Computer Networks Lab

Transcription

1 Computer Networks Lab Room: BB 219 Additional Information: 1. Practical Training: Network planning and installation of a file server 2. Practical Training: Web server installation and dynamic Web pages 3. Practical Training: Installation and configuration of a Firewall 4. Practical Training: Installation of a VPN for the connection of two networks 5. Practical Training: Programming attempt; Client/Server connection over Sockets 6. Practical Training: Network Monitoring Name: Matriculation No.: Supervisor Signature: Contact: Joachim Zumbrägel BB 320 Tel: 0203/ joachim.zumbraegel@uni-due.de Equipment for each group: - 1 Server computer (OS: Windows Server 2016 Standard, virtual machine) - 1 Client computer (OS: Windows 7, virtual machine) - 1 Computer as Router / Gateway (OS: Linux) - 1 Switch and network cables Hint: We are using virtual computers for our client and our server operating system. The Software which is running on our physical computer (so called Host-System) is VMware Workstation 12 Player. It has to be considered that each machine (virtual and physical computer) has a specific IP address. 1. Introduction Computers in small companies without much space or those in households are commonly connected to form a network in order to share resources (e.g. printer, Internet, files). The setup of a (simple) network with current operating systems is relatively trivial. For networks with up to ten computers a Peer to Peer network is suitable. Peer to Peer implies that computers in such a network are considered equal and thus a central Server for administrating data traffic is not required. In the Windows OS environment a Peer to Peer network structure is called Workgroup and is based on the same principle. For larger networks, however, at least one Server should be used to centrally administrate network resources. This type of structure is called Domain in the Windows OS environment. 2. Network basics In this practical training both models are to be successively carried out. Before configuring your computers for the network, the physical connections have to be created. All computers in the laboratory are equipped with a network card and a network cable. In addition, each group is provided with a SWITCH. The STAR configuration will be physically implemented (see Fig. 1.2). In order to exchange data in a network, computers must speak the same language, which is the role of Network Protocols. They specify the 1 2

2 common language in each case. Usually, in local networks the TCP/IP protocol is used, upon which the Internet is also based. In Windows Server 2016, TCP/IP is installed with the operating system and remains active after the installation. We just have to configure it. Before we do that, we need to enter some general information (e.g. Computer Name and Workgroup or Domain Name). Question 1: What is the Computer Name for? Computer Name and ClientN respectively and the Workgroup as WorkgroupN, where N represents your network number (you will be informed of your network number in the beginning of the practical training). Workgroup Server Client Question 2: What is the difference between Workgroup and Domain? 2.1 The Workgroup Model Each computer in your network needs to have a Name and has to belong to a Workgroup (workgroups are protocol independent). The Name of each computer must be unique, thus it cannot occur more than once in a network. To change the settings mentioned above you need to proceed as follows: On Windows 7 and Windows Server 2016 Go to start Control Panel System and security System and choose Change settings under the Computer name, domain, and workgroup settings field Click on Change after which the dialogue box in Fig should appear Fill the Computer Name and Workgroup fields and confirm your entries with OK Exercise 1: Set up the Computer Name and Workgroup, and complete the table below. Designate the computers in your network as ServerN Fig : Computer name and Workgroup or Domain 2.2 TCP/IP, IP addressing, IP address classes Communication between the individual computers in our LAN (as well as in the Internet) can be established by using the TCP/IP protocol and its IP addresses. IP addresses consist of 4 octets (bytes), which are normally represented in decimal form and separated by dots (dotted decimal notation). Example:

