Part – 1
1.
Compare and contrast switches, routers, and gateways.
Bridges operate at the data link layer. They connect two or more network segments that use the same data link and network protocol. They understand only data link layer protocols and MAC addresses. They may connect the same or different types of cable.
Routers operate at the network layer. Routers connect two or more network that use the same or different data link protocols, but the same network protocol. They may connect the same or different types of cable. One major feature of a router is that it can choose the “best” route between networks when there are several possible routes between them.
Because a router knows its own location, as well as the packet’s find destination, it looks in a routing table to identify the best route or path.
One other important difference between a router and a bridge is that router only processes messages that are specifically addressed to it. Bridges process all messages that appear on the network and forward them to the appropriate network based on their data link layer address. Bridges simply forward the message unchanged onto the other network.
Gateways operate at the network layer and use network layer addresses in processing messages. Gateways are more complex than bridges or routers because they are the interface between two or more dissimilar networks. Gateways connect two or more networks that use the same or different (usually different) data link and network protocols. They may connect the same or different types of cable. Some gateways operate at the application layer as well. Gateways process only those messages

explicitly addressed to them (i.e., using their data link layer address) and route those messages that need to go to other networks. Gateways translate one network layer protocol into another, translate data link layer protocols, and open sessions between application programs, thus overcoming both hardware and software incompatibilities.
2.
How does a layer-2 switch differ from a layer-3 switch?
Ethernet is a data link layer or layer-2 protocol, this type of switch is called a layer-2 switch. Layer-3 switches function in the same way as layer-2 switches, but they switch messages on the basis of their network layer address (usually IP address). These switches provide the best of both switches and routers. They can be used in place of routers but provide the benefits of traditional layer-2 switches: much faster transmission and more simultaneously active ports than routers.
3.
How does a router differ from a layer-3 switch?
Routers operate at the network layer. Routers connect two or more network segments that use the same or different data link protocols but the same network protocol. They may connect the same or different types of cable. In general, they perform more processing on each message than switches and therefore operate more slowly. One other important difference between a router and a switch is that a router processes only those messages that are specifically addressed to it. Switches process all messages that appear on the network and forward them to the appropriate network on the basis of their data link layer address. Switches simply forward the messages unchanged to the other network. In contrast, because routers operate at the network layer, the router’s data link layer

must first recognize that the incoming message is specifically addressed to the router at the data link layer level before the message is passed to the network layer for processing. The router will then process the message by building an entirely new data link layer packet, and then transmit it to the other network.
4.
Under what circumstances do you want to use a router?
The main feature of a router is that it can choose the “best” route between networks when there are several possible routes between them.
Because a router knows its own location, as well as the packet’s final destination, it looks in a routing table to identify the best route or path.
5.
Under what circumstances do you want to use multiprotocol router?
You would want to use a multiprotocol router when you need to serve networks with different data link environments. Multiprotocol routers can understand several different network layer protocols. If they receive a message in one protocol, they process it and send it out using the same protocol.
The most common multiprotocol routers understand both TCP/IP and IPX/SPX and are commonly used in Novell LANs connected through the backbone to the Internet. They enable the LAN to use IPX/SPX internally or for communications to other Novell LANs inside the organizations, and simultaneously to use TCP/IP for Internet access. Examples of heterogeneous proprietary protocol requirements where a multiprotocol router could be used would be a configuration including an IBM mainframe and a VAX cluster.

6.
What is an enterprise network?
An enterprise network connects all networks within a company, regardless of whether it crosses state, national, or international boundaries.
7.
What are three technology layers important in backbone design?
The three backbone design technology layers are the access layer, distribution layer and the core layer. The access layer consisting of layer-2 technology of LAN s connected to a backbone network (BN), the distribution layer is the part of the BN technology that connects the LANs together and containing “TCP/IP gateways” (or, most likely, routers) that are usually located within a single building, and the core layer that connects the different BNs together, often from building to building.
8.
Explain how routed backbone s work.
Routed backbones move packets along the backbone based on their network layer address (i.e., layer 3 address). The most common form of routed backbone uses a bus topology (e.g., using Ethernet 100Base-T).
At the distribution layer a routed backbone uses routers or layers 3 switches to connect a series Of LANs (access layer) to a single shared media backbone network. Each of the LANs is a separate subnet. Message traffic stays within each subnet unless it specifically needs to leave the subnet to travel elsewhere on the network, in which case the network layer address
(e.g., TCP/IP) is used to move the packet.
9.
Where are routed backbones most commonly used?
Routed backbones can be used at the core or distribution layers.

