STATE COMMITTEE FOR COMMUNICATIONS AND INFORMATION OF UKRAINE

Odessa National Academy of Telecommunications after A.S. Popov

Department of Communication Networks

Laboratory work on course tis

“Studying and setting of ports of TCP/IP stack “

Odessa, 2004

Subject: Studying and control of ports of a stack of the TCP/IP protocols

Work purpose: 1. Research of the basic principles of work of a stack of the TCP/IP protocols.

2. Getting of practical skills on setting of the main ports of the TCP/IP stack protocol by organization of the IP – firewall using built-in means of Windows 2000 and XP.

2.Key positions

Transmission Control Protocol/Internet Protocol (TCP/IP) is an industrial standard of a stack of the protocols, developed for global networks. The protocol is rules of work of the software. Are distinguished :

• connection oriented protocols - establish connection between applications before the beginning of data transmission;

• connection non-oriented protocols - don't establish direct network connection;

• secure protocols - guarantee delivery of data;

• unsecure protocols - don't guarantee delivery of data;

• stream protocols - consider data as a consecutive continuous stream;

• datagram protocols - consider data as independent single blocks.

As the term "TCP/IP" usually is understood everything that is connected with the TCP and IP protocols. This are not only protocols of TCP and IP, but also the protocols constructed on their basis, and applications.

The main task of a stack of TCP/IP is uniting in a network of packet subnets through gateways. Each network works under it’s own laws, however it is supposed that the gateway can receive a packet from other network and to deliver it to the specified address. Really, the packet from one network is transferred in other subnet through sequence of gateways which provides through routing of packets on whole network. In this case, the gateway is understood as a point of connection of networks. Thus can connect both local networks, and global networks. As a gateway can act as special devices, routers, for example, and computers which have the software which is carrying out routing of packets. Routing is a procedure of finding the transit of a packet from one network to another.

The TCP/IP standards are published in a series of the documents called Request for Comment (RFC). The RFC documents describe internal work of the Internet network. Some RFC describe network services or protocols and their realization while others-generalize application conditions. The TCP/IP standards are always published in a type of the RFC documents, but not all RFC define standards.

2.1 Structure of a stack of tcp/ip. Short characteristic of protocols

By consideration of procedures of inter-network interaction always lean on the standards developed by International Standard Organization (ISO). These standards received the name "Seven-layer model of a network exchange". In this model exchange of information can be presented in the form of a stack presented in figure 1.

Figure 1. OSI model.

T he stack of the TCP/IP protocols differs from an OSI model stack. Usually it is possible to present it in the form of the model presented on Figure 2.

Figure 2. Structure of TCP/IP stack protocols

Structure of stack of protocols TCP/IP and it’s correspondence to OSI model is represented on figure 3

Figure 3. Structure of stack of protocols TCP/IP and it’s correspondence to OSI model

The lowest (level IV) corresponds to physical and channel levels of the OSI model. This level in the TCP/IP protocols isn't regulated, but supports all popular standards of physical and channel level: for local networks it is Ethernet, Token Ring, FDDI, Fast Ethernet, for global networks - protocols of connections SLIP and PPP "point-to-point", protocols of territorial networks with switching of packets X.25, frame relay, ATM.

The following level (level III) is level of inter-network interaction which transfers packets with using of various transport technologies of local networks, territorial networks, lines of special communication, etc.

The main protocol of network layer (in terms of OSI model ) in a stack is IP protocol which was initially projected as the protocol of transfer of packets in the compound networks consisting of a large number of local networks, united using both local, and global links. Therefore the IP protocol works well in networks with difficult topology, rationally using existence in them of subsystems and economically spending capacity of low-speed communication lines. The IP protocol is the datagram protocol, it means that he doesn't guarantee delivery of packets to destination node, but it tries to make it.

All protocols connected with forming and updating of tables of routing belong to level of inter-network interaction, such as protocols of collecting of route information RIP (Routing Internet Protocol) and OSPF (Open Shortest Path First), and also the protocol of inter-network managing messages ICMP (Internet Control Message Protocol) . The last protocol is intended for exchange of information about mistakes between routers of a network and node- a source of a packet (ping). By means of special ICMP packets it is reported about impossibility of delivery of a packet, about excess of time of life or duration of assembly of a packet from fragments, about abnormal values of parameters, about change of a route of transfer and service type, about a system state, etc

The following level (level II) is called the basic. At this level works the protocol of management of transmitting TCP (Transfer Control Protocol) and the protocol of user’s datagrams UDP (User Datagram Protocol). The TCP protocol provides secure transmission of messages between remote applications with the help of formation of virtual connections. The UDP protocol provides transfer of application’s packets by datagram way, as well as IP, and carries out only link functions between the network protocol and numerous applications.

The top level (level I) is called application layer. At this level work the following protocols - the protocol of a file transfer of FTP, the protocol of emulation of the terminal-telnet, the post SMTP protocol and others.

At work with such programs at application layer as FTP or telnet, is formed a stack of protocols with the TCP module use, presented in figure 4.

Fig.4 Stack of protocols when using TCP module.

At work with the applications using the transport UDP protocol, for example, software of Network File System (NFS), another stack is used where instead of the TCP module the UDP module is used - figure 5

Fig.5 Stack of protocols when using transport protocol UDP