CS 3201 Computer Networks 2014/2015 Handout: Lab 4

Transcription

1 CS 3201 Computer Networks 2014/2015 Handout: Lab 4 Lab Content: - IP Addressing - IP Ports TCP/IP Fundamentals TCP/IP Settings - TCP/IP is a protocol that requires a little bit of knowledge to configure the systems properly. When you configure TCP/IP, you are required to know the settings for the IP address, subnet mask, and default gateway. Let s start with the IP address! IP Address - The IP address is a 32-bit value that uniquely identifies the system on the network (or the Internet). An IP address looks similar in appearance to There are four decimal values in an IP address separated by periods (.). Each decimal value is made up of 8 bits (1s and 0s), and there are four decimal values, so 8 bits times 4 equals the 32-bit address. - Since each of the decimal values is made up of 8 bits (for example, the 192), we refer to each of the decimal values as an octet. There are four octets in an IP address. It is very important to understand that the four octets in an IP address are divided into two parts a network ID and a host ID. The subnet mask determines the number of bits that make up the network ID and the number of bits that make up the host ID. Let s see how this works. Subnet Mask - When looking at a subnet mask, if there is a 255 in an octet, then the corresponding octet in the IP address is part of the network ID. For example, if I had an IP address of and a subnet mask of , the first three octets would make up the network ID and the last octet would be the host ID. The network ID assigns a unique address to the network itself, while the host ID uniquely identifies the system on the network. Table 4-1 summarizes this example. The network ID (shown with an N ) is , and the host ID is the last octet with a value of 15. This means that this system is on the network and any other system on the same network will have the same network ID. - To use a different example, if I had a subnet mask of , it would mean that the first octet of the IP address is used as the network ID portion, while the last three octets are the host ID portion of the IP address. So what is the purpose of the subnet masks? Or better yet, why do we have a subnet mask that breaks the IP address into a network ID part and a host ID? - The reason is so that when a system such as , with a subnet mask of , sends a piece of data to , the sending system first needs to determine whether the target computer exists on the same network or not. It does this by comparing the network IDs (Table 4-2); if the network IDs are the same, then both systems exist on the same network and one system can send to the other without the use of a router. If the systems exist on different networks, the data will need to be passed to the router so that the router can send the data to the other network. Eng. Maha Talaat Eng. Nareeman Sabry CN Lab (4) 1

2 TCP/IP Addressing Understanding Binary - You know from the previous discussion that the IP address is a 32-bit address divided into four 8- bit blocks (called octets). The four octets are normally displayed as decimal values but also have a binary representation that looks like Notice that there are four sets of 8 bits (1 or 0), which makes up the 32 bits (8 4 sets) of an IP address. Let s take a look at how you can determine the binary representation of an octet. - To calculate the binary value of an octet with a decimal number such as 192, you need to enable, or turn on, the bits that will add up to the number of 192, - Notice that the foregoing table has bit eight and bit seven turned on to give you a value of , which equals 192. The remaining bits will take an off state, which means they are not included in the calculation. A bit that has an on state takes a 1, and an off state takes a 0. So the combination of 8 bits to make the number 192 would be Now that you know how to convert a decimal value to binary and a binary value to decimal, try out Exercise 4-2 before moving on to the section on address classes. Address Classes - Every IP address belongs to a distinct address class. The Internet community defined these classes to accommodate networks of various sizes. The class to which the IP address belongs initially determines the network ID and host ID portions of the address, along with the number of hosts that are supported on that network. The different class addresses are named class A, class B, class C, class D, and class E. This section details each class of addresses. Class A Addresses - A class A address has a default subnet mask of , which means that the first octet is the network ID and the last three octets belong to the host ID portion of the address. Each octet can contain 256 possible values (0 255), so a class A address supports 16,777,216 hosts on the network ( ). Actually, there are only 16,777,214 valid addresses to use on systems, inasmuch as there are two addresses on each IP network you are not allowed to assign to systems because they are reserved. These are the addresses with all host bits set to 0s (the network ID) and all host bits set to 1s (the broadcast address). So with a class A address, you will not be able to assign n or n (where n is your network ID) to any hosts on the network. - You can always identify a class A address, because the value of the first octet falls between the numbers 1 and 126. Actually, an address that starts with 127 is a class A address as well, but you are not allowed to use any address that starts with 127, because it is reserved for the loopback address (more on the loopback address later). For example, the IP address is a class A address because the first octet is 12, which falls in the range Class B Addresses - Class B addresses have a default subnet mask of , which means that the first two octets are the network ID and the last two octets are the host ID portion of the address. This Eng. Maha Talaat Eng. Nareeman Sabry CN Lab (4) 2

