Network Protocols Chapter 5 (TCP/IP Suite Book): IPv4 Addresses Copyright © Lopamudra Roychoudhuri 1
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Network Protocols
Chapter 5 (TCP/IP Suite Book): IPv4 Addresses
Copyright © Lopamudra Roychoudhuri 1
Agenda
IPv4 Addresses: IPv4 addresses and classes Classful addressing Network addresses and masks Network Address Translation (NAT)
2
Network Layer The network layer is designed as a packet-
switched network. Packet-switched network can provide either
a connectionless service or a connection-oriented service.
When the network layer provides a connectionless service, each packet traveling in the Internet is an independent entity; there is no relationship between packets belonging to the same message.
In a connection-oriented service, there is a virtual connection between all packets belonging to a message. 3
Network Layer This means that the packet at the
source is divided into manageable packets, normally called datagrams.
Individual datagrams are then transferred from the source to the destination.
The received datagrams are assembled at the destination before recreating the original message.
The packet-switched network layer of the Internet was originally designed as a connectionless service.
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Sender Network
Network
ReceiverOut of orderR3
R4
R5
R1 R2
A connectionlesspacket-swtiched network
Figure 4.3 A connectionless packet-switched network
4 3 2 1
1
2
3
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3 31
4 43 21
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The network layer is responsible for delivery of packets from the source to the destination.
Figure 4.4 Forwarding process in a connectionless network
1 2
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Outputinterface
Destinationaddress
Routing table
12
3
AB
HDestination
address
SA DA Data
Send the packetout of interface 2
SA DA Data
LegendSA: Source addressDA: Destination address
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The source address may be used to send an error message to the source if the packet is discarded.
The forwarding decision is based on the destination address of the packet.
IP Addresses
The identifier used in the IP layer of the TCP/IP protocol suite to identify each device connected to the Internet
Uniquely and universally defines the connection of a host or a router to the Internet
32 bits, 4 bytes long dotted decimal notation
Each of the 4 values is in range 0 – 255, such as, 150.21.39.52
The address space of IPv4 is 232 or 4,294,967,296.
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IP Addresses cont. How does every device on the
Internet get a different IP address? IP Address Prefixes assigned to
organizations by the Internet Assigned Numbers Authority (IANA) Distributes IP address pools to Regional
Internet Registry (RIR) organizations, such as Réseaux IP Européens Network Coordination Centre (RIPE NCC)
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http://www.iana.org/numbers/
IP Addresses cont. RIPE NCC hands over IP address
prefixes to Organizations: ISPs, Universities, large businesses
These organizations then control all IP addresses starting with that prefix
Small businesses are loaned a group of IP addresses by ISP
Individual PCs get a dynamically assigned IP address from ISP each time they dial up. 9
0x80 0x0B 0x03 0x3F
IP Addresses cont.
Binary notation
Dotted Decimal notation
Hexadecimal notation
• An IP address can also be thought of as a number in base 256.
• i.e., 128.11.3.31 is nothing but • 128*256^3 + 11*256^2 + 3*256^1 + 31*256^0• (See TCP/IP Textbook appendix B, Page 898)
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IP Addresses
IP address is designed to identify A particular IP Network that this
packet should be delivered to by
Internet routers
A particular IP host machine on that
network that this packet should be
delivered to by local router at the
destination site
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IP addresses, when started a few decades ago, used the concept of classes. This architecture is called classful addressing.
Class A: for Large networks Class B: for Medium networks
Class C: for Small networks Class D: Multicast
Classful IP Addresses
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Figure 5.7 Finding the class of an address using continuous checking
1
Class: A
0Start
1
0
Class: B
1
0
Class: C
1
0
Class: D Class: E
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00000000 0 ……0 01111111 1 ……1
10000000 0 ……0 10111111 1 ……1
11000000 0 ……0 11011111 1 ……1
11100000 0 ……0 11101111 1 ……1
11110000 0 ……0 11111111 1 ……1
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Occupation of the address space
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Figure 5.15 Information extraction in classful addressing
netid
First address
000 ... 0
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17
Change the following IPv4 addresses from binary notation to dotted-decimal notation.
Example 19.1
Solution
We replace each group of 8 bits with its equivalent decimal number (see Appendix B) and add dots
for separation.
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Change the following IPv4 addresses from dotted-decimal notation to binary notation.
Example 19.2
Solution
We replace each decimal number with its binary equivalent .
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Find the error, if any, in the following IPv4 addresses.
Example 19.3
Solution
a. There must be no leading zero (045).
b. There can be no more than four numbers.
c. Each number needs to be less than or equal to 255.
d. A mixture of binary notation and dotted-decimal
notation is not allowed.
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Find the class of each address.
a. 00000001 00001011 00001011 11101111
b. 11000001 10000011 00011011 11111111
c. 14.23.120.8
d. 252.5.15.111
Example 19.4
Solution
a. The first bit is 0. This is a class A address.
b. The first 2 bits are 1; the third bit is 0. This is a class C address.
c. The first byte is 14; the class is A.
d. The first byte is 252; the class is E.
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In classful addressing, a large part of the available addresses were
wasted.
Note
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Classful addressing, which is almost obsolete, is replaced with
classless addressing.
Note
Find the number of addresses in a range if the first
address is 146.102.29.0 and the last address is
146.102.32.255.
Solution
We can subtract the first address from the last address
in base 256 (see Appendix B). The result is 0.0.3.255 in
this base. To find the number of addresses in the range
(in decimal), we convert this number to base 10 and
add 1 to the result.
