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The 802.3 specification defines how data must be sent over an Ethernet network. Ethernet breaks data into small pieces called frames. Each frame contains between 46 and 1500 bytes of data. When you send data over an Ethernet network, the data is broken down into frames, sent over the wire, and then reassembled by the receiving computer. Each frame contains header information noting the beginning of the frame, where it is coming from, and where the frame is going. Additionally, each frame has a component called a cyclical redundancy check (CRC). The CRC allows the receiving computer to check the frame to make sure that the data in the frame has arrived intact. If it has not, the receiving computer can use the header information to request that the sending computer resend the data. This frame-sending format has been used for years and is highly reliable. Ethernet is considered a bus topology, which refers to the shared physical layout of the network. More commonly, Ethernet is called a star-bus topology because all computers radiate from a central hub that resembles a star pattern, as shown in the following illustration.

Query all servers on all adapters under consideration. No No Positive Negative response response received returned Yes within two Yes seconds Adapter removed from consideration. Yes Any adapters still under No consideration D Return to flowchart DNS Name Resolution. Query all servers on all adapters still under consideration. No No Positive Negative response response received Yes returned within four seconds Yes Adapter removed from consideration. Yes Any adapters still under No consideration

Figure 24-10

If it has not received a response from any server within those eight seconds, the resolver responds with a time-out. Also, if it has not received a response from any server on a specified adapter s search list, the resolver, for the next 30 seconds, responds to all queries destined for servers on that adapter s search list with a time-out and does not query those servers. If, at any point, the resolver receives a negative response from a server, it removes every server connected to that adapter from consideration during this search. For example, if in step 2, the first server on alternate adapter A gave a negative response, the resolver would not send the query to any other server on the list for alternate adapter A.

Ethernet networks use the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) access method to send data over the network and manage transmission problems. (In fact, if you have been studying residential gateways and related products, you might have noticed that the CSMA/CD method appears on the products specification sheets.) CSMA/CD does not need to be configured it just tells you that the device fully supports Ethernet s mechanism for sending data. CSMA/CD uses a method where computers listen to the network cable to see if any other computers are transmitting frames. If not, the computer sends the data. If there is traffic, the computer waits until the line is clear. In the event that two computers transmit data on the wire at the same time, a collision will occur. In this case, the data is destroyed. However, the Collision Detection feature of CSMA/CD enables the computers to detect the collision so that data can be resent.

Part IV:

For any adapter that does not respond within eight seconds, resolver gives time-out on all queries for the next 30 seconds.

Figure 24-11

Ethernet devices can support three speed standards:

The resolver also keeps track of which servers answer queries more quickly, and it might move servers up or down on the list based on how quickly they reply to queries. If all DNS servers on an adapter are queried and none reply, either positively or negatively, all subsequent name queries to any server listed on that adapter will fail for a default period of 30 seconds. This feature decreases network traffic. Figure 24-12 shows how the resolver queries each server on each adapter.

24:

Figure 24-12

3

A using directive does not give you access to any namespaces that are nested in the namespace you specify.

To specify a preferred and alternate DNS server 1. In Control Panel, select Network and Internet Connections. 2. In the Network and Internet Connections sheet, select Network Connections. 3. In Network Connections, right-click the local area network connection that you want to change and then click Properties. 4. Select Internet Protocol (TCP/IP), and then click Properties. 5. On the General tab of the TCP/IP Properties sheet, select the method to be used to access the DNS servers for your network: