CCNA Exploration Chapter 10 Plan and Cable. Study questions. Answers

 

Answers in white font.

 

10.1

Which devices are used within a LAN to connect end devices together?

 

Switches and hubs.

 

Which devices are used to connect one network to another?

 

Routers.

 

What does a hub do with an incoming frame?

 

Regenerates it and forwards it through all ports except the incoming port.

 

What does a switch do with an incoming frame?

 

Regenerates it and forwards it through one port to the destination.

 

Why is a switch a better choice than a hub on a medium to large network?

 

Devices connected to a hub share the medium. They share bandwidth and they are in the same collision domain. On a large network with a hub there will be a large number of collisions and performance is likely to be poor. Devices connected to a switch do not share the medium. Each device has a point to point dedicated link to the switch and has the full bandwidth. The switch segments the network into separate collision domains. Performance is much better than with a hub.

 

What factors are likely to affect the choice of networking devices?

 

Cost

Speed and Types of Ports/Interfaces

Expandability (modular or not)

Manageability

Additional Features and Services

 

You could try to cut down on cost by connecting all network devices to one central switch. Why is this often not the best option?

 

If the one switch fails then the whole network stops working. It is better to have redundancy – extra switches and connections. If one switch fails then the network can still operate. Also, if very long cables are needed to connect devices to a central switch, it may be necessary to use more expensive cables.

 

What factors should you consider when choosing a router?

 

Expandability – will you want to add modules?

Media – serial ports, Ethernet ports, UTP or fibre optic, how many of each?

Operating System Features – what do you want the router to do?

 

10.2

What is the maximum allowed length of UTP cable connecting a PC and a switch, and how is this length of cable make up?

 

100 metres in total.  5 metres patch cable from the PC to the wall socket. 90 metres installed cable from the wall socket to the patch panel in the telecommunications room. 5 metres patch cable from the patch panel to the switch.

 

What is a work area and what cabling arrangements would you find there according to the standards?

 

A work area is where an individual user sits at a computer. Each work area should have at least two outlets. (One might be used for a PC and one for a phone.) Usually each device would be linked to an outlet using a straight through patch cable.

 

What would you find in a telecommunications room (or distribution facility)?

 

The switches and routers would be in the telecommunications room. There would be patch panels where the installed cabling is terminated. The switches would be linked to patch panels using patch cables. Often the network servers are kept in the same room.

 

What is horizontal cabling?

 

Cabling that connects the work areas to the telecommunications room.

 

What is vertical or backbone cabling?

 

Cabling that connects one telecommunications room or equipment room to another, or connects out to a WAN.

 

10.2.1 Cable length

 

What factors should you consider when choosing a transmission medium?

 

Distance – what cable length or wireless range do you need?

Cost – what can you afford?

Bandwidth – How much do you need and will the medium allow it?

Ease of installation – Can you install it in-house or do you need to get a specialist team in?

Is there likely to be much interference: EMI/RFI?

 

What is attenuation?

 

As a signal travels across a medium it loses strength. This is attenuation. The longer the cable, the more attenuation. If a signal suffers too much attenuation then the receiving host will not be able to distinguish 1 from 0 clearly so the signal cannot be read.

 

What is a raceway?

 

A tube that encloses cables and keeps them neat.

 

Why is UTP cable easier to install than fibre optic cable?

 

UTP cable is thin, light and flexible, and it can be pulled without much risk of damage. It is easy to make the punch down connections needed for patch panels and wall outlets. Patch cables are relatively easy to make, or can be bought quite cheaply. Fibre optic cable is more delicate. It can be damaged if it goes round tight bends. Fitting connections is a skilled and specialised job.

 

Which medium is most susceptible to RFI, and which is least susceptible?

 

Wireless is most susceptible, fibre optic cable least.

 

When you connect two PCs via a switch or hub, you use straight through cables. How does the transmitter in one PC link to the receiver in the other PC?

 

The switch or hub manages the crossing over internally.

 

Is there only one way of correctly terminating a straight through cable?

 

No, there are two standards, T568A and T568B. Within a LAN, you should keep to one standard to avoid confusion.

 

Are switch ports always the MDIX type?

