabit ready":

[root@centos ~]# /sbin/ethtool eth0|grep -i 1000BaseT
1000baseT/Half 1000baseT/Full
1000baseT/Half 1000baseT/Full

If you're 100% sure there will be no troubles with enabling MTU > 1500, initiate a network reload:

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

4. Enable Jumbo Frames on Slackware Linux

To list the ethernet devices and check they are Gigabit ones issue:

bash-4.1# lspci | grep [Ee]ther
0c:00.0 Ethernet controller: D-Link System Inc Gigabit Ethernet Adapter (rev 11)
0c:01.0 Ethernet controller: D-Link System Inc Gigabit Ethernet Adapter (rev 11)

Setting up jumbo frames on Slackware Linux has two ways; the slackware way and the "universal" Linux way:

a.) the Slackware way

On Slackware Linux, all kind of network configurations are done in /etc/rc.d/rc.inet1.conf

Usual config for eth0 and eth1 interfaces looks like so:

# Config information for eth0:
# Config information for eth1:

To raise the MTU to 9000, the variables MTU[0]="9000" and MTU[1]="9000" has to be included after each interface config block, e.g.:

# Config information for eth0:
# Config information for eth1:

bash-4.1# /etc/rc.d/rc.inet1 restart

b.) The "Universal" Linux way

This way is working on most if not all Linux distributions.
Insert in /etc/rc.local:

/sbin/ifconfig eth0 mtu 9000 up
/sbin/ifconfig eth1 mtu 9000 up

5. Check if Jumbo Frames are properly enabled

There are at least two ways to display the MTU settings for eths.

a.) Using grepping the MTU from ifconfig

linux:~# /sbin/ifconfig eth0|grep -i mtu
linux:~# /sbin/ifconfig eth1|grep -i mtu

b.) Using ip command from iproute2 package to get MTU

linux:~# ip route get
local dev lo src
cache mtu 9000 advmss 1460 hoplimit 64

linux:~# ip route show dev wlan0 proto kernel scope link src
default via

You see MTU is now set to 9000, so the two server lans, are now able to communicate with increased network thoroughput.
Enjoy the accelerated network transfers 😉


How to add a range of virtual IPs to a CentOS and Fedora Linux server

Monday, July 18th, 2011

Recently I had the task to add a range of few IP addresses to as a virtual interface IPs.

The normal way to do that is of course using the all well known ifconfig eth0:0, ifconfig eth0:1 or using a tiny shell script which does it and set it up to run through /etc/rc.local .

However the Redhat guys could omit all this mambo jambo and do it The Redhat way TM 😉 by using a standard method documented in CentOS and RHEL documentation.
Here is how:

# go to network-script directory[root@centos ~]# cd /etc/sysconfig/network-scripts
# create ifcfg-eth0-range (if virtual ips are to be assigned on eth0 lan interface[root@centos network-scripts]# touch ifcfg-eth0-range

Now inside ifcfg-eth0-range, open up with a text editor or use the echo command to put inside:


Now save the /etc/sysconfig/network-scripts/ifcfg-eth0-range file and finally restart centos networking via the network script:

[root@centos network-scripts]# service network restart

That’s all now after the network gets reinitialized all the IPs starting with and ending in< will get assigned as virtual IPs for eth0 interface
Cheers 😉

Universal way to configure a static IP address on ethernet lan (eth0) interface in Linux

Friday, April 29th, 2011

One of the most precious commands I ever learned to use in Linux is ifconfig and route .

They have saved my life in configuring the static IP based internet of numerous Desktop Linux computers & notebooks.

Though the usage is very much known by most of the people who are into Linux, I believe it’s likely that the newer people who entered the world of Linux or some Unix system administrators are still lacking the knowledge on how to manually configure their eth0 lan card, thus I thought it might be handy for someone to share it, I know that for most unix users & admins especially the advanced ones this post might be funny, so if you’re an advanced administrator just skip the post and don’t laught at it 😉

Now the universal commands (works on each and every Linux host) to configure manually static IP internet connection on Linux are:

linux:~# /sbin/ifconfig eth0 netmask
linux:~# /sbin/route add default gw
linux:~# echo 'nameserver' >> /etc/resolv.conf

I’ve used this simple commands on thousands ot Linux hosts and it’s still handy 🙂

In above example is the static IP address provided by the ISP, netmask is the netmask and the second /sbin/route add default gw would set the default gateway to the example ip

The third final line would add up a resolver nameserver the Linux host would use.

Cheers 😉

Howto Change MAC address in Linux and Windows 2000, XP and Vista (Mac Spoofing :)

Sunday, September 20th, 2009

MAC stands for (Media Access Control) and stands for the computer physical address in LAN networks.
Ethernet MAC is a six byte number, usually expressed as a twelve digit hexadecimal number.
IPs are translated to Mac via a protocol called ARP (Address Resolution Protocol).
Let’s say Computer with IP wants to send information to another system on the LAN with anIP of will first send broadcast to all stations on the LAN asking who has the address of
Then the box possessing will respond to with it’s MAC address which would be temporary stored
in′s ARP’s table in order to make recognize later on.

Host 1 ( Hello everyone on the LAN (FF:FF:FF:FF:FF:FF), who has the IP My MAC is DE:AB:BE:EF:FF:FE so you can respond back to me.Host 2 ( Hello DE:AB:BE:EF:FF:FE, I have IP and my MAC address is 1C:43:B6:F8:9B:1E so you can send your IP packets to me.
There are a plenty of reasons that might force to wish for changing your mac. Though I’ll mention only one
1. To get across MAC filtering set on a router. Or in other words to bee able to access your internet withall your computers at home (don’t try them simultaneously!). For example recently a cousin of mine bought a secondnotebook for her daughter.
They desired to be able to access the internet with both the PCs. I contacted the ISPwith a request to add me a second MAC address, just to find that this wasn’t possible with this exact ISP.
Their computer ran dual boot install of a GNU/Linux system as well as Windows Vista, thus I needed to change their existing MACaddress in both Windows and Linux
Here is how I achieved that:
1. In Linux
Really simple:/sbin/ifconfig eth0 hw ether 00:00:00:00:00:00 (substitute here with your desired MAC)/sbin/ifconfig eth0 up
2. On BSD
/sbin/ifconfig xl0 link 00:00:00:AA:AA:AB (subst with MAC here), xl0 is your interface name/sbin/ifconfig xl0 up
3. In Windows XP
There are a couple of ways to go in Windows. The hardest way is to use regedit and to look and substitute some obscure values.
Another a bit easier way is to use either MacMakeUp , Smac or EtherChange
The classic way to change Mac in Windows XP is:
Go to Start->Settings->Control Panel and double click on Network and Dial-up Connectionsa) Right click on the NIC you want to change the MAC address and click on properties.b) Under “General” tab, click on the “Configure” buttonc) Click on “Advanced” tabd) Under “Property section”, you should see an item called “Network Address” or “Locally Administered Address”, click on it.e) On the right side, under “Value”, type in the New MAC address you want to assign to your NIC. Usually this value is entered without the “-” between the MAC address numbers.f) Goto command prompt and type in “ipconfig /all” or “net config rdr” to verify the changes are applied.
4. In Windows Vista
Go to Control Panel -> Network Connections -> Properties (on Connection using …) Configure -> Advanced -> Network Address (Then type your MAC Here)
All the credits for this post go to the article Changing Your MAC Address In Window XP/Vista, Linux And Mac OS X which explains what you read above even more thoroughly.
Most of the information here is originally found in the above article.END—–