Network Devices

1
Network Devices

• Lecture 2

2
Cabling

• Computer to computer crossover cable
• Computer to hub straight-through cable
• Hub to switch or Hub to hub
• MDI-X port to MDI port straight-through
• MDI port to MDI-X port straight-through
• MDI-X port to MDI-X port cross-over

3
LEDs

• Light emitting diodes
• Present on both hubs, switches, and routers
• Green live connection at that port on that
  piece of equipment
• Flashing green activity (traffic)
• Amber problem
• Red or no light not working

4
Managed v. Unmanaged

• Applies to both switches and hubs
• Has an interface that can be configured
• Speed
• VLANS (switches)

5
Number of Ports

• Hubs and Switches
• 8
• 16
• 24
• 32

6
Packet
The protocol data unit that is transmitted over a
WAN or between LANs when using a router.
Network Header
Data
7
IP Address

• Logical Address or Network Address
• ...

8
Routers

• Intelligent network device
• Has CPU built in
• Determines best path for packet to get to
  destination
• Bases decision on IP address
• Synonyms logical address, network address
• Refers to its routing table to make decisions
  about which port to send the packet
• Configurable
• Can connect two LAN segments
• Can connect a LAN to a WAN

AUI ports notice the transceivers on the second
router on the rack.
Serial ports to connect LAN to WAN
9
Routable (Routed) Protocols

• Responsible for sending messages between nodes.
• IP Internet Protocol (part of the TCP/IP
  protocol suite
• IPX/SPX Novell going away replaced by IP
• Appletalk MacIntosh replaced by IP

10
NetBeui

• This network protocol is non-routable.

11
Routing Protocols

• Routing protocols route routable protocols
• Responsible for updating routing tables between
  routers so they can know the topology of the
  network and determine best path.
• Routing tables lists of networks and the
  associated port to each network
• Routing can be dynamic (automatic) or
  administrator can configure a static route.

12
Routing Table Example
Network201.100.11.1
S0
E0
Network Interface 192.5.5.0 E0 205.7.5.0 E1 201.
100.11.0 S0
Network 192.5.5.0
E1
Network205.7.5.0
13
Routing Protocols

• Distance Vector
• Link State

14
Distance Vector

• Routers send routing table updates to each
  neighboring router periodically.
• Examples
• RIP (Routing Information Protocol)
• IGRP (Interior Gateway Routing Protocol)
• Movement from one router to the next is
  considered a hop.
• DV metric (measurement) is hops.
• Lower number of hops is better determines best
  path

15
DV Disadvantage

• Each router transmits its entire routing table
  every 30 seconds (RIP) creating a lot of network
  traffic.

16
Convergence

• The amount of time needed for all routers in a
  network to have common knowledge routing tables
  all have the same information in them.

17
Routing Loops
E
A
Network 1
D
Network 1 goes down. Router E sends its routing
table without Network 1. Router A updates its
routing table. At the next update (after 30
seconds), Router A sends its table to D and B.
They have to update their tables. Meanwhile,
Router C doesnt have the update about Network 1
so it sends its table to D B. D may assume
that theres another path through C -gt B to
Network 1 so it updates its table. Next round,
it updates Router A. Router A assumes there is
another path. Now they all have inaccurate
information and the loop continues.
At first, all routers have common routing tables.

B
C
18
Split Horizon
E
A
Network 1
D
Split horizon will not allow an update from the
opposite direction of the first update. So, A
notified D and B and they cannot send erroneous
tables back to A thereby preventing routing loops.
B
C
19
Link State Protocols

• Examples
• OSPF Open Shortest Path First
• NLSP Network Link State Protocol
• When network is installed and OSPF configured as
  the routing protocol, OSPF uses LSAs (Link State
  Advertisements) to collect information about the
  network and build a database of the entire
  topology.
• During the initial stage where it is learning the
  topology, the process causes a lot of activity on
  the network. After the database is built and
  best paths chosen, traffic is minimized because
  updates only occur when there is a topology
  change, (for example, a network goes down) and
  LSAs are exchanged to make the update in the
  database.
• Disadvantage
• Requires more RAM to store the database than DV
  protocols.

20
Server-based Routers

• Servers can have two NICS installed and act as a
  limited router.

21
Brouter

• Device that can function as both a router and a
  bridge depending upon the protocol of the
  message. If it is a routable protocol, it routes
  it. If the message protocol is an Ethernet
  protocol, it either forwards it or blocks it
  (functions as a bridge).

22
Gateways

• A device, system, or software that can perform
  the function of translating data from one
  protocol to another (TR to Ethernet), and one
  format to another.
• Usually a server.
• Slows network traffic because of translation time.

23
CSU/DSUs

• Channel Service Unit/Digital Service Unit
• Changes signal from one digital format to
  another.

24
ISDN Terminal Adapters

• Translates digital signal between two digital
  formats.

25
Modem

• Modulator/Demodulator
• Translates from digital to analog and back.
• 56 kbps maximum connection speed. Actual
  transfer speed is less around 43 kbps.

26
Two Factors that Determine Modem Connection Speed

• Maximum connection speed of the Universal
  Asynchronous Receiver/Transmitter (UART) chip
• Actual modem speed

27
UART Chips Speeds

• Chip Speed bps
• 8250 9600
• 16450 115200
• 16550 115200
• 16650 430800
• 16750 921600
• 16950 921600

28
Modem Commands to Know

• ATA Answers incoming call
• ATH Hangs up current connection
• ATZ Resets the modem
• ATI3 Displays modem id info