The Transmission Control Protocol/Internet Protocol (TCP/IP) is combination of different protocols at various layers.TCP/IP is the basic communication language or protocol of the Internet and private networks either an intranet or an extranet. The TCP/IP suite has many design weaknesses so far as security and privacy are concerned. Some of these are protocol design weaknesses, where as rest are defects in the software that implements the protocols. In this paper, I focused mainly on protocol level issues, rather than implementation flaws. In this paper, we discuss about the security issues related to the some of the protocols in the TCP/IP suite.