3 This form of representation is used only for the input and/or display of IP addresses on the computer. Internally, however, the computer always works with the binary representation of IP addresses. Example: (the computer does not set the dots between the individual octets. They were used here only to facilitate and/or to distinguish between the individual values of the binary representation of the "dotted decimal notation"). IP addresses consist of two parts: Network address Host address These two parts are identified through the subnet mask. By definition the network part of an IP address is represented by 1s and the host part by 0s. The network part identifies the network address, where the computer (associated with its IP address) is located. The host part identifies the computer address within that network. This structure allows TCP/IP to be defined as a routing protocol. Example: IP Address: Subnet mask: The first 3 bytes represent the Network address (1s) and the last byte represents the Host address (0s) Network classes In former times IP addresses were divided into classes in order to set up a network addressing architecture. There were 5 different classes of available IP ranges: Class A, Class B, Class C, Class D and Class E, where classes A, B and C were most commonly used. The table below lists the ranges of IP addresses for the 3 main classes: Address class (Name) Values of the first bits (Definition) Remaining values of the first byte (decimal) Network (N)/ Host (H) Part Number of available addresses (per network) Class A 0xxx xxxx N.H.H.H Class B 10xx xxxx N.N.H.H Class C 110x xxxx N.N.N.H 256 Table With the introduction of CIDR (Classless Inter-Domain-Routing) in 1993 the concept of the network classes plays nowadays in practice only a limited role (e.g. default subnet mask which is a proposed value when you set up an IP address manually). Every network has two addresses reserved: network address and broadcast address. A broadcast address is characterised by 1s in the host part and a network address is characterised by 0s in the host part. The result of a logical AND operation (multiplication) between any valid IP address from a certain network and the subnet mask of that network is the network address. Due to an exponential increase of users and computers connected to the Internet, the number of unused IP addresses decreases considerably. A new version IPv6 (IP version 6) was designated in 1998 as the successor of version 4. Due to the IPv4 shortage, private addresses were reserved. These are never assigned in the Internet and are never routed. They are intended for private network use only. The private addresses range is listed below: 10.x.x.x from x.x to x.x x.x Table = a Class A address = 16 Class B addresses = 256 Class C addresses 5 6

4 The address : The address plays a special role - by definition it always addresses the local computer. It generally holds the name "local host". According to standard, the use of the network 127.x.x.x is inadmissible ("An address with 127.x.x.x should never be part of a network!"). The can only be used to examine the configuration of the particular computer (ISO Layers 3 to 7)! Network division and subnets creation Creating subnets (or subnetting) is used to divide networks into smaller portions (subnets). With the help of subnet masks, networks can be masked out bit by bit, by setting some of the subnet mask section bits to a different value. This makes the definition of subnets possible. For example for the subnet mask (with binary representation: ) only the last seven bits are available for host addressing. This way a Class C network is divided into two subnets with 126 hosts each. With the creation of such subnets, network administration can be simplified tremendously. broadcast address, is passed on automatically to each host in the corresponding network. As a result of the sent ARP Signal (ARP = Address Resolution Protocol), the target host, which is addressed by its IP address, announces its MAC address. By use of MAC addresses the computers in a network are capable of exchanging data packages on the physical layer level. The mapping of IP addresses to MAC addresses is done by the Address Resolution Protocol (ARP). A MAC address has a length of 6 bytes three bytes to identify the manufacturer and three bytes representing a sequential number. Each MAC address is unique and usually burned into the network card. Nevertheless, it is possible to assign MAC addresses manually. Question 3: What helps distinguish one IP address class from another? Question 4: What is the use of the subnet mask? Example of a network division: Class C Network Network mask st half 2-nd half Network address Broadcast address IP Range (126) (254) Table Question 5: What is a Gateway? Question 6: What does the abbreviation DNS stand for? What is its use? Network division must always be achieved in a symmetric manner, i.e. a Class C network for example can be divided into 2 subnets, both of which can be further divided in another 2 subnets Broadcasting and Address Resolution Protocol As already described above, the second reserved address in a network is the broadcast address. A message (broadcast), which is sent to the 7 8

5 Question 7: What is the difference between private and public IP addresses? The following scheme describes the structure of a group s network: Internet Question 8: What does the abbreviation NAT stand for? What is its use? Switch Exercise 2: Network parameters setup. For the network setup in our laboratory a private network is to be established with IP address N.xxx where N represents your network number. The following guidelines hold for all groups: - The Gateway (router/firewall) got already the highest usable IP address from the range. - The switch (router/firewall) got already the lowest usable IP address from the range. - The host-operating system of the server got already the second lowest IP address from the range. - The host-operating system of the client got already the third lowest IP address from the range. Hint: keep in mind that we are using virtual machines for our client and as well for our server. For that reason also the hosts machines (the host machines are the machines where the virtual machines are running on) need IPaddresses. Firewall N/ Router N Switch N Workgroup X Fill in the table the IP-Addresses of your network: IP-Address Switch Host Operating system (server) Host Operating system (client) Gateway Table Server N Client N Workgroup N Fig : Network in the laboratory Workgroup Y 9 10

