Data Communications & Networks

Local Area Network (LAN)

Design Issues

UCCN 1003 (May 2010)

(Lecture 03a)

LAN Design Issues

Describing various design issues, principle, and guidelines of LAN,

especially on the physical aspect of LAN

(e.g. topology, cables, boundary of LAN, etc)

Overview of LAN Issues

• There are two aspect of LAN design issues:– Physical issues

– Issues from IP address

• Physical Issues of LAN deals with– Network Topology

– LAN boundary

– Cables and connecting the equipments

– Placement of servers/services

• Issues from IP address (Later lecture)– IP address design after physical LAN layout

– IP subnet rules

LAN to Enterprise Network

• Multiple LANs form enterprise network within an institution/corporation/company. – Enterprise network can get rather

complicated.

Internet

Network Topology

End Devices & Networking Devices

• In Lecture 1b, we have studied

• End-devices:

• Networking devices (with cables too):

• In LAN design:

– We need to learn how to connect these devices together with cables in order to form a network.

– Network topology shows us a few way to do this.

Network Topology - 1

• Network topology: is the study of the arrangement or mapping of the elements (links, nodes, etc.) of a network, especially the physical (real) and logical (virtual) interconnections between nodes.– In bus topology, the nodes connect to a common backbone or trunk, called the

bus.

– Star topology links all nodes of the network to a central node.

– In ring topology, each node connects to another in a closed loop.

– In mesh topology, nodes are “randomly” connected to one or many nodes.

– A node can be an end device or a network device.

Point-to-point

Network Topology - 2

• Network can be formed with any combination of these network topologies in order to connect the network devices.– Meaning network can be formed with mesh, star and hierarchical.

Topology of the Lecture 2b Network

• LAN where PCs and server connected to a switch forms a star-topology

• The whole big network forms a tree or hierarchical topology

star

star hierachical

Quick Quiz

• What is the network topologies of this network?

Answer

• This network has a combination of 4 topologies– Star

• In the LAN with switch

– Mesh• The Routers’

network

– Point-to-point• In the LAN with PC

directly connected to router

– Extended Tree• Quiz: Where is it?

starstar

Point-to-pointPoint-to-point

Mesh

LAN – Star Topology

• In our LAN design, the most common topology is star topology– All data that is transmitted between nodes in the network is transmitted to

this central node, then retransmits the data to some or all of the other nodes in the network

• Star-topology LAN is normally formed by connecting the servers and PCs to a switch, or a hub.– Switches and hubs are normally not required to be configured to form a

LAN (versus router has to be configured).

– Switches and hub will automatically communicate and transfer data among hosts (PCs), once these hosts are connected to the switch or hub.

• But switch is a much superior central node than hub since switchprovide higher data transmission (or bandwidth) than hub.

Enterprise Network – Tree Topology

• In enterprise network, tree (or hierarchical) topology is normally the preferred network topology.– An efficient enterprise network is normally organized as a hierarchy

or trees of LANs.

Intenet – Mesh Topology

Issues of Network Topology

• Mesh– Full connectivity, good fault isolation

– Require a lot resources (cable, I/O ports)

• Ring– Less wire used than mesh

– Medium efficiency and fault isolation

• Bus– Least wire used

– Disastrous if link is fail. Not efficient as host increases

• Star and Extended Star– Cheaper than mesh, good fault isolation, easy to install, good

connectivity

– Bottle neck in the central hub.

• Hierarchical (or tree)– Hierarchical organized, most widespread network infrastructure

topology

– Need multiplexing equipment, bottleneck at the top node

LAN Boundary

Overview of LAN Boudary

• In UCCN1003, LAN = – end-devices connected to switches/hubs bound by

routers.

Still the same LAN with switches and hubs

• No matter how many switches and hubs (of different models) are connected together, functionally they still

form the same one LAN.

Still 1 LAN

PC0 is still in the same LAN as Server1, Printer0, PC1, PC2, PC3,…

Routers - Boundary of LAN

• Router is the boundary of the LAN

• This “boundary” of a LAN is the location of the gateway, which is router port configured with an IP address.

• Every host in that LAN has to set its gateway to that IP address.

LAN 1

LAN 2

LAN 3

LAN 4

LAN 5

Routers - Boundary of LAN

• Unlike switch, you have to configure a router before it can be used in a network

– At least you need to configure the IP addresses for the router ports

• Gateways are the “escape door” from a LAN to the next LAN.

• A LAN can have more than 1 gateway.

Gatewayfor LAN 5

Gatewayfor LAN 4

Gatewayfor LAN 2

Gatewaysfor LAN 3

Gatewayfor LAN 1

Cables and Connections

Common Types of Cables in Network

• In network, we use cables to connect various end-devices and networking devices.

