Answers to the Chapter 4 Do I Know This Already Quiz

1 What do the letters MAC stand for? What other terms have you heard to describe the same or similar concept?

Media Access Control (MAC). Many terms are used to describe a MAC address: NIC, LAN, hardware, BIA, universally administered address (UAA), locally administered address (LAA), Ethernet, Token Ring, FDDI, card, wire, and real are all terms used to describe this same address in different instances.

2 If a Fast Ethernet NIC currently is receiving a frame, can it begin sending a frame? Yes, if the NIC is operating in full-duplex mode.

3 What are the two key differences between a 10-Mbps NIC and a 10/100 NIC?

The obvious benefit is that the 10/100 NIC can run at 100 Mbps. The other benefit is that 10/100 NICs can autonegotiate both speed and duplex between itself and the device that it is cabled to, typically a LAN switch.

4 What is the distance limitation of a single cable for 10BaseT? 100BaseTX?

10BaseT allows 100 meters between the device and the hub or switch, as does 100BaseTX. Table 4-5 summarizes the lengths for all Ethernet LAN types.

5 What routing protocol does a transparent bridge use to learn about Layer 3 addressing groupings?

None. Bridges do not use routing protocols. Transparent bridges do not care about Layer 3 address groupings. Devices on either side of a transparent bridge are in the same Layer 3 group—in other words, the same IP subnet or IPX network.

6 Name two of the methods of internal switching on typical switches today. Which provides less latency for an individual frame?

Store-and-forward, cut-through, and FragmentFree switching. Cut-through switching has less latency per frame but does not check for bit errors in the frame, including errors caused by collisions. Store-and-forward switching stores the entire received frame, verifies that the FCS is correct, and then sends the frame. Cut-through switching sends out the first bytes of the frame before the last bytes of the incoming frame have been received. FragmentFree switching is similar to cut-through switching in that the frame can be sent before the incoming frame is totally received; however, FragmentFree processing waits to receive the first 64 bytes, to ensure no collisions, before beginning to forward the frame.

7 Describe how a transparent bridge decides whether it should forward a frame, and tell how it chooses the interface out which to forward the frame.

The bridge examines the destination MAC address of a frame and looks for the address in its bridge (or address) table. If found, the matching entry tells the bridge which output interface to use to forward the frame. If not found, the bridge forwards the frame out all other interfaces (except for interfaces blocked by spanning tree and the interface in which the frame was received). The bridge table is built by examining incoming frames' source MAC addresses.

8 Define the term collision domain.

A collision domain is a set of Ethernet devices for which concurrent transmission of a frame by any two of them will result in a collision. Bridges, switches, and routers separate LAN segments into different collision domains. Repeaters and shared hubs do not separate segments into different collision domains.

9 How many IP addresses must be configured for network management on a Cisco Catalyst 1900 switch if eight ports are to be used with three VLANs?

A single IP address is needed. No need exists for an IP address per port because the switch is not a router. The management IP address is considered to be in VLAN 1.

10 How do EXEC and configuration commands refer to the two Fast Ethernet ports on a Catalyst 1912 switch?

These two ports are known as fastethernet 0/26 and 0/27. 0/25 is always reserved for the AUI port, and 0/1 through 0/24 are always reserved for the (up to) first 24 Ethernet ports.

11 Configuration is added to the running configuration in RAM when commands are typed in Catalyst 1900 configuration mode. What causes these commands to be saved into NVRAM?

Unlike the router IOS, commands are saved in both running config and NVRAM as the user enters the configuration commands. No separate command, such as copy running-config startup-config in the router IOS, is needed.

12 What command erases the startup config in a Catalyst 1900 switch?

The delete nvram EXEC command erases the configuration file in NVRAM. In fact, although it is easy to call it the startup config, commands instead refer to this configuration file as NVRAM.

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