6 To setup your network with Windows Server 2016/Windows 7, proceed as follows: On Windows 7 navigate to Start Control Panel Network and Internet Network and sharing centre local area connection) On Windows Server 2016 navigate to Start Control Panel Network and Sharing Centre Click on Ethernet Open the Local Area Connection (or Ethernet) corresponding to your NIC (Network Interface Card). The dialogue box in Fig should appear. Select the Properties button after which the dialogue box in Fig should appear. In the list of items the connection uses choose Properties for Internet Protocol Version 4 (TCP/IPv4) The dialogue box in Fig should appear. Change the network settings on the machines in your group and fill in the table below: Fig : Local Area Connection Fig : LAN Properties Server Client IP-Address Subnet mask: Gateway: 1. DNS: DNS: Not necessary Not necessary Table Exercise 3: Test your TCP/IP set up. To test your network connection setup, proceed as follows: Navigate to Start Run and type cmd in the field to open the DOS command prompt window Press ENTER to confirm and the command prompt consol should appear As shown in Fig with the instruction line ipconfig /all you can look at the configuration of all network adapters in your system 11 12

7 Fig : ipconfig /all on the Command Prompt Console Compare the output of the console with the configuration you entered earlier in Table To check if the computers (ServerN, ClientN, and Gateway) are communicating with each other use the command line Ping <followed by the IP address> - e.g.: ping <press enter> As a result of the ping command line you should get four answers from the computer you pinged. Repeat the same command for all computers you configured. Ping the localhost, your local IP address and the IP addresses in your network. Fig : IPv4 Properties 3. User Administration A user account contains unique information about a user and allows him to register and get access to the domain, in order to take advantages of the different network resources. Through an account a user can also gain access to a specific computer s resources. Everybody who regularly uses the network should have a user account. Windows Server 2016 has 3 types of user accounts: 1. Domain user accounts 2. Predefined user accounts 3. Local user accounts We will cover Domain user accounts later in the practical training. The predefined user account administrator, has already been used in the first part of this practical training, when we set up the network configurations. The predefined user account guest (with very restricted rights), is intended for temporal network access. The local user accounts allow access to the local computer and its resources

8 If the users of all computers in a local network (not a domain) require access to different resources, then a user account must be created on each computer for every user. When the network holds many computers (more than 10) the setup and maintenance of such a system gets very complex and time consuming. That is why the domain model is recommended for larger networks. A domain user account identifies a person who uses a computer within the domain. This account can then be given access to resources in the network. The user account and the shared resources reside on a server computer configures as domain controller, centralizing administration and security. A user account created on the domain controller applies to all computers within that domain. Before user accounts are created, guidelines should be specified for them, e.g. name conventions, password guidelines, account options. In this practical training these guidelines are not taken into account. Fig. 3.1: Local Users and Groups in Computer Management Usernames in Windows Server 2016 must be unique for the network, are not case-sensitive and cannot be more than 20 characters long. To create a user account in Windows Server 2016/Windows7, proceed as follows: Navigate to Start Control Panel Open Administrative Tools Computer Management Extend Local Users and Groups located on the left part of the window. Right click on Users and select New User as illustrated in Fig. 3.1 The New User dialogue box should pop out. Enter the properties for the desired user and click on Create as shown in Fig When you are done, click on Close. Fig. 3.2: New User dialogue box 15 16