3 means that we can have 65,536 hosts ( ) on the network. Oh, but wait! Don t forget to take off the two illegal addresses, so that gives us 65,534 addresses that can be assigned to hosts on the network. - Due to the number of hosts that are supported on a class B address, you usually find that a medium-sized company has a class B address. You can identify a class B address because the first octet starts with a number that falls between 128 and 191. Class C Addresses - Class C addresses have a subnet mask of , which means that the first three octets are the network ID and the last octet is the host ID. Having only one octet as the host ID means that a class C address can support only 254 hosts (256 2) on the network. - You can identify a class C address because it has a value for the first octet that ranges between 192 and 223. For example, an IP address of is a class C address because 202 falls between 192 and 223. You also know that this system has a subnet mask of because it is a class C address. Class D Addresses - Class D addresses are used for special types of applications on the network known as multicasting applications. Multicasting applications send data to a number of systems at the same time by sending data to the multicast address, and anyone who has registered with that address will receive the data. A multicast address is what class D addresses are used for, so you will not be assigning them specifically to hosts on the network for normal network communication. - Class D addresses have a value on the first octet that ranges from 224 to 239. With that many ranges, class D has the potential for 268,435,456 unique multicast groups that users can subscribe to from a multicast application. Class E Addresses - The funny thing about class E addresses is that they were designed for experimental purposes only, so you will never see a class E address on a network. - Class E addresses have a first octet with a value that falls in the range of Now that you are familiar with the different class addresses, Private Addresses - Another type of address you need to be aware of is what is known as a private address. A private address is an address that can be assigned to a system but cannot be used for any kind of Internet connectivity. The private addresses are nonroutable addresses, so any system using them will not be able to function off the network. The following are the three address ranges that are private: o o o Addressing Schemes - When sending data on the network, there are different ways that the data can be sent to the destination. The data can be sent to a unicast address, a broadcast address, or a multicast address. The following outlines the difference between unicast, broadcast, and multicast: o Unicast Is the sending of information to one system. With the IP protocol this is accomplished by sending data to the IP address of the intended destination system. o Broadcast Is the sending of information to all systems on the network. Data that is destined for all systems is sent by using the broadcast address for the network. An example of a broadcast address for a network is Eng. Maha Talaat Eng. Nareeman Sabry CN Lab (4) 3

4 o The broadcast address is determined by setting all host bits to 1 and then converting the octet to a decimal number. Multicast Is the sending of information to a selected group of systems. Typically this is accomplished by having the systems subscribe to a multicast address. Any data that is sent to the multicast address is then received by all systems subscribed to the address. Most multicast addresses start with 224.x.y.z and are considered class D addresses. IPv6 - Our entire discussion so far about TCP/IP is based on version 4 of TCP/IP, known as IPv4. The use of TCP/IP over the years has far exceeded expectations, and we are running out of IP addresses. For that reason, TCP/IP has been redesigned and the new version is IP version 6 (IPv6). - There are major changes to IPv6 from what we know of IPv4. For starters, IPv4 uses a 32-bit address scheme, while IPv6 will use a 128-bit address scheme. This will give us an insane number of unique possible addresses to be exact (2128)! This is a huge improvement over 232=4 billion unique addresses with IPv4. An IPv6 address will no longer use four octets. The IPv6 address is divided into eight hexadecimal values that are separated by a colon (:) as shown in the following example: 65b3:b834:45a3:0000:0000:762e:0270:5224 TCP/IP Ports - An application or process uses a TCP/IP port as an identifier for that application running on a system. - When you send data from one computer to another, you send data to the port used by that application. For example, when you type the IP address of a web site in your web browser, the web browser connects to the web server (or web application) running at that system by sending data to port 80. Port 80 is the default port of a web server. When the web server answers your request by sending the web page to your browser, the browser is running on a particular port as well and the web server sends the page to the port of the web browser. Server applications typically use low port numbers that fall under 1024, whereas client applications usually run on ports over Port numbers that are used by servers are known as well-known ports (under 1024), whereas port numbers over 1024 used by client applications are known as dynamic ports. They are called dynamic ports because many times the port is selected at runtime by the application TCP/IP Configuration Concepts Eng. Maha Talaat Eng. Nareeman Sabry CN Lab (4) 4

