3.7. Determining the Impact of Network Configurations
The connectivity of a network is both physical and logical. In order to have a functioning network, all of the components of both physical and logical connectivity must be configured properly. In this section, we focus on the logical configuration of the network, such as ports, authentication protocols, and encryption protocols. These must all be configured properly between computers in order for the network to operate effectively.
If 99 percent of the logical configuration is correct but only one part is misconfigured, the result will often be the same as if 100 percent of the network were misconfigured: no connectivity. Because of this fact, it is very important that you understand all of the components involved in the configuration. Once you do, you will be able to determine the potential impact if one of the components is misconfigured.
3.7.1. Critical Information
You should understand the impact of a misconfiguration in regard to the main logical components in a network configuration. Be able to determine the impact on network functionality of each of the logical components both when they are configured properly and when they are misconfigured.
3.7.1.1. Port Blocking
As we discussed in Chapter 2, ports are logical locations in the computer at which a particular application is received. If a specific port is blocked by a firewall configuration or other type of filtering software or device, then the application that corresponds to the blocked port will not function. You might well be able to determine that a port must be blocked because of the fact that all other applications function normally. For example, if a firewall blocks port 80, you will not be able to use the connection to browse the Web but, as long as ports 20 and 21 are not blocked, you will be able to use FTP on the same connection. You can obtain a short list of port numbers from Chapter 2 of this book. A more complete list is also available on the Web at http://www.iana.org/assignments/port-numbers.
3.7.1.2. Authentication Protocols
A variety of authentication protocols can be used to prove a computer's and/or a user's identity over a network. As we discussed in Chapter 2, these protocols have evolved over the years and have become increasingly sophisticated. It is important that the protocols be configured the same on both (or all) of the computers that will need to authenticate to each other. You can configure most servers to accept multiple protocols of varying sophistication so that each client can then be configured with the most secure protocols that it can handle. For example, since Windows 2000 and Windows XP clients can use MS-CHAP v2 but Windows NT Workstation cannot, you should configure the server with MS-CHAP v2 as well as MS-CHAP, but you should configure the Windows 2000 and Windows XP clients with only MS-CHAP v2 and the Windows NT Workstation clients with only MS-CHAP. In this way, each client will use its strongest available authentication protocol. The only exception to this rule will be in the case that other servers in your network cannot use MS-CHAP v2. In that case, you should configure both protocols on the clients as well.
If authentication protocols are configured properly on both sides of a connection, then the computers will reach an agreement on how to authenticate to each other and authentication will take place. This process will take some time. Often the amount of time that authentication requires is not of great concern, but you should know that the connection will take longer to establish than if the authentication did not have to be performed. Some software indicates to the user that the connecting computers are currently authenticating and asks the user to wait.
If authentication protocols are not configured the same on both sides of a connection, such that the computers can reach some common agreement in regard to authentication, then the connection will fail and the error will likely indicate that the computers could not authenticate. This message is usually different from an "Access Denied" message or a message that indicates that the computers could not connect. This is because the computers actually did connect with each other and they had a short conversation, but either they could not agree on an authentication protocol that both could use or the authentication failed.
3.7.1.3. Encryption Protocols
Whereas authentication is proving one's identity, encryption is scrambling up messages so that they can be read only by the sender and the intended recipient(s). Encryption protocols must also be configured the same on both sides of a connection in order for communication to occur normally. The difference is that an errant encryption protocol could very possibly look like a lack of any connection at all, since the computers might not be able to see each other. Actually, there are two instances in which encryption protocols are used: first they are used to secure the logon and authentication of a connection, and then they are used to scramble the data that is being sent over the connection. The types of encryption protocols that you use will depend on the type of client that you are using and the type of application that is being used. For example, encryption protocols such as Secure Hash Algorithm (SHA) or Data Encryption Standard (DES) might be used to encrypt authentication and/or data during a session.
3.7.2. Exam Essentials
Know how port blocking can affect network functionality. Each port is very specific to an application. If a port is blocked, the application associated with it will not be able to operate through the connection. The best indicator that a port may be blocked will be that other applications will function through the same connection.
Understand how authentication protocols can affect network functionality. The key to authentication is that both of the computers in the communication must be able to use the same authentication protocol to authenticate. You can configure computers with multiple authentication protocols, and this is typically done with servers rather than with clients; however, clients that might connect to multiple servers could also benefit from being configured with multiple authentication protocols. Authentication-related errors will most likely be indicated by a clear message from the software.
Explain how encryption protocols affect network functionality. Encryption protocols are used when computers are authenticating as well as when data is being transferred between the computers. A failure in regard to an encryption protocol that would be used to authenticate could manifest itself as a failure to connect at all. The specific type of encryption protocols used will depend on the client and the applications used.