Transcript PPP/SLIP Installation

Subnetting
129.123.7.55 AND 255.255.255.0= 129.123.7.0
129.123.7.148 AND 255.255.255.0=129.123.7.0
129.123.7.0 COMPARED (MINUS) TO 129.123.7.0= 0.0.0.0
129.123.25.77 AND 255.255.255.0=129.123.25.0
129.123.7.0 COMPARED (MINUS) TO
129.123.25.0=0.0.18.0
Since there is a non-zero result, the request must be
forwarded to the routed via the gateway address.
Subnetting continued
Address range
129.123.51.1-62
129.123.51.65-125
129.123.51.129-189
129.123.51.193-253
Subnet Mask
255.255.255.192
255.255.255.192
255.255.255.192
255.255.255.192
Gateway
129.123.51.63
129.123.51.126
129.123.51.190
129.123.51.254
129.123.51.50 AND 255.255.255.192 = 129.123.51.0
129.123.51.70 AND 255.255.255.192 = 129.123.51.64
COMARISON: ABS(0 – 64) = 64, go to router (gateway)
Link Layer
• Ethernet
• PPP
• Token rings
Link Layer Terms
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Framing
Link Access
Reliable Delivery
Flow Control
Error Detection
Error Correction
Half and Full Duplex
Ethernet Hardware
• Network Interface Cards
• Physical Link
– Twisted Pair
• 100 Meter length limit
• Point to Point
– Fiber
• Expensive
• Point to Point
• 2000 meter length limit
Error Detection
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Parity Checks (16 bit example)
Data bits:
Parity
0111000110101011
1
One bit even parity
Can’t tell which bit is wrong
Two dimensional Even Parity
10101
11110
01110
00101
Parity Ok
1
0
1
0
10101
1
10110
0
01110
1
00101
0
Parity Error
Forward Error Correction possible
Checksumming (CRC)
D
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2r XOR R D=# of data bits,
r = CRC bits
Polynomial Code
See example on page 429 in book.
Multiple Access methods
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Shared Wire (ethernet)
Shared Wireless (WiFi, 802.11a/b/g)
Satellite
Cocktail party
Multiplexing
• Time division
– Each packet has a defined time slot
– Requires precise timing
• Frequency division
– Each packet has it’s own frequency allocation
– Requires large bandwidth for many channels
• CDMA (Code division multiple access)
– Assigned codes (wireless techniques, Ch. 6)
CSMA (carrier sense multiple access)
• Listen before speaking
• If someone else begins talking at the same
time then stop talking (collision detection).
Packet Traffic
Network Cable
Collisions
5
Signal 1
0
5
Signal 2
0
10
Sum of 1 and 2
0
Ethernet threshold
MAC (Media access control addressing)
• 12 digit hexadecimal address
• Unique to every system on the LAN
• Usually hard coded into the NIC but can be
changed in software
• Broadcast address ff:ff:ff:ff:ff:ff
Address Resolution Protocol (ARP)
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Translates IP addresses to MAC addresses.
Keeps in subnet traffic inside the subnet.
Uses timers to clear ARP tables
arp –a lists arp entries (PC or Unix)
arp –d deletes an arp entry
DHCP
• Dynamic Host Configuration Protocol
• Configure many machines from one server
at boot.
• Multiple servers, uses router helper
addresses to discover servers.
• Addresses can be static (same address for
every lease period) or Dynamic (different
address for each lease period).
DHCP Interchange
Ethernet Cabling Cont.
– Coax (10 MB ethernet only)
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obsolete
inexpensive
Bus System (party line)
Thin (185 Meter length limit)
– 30 connections/cable, min 18 inches between
• Thick (500 meter length limit)
– 200 connections, min 2.5M between
• Transceivers
10baseT/100baseT
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2 twisted pairs
Transmit/Receive
100 meter/328 foot distance limit
Uses standard telephone modular plugs
Category 3 (10mb) vs. Category 5 (100mb)
Twisted Pair Ethernet
• Ethernet uses wires 1 and 2 for one pair and
3 and 6 for the other pair.
• Wires 4 and 5 are used for analog (single
pair) telephone
• Ethernet data is transmitted on one pair and
received on the other pair in the cable.
RJ45 Connector
12345678
Looking from the CABLE end
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2
3
4
White/Orange
Orange/White
White/Green
Blue/White
5
6
White/Blue
Green/White
7
White/Brown
8
Brown/White
Ethernet Twist (hub-hub)
W/O
transmit
O/W
G/W
receive
W/G
1
2
3
6
1
transmit
2
3
receive
6
This can be used to connect two pc’s together
Hubs and Repeaters
• Hubs (Star topology)
Twisted Pair
Backbone
Fiber, Coax, Twisted Pair
(Twisted Pair may need
a twist!)
Hub Advantages
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Standard Telephone Wiring
Standard Punch Blocks and Cross Connects
Ability to disable a single port
Easier to monitor traffic patterns
Visible Indication of Link Status
If a wire is cut only one port is affected
– Unless the backbone feed is cut!
10/100 Switch
10BaseT hubs
Telephone
connections
Coaxial Installation
Backbone
• Multidrop (Bus topology)
T
T=terminator
(50 ohm resistor)
Other computers
T Repeater T T
Repeater Rule 10MB
• 3 repeater rule
Repeater
System 1 can talk to Sys 2 but not Sys3
Repeater
Repeater
Repeater
System 1
Sys 2
Sys3
Network Diameter (100MB)
• 205 Meter Limit
5M
10MB diameter is 500M
Repeater
Repeater
100M
100M
Switches and Bridges
Repeater
Repeater
Bridge
Repeater
Repeater
Bridge Insides
Filter based on
ethernet address
Interface
Interface
LAN A
LAN B
Switch Insides
A
F
B
C
G
D
E
Switching based on
ethernet address
10baseT
100baseT to 10baseT
Hub/Bridge
100baseT hub
10baseT hub
100baseT
to
10baseT
Bridge
Module
100baseT
10MB Ethernet Rules
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3 repeater (populated) limit
5 repeater per segment limit
7 bridges per ethernet lan
Cable lengths
1024 stations per ethernet lan
Hubs
How to get around limits?
Switch
Other Lans
(switching
based on
IP address)
Firewall
ROUTER
To the Internet
Ethernet Errors
• Carrier Loss
– Link Lights?
• Collisions
– What does the collision light indicate?
• Troubleshooting tools
– tcpdump, snoop, traceroute, ping
Routed vs. Switched Network
• Routed
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IP/IPX Layer Routing
Subnetted Network
Broadcast Filtering
More Expensive
Complex
Configuration
– Better Control
• Switched
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Ethernet Layer Routing
Flat Network
Broadcasts propagate
Less Expensive
Simple Configuration
Loose Control
Network Diameter
limit
Token Ring
• Special packets called tokens circulate in a
ring from computer to computer.
– If a free token is detected then a computer will
take control and send it’s data
– If a token is destined for a specific computer
that computer takes the token
– One one computer at a time can use the token
so no collisions take place.
Token Ring
4 or 16 MB/s
Mic (Media Interface Connector at each
computer)
MAU
• Multistation Access Unit
``
Ring in Ring out
Computer Ports
PPP Protocol
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Modem Pools
Multiple Network Layer Protocols
Multiple types of links
Error Detection
Failure detection (liveness)
Address negotiation
Simple
Link Layer
The End
REMEMBER TEST NEXT WEEK!