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9Sep/16Off

Adding IP Addresses CentOS

You will need to be the root user and navigate to: /etc/sysconfig/network-scripts

# cd /etc/sysconfig/network-scripts

When getting a list of files in the directory you will see "ifcfg-eth0" (or eth1 if you're doing it for a different adapter)

Now adding the virtual adapters is easy. Basically if the main adapter is called "eth0" you have to call the next (virtual) adapter in a sequential order like so:

  • ifcfg-eth0 (primary adapter, physical)
  • ifcfg-eth0:1 (first virtual adapter to the physical primary adapter)
  • ifcfg-eth0:2 (second virtual adapter to the physical primary adapter)
  • and so on...

That being said, lets go ahead and copy our primary adapter configuration file and name it to be the first virtual adapter for the physical primary:

# cp ifcfg-eth0 ifcfg-eth0:1
# ls -l | grep ifcfg-eth
-rw-r--r-- 1 root root   119 Jan 11 19:16 ifcfg-eth0
-rw-r--r-- 1 root root   119 Feb 24 08:53 ifcfg-eth0:1
-rw-r--r-- 1 root root   119 Jan  3 08:45 ifcfg-eth0.bak
-rw-r--r-- 1 root root   119 Feb 24 04:34 ifcfg-eth1
-rw-r--r-- 1 root root   128 Jan 19 18:20 ifcfg-eth1.bak

Now, we have to configure this virtual adapter to be: a static IP (of course), no hardware address (MAC), configure netmask and of course rename the device.

# vim ifcfg-eth0:1
DEVICE=eth0:1
BOOTPROTO=static
ONBOOT=yes
IPADDR=10.1.1.2
NETMASK=255.255.255.0

There is no need to specify a MAC address as it is a virtual adapter and there is also no need to specify a default gateway as it is already routed through the primary adapter. Basically there are only four things that you will need to change:

  • File name for the adapter itself
  • DEVICE=<device name> (should correspond with the file name)
  • IPADDR=<ip address>
  • NETMASK=<netmask>

Afterwards, just restart the networking service:

# service network restart

That's it; lets check ifconfig to make sure the virtual adapter is there and working:

# ifconfig eth0:1
eth0:1    Link encap:Ethernet  HWaddr 08:00:27:ED:05:B7
inet addr:10.1.1.2  Bcast:10.1.1.255  Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1

# ping 10.1.1.2
PING 10.1.1.2 (10.1.1.2) 56(84) bytes of data.
64 bytes from 10.1.1.2: icmp_seq=1 ttl=64 time=0.073 ms
64 bytes from 10.1.1.2: icmp_seq=2 ttl=64 time=0.042 ms
64 bytes from 10.1.1.2: icmp_seq=3 ttl=64 time=0.029 ms
64 bytes from 10.1.1.2: icmp_seq=4 ttl=64 time=0.029 ms
--- 10.1.1.2 ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 2999ms
rtt min/avg/max/mdev = 0.029/0.043/0.073/0.018 ms

Per Steven's comment: a second note. If you're not sure if you've done it right and you do not want to restart the entire network server, you can use the following:

# ifup eth0:1
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17Feb/12Off

How to assign dedicated IP to subdomain

You might want to assign dedicated IP to your subdomain for some reason such as apply SSL to your subdomain.

If you are using cPanel and wish to set dedicated IP to your subdomain, you will find no else where to do that.

However, this could still be able to fix as this article.

Scenario,
- You have domain domain.com and subdomain blog.domain.com.
- You wish to set dedicated IP for blog.domain.com which originally 100.100.100.100 and result as blog.domain.com resolve to 10.0.0.1.

1. Log into SSH, go to the folder of /var/cpanel/userdata,
cd /var/cpanel/userdata
2. Select the cPanel username folder such as mickgenie.
cd /var/cpanel/userdata/mickgenie
3. You will now see the following file,
domain.com
domain.com.cache
blog.domain.com
blog.domain.com.cache
main
main.cache

4. Open the file named blog.domain.com,
vi blog.domain.com
5. You should find the content as below,
ip: 100.100.100.100
6. Change it to detail as below,
ip: 10.0.0.1
7. Now, you have done but you will need to rebuilt the Apache,
/usr/local/cpanel/scripts/rebuildhttpdconf
8. Restart the Apache services,
/usr/local/cpanel/scripts/restartsrv_apache

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