Adding Range of IPs to a Redhat/CENTOS Linux server
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make ifcfg-eth0-range0 file in /etc/sysconfig/network-scripts/
[root@localhost network-scripts]# more ifcfg-eth0-range0

ONBOOT=yes
IPADDR_START=10.10.10.101
IPADDR_END=10.10.10.121
NETMASK=255.255.255.0
CLONENUM_START=0

If you have another range of ips:
make another file called; ifcfg-eth0-range1
then ifcfg-eth0-range2, etc..

then do: CLONENUM_START=#
where # = the number of ips already added to the box + 1.
example, if you have 10 ips in range0, then colonenum =11

ie, the next set of alias ips should start at that range (eth0:11)

Then run : service network restart

Windows 2000/XP/2003:
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1)Click on Start, Settings, Control-Panel, Network Connections
2) Right click on Local Area Network or Which ever nic is active and choose Properties
3)Click on Internet Protocol (TCP/IP), then click Properties
4) Change your ip address info for the Primary ip there.

To add more ips other then primary ip, click Advanced at the bottom right.
5) Under IP Settings Tab, Ip addresses, Click Add
6) Add in the new IP Address + Netmask, then click Add
7) Under Default Gateway, Click Add
8) Enter the gateway information for that new ip and click Add.
9) Hit okay, then okay, then okay!
10) All done, ips are added. You do not need to reboot for changes to take affect.