Question : IP Spoofing

Can one really spoof source address in an internet ? The internet address is routable and hence, if this address is changed, it couldn't be routed back to the originator. So, how does IP spoofing work ?

Thanks

Answer : IP Spoofing

http://en.wikipedia.org/wiki/IP_address_spoofing

All data packets on a network are just sequences of bits.  The sending computer determines what bits to transmit.  Normally, it sends the correct return address, but there is no guarantee of this.

As pointed out in the article, IP spoofing is usually used when the response doesn't matter (e.g., in Denial of Service (DoS) attacks) or when the response can be guessed by the sender.