5 Manual Configuration - To configure TCP/IP on a Windows XP client, you will click the Start button and then right-click My Network Places and choose Properties. - The network connections window appears, and you should see your LAN connection. If you right-click your LAN connection and choose Properties, you will see your network settings, including the TCP/IP protocol. - To configure TCP/IP, select TCP/IP and choose Properties - To configure your system with a specific address, select Use The Following IP Address and then type the IP address, the subnet mask, and the default gateway; then choose OK. Once you have finished configuring TCP/IP, you will be able to communicate with network resources using the newly configured system. - Configuring a system manually is not the best approach to take on a network for a number of reasons: o Workload The amount of work involved in manually configuring each system on the network is too much for any network administrator. o Typos The potential for human error is great when inputting the parameters on multiple systems simply due to the fact that it is such a laborious task. It is also very easy to assign a duplicate address on the network, which would result in an error. o Change management It is very hard to implement major changes to your IP infrastructure when you are manually configuring systems. For example, a change to a router address would require a lot of time to update the default gateway entry on the clients. Dynamic Host Configuration Protocol (DHCP) - Configuring IP addressing on a large TCP/IP-based network can be a nightmare, especially if machines are moved from one network to another frequently. - The Dynamic Host Configuration Protocol (DHCP) can help with the workload of configuring systems on a network by assigning addresses to systems on boot-up automatically. - The process of dynamically assigning IP addresses is managed via a DHCP server. - The DHCP server is configured with a set of usable IP addresses, called a scope. - The scope can also include the subnet mask, IP addresses of the default gateway, DNS servers, WINS servers, and other necessary addresses. - When a PC comes online and is set up to use a DHCP server, it requests an IP address by transmitting a broadcast request packet looking for any DHCP servers on the network (known as DHCP Discovery). - The DHCP server responds with an offer containing an IP address that the client can lease (known as the DHCP Offer). - The client then accepts the offer by sending a request message for that address from the DHCP server (known as the DHCP Request), and then the server responds with an acknowledgment to the client that it has that address and additional settings for the lease time (known as the DHCP ACK). - The DHCP server marks the IP address in its database as being in use so that it is not assigned again. - When configuring the DHCP server, you will need to configure a scope with the following settings: o IP addresses The DHCP server issues an IP address to each DHCP client system on the network. Each system connected to a TCP/IP-based network is identified by a unique IP address. As you learned in this chapter, the IP address consists of four 8-bit octets separated by periods. The IP address is normally shown in dotted-decimal notation for example, Eng. Maha Talaat Eng. Nareeman Sabry CN Lab (4) 5

