What is ip address format?

Just a little caveat here, what Archangel dmitry lists here is true but should be regarded as only historical information since classed IP address assignment has not been used in over 20 years. It was replaced in 1993 by Classless Inter-Domain Routing. This was put in place to help deal with the quick depletion of available public IP addresses. In the modern day, IP addresses are assigned as needed rather than as blocks as was done when classed addressing was used.