9 Description of the properties for a new user account: User name the unique registration name of the user based on the naming convention, you defined. Full name the user s complete name. Description additional user information (i.e. his department, duties). This field is optional. Now you are able to log on to the computer with the newly created user account. Access to resources from that user account depends on the granted rights. User rights are usually set for a group of users. Predefined groups, like predefined user accounts, also exist. The four most important user groups are: 1. Administrators 2. Users 3. Power Users 4. Backup Operators Administrator group members are allowed to implement all of the operating system support functions. The group Users is the safest environment for program execution. The Power Users group possesses most administrative powers with some restrictions. The users with Backup Operators rights can save and change files no matter if they are authorized or not. An exact explanation of the rights of these groups is out of the scope of this practical training. Further information is available on the Windows 2016 Help and Support. It is also possible to create new user groups and assign rights to them or prevent new groups from receiving undesired rights. Exercise 4: User Accounts and User Groups. Create a user account for each member of your team. Create a group for your team and add the previously created users to that group. To Log On with another user, you first need to Log Off by going to start Sign out as illustrated in Fig. 3.3 below. Fig. 3.3: Log Off on Windows Server 2016 Don t use alt + Ctrl + Delete (German keyboard: AltGr + Strg +Entf) for the log on. This only applies to the host machine. Use alt + Ctrl + Insert (German keyboard: AltGr + Strg+ Eingf) for the log on virtual machine. Log On to the system with the newly created users and try to access and modify the properties of the internet protocol TCP/IP. Is it possible? If not, what changes should be made so that the newly created user account can do those changes? Access to various computers in the network could be granted by creating user accounts for that user on the corresponding machines. This type of user accounts administration can be extremely simplified by introducing the domain model to the network. 4. Domains and Active Directory The corner stone of a domain is the domain controller. A domain controller is a server, which stores a copy of the Active Directory (AD) 17 18

10 data base and thus user rights, which will govern their access to resources within the domain. Installing AD on a server turns it into a domain controller. AD requires a DNS server to function correctly and that is why Windows Server 2016 installs a DNS server when building the domain controller. Exercise 5: Active Directory (AD) and DNS. Install the Active Directory Domain Service on the Server computer. Log On as Administrator and proceed as follows: Navigate to Start Server Manager Extend Manage and select Add Roles and Features The windows shows Before you begin Click on Next Select the Installation type Role-based or featurebased Installation Select a server from the server pool Select the Active Directory Domain Services and DNS- Server roles and click on Next. Don t select roles for feature and install the AD and DNS tools. After the installation is complete we need to configure our domain controller. Click on promote this server to a domain controller Select Add an new forest by deployment operation Name the new domain - DomainN.local - where N is the number of your network. Select Windows Server 2016 for the functional level of the new forest and root domain. Type the DSRM-Password (Tip: use the same password for user BB219 ). Don t change the location in next steps. Restart your computer after Installation Remark: It is important to add all Client computers to the Domain in order to administrate them through the domain controller. Each computer must have a user account to access the Domain with. Exercise 6: Joining the Domain. To add computers to a domain, proceed as follows: On the Client computer: Log On as administrator and navigate to Computer Name Changes as described in chapter 2.1, Fig In the section Member of select Domain and enter the name of your domain (DomainN or DomainN.local). Click OK and follow the OS instructions Your network now corresponds to a domain model. All components of the network (user, computer, etc.) will be administrated from the active directory, e.g. a user account created on the domain controller (in the AD) is valid throughout the domain. Exercise 7: Users in the Domain. As in exercise 4, create a user account for all your team members and a local security group. Add all users to that group and try to log on to both the domain controller and the client computers. On a domain controller the users and groups will no longer be managed by the Computer Management, but rather by the Active Directory. To add a user to the AD, proceed as follows: Open Start Administrative Tools Active Directory Users and Computer Extend to DomainN, where N is your network number Right click on Users and select New, then you can choose either User or Group depending on what you want to create 19 20

11 5. File Server A file server provides location for shared space and files, making them available to clients connected to the network. We can share files and folders in several different ways in a Microsoft network. One way would be to share data by copying it to the Public Folder, meaning that you do not make any access restrictions. Everyone with a user account on the server has access to the Public Folder. Another method for sharing files and folders is to share them directly from their current location. We will use this type of sharing because it gives us more control on user rights and files. User rights determine the type of access to a specific folder. There are two types of access rights: Share Permissions o Full Control o Change o Read Right click on the folder you would like to share and select Sharing on properties The folder properties dialogue box with selected Sharing tab should appear as shown in Fig. 5.1 Click on Advanced Sharing The advanced sharing dialogue box should come up. Check the Share this folder check box as shown in Fig. 5.2 Type in the name of your shared folder and click on the Permissions button to define user rights To add a user account or a group to the permissions list, click on the Add button (Fig. 5.4) and as illustrated in Fig. 5.3 type the user account name you would like to define the rights for. Check by pressing Check Names and confirm with OK To change permission for an account/group, select it from the list as shown in Fig. 5.4 and tick the desired access rights below NTFS Permissions o Full Control o Modify o Read and Execute o Read o Write The ultimate user rights are obtained through a combination of the two types. NTFS rights define user access to folders and files regardless of them being on the local machine or a remote one. The share permissions will be effective only when the user is accessing the folders or files over the network. In this case a combination of the two kinds of access rights applies. The most restrictive one of the two is used. Follow these steps to share a folder on the network: 21 22

