1. Ch 3: Underlying Technologies (remainder)
Lecture #5
Reminder - Exam 1 on Tuesday
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2. CONNECTING DEVICES
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3. Repeater Operates at the physical layer – layer 1
Receives the signal and regenerates the signal in it’s original pattern
A repeater forwards every bit; it has no filtering capability
Is there a difference between a regen or repeater and an amp ??
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4. Repeaters d
For the architecture above, will a signal ever traverse through more than 2 repeaters ?
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5. Hubs Hub – multi-port repeater
Typically used to create a physical star topology
Also used to create multiple levels of hierarchy
For bus technology type networks, hubs can be used to increase the collision domain
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6. Bridge Operates at both the physical and data link layers
At layer 1, it regenerates the signal. At layer 2, it checks the Tx/Rx physical address (using a bridge table)
Example Below:
If packet arrives to bridge-interface #1 for either of the 71….. stations, the packet is dropped because the 71…. Stations will see the packet
If packet arrives to bridge-interface #2 for either of the 71….. stations, the packet is forwarded to bridge-interface #1
With such an approach, the “bridged” network segments will acted as a single larger network
What is a “smart” bridge ??
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7. Routers Show example where a decision is needed d d
Is a 3-layer device: (1) at layer 1, regen the signals, (2) at layer 2, check physical address and (3) at layer 3, check network addresses
Routers are internetworking devices
Routers contain a physical and logical/IP address for it’s interfaces (repeaters/bridges don’t)
Routers only act on the packets needing to pass through
Routers change the physical address of the packets needing to pass through (repeaters/bridges don’t change physical addresses)
Show example where a decision is needed d d
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8. Routing example LAN 1 LAN2
Routers can change the physical address of a packet
Example: as a packet flow from LAN 1 to LAN 2
In LAN 1, the source address is the Tx’s address and the destination address is the Router’s interface address
In LAN 2, the source address is the Router’s interface address and the destination address is the Rx’s address
LAN LAN2
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9. You are a High Priced Network Consultant
Marketing Dept
Engineering Dept
(Super Computer)
Manufacturing Dept (Robots) d
They want all departments to communicate with one another; you want the network to maintain top performance – which design would you recommend ? Which devices would you recommend for empty circles ? – the least cost solution is the best solution
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10. Note: Lectures for Exam 1 just ended. We now start lectures for Exam 2
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11. Chapters 4 & 5 Addressing
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12. IP ADDRESSING (Ch 4)
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13. IP Addresses
Internetworking Protocol (IP) of the Network Layer is responsible for uniquely identifying all devices and connections on the Internet
The unique identifier is called an IP address
IP address consist of 32 bits (for version 4)
Keep in mind that, if a single device had multiple connections to the Internet, you would need an IP address for each connection
Address space is 232 = 4,294,967, bit addresses
In theoretical terms, 4,294,967,296 connections can be made to the Internet (not really true in real life)
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14. IP Addresses
The IP Address has 3 notations: Binary, Dotted-decimal and Hexadecimal
Binary: 4 Octets:
Dotted-Decimal (or dot notation):
For Dotted-Decimal, each number can range from 0 to 255
Hexadecimal:
D EA
75951DEA
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15. EXAMPLES
Change the following IP address from binary notation to dotted-decimal notation:
Solution
Change the following IP address from dotted-decimal notation to binary notation:
Solution
Find the error, if any, in the following IP address:
Solution
There are no leading zeroes in dotted-decimal notation (045).
Change the following IP addresses from binary notation to hexadecimal notation:
810B0BEF16
Solution
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16. IP Addresses: Classful Addressing
When IP addressing was first started, it used a concept called “classful addressing”. A newer concept called “classless addressing” is slowly replacing it though.
Regarding “classful addressing”, the address space is divided into five classes: A, B, C, D and E.
Class
# of addresses
Percent of the Space A
231=
50% B
230=
25% C
229=
12.5% D
228=
6.25% E
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17. Finding the class in binary notation
Finding the class in decimal notation
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18. EXAMPLES Solution Find the class of the address:
The first bit is 0. This is a class A address.
Solution
Find the class of the address:
The first 2 bits are 1; the third bit is 0. This is a class C address.
Solution
Find the class of the address:
The first byte is 227 (between 224 and 239);
the class is D.
