Transcript Cisco – Chapter 3

Cisco – Chapter 2
LAN
LAN Teaching Topology
• physical topology is the actual layout of the wire
(media)
• logical topology defines how the media is
accessed by the hosts
– Logical topologies are Broadcast (Ethernet) and Tokenpassing.
• Broadcast - each host sends its data to all other hosts on the
network medium – CSMA/CD
• Token Passing -Pass electronic token sequentially to each host.
LAN Topologies
• Physical – how the network is wired
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Bus
Ring
single and dual
Star and Extended Star
Hierarchical
Mesh
• Logical – how medium is accessed by hosts for
sending data
– Broadcast (Ethernet), token ring,
LAN Devices
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2 NICs
1 Media
1 Repeaters
1 Hubs
2 Bridges
2 Switches
3 Routers
1-7 Clouds
1 Network Segments
NICS – Layer 2
• printed circuit board that fits into the
expansion slot of a bus on a computer’s
motherboard or peripheral device
• also called a network (LAN) adapter
• Layer 2 devices because each individual
NIC carries a unique code(looks at MAC –
physical address)
• Controls the host's access to the medium.
AUI
• AUI does not always match (Cisco 2500 router)
• transceiver (transmitter/receiver) is used to
connect – Layer 1
– transceiver converts one type of signal or connector to
another
– convert electrical signals to optical signals
– considered a Layer 1 device, because it only looks at
bits
Security Devices
• Firewalls – combination of hardware and
software to protect internal network
– Examines each packet to determine whether to
discard or forward
• AAA Server – authenticates, authorizes, and
provides accounting information
– Kerabos, TACACS+, RADIUS
• VPN Concentrator –used with VPNs
Wireless
• Wireless NICs – client adapter; available as
PCMCIA and PCI cards
• Wireless Access Points – WAPs, a
transceiver that connects wireless to wired
networks
• Wireless Bridges – high speed, long-range
line-of-sight wireless connectivity
Media Layer 1
• basic functions of media are to carry a
flow of information, in the form of bits
and bytes, through a LAN
• networking media confine network
signals to a wire, cable, or fiber and
wireless
• PAN (Personal area network) – uses
human body as medium
Media 2
• Selection criteria include:
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Cable length
Cost
Ease of installation
Total number of hosts
• Most common medium is Cat 5 UTP
Repeaters – Layer 1
• Extend length of cable run beyond
maximum length for that medium
– Concept originated from early form of visual
communication when signals were sent from
hill to hill visually
– Purpose is to regenerate (amplify) and retime
signals
– Single-port in and single-port out device
– Act only on bit level
Hubs – Layer 1
• Regenerate (amplify) and retime network signals
• Create a central connection point for the wiring
media
• Increase in the reliability of the network (one
connection point)
• Active hubs extend signal length; passive hubs do
not extend length
• Role in Token ring is played by MAU, a.k.a.
concentrator
• A.K.A. multi-port repeater
Bridges – Layer 2
• designed to connect two LAN segments
• filters traffic on a LAN to keep local traffic
local
• allows connectivity to other parts
(segments) of the LAN
• Uses MAC address to make filtering
decision
• Are being replaced by switches & routers
Switches – Layer 2
• Called a multi-port bridge
• Make decisions based on MAC addresses
• Switch data only out port to which proper
host is connected
• Part of function is connectivity
concentration (allow many devices to
connect to one point in network)
• Can provide each port with full bandwidth
Routers – Layer 3
• Makes decisions based on groups of network
addresses (logical addressing)
• Can also connect different layer 2 technologies,
such as Ethernet, Token-ring, and FDDI.
• Have become the backbone of the Internet,
running the IP protocol.
• Choose best path and switch to proper port
• Primary functions – path selection & switching
Cloud – Layer 1- 7
• Reminds us there is a way to connect but
does not supply details of connection or
network
• Represents a large group of details that are
not pertinent to the situation
Network Segments – Layer 1
• Identifies the layer 1 media that is the
common path for data transmission in a
LAN; sometimes called WIRE
• Each time an electronic device is used to
extend the length or manage data on the
media a new segment is created
• It means segments of the network here; it
does have a different meaning at Layer 4
Network Milestones
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1950s – Mainframe computers
1960s – Mini computers
1970s – Advent of personal computers
1970s – Beginning of Internet
1980s – Gateways – special purpose
computers to interconnect LANs
• 2000 – Convergence of voice, video, and
data into one information stream
Encapsulation
• Top three layers prepare data for transmission by
creating a common format
• Transport layer breaks data up into units called
segments & assigns sequence #s
• Network layer encapsulates segment into a packet
& adds IP addresses
• Data-Link Layer encapsulates packet into a frame
and adds MAC addresses
• Physical Layer sends out binary bits on media
Encapsulation 2
• Bottom three layers are primary movers of
data
– Physical, Data Link, and Network
• Exception is a Gateway – a device designed
to convert data from one format to another
– Gateway uses all 7 layers of OIS model
• Data – Segments – Packets – Frames - Bits