CHAPTER 7: TCP/IP and Routing 346 identifiers of a number of private hosts to be multiplexed into the transport identifiers of a single global IP address. PAT allows numerous hosts from the internal network to share a single external network IP address. The advan- tage of this type of translation is that only one global IP address is needed, whereas with NAT, each internal host must translate to a unique external IP address. PAT can be particularly useful for locations or users connected via cable modem, digital subscriber line (DSL), or other similar arrangement wherein they are provided a single global, public IP address. In such sce- narios, all inside addresses are translated to this single address. SUMMARY OF EXAM OBJECTIVES Understanding TCP/IP from the ground up is required to effectively manage a network whether LAN or WAN. TCP/IP is a suite of protocols originally developed by the Department of Defense in a project called the Advanced Research Projects Agency (DARPA). The first WAN implemented using these protocols was called the Advanced Research Projects Agency Network (ARPANET). It was during this time that TCP/IP was designed and developed as a standardized way for computers to communicate across a network. From the DARPA experiment came the understanding that networking would become increasingly common – and increasingly complex. The OSI model was developed, based on the DARPA model, and approved by OSI subcommittee of the International Organization for Standardization (ISO). The OSI model defined seven layers for standard, reliable network commu- nications: physical, data link, network, transport, session, presentation, and application. The acronym commonly used to remember this is (in reverse order): All People Seem To Need Data Processing. The OSI model was cov- ered in depth in Chapter 5. It will, however, continue to be used through the rest of the text. As you can see, the use of it becomes very important when discussing network protocols, the heart of this chapter’s content. For the Network exam, make certain that you memorize the OSI model and the placement of TCP/IP within it. The TCP/IP suite provides the functionality specified in the OSI model using the four related layers of the DoD model: network interface, inter- net, host-to-host, and application. This is because it’s hard to map TCP/ IP to the OSI model, also discussed in the previous chapter. The network Exam Warning NAT hides the local internal IP addresses from external Internet users, which provides a layer of security to your network. Summary of Exam Objectives 347 interface maps to the physical and data link layers; the Internet Layer maps to the OSI’s network layer; the host-to-host layer maps to the transport layer; and DoD’s application layer maps to the session, presentation, and application layers of the OSI model. Some of the more commonly known application layer protocols are FTP, HTTP, POP3, WINS, DNS, and DHCP. Within these layers are protocols that are covered in this chapter, all of which you must remember for the exam. At the Internet layer is the IP used for addressing data for delivery across a network. Understanding IP addressing is a fundamental skill needed both on the job and for this exam. IP addresses are 32-bit addresses represented in dotted decimal format (w.x.y.z). The 32 bits contain both a network and host ID. To understand IP addressing, you must first understand how to convert the dotted decimal numbers into binary and back to decimal. To send data to the correct location, the IP address in the packet is compared, using bitwise ANDing, to the subnet mask. If the result is the local network address, the packet stays on the local network. If ANDing indicates that the network address is external to the local network, the packet is sent to the defined default gateway for forwarding. Network addresses were originally designed in a class-based system. Class A networks use the first octet (w) and have an address range of 1.x.y.z to 126.x.y.z. Class B networks use the first two octets for the network ID and have an address range of 128.0.y.z to 191.255.y.z. Class C networks use the first three octets for the network ID and have an address range of 192.0.0.z to 223.255.255.z. Each class of network, when undivided, uses a default sub- net mask, which identifies which bits of the IP address represent the network ID. The default subnet masks are: Class A, 255.0.0.0; Class B, 255.255.0.0; Class C, 255.255.255.0. Classful networks can be subdivided for greater