6 o o Subnet mask The IP address actually consists of two parts: the network ID and the host ID. The subnet mask is used to identify the part of the IP address that is the network ID and the part that is the host ID. Subnet masks assign 1s to the network ID bits and 0s to the host ID bits of the IP address. Default gateway A default gateway is required when the client system needs to communicate outside its own subnet. Normally, the default gateway is a router connected to the local subnet, which enables IP packets to be passed to other network segments. APIPA - Windows clients support a feature known as automatic private IP addressing (APIPA), which is a feature that provides that, when a Windows client boots up and cannot contact a DHCP server, it will configure itself automatically with a x.y address. If there is something wrong with the DHCP server and all the systems on the network cannot obtain an address from the DHCP server, the clients will all assign themselves an address within the address range and then be able to communicate with one another. - APIPA does not assign a default gateway, so you will be unable to access resources on a remote network and the Internet but you can still communicate with systems on your network. When troubleshooting to find out why a machine cannot communicate on the network, watch for systems that have the x.y address range because it means they could not find a DHCP server. Domain Name System - One service that is used throughout networks and the Internet is the Domain Name System (DNS). Most users on the network connect to resources by using a friendly name such as this style of name, known as a fully qualified domain name (FQDN), must be converted to an IP address before communication can occur. DNS is used as our solution to convert FQDNs to IP addresses. - Let s walk through an example of a name being resolved. You are sitting in your office on your network, and you try to connect to which means that your client computer will send a query to the DNS server Top-Level Domains - The root servers are responsible for ensuring that any requests for an Internet resource are forwarded to the correct top-level domain. To help organize Internet resources in the DNS distributed database, there are specific top-level domain names created, and a company or organization has to register under a top-level domain. - For example, if you are trying to connect to microsoft.com, the root DNS server forwards you to the.com top-level domain namespace. The following is a description of the most popular DNS top-level domains found on the Internet: o.com This is the commercial organizations group and is by far the largest. Almost everyone wants to be found in this domain, because it is where most customers will try to find you. o.org This is for nonprofit organizations. o.net This is for networking organizations such as island.net and nfs.net, as well as for Internet service providers such as netzero.net. o.mil This is for military organizations such as army.mil and navy.mil. o.gov This is for U.S. government offices only. o.edu This is for educational organizations. Eng. Maha Talaat Eng. Nareeman Sabry CN Lab (4) 6

7 Country Domain Names - With only six top-level domain names and the requirement that all organizations register under one of those top levels if they wanted an Internet name, this soon became a problem because there were so many names to be registered and so few choices on the top levels. Eventually, top-level names were created for country domains; therefore, if you resided in a certain country, you could register under that country domain so that your customers could find you easily. Here are a few of the most common country domain names: o.ca Canada o.ie Ireland o.uk United Kingdom o.us United States DNS Files - Most DNS servers maintain their DNS data in a number of files that exist on the hard disk of the server. In the old days, you managed the records by updating these text files, but today most DNS server environments support a graphic tool. - When you create the records graphically, the DNS files are updated. Windows servers store their DNS files in %systemroot%\system32\dns. Hosts File - Before DNS became a popular solution to hostname resolution, there was a more manual method of creating and modifying a file on the local hard disk of every system. This file would need to be updated on every system if a change was made to a server s IP address and you wanted the client applications to be aware of the change. This file, known as the hosts file, was located on each client system. Before DNS servers became a standard, network administrators used to create a text file known as the hosts file, which was used to resolve the FQDN to matching IP addresses. This text file was stored locally on each system; in the Windows word, it is stored in the %systemroot%\system32\drivers\etc folder and contains two columns one for the IP address and the other for the FQDN. Windows Internet Naming Service - The Windows Internet Naming Service (WINS) provides name resolution for NetBIOS names to matching IP addresses and is popular on large Microsoft networks. WINS is very similar to DNS but contains a database of different-style names NetBIOS names instead of fully qualified domain names. When a WINS client boots up, it registers its names within the WINS database and then queries that server any time it needs to have a computer name resolved to a matching IP address. When the WINS client shuts down, it also de-registers its names from the WINS database so that another system can register the names while it is offline. - Before WINS, the LMHOSTS file was used to assist with remote NetBIOS name resolution. The LMHOSTS file is a static file that maps NetBIOS names to IP addresses. This file is similar to the hosts file in functionality; the only difference is that the hosts file is used for mapping hostnames to IP addresses. - Name resolution is a very important part of troubleshooting networking problems chances are a large percentage of communication problems come from name resolution. Eng. Maha Talaat Eng. Nareeman Sabry CN Lab (4) 7