• The cables used in Packet Tracer:– Rollover cable

– Ethernet copper straight through– Ethernet copper cross-over

– Fiber optics– Telephone cables

– Coaxial– Serial cables

Rollover Cable

• Rollover cable is a cable with a serial comm connect at one end, and a RJ-45 connector at the other end.

• Rollover connects the serial comm port of a PC to the console port of a router.

• Rollover cable is only used for router configuration, not data transfer in network.

PCRouter

Ethernet Copper Cable (Cat 5)

• There are two types of cable to connect the Ethernet ports in the LAN of the PC, switches, and routers.

– Straight-through and Crossover

• Both type of cables are a type of twisted pair copper wire cable for local area network (LAN) use for which the RJ-45 connectors at each end

• Both of them look the same, except for the conductors arrangement shown below.

• Straight-through cables have the same pinout (i.e., arrangement of conductors).

• Crossover cable, the wires on the cable are crossed over so that the receive signal pins on the connector on one end are connected to the transmit signal pins on the connector on the other end.

RJ-45 connector

Straight-through cables are used in…

Straight-through cable are represented by solid line in Packet Tracer

Cross-over cable are used in…

Cross-over cable are represented by dashed line in Packet Tracer

Fiber Optics

• Optical fibers are used to transmit data using light, which permits transmission over longer distances and at higher bandwidths (data rates) than other forms of communications.– Undersea Internet cables are almost all in fiber-optics.

– Transmit up to tens of giga bits per second.

– Immune to electromagnetic interference.

Telephone Cable

• Used to connect phones.– Used in ADSL modem to connect to phone plug for accessing the

Internet.

• Quite similar to Ethernet cable but smaller.

Coaxial Cable

• For TV used.• Used in connection from cable modem to cable TV

outlet/plug.– Not popular in Malaysia, but quite widely used in US.

Serial Cable

• Used in connecting router of an enterprise network to Internet (via Telephone companies (telco), or Internet service provider (ISP))

Placement of Services/Servers

DHCP service in a LAN

• DHCP service only works within a LAN.

• DHCP service does not function beyond a router.

PC1 can’t get

the dynamic IP

from Server0

because Router0

has blocked it.

DHCP Server placement

• 1 DHCP server serve 1 LAN

– Rule of thumb: 1 DHCP service for 1 LAN (either from server or router)

• 2 LANs need 2 DHCP servers (or service).

• Router (and ADSL router) can provide DHCP service.

• You can have a few DHCP service within a LAN

– As long as the DHCP IP range does not clash with each other

– Will serve as good backup in case one DHCP server fails

IP Issues on DHCP service

• The DHCP servers has to set with static IP!!– You can NOT set the IP of DHCP servers to dynamic IP!!!

• In the following example, the DHCP static IP and gateway IP are in the range of the DHCP service– DHCP service can detect it and won’t assign duplicate IP in the LAN.

DNS Server

• DNS server can be set within the LAN (local DNS server).

• Unlike DHCP, you can request DNS service beyond your LAN.

• Public DNS servers are a GLOBALLY linked.

– All the public DNS servers in the world work as “a team” to provide the service to the world.

• The DNS server in Packet Tracer is greatly simplified.

Difference between FTP and TFTP

• Both FTP and TFTP are file services

• TFTP (trivial file transfer protocol)– Unsecured, no login and password

– As a LAN backup file server– Best not to be assessed across the Internet

– Not widely deployed.– In this class, it is only used for backing up the running-

config and start-config files of router.

• FTP– Secured, with login and password– sftp (secure ftp), where login, password, and data are

encrypted.

– For Internet access.

Local Servers and Remote Servers

• Local servers : servers that are best placed within LAN (or within the enterprise network)– TFTP server– DHCP server

– Print server– Security server (e.g. AAA, NTP, Syslog, not taught in

this class)

• Remote servers: servers that can be accessed across the Internet– Email server– Web server

– DNS server

– FTP server

Quiz

Quick Quiz

• How many LANs are there in following 2 figures?

• In the following figure:• Do you see a problem if Server0 is a DNS server? (Yes/No) _______• Do you see a problem if Server0 is a DHCP server? (Yes/No) _______

Answers

• How many LANs are there in following 2 figures?