At the core layer routed backbones are sometimes called sub netted backbones or hierarchical backbones and are most commonly used to connect different buildings within the same campus network. At the distribution layer a routed backbone uses routers or layer 3switches to connect a series of LANs (access layer) to a single shared media backbone network. Each of the LANs is a separate subnet. Message traffic stays within
Each subnet unless it specifically needs to leave the subnet to travel elsewhere on the network, in which case the network layer address (e.g.,
TCP/IP) is used to move the packet.
10.
Explain how collapsed backbones work.
Collapsed backbone networks use a star topology with one device, usually a switch, at its center. The traditional backbone circuit and set of routers or bridges is replaced by one switch and a set of circuits to each
LAN. The collapsed backbone has more cable, but fewer devices. There is no backbone cable. The “backbone” exists only in the switch, which is why this is called a collapsed backbone. The original collapsed backbone technology uses layer-2 switches and suffers some disadvantage due to the load of data link layer overhead message traffic and limitations on network segmentation. As this weakness has been recognized, collapsed backbone technology is adapting by evolving to the use of layer-3 switches to overcome these problems. The result is better performance and improved network management capabilities for collapsed backbone networks.
Collapsed backbones are probably the most common type of backbone network used in the distribution layer (i.e., within a building). Most new building backbone networks designed today use collapsed backbones. They

also are making their way into the core layers as the campus backbone, but routed backbones still remain common.
11.
What the key advantages and disadvantages are of routed and collapsed backbones.
Routed backbones:
Advantages: Clear segmentation of parts of the network connected to the backbone as each network has a subnet address and can be managed separately.
Disadvantages: Slower performance as routing takes more time than bridging or switching.
Collapsed backbones:
Advantages: Performance is improved. With the traditional backbone network, the backbone circuit was shared among many LANs; each had to take turns sending messages.
With the collapsed backbone, each connection into the switch is a separate point-to-point circuit. The switch enables simultaneous access, so that several LANs can send messages to other LANs at the same time. Software configurations can replace hardware configurations.
Since there are far fewer networking devices in the network, this reduces costs and greatly simplifies network management. All the key backbone devices are in the same physical location, and all traffic must flow through the switch. If something goes wrong or if new cabling is needed, it can all be done in one place.

Disadvantages: Because data link layer addresses are used to move packets, there is more broadcast traffic flowing through the network and it is harder to isolate and separately manage the individually attached LANs. Layer 3 switches can use the network layer address, so future collapsed backbones built with layer 3 will not suffer from this problem.
Collapsed backbones use more cable, and the cable must be run longer distances, which often means that fiber optic cables must be used.
It the switch fails, so does the entire backbone network. If the reliability of the switch has the same reliability as the reliability of the routers, then there is less chance of failure. For most organizations, the relatively minor disadvantages of cable requirements and impacts of potential switch failure are outweighed by the benefits.
12. Compare and contrast rack-based and chassis switch based collapsed backbones.
The rack-based collapsed backbone has the advantage of placing all network equipment in one place for easy maintenance and upgrade, but does require more cable. In most cases, the cost of the cable itself is only a smaller part of the overall cost to install the network, so the cost is greatly outweighed by the simplicity of maintenance and the flexibility it provides for future upgrades. The room containing the rack of equipment is sometimes called the main distribution facility (MDF) or central distribution facility (CDF). The cables from all computers and devices in the area served by the MDF (often hundreds of cables) are run into the MDF room. Once in the run they are connected into the various devices. The devices in the rack

are connected among themselves using very short cables called patch cables. With rack-based equipment, it becomes simple to move computes from one LAN to another. This convenience is used to spread the traffic around the network more efficiently so that network capacity is no longer tied to the physical location of the computers. Computers in the same physical area can be connected into very different network segments conveniently in the MDF.
A chassis switch enables users to plug modules directly into the switch.
Each module is a certain type of network device. The key advantage of chassis switches is their flexibility. It becomes simple to add new modules with additional ports as the LAN grows, and to upgrade the switch to use new technologies. For example, if you want to add gigabit Ethernet or ATM you simplify lay the cable and insert the appropriate module into the switch.
17. What is IEEE 802.lq?
IEEE 802.lq is an emerging standard that inserts 16-bytes of VLAN information into the normal IEEE 802.3 Ethernet packet. When a packet needs to go from one VLAN switch to another VLAN switch, the first switch replaces the incoming Ethernet packet with an 802.lq packet that contains all the information in the original 802.3 Ethernet packet, plus 16-bytes of
VLAN information. The additional VLAN information is used to move the packet from switch to switch within the VLAN network. When the packet arrives at the final destination switch, the IEEE 802.lq packet is stripped off and replaced with a new Ethernet packet that is identical to the one with which it entered the VLAN.

Part – 2
1.
Screen shot of LAN state.
2.
Screen shot of LAN surveyor