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19. Netid and hostid
A, B and C class-addresses are divided into network id and host id
For Class A, Netid=1 byte, Hostid = 3 bytes
For Class B, Netid=2 bytes, Hostid = 2 bytes
For Class C, Netid=3 bytes, Hostid = 1 byte
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20. Blocks in class A Example Netid 73 is assigned
Class A has 128 blocks or network ids
First byte is the same (netid), the remaining 3 bytes can change (hostids)
Network id 0 (first), Net id 127 (last) and Net id 10 are reserved – leaving 125 ids to be assigned to organizations/companies
Each block contains 16,777,216 addresses – this block should be used by large organizations. How many Host can be addressed ????
The first address in the block is called the “network address” – defines the network of the organization
Example
Netid 73 is assigned
Last address is reserved
Recall: routers have addressees
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21. Blocks in class B Example Netid 180.8 is assigned
Class B is divided into 16,384 blocks (65,536 addresses each)
16 blocks are reserved
First 2 bytes are the same (netid), the remaining 2 bytes can change (hostids)
For example, Network id covers addresses to
Network id is the last netid for this block
Example
Netid is assigned
Last address is reserved
Recall: routers have addresses
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22. Blocks in class C
Class C is divided into 2,097,152 blocks (256 addresses each)
256 blocks are reserved
First 3 bytes are the same (netid), the remaining 1 byte can change (hostids)
For example, Network id covers addresses to
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23. Class D addresses are used for multicasting; there is only one block in this class.
Class E addresses are reserved for special purposes; most of the block is wasted.
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24. Network Addresses The network address is the first address.
The network address defines the network to the rest of the Internet.
Given the network address, we can find the class of the address, the block, and the range of the addresses in the block
Given the network address , find the class, the block, and the range of the addresses.
The class is A because the first byte is between 0 and 127. The block has a netid of 17. The addresses range from to
Solution
Given the network address , find the class, the block, and the range of the addresses.
The class is B because the first byte is between 128 and 191. The block has a netid of The addresses range from to
Solution
Given the network address , find the class, the block, and the range of the addresses.
The class is C because the first byte is between 192 and 223. The block has a netid of The addresses range from to
Solution
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25. REMINDER: Go Over Converting Binary to Decimal and Vice Versa
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26. Converting Number Systems - Review
Base-10
The decimal number system is based on power of the base 10. For example, for the number 1259,
the 9 is in the 10^0 column - 1s column
the 5 is in the 10^1 column - 10s column
the 2 is in the 10^2 column - 100s column
the 1 is in the 10^3 column s column
1259 is
9 X 1 = 9
+ 5 X 10 = 50
+ 2 X 100 = 200
+ 1 X 1000 = 1000
-----
1259
Base-2 (Binary)
The Binary number system uses the same mechanism and concept however, the base is 2 versus 10
 The place values for binary are based on powers of the base 2:
… 2^7 2^6 2^5 2^4 2^3 2^2 2^1 2^0
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27. Converting Number Systems - Review
So, the binary number can be converted to a decimal number
1 X 1 = 1 (right most bit or position)
1 X 2 = 2
0 X 4 = 0
0 X 8 = 0
1 X 16 = 16
1 X 32 = 32
0 X 64 = 0
1 X 128 = 128 (left most bit or position)
------
179 in decimal
To convert from decimal to binary requires a different method called the division/remainder method. The idea is to repeatedly divide the decimal number and resulting quotients by 2. The answer will be the remainders.
Example: convert 155 to binary (Start from the top and work down)
155/2 Q = 77, R = 1 (Start)
77/2 Q = 38, R = 1
38/2 Q = 19, R = 0
19/2 Q = 9, R = 1
9/2 Q = 4, R = 1
4/2 Q = 2, R = 0
2/2 Q = 1, R = 0
1/2 Q = 0, R = 1 (Stop)
Answer is Be careful to place the digits in the correct order.
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28. Converting Number Systems - Review
Check the answer ( ) :
1 X 1 = 1
1 X 2 = 2
0 X 4 = 0
1 X 8 = 8
1 X 16 = 16
0 X 32 = 0
0 X 64 = 0
1 X 128 = 128
-----
155
Base-16 (Hex)
The hexadecimal number system is based 16, and uses the same mechanisms and conversion routines we have already examined. The place values for hexadecimal are based on powers of the base 16
The digits for are the letters A - F (A is 10, …….., F is 15)
…….. 16^ ^ ^ ^0
The binary number can be converted to hexadecimal by grouping bits into groups of 4 bits: B
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29. Mask
Given the network address, we can easily determine the block and range of addresses
Suppose given the IP address, can we determine the network address (beginning of the block) ?
