Administration CentOS 6 Networking

Adding Additional IP Addresses CentOS

ssh to the server

# cd /etc/sysconfig/network-scripts
# 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 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

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)

Copy our primary adapter configuration file and name it to be the first virtual adapter:


# 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

Configure this virtual adapter to be a static IP, 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 – 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= (should correspond with the file name)
IPADDR=
NETMASK=

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