• In the following figure:• Do you see a problem if Server0 is a DNS server? (Yes/No) __No__• Do you see a problem if Server0 is a DHCP server? (Yes/No) __Yes__

2 6

True/False Questions

1. DHCP server should have a static IP.

2. You can’t have 2 DHCP services in a LAN.

3. A Switch with 4 ports/interfaces requires 4 IP address.

4. In general, the more routers in a network, the more LAN we have. (compared to switches)

5. Gateway IP is not required if a LAN is not connected to any routers (only switches and hubs).

6. Switch ports are assigned with port numbers.

7. You can’t test a switch with a direct ping command.

8. DHCP service supplies a default gateway MAC address for PCs

9. Dynamic IP is easier to be managed for PCs than static IPs.

10. Aux port in routers are used to transfer data through phone lines.

11. CLI can’t be accessed through Fast Ethernet ports.

12. Router Ethernet interface can’t accept IP from DHCP service

13. Cross over cables uses a bigger size RJ-45 connector than straight through cables.

14. Roll over cables use connectors of different types at both ends.

15. Fully connected network topology requires the most amount of cables

16. Server must be set with the first IPs in the given IP range.

17. telnet is used to configure router through console port

18. Different CLI mode (or prompt) only accepts different sets of commands.

19. Interface mode in CLI accepts “no shut” command.

True/False Questions

1. Answer: T

2. Answer: F

3. Answer: F

4. Answer: T

5. Answer: T

6. Answer: F

7. Answer: T

8. Answer: F

9. Answer: T

10. Answer: F

11. Answer: F

12. Answer: T

13. Answer: F

14. Answer: T

15. Answer: T

16. Answer: F

17. Answer: F

18. Answer: T

19. Answer: T

MCQ

• You can place the DHCP server ________ from your PC that requires dynamic IP.– A) in the neighboring LAN B) 2 routers away– C) 5 switches away D) 2 hubs and 1 router away– E) 2 hubs and 4 switches away– F) 1 cross-over cable point-to-point connection

• You can place the DNS server ________ from your PC that requires domain name support.– A) 3 LAN away – B) 1 straight-thru cable point-to-point connection– C) 10 switches away D) 12 routers away– E) 1 hub, and 2 switches away F) within the same LAN

Answer

• Answer: C, E, F

• Answer: A, C, D, E, F

MCQ

• Default gateway can be in:– A) switch B) PC C) router– D) hub E) cable F) printer

– G) IP phone H) wireless access point

• The DHCP server will supply an IP to a PC if:– A) “www.cnn.com” is typed

– B) “ipconfig /release” is typed– C) Server sends information to default gateway

– D) “nslookup dhcp”.com is type– E) “netstat –b dhcp” is typed

– F) “no shutdown” is typed

Answer

• Answer: B, C

• Answer: None

MCQ

• Which of the following network topology is the most fault-tolerant?– A) Mesh B) Line C) Tree

– D) Star E) Fully Connected

– F) Point-to-Point G) Bus H) Hierarchical

• You have a TCP/IP network comprising nearly 30 computers. Currently, all computers have been assigned IP addresses manually. You havedecided to install DHCP services on one of the servers. Identify which of the following are the advantages of using the DHCP server in thenetwork. – A) The domain name resolution process will be automated.

– B) The network can be monitored more efficiently.

– C) Assignment of IP addresses will be automated.

– D) Network traffic problems can be resolved.

– E) Network administration workload can be reduced.

Answer

• Answer: E

• Answer: C, E

MCQ

• One of the following components can cause the entire network to suffer a complete failure if a fault develops in it. Identify this component.

– A. NIC B. Hub C. Crossover Cable

– D. Local FTP server E. Switch

– F. DNS G. DHCP server H. Router

• Refer to the following diagram. You have set up a DHCP server in one segment of your network. When the DHCP server is fully functional, both PC3 and PC4 is not able to get IP addresses automatically from the DHCP server. What would be the solution to the problem?

– A) Attached another DHCP server to Hub0.

– B) Replace the hub with a switch.

– C) Replace the router with a switch.

– D) Set the IP addresses of PC3 and PC4 to be in the same LAN range of the DHCP server.

DHCP ServerDHCP Server

Answer

• Answer: B, E

• Answer: A, C

MCQ

• You have installed a NIC and TCP/IP in a workstation running Windows XP. When the workstation is connected to the hub and restarted, the activity link light on the NIC does not glow. Which of the following is least likely to be the cause of the problem?– A) The Ethernet cable B) Wrong IP address

– C) A bad port on the hub D) The NIC is not properly slotted in the PC

– E) DHCP server is not working

– F) Router is not set properly

• Which of the following configuration change on a local computer does not affect its functioning on the network?– A) Adding a new NIC B) Installing new applications

– C) Updating the driver of a currently installed NIC

– D) Adding a new user to access the shared resources

– E) Adding or removing a network protocol

– F) Changing IP address

Answer

• Answer: B, E, F

• Answer: B, D