 

No. Some switches have ports that can be converted between MDI and MDIX by moving a little switch. Some switches can be configured to have ports either MDI or MDIX. Some switches are able to detect automatically whether an MDI or MDIX port is needed. (Also, uplink ports may be different from the other ports.)

 

What are DTE and DCE?

 

Data Communications Equipment (DCE) is typically provided by a WAN access provider. It links to the customer’s  Data Terminal Equipment (DTE) which is usually a router.  The DCE supplies the clocking service for the link. The DTE adjusts to the clock rate supplied by the DCE.

 

10.3

 

What is the first step in producing an addressing scheme for a set of networks?

 

Count the number of hosts that will need addresses on each network/subnet. Include router ports, switches, servers, admin and general workstations, printers and IP phones – anything that needs an address.

 

If you have 4 bits in the host part of an IP address, how many host addresses can you have?

 

The formula is 2n – 2 so we have 24 – 2 = 16 - 2 = 14

 

If you have 6 bits in the host part of an IP address, how many host addresses can you have?

 

The formula is 2n – 2 so we have 26 – 2 = 64 - 2 = 62

 

If you have 10 bits in the host part of an IP address, how many host addresses can you have?

 

The formula is 2n – 2 so we have 210 – 2 = 1024 - 2 = 1022

 

You need 18 host addresses on a subnet. How many host bits do you need?

 

5 host bits giving 30 addresses. (We can’t have 4 bits because there would only be 14 addresses.)

 

You need 300 host addresses on a subnet. How many host bits do you need?

 

9 host bits giving 510 addresses. (We can’t have 8 bits because there would only be 254 addresses.)

 

Give three reasons for dividing a network into subnets.

 

To cut down the number of broadcasts. Splitting the network into subnets also splits it into separate broadcast domains.

To provide different facilities for different groups of users.

For security. Traffic between subnets can be controlled.

 

What address should you give to a router interface that is the default gateway for a LAN?

 

Either the lowest or highest host address on the LAN. Some organisations use the lowest and some the highest. Within an organisation, always be consistent and make it the same for every network.

 

Why should you group different categories of devices together into blocks of addresses (e.g. general users, admin users, routers, switches, servers) and use the same pattern of addressing on every network in an organisation?

 

It helps with troubleshooting. Also it allows security setting to be different for the different groups of devices.

 

10.4

 

You are given 192.168.1.0/24

There are 7 networks to address as follows:

Abingdon: 80 hosts

Benson: 40 hosts

Cumnor: 8 hosts

Didcot: 7 hosts

WAN1: 2 hosts

WAN2: 2 hosts

WAN3: 2 hosts

Use VLSM and produce a subnet scheme.

 

Subnet

Network address

Host range

Broadcast address

Abingdon

192.168.1.0

192.168.1.1 - 192.168.1.126

192.168.1.127

Benson

192.168.1.128

192.168.1.129 - 192.168.1.190

192.168.1.191

Cumnor

192.168.1.192

192.168.1.93 - 192.168.1.206

192.168.1.207

Didcot

192.168.1.208

192.168.1.209 - 192.168.1.222

192.168.1.223

WAN1

192.168.1.224

192.168.1.225 - 192.168.1.226

192.168.1.227

WAN2

192.168.1.228

192.168.1.229 - 192.168.1.230

192.168.1.231

WAN3

192.168.1.232

192.168.1.233 - 192.168.1.234

192.168.1.235

 

10.5

What interfaces do you find on the lab routers and what is the purpose of each? (Other types of interface exist.)

 

Fast Ethernet interfaces for connecting to a LAN.

Serial interfaces for connecting to (or simulating) a WAN

Console Interface for configuring a router.

Auxiliary (AUX) Interface for connecting to a modem for remote management of the router.

 

What type of cable would you use to connect a PC to a router’s console port for configuration purposes?

 

Rollover cable

 

Which PC port would you connect the cable to?

 

Serial port. (DB9, com 1)

 

What program do you have to run on the PC in order to configure the router?

 

A terminal emulation program, normally Hyperterminal.

 

When you start Hyperterminal you configure the serial port. What setting should you use for bits per second?

 

9600.