Chapter 8: Backbone Networks Flashcards by Joel Sanborn (2024)

Switches

Operate at the data link layer (layer-2 switches).

Routers

Operate at the network layer and connect two different TCP/IP subnets. Routers strip off the data link layer packet, process the network layer packet, and forward only those messages that need to go to other networks on the basis of their network layer address.

Switched backbones

BN that use a star topology with one switch at its center. Each LAN has a switch that connects into this central switch.

Routed backbones

Move packets along the backbone on the basis of their network layer address. Sometimes called sub netted or hierarchical backbones commonly used to connect different buildings on the same enterprise campus. There are a series of LANS (access layer) connected to a switched backbone (distribution layer). Each backbone switch is connected to a router. Each router is connected to a core router (core layer). These routers break the network into different subnets.

VLAN

A new type of LAN-BN architecture made possible by intelligent, high-speed switches. VLANs are networks in which computes are assigned to LAN segments by software rather than by hardware. Instead of having to physically unplugging a cable to move a computer to a different hub, the software is able to perform this function virtually.

VLAN Trunk

Circuits that connect two VLAN switches and enable traffic to flow from one switch to another.

How does a layer-2 switch differ from a router?

A Layer-2 Switch operates at the data link layer and use the data link layer address to forward packets between network segments. Routers operate at the network layer and connect two different TCP/IP subnets.

How does a layer-2 switch differ from a VLAN?

VLANs are a special combination of layer-2 switches and routers. They are complex devices intended for use in large networks that have special requirements.

Under what circ*mstances would you use a VLAN backbone?

Large organizations with large networks that need LANs to be faster and provide greater opportunities to manage the flow of traffic on the LAN and BN through software instead of physically moving cables.

Explain how routed backbones work.

Routed backbones move packets along the backbone based on their network layer address. There are a series of LANs (access layer) connected to a switch backbone (distribution layer). Each backbone switch is connected to a router. Each router is connected to a core router (core layer). These routers break the network into separate subnets.

What are the key advantages and disadvantages of routed and switched backbones?

The primary advantage of the routed backbone is that it clearly segments each part of the network connected to the backbone. Each segment has its own subnet addresses that can be managed by a different network manager. There are two primary disadvantages to routed backbones. First, the routers in the network impose time delays. Routing takes more time than switching, so routed networks can sometimes be slower. Second, routers are more expensive and require more management than switches.

What are the advantages and disadvantages of VLANS?

With VLANs you can put different computers in different geographical location in the same subnet. Their ability to manage the flow of traffic on the LAN and backbone very precisely. VLANs make is simpler to manage broadcast traffic, which has the potential to reduce performance and to allocate resources to different types of traffic more precisely. They also can prioritize traffic. However, the biggest drawbacks to VLANs are their cost and management complexity.

How can you improve the performance of a BN?

If the devices and computers are a bottleneck, routing can be improved with faster devices or a faster routing protocol. If network circuits are a bottleneck, there are several options. One is to increase circuit capacity. Another option is to add additional circuits alongside heavily used ones so that there are several circuits between some devices. Another way is to reduce network demand by restricting applications that use a lot of network capacity, such as desktop videoconferencing.

What are the preferred architectures used in each part of the backbone?

Today, the most effective architecture of the distribution layer in terms of cost and performance is a switched backbone. For the core layer, most organizations use a routed backbone. However, given the tradeoffs on cost the best architectures for the distribution layer are switched backbones or VLANs.