Chapter 7 teaches you about some of the protocols that are in the TCP/IP suite. The objectives important to this chapter are on page 7-1:
Concepts:The Internet Protocol suite was developed before the ISO-OSI model. The graphic on page 7-2 shows how several TCP/IP protocols map to the ISO model, as well as to the Department of Defense (DoD) model. The Department of Defense was instrumental in the construction of the Internet, along with the Defense Advanced Research Projects Agency (DARPA). The DoD model is the one that was used to plan and develop the TCP/IP suite. To compare the models, consider this chart:
The four layers of the DoD model address the topics found in the ISO model. If you understand the ISO model, you already understand the DoD model. The TCP/IP suite does not address topics at the Network Access layer (DoD model). This makes it independent of any networking topology. TCP/IP is the most popular suite due to the popularity of the Internet. Major protocols in this suite include HyperText Transfer Protocol (HTTP) for the World Wide Web, Simple Mail Transfer Protocol (SMTP) for e-mail, and File Transfer Protocol (FTP) for uploading and downloading files. On page 7-4, you see a schematic diagram showing the protocols that operate at the Network layer (ISO model). Refer to the chart on page 7-2, to remember that this is the Internetwork layer of the DoD model. The IP protocol works at this layer. It provides connectionless service, addressing and packet switching. Remember: IP is connectionless. Note, also, that dynamic routing does not take place at this layer in the IP suite. Terminology from page 7-4:
EGPs are used to communicate between autonomous systems. Border Gateway Protocol is an improved version of Exterior Gateway Protocol. Page 7-6 begins a discussion of Routing Information Protocol (RIP). RIP is the Distance Vector protocol for TCP/IP. The discussion reviews what was discussed in Chapter 3. Page 7-8 reminds us that Distance Vector protocols are slow to converge and are subject to the count-to-infinity problem. Page 7-9 and 7-10 review the Split Horizon and Poison Reverse methods to counter the count-to-infinity problem. Page 7-11 describes an improvement on RIP, RIP II. Four improvements are listed:
Page 7-12 begins a review of the Link State information from Chapter 3. The Link State protocol for TCP/IP is Open Shortest Path First Protocol (OSPF). Points to remember:
Page 7-19 adds to the terminology of OSPF systems. An autonomous system (AS) can contain many routers, at least one of which will be a border with another system or the Internet. The router on this border is an Autonomous System Border Router (ASBR). Some autonomous systems are very large and complex. They need to be subdivided into areas, so the routing table do not become unusable. Routers on the border between areas are Area Border Routers (ABRs). Typically, ABRs will connect their area to a backbone area. This is a common area that all areas in an autonomous system connect through. Naturally, this area needs to have higher bandwidth. If an area is not the backbone area, it is one of two other types:
Page 7-22 compares OSPF to RIP:
Page 7-25 begins a discussion of other TCP/IP protocols. IP and ICMP are Internet Layer protocols. Internet Protocol (IP) is a connectionless protocol that supports routing, fragmentation and reassembly. (Note: if you have to decide if a protocol is connectionless (IP, IPX) or connection-oriented (TCP, SPX), it is connectionless if it starts with a vowel.) Internet Control Message Protocol (ICMP) is used to send error and control messages to Upper Layer Protocols (because they are concerned with error and flow control). Possible message topics appear on pages 7-27 and 7-28. Address Resolution Protocol (ARP) is used on IP networks to resolve an IP address (4 bytes) to a MAC address (6 bytes). You may wish to review the fact that MAC addresses are typically shown as 12-character Hexadecimal strings. One byte can be expressed as two Hex characters. Reverse Address Resolution Protocol (RARP) is the reverse of ARP: it is used to resolve a known MAC address to an unknown IP address. ARP tables are constructed by sending broadcast ARP requests to the network, and recording the responses as IP address/MAC address pairs. Page 7-33 describes Reverse Address Resolution Protocol (RARP) and BOOTP. These protocols are designed to give an IP address to a workstation on boot. They are typically used on diskless workstations, which have no medium on which to record their IP addresses. A newer protocol for assigning IP addresses is Dynamic Host Configuration Protocol (DHCP), described on page 7-34. This protocol is used with standard workstations, not because they cannot remember an IP address, but for the benefit of the administrator. Three methods for using DHCP are listed:
DHCP provides not only the IP address, but also configuration settings for the host. DHCP requests are broadcast requests. Broadcast requests are not forwarded by routers, so a DHCP server must be on the same network segment as the device making the request. To get around this problem, Novell provides relay agents. Relay agents are software that run on a router. A relay agent sees DHCP requests, forwards them to a DHCP server on another segment, and returns the DHCP response to the requester. Page 7-36 begins the discussion of Host-to-Host Layer protocols (which correspond to the Transport Layer in the ISO model). The key protocol on this layer is Transmission Control Protocol (TCP), which is connection-oriented. This is the protocol that makes the TCP/IP suite reliable. The next protocol is User Datagram Protocol (UDP). UDP operates in the Host-to-Host Layer, but it is connectionless, so it is faster than TCP. Several protocols are described that operate at the Process/Application Layer:
Page 7-46 lists three network analysis tools for TCP/IP networks:
Page 7-47 presents the final topic of the chapter: IPv6. Several features are listed:
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