Subnet addresses are present only if the network administrator has decided that the network should be divided into subnetworks. The first part designates the network address, the second part (if present) designates the subnet address, and the final part designates the host address. An IP address is 32 bits in length, divided into either two or three parts.
Tcp packet types series#
One bit specifies whether the packet can be fragmented the second bit specifies whether the packet is the last fragment in a series of fragmented packets. Flags-Consists of 3 bits, of which the low-order 2 bits control fragmentation.This field is used to help piece together datagram fragments.
Identification-Consists of an integer identifying this datagram.Total Length-Specifies the length of the entire IP packet, including data and header, in bytes.The last 2 bits, or CU, are ignored by DiffServ-compliant nodes. The first 6 bits are used for the DSCP codepoint, which is used to differentiate traffic. RFC 2474 describes a method by which the TOS field is replaced by a DS field that is used to provide differentiated services (DiffServ) on networks. Today this field is used primarily to provide quality of service (QoS) capabilities to TCP/IP for applications requiring predictable bandwidth or delay. Datagrams can be assigned various levels of importance using this field. Type-of-Service-Specifies how a particular upper-layer protocol would like the current datagram to be handled.IP Header Length (IHL)-Indicates the datagram header length in 32-bit words.Version-Indicates the version of this IP datagram.The fields of the IP packet are as follows: This is why TCP/IP doesn't generally fit all that well into the seven-layer OSI model.įigure 7-1 The Internet Protocol Suite and the OSI Reference Model DARPA used a four-layer model instead, which the OSI later expanded to seven layers. Figure 7-1 shows some of the most important Internet protocols and their relationships to the OSI reference model.Īs an interesting side note, the seven-layer model actually came about after TCP/IP. The Internet suite includes not only lower-layer specifications (such as TCP and IP), but also specifications for such common applications as e-mail, terminal emulation, and file transfer. They are equally well suited for local-area network (LAN) and wide-area network (WAN) communications. Internet protocols can be used to communicate across any set of interconnected networks. Although a lot of work has gone into developing IPv6, no wide-scale deployment has occurred because of this, IPv6 has been excluded from this text. In 1995, a new standard, RFC 1883-which addressed some of the problems with IPv4, including address space limitations-was proposed. The most widespread implementation of TCP/IP is IPv4 (or IP version 4). The result of this development effort, completed in the late 1970s, was the Internet Protocol suite, of which the Transmission Control Protocol (TCP) and the Internet Protocol (IP) are the two best-known protocols. With the goal of heterogeneous connectivity in mind, DARPA funded research by Stanford University and Bolt, Beranek, and Newman (BBN) to create a series of communication protocols. DARPA and other government organizations understood the potential of packet-switched technology and were just beginning to face the problem that virtually all companies with networks now have-communication between dissimilar computer systems. In the mid-1970s, the Defense Advanced Research Projects Agency (DARPA) became interested in establishing a packet-switched network to provide communications between research institutions in the United States. Troubleshooting Hot Standby Router Protocol (HSRP).Troubleshooting Physical Connectivity Problems.General IP Troubleshooting Theory and Suggestions.The sections in this chapter describe common features of TCP/IP and provide solutions to some of the most common TCP/IP problems. Troubleshooting Domain Name Server Problemsīefore Calling Cisco Systems' Technical Assistance Center Troubleshooting IP Connectivity and Routing Problems Troubleshooting Physical Connectivity Problems Troubleshooting Local Connectivity Problems
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