The TCP/IP protocol suite is the foundation of Internet and is ubiquitous in almost all networks worldwide. It was written as a robust protocol, which is able to communicate despite node failures. The design parameters of TCP did not weigh security as important and placed an implicit trust on nodes. The result was a protocol which was reliable and robust, but contained myriad inherent security flaws, open to be exploited by a malicious entity as was amply demonstrated by Morris worm [1]. The 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, whereas rest is defects in the software that implements the protocols. In this paper, we focused mainly on protocol level issues, rather than implementation flaws and discuss about the security issues related to the some of the protocols in the TCP/IP suite.