Additional IP addresses (Host)
Setting up additional single IPv4 addresses
The IP addresses can be made temporarily available in two different ways:
ifconfig eth0:1 192.0.2.10 netmask 255.255.255.255
or
ip addr add 192.0.2.10/32 dev eth0
CentOS
A permanent configuration is only possible by default via alias interfaces (eth0:1, eth0:2 etc.). A file needs to be created for each IP address:
/etc/sysconfig/network-scripts/ifcfg-eth0:1 /etc/sysconfig/network-scripts/ifcfg-eth0:2
These files must include the following information:
DEVICE=eth0:1 BOOTPROTO=none ONBOOT=yes IPADDR=<IP Address> NETMASK=255.255.255.255
Finally, a "service network restart" needs to be initiated or the server needs to be restarted ("reboot").
Setting up additional IPv4 subnets
Subnets are routed on the main IP of a server. In general the first (Network IP) and the last (Broadcast IP) cannot be used. This leaves six usable addresses for a /29 subnet.
A /29 subnet consisting of 8 IP addresses will look like this:
aaa.aaa.aaa.aaa (Network IP) bbb.bbb.bbb.bbb ccc.ccc.ccc.ccc ddd.ddd.ddd.ddd eee.eee.eee.eee fff.fff.fff.fff ggg.ggg.ggg.ggg hhh.hhh.hhh.hhh (Broadcast IP)
The IPs "b" to "g" can be configured and used as single IPs. Alternatively, a file can be created:
/etc/sysconfig/network-scripts/ifcfg-eth0-range0
IPADDR_START=<Your Network Address + 1> IPADDR_END=<Your Network Address + 6> BROADCAST=<Your Network Address + 7> CLONENUM_START=0 NETMASK=255.255.255.248
Restart the service network using "service network restart".