To route packets to the correct network, a router must extract the network address from the destination IP address
For example, given , we know this is a class B, therefore is the netid and is the network address (starting address of the block)
How would we EXTRACT the network address from the IP address? We would use a MASK.
A mask is a 32-bit binary number that gives the first address in the block (the network address) when bitwise ANDed with an address in the block.
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30. AND operation
If bit is ANDed with 1, it’s preserved
If bit is ANDed with 0, it’s changed to a 0.
There are 3 default masks: one for each class. The default masks preserve the netid when ANDed with the addresses
Class A Default Mask:
Class B Default Mask:
Class C Default Mask:
A simple way to determine the netid for un-subnetted cases: (1) if mask byte is 255, retain corresponding byte of the address, (2) if mask byte is 0, set corresponding address byte to 0.
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31. Examples
Given the address and the default class A mask, find the beginning address (network address).
The default mask is , which means that only the first byte is preserved and the other 3 bytes are set to 0s. The network address is
Solution
Given the address and the default class B mask, find the beginning address (network address).
The default mask is , which means that the first 2 bytes are preserved and the other 2 bytes are set to 0s. The network address is
Solution
Given the address and the class C default mask, find the beginning address (network address).
The default mask is , which means that the first 3 bytes are preserved and the last byte is set to 0. The network address is
Solution
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32. 5-bit Address Space Illustration
No Netid case
32 addresses/block
Number of blocks: 1
Address range per block: 0 to 31
Netids: N/A
Network Addresses : 00000
Broadcast Addresses: 11111
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33. 5-bit Address Space Illustration
1-bit Netid case
16 addresses/block
Number of blocks: 2
Address range per block: 0 to 15
Netids: 0, 1
Network Addresses : 00000, 10000
Broadcast Addresses: 01111, 11111
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34. 5-bit Address Space Illustration
2-bit Netid Case
8 addresses/block
Number of blocks: 4
Address range per block: 0 to 7
Netids: 00, 01, 10, 11
Network Addresses : 00000, 01000, 10000, 11000
Broadcast Addresses: 00111, 01111, 10111, 11111
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35. 5-bit Address Space Illustration
3-bit Netid Case
4 addresses/block
Number of blocks: 8
Address range per block: 0 to 3
Netids: 000, 001, 010, 011, 100, 101, 110, 111
Network Addresses : 00000, 00100, 01000, 01100
10000, 10100, 11000, 11100
Broadcast Addresses: 00011, 00111, 01011, 01111
10011, 10111, 11011, 11111
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36. Mixing 3-bit & 2-bit Cases (think of the 32-bit case)
4 addresses/block and 8 addresses/block
Number of blocks: 6
Address range per block: 0 to 3 and 0 to 7
Netids: 000, 001, 010, 011, 10, 11
Network Addresses : 00000, 00100, 01000, 01100
10000, 11000
Broadcast Addresses: 00011, 00111, 01011, 01111
10111, 11111
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37. Multihomed devices
As we mentioned that, any device with one or more connections to the Internet will need an IP address for EACH connection – such devices are called “multihomed” devices.
A Router could be a multihomed device
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38. Example of direct broadcast address
Router sending to all hosts on a network
If the hostid is all 1’s, it’s called a “broadcast address” and the router use it to send a packet to all host in a specific network. In this case, hosts 20, 64, 126 and etc. will receive the packet from the router
Example of limited broadcast address
Host sending to all other hosts on a network
If the hostid and netid are all 1’s, it’s called a “limited broadcast address”. If the host wants to send a packet to all host in a specific network, it would use this address. The router would block this address so that data stays contained within a specific network.
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39. Example of this host on this address
IPless Host sending message to bootstrap server
An address of all 0’s is used during bootstrap time if the host doesn’t know it’s IP address. The un-named host sends an all 0 source address and limited broadcast (all 1’s) destination address to the bootstrap server.
Example of specific host on this network
Host sending to some other specific host on a network
An address with a netid of all 0’s is used by a host or router to send another host with in the same network a message.
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40. Example of loopback address
The IP address with the 1st byte equal to 127 is used for the loop back address.
Loopback address is used to test software on a machine – the packet never leaves the machine – it returns to the protocol software
Example: a “ping” command can send a packet with a loopback address as the destination address to see if the IP software is capable of receiving and processing a packet.
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41. Sample internet With your new found knowledge, think about Project 2
Ethernet
ATM
Token Ring
Ethernet
With your new found knowledge, think about Project 2
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