Download Network Devices - York Technical College

Network Devices
Lecture 2
Cabling
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Computer to computer – crossover
cable
Computer to hub – straight-through
cable
Hub to switch or Hub to hub
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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
LEDs
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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
Managed v. Unmanaged
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Applies to both switches and hubs
Has an interface that can be configured
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Speed
VLANS (switches)
Number of Ports
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Hubs and Switches
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8
16
24
32
Packet
The protocol data unit that is transmitted over a WAN
or between LANs when using a router.
Network Header
Data
IP Address
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Logical Address or Network Address
#.#.#.#
Routers
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Intelligent network device
Has CPU built in
Determines best path for
packet to get to destination
Bases decision on IP address
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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
Routable (Routed) Protocols
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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
NetBeui
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This network protocol is non-routable.
Routing Protocols
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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.
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Routing tables – lists of networks and the
associated port to each network
Routing can be dynamic (automatic) or
administrator can configure a static route.
Network
201.100.11.1
Routing Table Example
S0
E0
Network
192.5.5.0
Interface
E0
205.7.5.0
E1
201.100.11.0
S0
Network
192.5.5.0
E1
Network
205.7.5.0
Routing Protocols
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Distance Vector
Link State
Distance Vector
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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
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DV Disadvantage
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Each router transmits its entire routing
table every 30 seconds (RIP) creating a
lot of network traffic.
Convergence
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The amount of time needed for all
routers in a network to have common
knowledge – routing tables all have the
same information in them.
Routing Loops
E
A
Network 1
D
At first, all
routers have
common
routing
tables.
C
B
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 doesn’t have
the update about Network 1 so it
sends its table to D & B. D may
assume that there’s another path
through C -> 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.
Split Horizon
E
A
Network 1
D
C
B
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.
Link State Protocols
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Examples
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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
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Requires more RAM to store the database than DV protocols.
Server-based Routers
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Servers can have two NICS installed
and act as a limited router.
Brouter
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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).
Gateways
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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.
CSU/DSUs
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Channel Service Unit/Digital Service
Unit
Changes signal from one digital format
to another.
ISDN Terminal Adapters
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Translates digital signal between two
digital formats.
Modem
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Modulator/Demodulator
Translates from digital to analog and
back.
56 kbps maximum connection speed.
Actual transfer speed is less – around
43 kbps.
Two Factors that Determine
Modem Connection Speed
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Maximum connection speed of the
Universal Asynchronous
Receiver/Transmitter (UART) chip
Actual modem speed
UART Chips & Speeds
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Chip
8250
16450
16550
16650
16750
16950
Speed bps
9600
115200
115200
430800
921600
921600
Modem Commands to Know
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ATA – Answers incoming call
ATH – Hangs up current connection
ATZ – Resets the modem
ATI3 – Displays modem id info