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...
TRANSCRIPT
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 Subnet Mask Gateway
129.123.51.1-62 255.255.255.192 129.123.51.63
129.123.51.65-125 255.255.255.192 129.123.51.126
129.123.51.129-189 255.255.255.192 129.123.51.190
129.123.51.193-253 255.255.255.192 129.123.51.254
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
• 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
• 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 1 10101 1
11110 0 10110 0
01110 1 01110 1
00101 0 00101 0
Parity Ok Parity Error
Forward Error Correction possible
Checksumming (CRC)
D . 2r XOR R D=# of data bits,
r = CRC bits
Polynomial Code
See example on page 429 in book.
Multiple Access methods
• 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
Signal 1
Signal 2
0
50
5
0
10
Sum of 1 and 2
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)
• 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)• 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
• 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 Connector1 2 3 4 5 6 7 8
Looking from the CABLE end
1
2
3
4
5
7
8
6
White/Orange
Orange/White
White/Green
Green/White
Blue/WhiteWhite/Blue
White/Brown
Brown/White
Ethernet Twist (hub-hub)
W/O
O/W
G/W
W/G
1
2
3
6
1
2
3
6
transmit
receive
transmit
receive
This can be used to connect two pc’s together
Hubs and Repeaters
• Hubs (Star topology)
Twisted Pair
Fiber, Coax, Twisted Pair
Backbone
(Twisted Pair may needa twist!)
Hub Advantages
• 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
Telephoneconnections
Coaxial Installation
• Multidrop (Bus topology)
T
T=terminator(50 ohm resistor)
Repeater
Backbone
Other computersTTT
Repeater Rule 10MB
• 3 repeater rule
Repeater
Repeater
Repeater
Repeater
System 1
Sys 2 Sys3
System 1 can talk to Sys 2 but not Sys3
Network Diameter (100MB)
• 205 Meter Limit
Repeater
Repeater
100M
5M
100M
10MB diameter is 500M
Switches and Bridges
Repeater
Repeater
Repeater
RepeaterB
ridge
Bridge Insides
Interface
Interface
Filter based on ethernet address
LAN A LAN B
Switch Insides
A
B
C
D
E
F
G
Switching based onethernet address
100baseT to 10baseTHub/Bridge10baseT 100baseT
10baseT hub
100baseT hub
100baseTto10baseTBridgeModule
10MB Ethernet Rules
• 3 repeater (populated) limit
• 5 repeater per segment limit
• 7 bridges per ethernet lan
• Cable lengths
• 1024 stations per ethernet lan
How to get around limits?Hubs
Switch
ROUTER
Other Lans
To the Internet(switchingbased onIP address)
Firew
all
Ethernet Errors
• Carrier Loss– Link Lights?
• Collisions– What does the collision light indicate?
• Troubleshooting tools– tcpdump, snoop, traceroute, ping
Routed vs. Switched Network
• Routed– IP/IPX Layer Routing
– Subnetted Network
– Broadcast Filtering
– More Expensive
– Complex Configuration
– Better Control
• Switched– 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
Mic (Media Interface Connector at eachcomputer)
4 or 16 MB/s
MAU
• Multistation Access Unit
``Ring in Ring out
Computer Ports
PPP Protocol
• Modem Pools
• Multiple Network Layer Protocols
• Multiple types of links
• Error Detection
• Failure detection (liveness)
• Address negotiation
• Simple
Link Layer
The EndREMEMBER TEST NEXT WEEK!