efficiency by reducing the number of hosts per segment, thus reducing network traffic. Sub- netting requires the subdividing of the class-based network IDs using custom subnet masks. These are developed by using bits from the host address space. The number of subnets that can be created from the net- work ID depends on the number of bits taken from the host address space. There is an inverse relationship between the number of subnets and the number of hosts per subnet. Typically, organizations choose to have a maximum of 256 devices per subnet for the most efficient use of network bandwidth. Packets destined for networks that are not local are forwarded using gateways or routers. IP routing involves resolving the hostname or NetBIOS name to an IP address and resolving the IP address to a MAC address. NetBIOS name resolution uses four different node types to resolve names to CHAPTER 7: TCP/IP and Routing 348 IP addresses: broadcast (B-node), peer-to-peer (P-node), mixed (M-node), and hybrid (H-node). Names can also be resolved by using a host file or through the DNS. Names must be resolved to IP addresses. The Address Resolution Protocol (ARP) is used to resolve the IP address to the Media Access Control (MAC) address that is unique to each NIC manufactured. Routing on a network can be static or dynamic, depending on whether or not Dynamic Routing Protocols are installed. Many computers designed as routers include this function, but a Windows Server 2003 computer can be set up as a router by installing two NICs, enabling the Routing and Remote Access Service (RRAS) via the registry and installing and config- uring both the RIP and OSPF Dynamic Routing Protocols. Four com- monly used routing utilities are route, ping, tracert, and pathping. Each can be run from the command line in Windows. Protocols such as APIPA and DHCP help to get systems logically addressed dynamically. Protocols such as DNS and WINS help to provide name resolution as well. In this chapter, we also covered the use of protocol ports and the impor- tance of them. You must memorize these port assignments for the Network exam. You will definitely not only see them there, but also need to use them daily on the job as a Network certified technician. Understanding the details of the TCP/IP suite is fundamental to manag- ing computers in today’s networked environment as well as to passing the Nework exam. EXAM OBJECTIVES FAST TRACK TCP/IP The TCP/IP stack does not map neatly to the OSI model, as the  OSI model was developed after TCP/IP. In the following table, Class A, B, and C addresses are listed for  quick recall. It’s imperative for the Network exam to have the following information memorized. The primary role of IP is to provide logical addresses and support  the routing of traffic to its destination. Class A 1 1.x.y.z 126.x.y.z 126 Class B 2 128.0.y.z 191.255.y.z 16,384 Class C 3 192.0.0.z 223.255.255.z 2,097152 Exam Objectives Fast Track 349 IPv4 IPv4 addresses are 32-bit addresses expressed in dotted decimal  notation of four octets, w.x.y.z. Packets are sent with a destination name or IP address included in  the packet headers. IPv6 IPv6 addresses are 128-bit addresses expressed as AAAA:AAAA:  AAAA:AAAA:AAAA:AAAA:AAAA:AAAA. IPv6 addresses are 128-bit identifiers for interfaces and sets of  interfaces, not nodes. Three general types of addresses exist within IPv6: unicast, anycast,  and multicast. Understanding IP Addressing IP addresses contain the network address space followed by the host  address space. Originally, IP addresses were assigned four classes: A, B, C, and D.  Class E is considered experimental and is not supported in Windows Server 2003. Remember that 127.0.0.0 is reserved for loopback addresses. Dotted decimal notation can be converted to its binary equivalent  by using weighted binary bits notated with 2 n where n is the num- ber of bits. Public IP addresses are IP addresses that fall in a range other than  those designated as private. Public IP addressing is addressing assigned to you for use on the public Internet. Two such organiza- tions were created to manage the use of such addressing: IANA and the ICANN. Understanding Subnetting The default subnet masks for Class A, B, C, and D are, respectively,  255.0.0.0, 255.255.0.0, 255.255.255.0, and 255.255.255.255. CHAPTER 7: TCP/IP and Routing 350 Custom subnet masks (also called variable length subnet masks)  are used when a network is divided, by using bits from the host address space that are added to the network address space. A logical bitwise AND comparison is used to compare the bits of  the IP address to the subnet mask. The result of the comparison is the network ID. Default subnet masks are defined for undivided Class A, B, C, and  D networks. Strategies to Conserve Addresses The growth of networking required a new solution. CIDR was  implemented as a classless addressing schema. CIDR reduces route table sizes as well as IP address waste. Instead  of full Class A, B, or C addresses, organizations can be allocated subnet blocks. VLSMs conserve IP addresses by tailoring the mask to each subnet.  