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Chapter 15
Network Hardware
Unix System Administration
If VirtualRatings.Com Had
Student Ratings, You’d Get a 10
• Network technologies & topologies
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–
–
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Ethernet - bus, star
Token-Ring
FDDI - ring
ATM - star
• Networking Devices
– Hubs
– Bridges/switches
– Routers
You’ve Got Some Nice Toplogies
• Ethernet
– Bus technology
– Can be wired in a bus or physical star topology
– The Polite Dinner Party - CSMA/CD
• Carrier sense
• Multiple access
• Collision detection
– Hubs, switches, bridges and routers
Wirez Wire
• Thicknet
– 10Base5 - 50 ohm RG-11
– Vampire Taps connect drop cable to thicknet
– Max length = 117m with 2.5m between devices
• Thinnet
– 10Base2 - 50 ohm RG-58
– BNC T connectors
– Max length = 185m
Twisting The Au Pairs
• Star configs using hubs or switches
• Wires are twisted to compensate for crosstalk - Don’t use a regular phone cable
• Two pairs (4-wires) are used even though
four pair cable is usually installed
• RJ-45 connector pins 1,2,3 & 6 are used
• Cabling is rated in levels
– Level III (3) is for up to 10Mbps
– Level V is for up to 100Mbps
How About More Fiber In Your
Diet?
• Fiber cable is basically a piece of glass
covered with a reflective cladding
• Fiber devices are always configured in a
star (point-to-point)
• Fiber is either multi-mode or single-mode
• I wouldn’t waste fiber on anything less than
100Mbps.
• Currently Gigabit Ethernet is only available
using fiber. SX-short wave, LX-long wave
Do It Yourself Laser Eye Surgery
• Fiber-optic safety
– Be Careful not to stick yourself with a broken
fiber
– Two types of signal source, LED and LASER
– NEVER look into a fiber cable if you don’t
know what’s connected to the other end
Is That a Token In Your Ring, or
Are You Just Happy To See Me?
• Token-Ring use a token passing scheme that
guarantees each device gets a chance to
transmit data
• FDDI works similar to token-ring but uses
fiber-optics in a 100Mbps dual counterrotating ring configuration
– Good at surviving a single ring cut
– Expensive
ATM, Your PIN # Please
• Asynchronous Transfer Mode
• For voice, video and data transmissions
• Uses 53-byte cells instead of packets in a
switching network similar to a telephone system.
• Never really took off in a LAN environment but is
very popular in the WAN or backbone
• Feature QoS and RSVP
• Big learning curve over Ethernet technologies
Hubs and Switches and Routers,
Oh My!
• Hubs
–
–
–
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Basically a multi-port repeater
Ethernet limits repeaters to 4 per segment
Each hub counts as a single repeater
Modern hubs usually have a way to connect
them without incurring a repeater hop
– Hubs being replaced by inexpensive switches
– I wouldn’t suggest a hub except in the most
trivial network setup
Bridges, Switches. What’s The
Difference?
• Bridge connects multiple segments of a
network together
• Bridges can also connect differing
topologies (e.g. token-ring & Ethernet)
• Switches are fast bridges
• Bridges and switches work at layer 2 of the
OSI model (data link) which means
decisions are based on MAC addresses
Routers Schmouters
• Routers connect networks/IP subnetworks
together.
• Routers work at Layer 3 of the OSI model
(Network)
• Routers are smart and can make decisions
based on IP (or IPX) addresses and can
filter based on TCP/UDP port numbers
Trans-topological Devices
• Layer 3 Switches
– a.k.a. fast routers
– Routes IP/IPX/Appletalk only
– VLANS (port, protocol or network-based)
• Layer 4 Switches/Routers
– Makes decisions based on protocol content, e.g.
URL
If You Slept Through Everything
Else, Pay Attention Now
Repeater/Hub Bridge/Switch Router
Collision
Domain
Single
Separate
Separate
Broadcast
Domain
Single
Single
Separate
10- Pure Perfection!..
• When would you pick a switch over a
bridge?
• When would you pick fiber over copper?
• When would you want to use ATM’s RSVP
and QoS?