12 Fig. 5.1: Folder sharing properties ig. 5.2: Advanced Sharing dialogue box Once you have defined the Share permissions, you need to allow NTFS permissions for the same user accounts. To change the NTFS permissions: Right click on the folder and select Properties Select the Security tab and click on Edit To add a user account to the list, proceed as explained in the share permissions steps above. Share permissions are usually not used to govern access because the files and folders already have NTFS permissions. It is preferable to set shares so that domain users have full control and then use NTFS permissions to restrict actual levels of access to the data. After sharing a folder and setting up the access permissions, all user accounts with rights should be able to access the shared data. To access network resources proceed as follows: Navigate to Start All Programs Accessories and open Windows Explorer (or press keyboard shortcut Win Key + E) In the Address Bar type two back slashes (\\) and the name of the Server or the server s IP address as shown in Fig. 5.5 e.g. \\Server1, \\ Navigate through the browser to the shared folder Fig. 5.3: Add users, computer, groups Fig. 5.4: Sharing permissions Fig

13 Exercise 8: Sharing resources Create a folder on the domain controller (Server computer). Give two of the previously created user accounts the NTFS permission Modify and the other two the NTFS permission Read. Create a text file in the newly created folder. Share the folder with Share permission Full control for the group created in Exercise 7. Try now to access the text file from the Client computer with all user accounts. Try to change the file and save the changes. Does it work for all four users? Which work and which do not? Change the Share permission of the group to Read and try once again to access the text file from the Client computer using the four users. Try to make some changes to the text file and save changes them. Could you save the changes? Why? 6. DHCP Server As we learned in the beginning of this practical training it is possible to manually setup the IP address of each computer in the network. However, in the case of larger networks an automatic distribution of IP addresses is highly recommended. This is where the DHCP Server comes into place (though it can achieve more). DHCP stands for Dynamic Host Configuration Protocol. It is a TCP/IP standard and its goal is to alleviate the complexity of IP addressing management (including other configuration details that come with it) by centralizing it through a Server on the network. Exercise 9: DHCP Server Install a DHCP Server for your network configuration. To install a DHCP Server Role on Windows Server 2016 proceed as follows: Navigate to Start Server Manager Extend Manage and select Add Roles and Features The windows shows Before you begin Click on Next Select the Installation type Role-based or featurebased Installation Select a server from the server pool Select DHCP-Server role and click on Next for installation. Authorize the DCHP Server with the current credentials Add a new scope of the IP addresses in your network. For that navigate to: Start Administrative tools DHCP Right Click on the IPv4 under ServerN.domainN.local and select new scope Type the name and description for the scope Enter the range of Client-addresses that the scope distributes. (Please pay attention to the used IP address of the physical and virtual machines). Set 8 days as a Duration for scope leases. Add an IP address for a router (Gateway) and click on Add. Enter your Server name and resolve an add your Server-IP address for a WINS Servers Activate the scope After the installation it is possible to reconfigure different parameters in the DHCP console like Gateway, DNS, WINS, etc. To reconfigure your DHCP Server navigate to: Start Administrative Tools DHCP Expand the Server and the IPv4 to reconfigure if needed

14 Notes: Log On as administrator on the Client computer and change the TCP/IP configuration to Obtain an IP address automatically and Obtain DNS server address automatically Verify with ipconfig/ all that the Client computer got a correct TCP/IP configuration from the DHCP Server. Using the command ping make sure that the Client computer can communicate with the other computers. 27