Subnet masks are appropriated to meet the amount of addresses required. RFC 1918 – Private Network Addresses RFC1918 conserves globally unique IP addresses by providing three  blocks of addresses that are never officially allocated to any organi- zation. Those address ranges are as follows: Static IP addressing is done manually. It is hard to manage and  adjust, as you have to visit every system that has an address if you want to change the addressing scheme from one range of IP addresses to another, such as from 192.168.1.0 to 10.1.1.0. Address Block Classful Equivalent Prefix Length Number of Addresses 10.0.0.0–10.255.255.255 1 Class A 256 Class B 65,536 Class C /8 16,777,216 172.16.0.0–172.31.255.255 16 Class B 4,096 Class C /12 1,048,576 192.168.0.0–192.168.255.255 1 Class B 256 Class C /16 65,536 Exam Objectives Fast Track 351 Dynamic IP addressing is done automatically. This can be done  with DHCP or with APIPA. Self-assigned (APIPA [Automatic Private Internet Protocol Address- ing]) is a Microsoft Windows-based service (but available to any OS) that will allow for a Windows 98, ME, 2000, 2003, or XP system to assign itself an address from a designated private block rang- ing from 169.254.0.1 to 169.254.255.254, with a subnet mask of 255.255.0.0. Name resolution occurs using WINS or an lmhosts file (for Net- BIOS names) or DNS or a hosts file (for hostnames). Multicast, Broadcast, and Unicast Multicasting benefits are not limited to video/audio needs. Multicast  can be used to push updates to multiple hosts simultaneously, thus reducing the effort and time involved in doing one update at a time. Multicast addresses cannot be used as source addresses for any traffic. Multicast addresses are not  assigned to a device; rather, a device proceeds to listen for and receive traffic destined to a multicast group that it has joined by some process. Unicast is the transmission of data from one host to another, one  host at a time. Broadcasts can consume a significant amount of bandwidth; con- nections are based on a one-to-all method transmission. Understanding Basic IP Routing MAC addresses are 16-byte addresses expressed as  AA:AA:AA:AA:AA:AA. Routers can use static or dynamic routing. Static routing requires  new entries to be entered manually. Dynamic routing updates route information automatically. Dynamic routing means that a protocol like RIP or OSPF is used to  handle the routing instead of you statically have to configure each routers RIT. Link State Routing Protocols include OSPF and IS-IS. CHAPTER 7: TCP/IP and Routing 352 Distance Vector Routing Protocols include RIP, RIPv2, and BGP. Hybrid Routing Protocols include the Cisco proprietary EIGRP. IGP or Interior Gateway Protocols are designed for routing use  inside of a LAN. Static routing is administered by the network technician and does  not change. Dynamic routing is able to change as conditions warrant it. This  requires the use of a routing protocol. Convergence is the state when all routers are making decisions  based on the same network information. IP address to MAC address resolution occurs through ARP request  and reply messages. The reverse, MAC to IP resolution, uses RARP requests and replies. EXAM OBJECTIVES FREQUENTLY ASKED QUESTIONS I’m still a bit rusty with binary, dotted decimal, conversions, and so Q: forth. Can’t I use a program to do all this for me when I’m working on my corporate network? Yes, there are programs available that will do all the conversions A: and subnet calculations you need. However, those won’t be avail- able on the exam and they may not always be available to you on the job. Keep working through the conversions and examples in this chapter until you feel confident of your understanding and application of the material. Will I be given a table of Class A, B, and C networks, subnets and Q: subnet masks for the exam? No, you will not. You’ll need to memorize the definitions of Class