1. UCCN 1003 (May 2010)
Data Communications & Networks
(Lecture 03a)
Local Area Network (LAN)
Design Issues
2. 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)
3. 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
4. LAN to Enterprise Network
• Multiple LANs form enterprise
network within an
institution/corporation/company.
– Enterprise network can get rather
complicated.
Internet
6. 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.
7. 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
8. 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.
9. 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 hierachical
star
10. Quick Quiz
• What is the
network topologies
of this network?
11. Answer
• This network has a
combination of 4
topologies
– Star
• In the LAN with
switch
star – Mesh
star • The Routers’
network
– Point-to-point
• In the LAN with PC
directly connected
to router
Mesh – Extended Tree
• Quiz: Where is it?
Point-to-point
Point-to-point
12. 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 switch
provide higher data transmission (or bandwidth) than hub.
13. 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.
15. 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
17. Overview of LAN Boudary
• In UCCN1003, LAN =
– end-devices connected to switches/hubs bound by
routers.
18. Still the same LAN with switches and hubs
Still 1 LAN
PC0 is still in the
same LAN as
Server1, Printer0,
PC1, PC2, PC3,…
• No matter how many switches and hubs (of different
models) are connected together, functionally they still
form the same one LAN.
19. Routers - Boundary of LAN
LAN 2 LAN 4
LAN 3
LAN 5
LAN 1
• 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.
20. Routers - Boundary of LAN
Gateway
for LAN 2
Gateway Gateway
for LAN 1 for LAN 4
Gateway
for LAN 5
Gateways
for LAN 3
• 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.
22. 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
23. 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.
Router PC
24. 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
26. Cross-over cable are used in…
Cross-over cable are represented by dashed line in Packet Tracer
27. 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.
28. 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.
29. 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.
30. Serial Cable
• Used in connecting router of an enterprise network to Internet
(via Telephone companies (telco), or Internet service provider
(ISP))
32. 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.
33. 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
34. 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.
35. 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.
36. 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.
37. 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
39. 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) _______
40. Answers
• How many LANs are there in following 2 figures?
2 6
• 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__
41. 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.
42. 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
43. 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
45. 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
47. 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 have
decided to install DHCP services on one of the servers. Identify which of
the following are the advantages of using the DHCP server in the
network.
– 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.
49. 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 Server
51. 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
