Adding, Modifying, or Removing Network Services

• Given a scenario, predict the impact of modifying, adding, or removing network services (e.g., DHCP, DNS, WINS, etc.) on network resources and users.

All network services require a certain amount of network resources in order to function. The amount of resources required depends on the exact service being used. Before implementing or removing any service on a network, it is very important to understand the impact that these services can have on the entire network. To provide some idea of the demands various services place on the network, this section outlines some of the most common network services and the impact their addition, modification, or removal might have on the network and clients.

Adding, Modifying, or Removing DHCP

DHCP automatically assigns TCP/IP addressing to computers when they join the network and automatically renews the addresses before they expire. The advantage of using DHCP is the reduced number of addressing errors, which makes network maintenance much easier. Remember from earlier in this chapter that each computer on a TCP/IP network requires a unique IP address.

One of the biggest benefits of using DHCP is that the reconfiguration of IP addressing can be performed from a central location, with little or no effect on the clients. In fact, you can reconfigure an entire IP addressing system without the user noticing. There is, as always, a cost associated with everything good, and with DHCP, the cost is increased network traffic.

DHCP Traffic

You know what the function of DHCP is and the service it provides to the network, but what impact does the DHCP service have on the network itself? Some network services can consume huge amounts of network bandwidth, but DHCP is not one of them. The traffic generated between the DHCP server and the DHCP client is minimal during normal usage periods.

The bulk of the network traffic generated by DHCP occurs during two phases of the DHCP communication process: when the lease of the IP address is initially granted to the client system and when that lease is renewed. The entire DHCP communication process takes less than a second, but if there is a large number of client systems, the communication process can slow down the network.

For most network environments, the traffic generated by the DHCP service is negligible. For environments where DHCP traffic is a concern, you can reduce this traffic by increasing the lease duration for the client systems, thereby reducing communication between the DHCP client and the server.

IN THE FIELD: DHCP LEASES Some network administrators choose to allow infinite DHCP leases, but this strategy is not always practical. In any network, there can be changes; for example, computers can be added or taken away, remote laptops can be used to connect to the main LAN, and NICs might need to be replaced. If a system is removed from a network that uses infinite DHCP leases, the IP address used by the removed system will be unavailable for reuse. A better option is to choose long duration periods ranging from one to two weeks. This ensures that the IP address will be able to be reused in the future.

If DHCP functionality is removed from the network (which is unusual), each system needs to be manually configured with IP addressing information.

DHCP is covered in greater detail in Chapter 6.

Adding, Modifying, or Removing WINS

WINS is used on Microsoft networks to facilitate communications between computers by resolving NetBIOS names to IP addresses. Each time a computer starts up, it registers itself with a WINS server by contacting that server over the network. If the system then needs to contact another system, it can contact the WINS server to get the NetBIOS name resolved to an IP address. If you are thinking about not using WINS, you should know that the alternative is for computers to identify themselves and resolve NetBIOS names to IP addresses via broadcasts. Broadcasts are inefficient because all data is transmitted to every device on the network segment. Broadcasts can be a significant problem for large network segments. Also, if a network has more than one segment, you will be unable to browse to remote segments because broadcasts are not typically forwarded by routers, which should eliminate this method of resolution.

Because WINS actually replaces the broadcast communication on a network, it has a positive impact on network resources and bandwidth usage. This does not mean that WINS does not generate any network traffic—just that the traffic is more organized and efficient. The amount of network traffic generated by WINS clients to the WINS server is minimal and should not have a negative impact in most network environments.

WINS server information can be entered manually into the TCP/IP configuration on a system, or it can be supplied via DHCP. If the WINS server addresses change and the client configuration is being performed manually, each system needs to be reconfigured with the new WINS server addresses. If you are using DHCP, you need to update only the DHCP scope with the new information.

Removing WINS from a network increases the amount of broadcast traffic and can potentially limit browsing to a single segment.

Adding, Modifying, or Removing DNS

As previously mentioned, the function of DNS is to resolve hostnames to IP addresses. Without such a service, network users would have to identify a remote system by its IP address rather than by its easy-to-remember hostname.

Name resolution can be provided dynamically by a DNS server, or it can be accomplished statically, using the HOSTS file on the client system. If you are using a DNS server, the IP address of the DNS server is required. DNS server addresses can be entered manually, or they can be supplied through a DHCP server.

A more detailed discussion of DNS is presented in Chapter 6.