A: A, B, and C networks, along with their associated default subnet masks. You will not need to calculate complex subnet masks for the Network exam, but you will need to understand the concepts behind it, as well as logical addressing of network protocols in general. Will I be expected to know about private addressing for the Q: Network exam? Yes, you will. You need to master the ranges listed. They are A: Self Test 353 10.0.0.0 to 10.255.255.255, 172.16.0.0 to 172.31.255.255, and 192.168.0.0 to 192.168.255.255. You will be expected to know these, not only for the exam, but also on the job. Will I need to know how to configure an e-mail server for this Q: exam? With all this talk about e-mail protocols such as SMTP, what do I need to focus my studies on? No, you will not need to know how to configure anything for the A: exam. The exam is more straightforward, asking you very simple paths to get to places in Windows that are very common. Other than that, all other questioning is pretty straightforward. SELF TEST You are a network administrator and you have 1,000 client 1. computer that you need to set up with IP addressing. What protocol would you use to set up these client computers with an IP address, subnet mask, default gateway, and preferred DNS server? A. DHCP B. APIPA C. BOOTP D. TFTP You have been given an IP address in binary form. The address 2. you have been given is 11000000.00000000.00000000.00000001. What is this IP address in decimal form? A. 127.0.0.1 B. 191.0.0.1 C. 137.0.0.1 D. 192.0.0.1 You have been asked by your colleague Bobbi about classfull 3. IP addresses. Which of the following is NOT a normal IP address class? A. CLASS A B. CLASS D C. CLASS F D. CLASS C CHAPTER 7: TCP/IP and Routing 354 You have been asked to explain what a certain IP address is 4. used for. The IP address is 224.0.0.1. What are addresses in the 224.0.0.0 range used for? A. SNMP B. HTTP C. POP3 D. Multicasting You are having a conversation with another networking profes-5. sional and the subject of protocols comes up. You are asked which of the following are IGP routing protocols? A. OSPF B. BGP C. IS-IS D. RIP You have been asked to lay out a new small office network. Which 6. of the following IP address ranges could you use because they are Private address ranges? A. 11.0.0.0 to 11.255.255.255.255 B. 137.1.0.0 to 137.1.255.255 C. 191.4.0.0 to 191.4.255.255 D. 192.168.5.0 to 192.168.5.255 You have a user who cannot get connected to the Internet. You 7. have the user run IPCONFIG/ALL and he reads you the IP address of 169.254.1.3. What is wrong with this system? A. System has a static IP address B. System has an APIPA address C. System has a bad address D. System has a classless address A user has been given an IP address of 192.168.1.1 with a subnet 8. mask of 255.255.255.0. How would you express the subnet mask for this address using CIDR notation? A. /24 B. /8 C. /16 D. /22 Self Test 355 A user has been given an address of fe80::9c5f:9695:f235:0051. 9. What kind of address has she been given? A. IPv4 address B. IPv6 address C. MAC address D. GUID You have a network with several thousand users. You do not want 10. to manually configure every user’s computer. What protocol would you use to automatically configure their IP addresses? A. SNMP B. APIPA C. DHCP D. TFTP You have been asked to implement routing on a simple corpo-11. rate local area network. All connections will be the same speed. Which routing protocol would you use for a simple network like this? A. OSPF B. RIP C. BGP D. IS-IS You have been asked to connect routing for your corporate network 12. to your ISP. Which routing protocol would you use for an exterior connection? A. OSPF B. RIP C. BGP D. EIGRP You have a main corporate location and several branch locations. 13. All locations access the Internet through corporate. What type of routing would you enable for this approach? A. None B. Dynamic C. Static D. Classless . you use because they are Private address ranges? A. 11.0.0.0 to 11.255.255.255.255 B. 137. 1.0.0 to 137. 1.255.255 C. 191.4.0.0 to 191.4.255.255 D. 192.168.5.0 to 192.168.5.255 You have a user. manage a network whether LAN or WAN. TCP/IP is a suite of protocols originally developed by the Department of Defense in a project called the Advanced Research Projects Agency (DARPA). The first. 11000000.00000000.00000000.00000001. What is this IP address in decimal form? A. 127.0.0.1 B. 191.0.0.1 C. 137. 0.0.1 D. 192.0.0.1 You have been asked by your colleague Bobbi about classfull 3. IP addresses.