Understanding Network Connectivity in an Enterprise (part 1) - Unicast, Multicast, and Broadcast & Using IPConfig

The concepts are pretty much the same with Windows 7 as they were with Windows XP and Windows Vista. If you've been working with networked clients for awhile, you can probably skim over this material.

Figure 1 shows several components of a typical network. You should understand the purpose and use of each of these components.

DHCP A Dynamic Host Configuration Protocol (DHCP) server issues TCP/IP configuration information to users. This includes an IP address, subnet mask, address of the DNS server, address of the default gateway, and more.

DNS The primary purpose of the Domain Name System (DNS) server is to resolve hostnames to IP addresses. The client sends the name of a host on the network, and the server responds with the IP address. It can also do reverse lookups (resolving the IP address to a name) with pointer (PTR) records and locate domain controllers with server (SRV) records.

Figure 1. Components of a typical network

WINS A Windows Internet Name Service (WINS) server is used to resolve NetBIOS names to IP addresses. The use of NetBIOS names is significantly reduced in current Microsoft networks (and is not shown in Figure 7.1), but they may still be used by legacy applications, requiring the use of a WINS server in a network.

Domain Controller A domain controller (DC) hosts Active Directory Domain Services (AD DS) in a Microsoft domain. AD DS holds objects (such as users, computers, and groups) that can be centrally managed and administered. Users and computers must have an account in AD DS to be able to log on to the domain and use domain resources. DNS is required for clients to locate DCs on the network.

Default Gateway A default gateway identifies the default path out of the subnet. All of the computers in the drawing to the left of the default gateway are on the same subnet, and their path to the Internet is through the default gateway. The default gateway is also referred to as the near side of a router, and it is specifically identified by the IP address assigned to the network interface connected to the subnet.

Router A router is a hardware device that routes data from one subnet to another. The router in the diagram has two network interfaces; one is the default gateway for the Internet network, and the other is the connection to the DMZ. Routers have filtering capabilities that allow them to restrict what traffic can be passed through the router. These filtering capabilities provide the router with firewall characteristics.

Firewall A firewall is designed to filter traffic so that only specific traffic is allowed into or out of a network. A firewall starts with basic router-filtering capabilities but can be much more sophisticated in how the traffic can be examined and filtered. The two firewalls shown in the diagram (to the left and right of the proxy server) are a combination of hardware and software. Host-based firewalls can be installed on any system and are referred to as software-based firewalls.

Proxy Server A proxy server can be used to access Internet resources. When it's used in a network, all clients would be configured to submit Internet requests to the proxy server, and the proxy server would then request the data from the Internet. Proxies can improve the performance of Internet access by caching data requested by users and providing this cached data when it's requested by another user. Proxies can also improve security or enforce business policies by preventing users from going to specific sites.

1. Unicast, Multicast, and Broadcast

IP traffic travels from host to host in networks using unicast, multicast, or broadcast methods.

Unicast Data travels from one computer to another computer. A unicast message will be processed only by the host with the destination IP address.

Multicast Data travels from one computer to multiple computers. This was mentioned and stressed as one of the benefits of Windows Deployment Services (WDS). WDS is able to multicast a single image to multiple computers at the same time. In contrast, if WDS did this as unicast, it would have to send a separate copy of the image over the network for each client.

Broadcast Data travels from one computer to all computers in the subnet. Each computer that receives the packet will process it and determine whether it needs to take action with the packet. Broadcast traffic is not passed through the router.

2. Using IPConfig

The IPConfig command is a familiar command to many people, but it has some extra capabilities that are sometimes overlooked. Just as with most command-prompt commands, it can be executed alone or with switches to modify what it does.

IPConfig and IPConfig /all are two commands commonly used to check the TCP/IP configuration of a system. IPConfig will provide the output shown in Listing 1.

Example 1. IPConfig output

Windows IP Configuration
Ethernet adapter Local Area Connection:
   Connection-specific DNS Suffix .  :
   IPv4 Address. . . . . . . . . . . : 192.168.1.15
   Subnet Mask . . . . . . . . . . . : 255.255.255.0
   Default Gateway . . . . . . . . . : 192.168.1.1

The IPconfig /all command will show much more information, starting with the hostname. Listing 2 shows the partial output of IPConfig /all for a system that is receiving TCP/IP configuration from a DHCP server. The output of only one adapter is shown, but depending on the configuration, you may see more data on your system.

Example 2. IPConfig /all output

C:\>ipconfig /all
Windows IP Configuration

   Host Name . . . . . . . . . . . . : Darril-PC
   Primary Dns Suffix . . . . . . .  :
   Node Type . . . . . . . . . . . . : Hybrid
   IP Routing Enabled. . . . . . . . : No
   WINS Proxy Enabled. . . . . . . . : No
   DNS Suffix Search List. . . . . . : Wiley.com

Ethernet adapter Local Area Connection:

   Connection-specific DNS Suffix .  : Wiley.com
   Description . . . . . . . . . . . : Realtek RTL8168C(P)/8111C(P)
                                       Family PCI-EGBE NIC #2
   Physical Address. . . . . . . . . : 00-23-5A-33-C4-CA
   DHCP Enabled. . . . . . . . . . . : Yes
   Autoconfiguration Enabled . . . . : Yes
   IPv4 Address. . . . . . . . . . . : 192.168.1.50(Preferred)
   Subnet Mask . . . . . . . . . . . : 255.255.255.0
   Lease Obtained. . . . . . . . . . : Tuesday, November 28, 2009 9:59:44 AM
   Lease Expires . . . . . . . . . . : Monday, December 4, 2009 9:59:43 AM
   Default Gateway . . . . . . . . . : 192.168.1.1
   DHCP Server . . . . . . . . . . . : 192.168.1.10
   DNS Servers . . . . . . . . . . . : 192.168.1.10
   NetBIOS over Tcpip. . . . . . . . : Enabled

					  

Notice that DHCP Enabled is set to Yes, indicating it is a DHCP client. In addition, it shows the IP address of the DHCP server, the DNS server, and the default gateway. The lease length for DHCP servers hosted on Windows Server 2008 is often set for either six days or eight days, and the output shows when the lease was obtained and when it expires.

Table 1 shows the switches available with the IPConfig command.