= 255 * 256^0 + 3 * 256^1 = 1023 + 1 = 1024
Example 5.5
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Net Address
First address in the block Network address defines the
network to rest of Internet Given network address we can find
the class of the address, the block, and range of addresses in the block
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Network Address
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Blocks in class A
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Class A Address
First byte value between 1 and 127 ICANN specifies value of 1st byte Organization chooses IP address for each
device by assigning value in last 3 bytes. Organization may have (256 * 256 * 256) =
16 million different IP addresses for devices!! Millions of class A addresses are
wasted.
List of Assigned class A addresses
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Blocks in class B
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Class B Address
First byte has value between 128 and 191 ICANN specifies value of 1st and 2nd bytes Organization chooses IP address for each
device by assigning value in last 2 bytes. Organization has (256 * 256) = 65,536 different
IP addresses for devices!! Many class B addresses are wasted.
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Blocks in class C
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Class C Address
First byte has value between 192 and 223 ICANN specifies value of 1st, 2nd and 3rd bytes Organization chooses particular IP address for
each device by assigning value in last byte. Organization gets 256 different IP addresses for
its devices The number of addresses in class C is smaller
than the needs of most organizations
Example: IP addresses 207.46.232.x are all controlled by Microsoft Corporation
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Unicast, Multicast, and Broadcast Addresses
Unicast communication is one-to-one.Multicast communication is one-to-many.Broadcast communication is one-to-all.
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Class D Address
First byte has value between 224 and 239 There is no Network ID or Host ID. The
entire address is used for multicasting Each address represents a group of hosts
that all listen to one sender Example: Address 224.0.0.9 can be used
to send routing information to all RIP2-aware routers on a network segment.
List of used multicast addresses
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Multicast Category addresses
Routing Information Protocol
Open Shortest Path First
Interior Gateway Routing Protocol
Distance Vector Multicast Routing Protocol
Internet Stream Protocol
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IP Special Addresses
Address Netid Hostid Src/Dest
Network Address
Specific All 0s None
Direct Broadcast
Specific All 1s Dest
Limited Broadcast
All 1s All 1s Dest
This host All 0s All 0s Source
Host on this network
All 0s Specific Dest
Loopback 127 Any Dest
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Direct Broadcast
Direct broadcast address is used by a router to send a message to every host on a local network
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Limited Broadcast Limited broadcast address is used by a host to send a
packet to every host on the same network However, the packet is blocked by routers
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This Host A host that does not know its IP address uses the IP
address 0.0.0.0 as the source address and 255.255.255.255 as the destination address to send a message to a boot strap server
Can be used only as a source address
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Loopback A packet with loopback address will not reach the
network Can be used by a client process to send a message to
a server process on the same machine Can only be used as a destination address
39
Private AddressesA number of blocks in each class are assigned for private use.
They are not recognized globally, hence cannot be used on public Internet
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Multihomed devices
A device that has more than one Internet address; a different address for each network connected to it
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Sample internet
1. A LAN with nw address 220.3.6.0 (class C)
2. A LAN with nw address 134.18.0.0 (class B)
3. A LAN with nw address 124.0.0.0 (class A)
4. A point-to-point WAN
5. A switched WAN
Note: The book does not show any IP address for point-to-point link end-pointsBut in reality point-to-point WAN interfaces are also assigned IP addresses.
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Question
How can you determine if an IP address belongs to a particular network?
Answer: Apply a netmask
A mask is a 32-bit binary number that gives the first address in the block, i.e. the network address when bitwise ANDed with an address in the block
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Network Address
The network address is the beginning address of each block.
It can be found by applying the default mask to any of the addresses in the block (including itself).
It keeps the netid of the block and sets the hostid to zero.
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Masking concept
bit bit45
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Anding & Oring Tables
Anding
Oring
0 0 00 1 00 0 11 1 1
0 0 01 1 01 0 11 1 1
Default Masks
10001101 00001110 01001000 00011000
11111111 11111111 00000000 00000000
10001101 00001110 00000000 00000000
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A block of addresses is granted to a small organization. We know that one of the addresses is
205.16.37.39/24. What is the first address in the block?
Solution
The binary representation of the given address is
11001101 00010000 00100101 00100111
If we used the default mask and And it with the IP address, we get
11001101 00010000 00100101 00000000
or
205.16.37.0.
Example 19.6
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The last address in the block can be found by setting the rightmost
32 − n bits to 1s.
Note
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An address in a block is given as 73.22.17.25. Find the number of addresses in the block, the first address, and the last address.
SolutionFigure 5.16 shows a possible configuration of the network that uses this block. 1. From the 1st byte we know that this is a class A address. Hence number of network bits (n) is 8. The number of addresses in this block is N = 232−n=232−8=224 =16,777,216.2. To find the first address, we keep the leftmost 8 bits and set the rightmost 24 bits all to 0s. The first address is 73.0.0.0, in which 8 is the value of n.3. To find the last address, we keep the leftmost 8 bits and set the rightmost 24 bits all to 1s. The last address is 73.255.255.255.
Example 5.13
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Figure 5.16 Solution to Example 5.13
51
An address in a block is given as 180.8.17.9. Find the number of addresses in the block, the first address, and the last address.
SolutionFigure 5.17 shows a possible configuration of the network that uses this block. 1. The number of addresses in this block is N = 232−n =
65,536.2. To find the first address, we keep the leftmost 16 bits and set the rightmost 16 bits all to 0s. The first address is 180.8.0.0, in which 16 is the value of n.3. To find the last address, we keep the leftmost 16 bits and set the rightmost 16 bits all to 1s. The last address is 180.8.255.255.
Example 5.14
52
Figure 5.17 Solution to Example 5.14
53
An address in a block is given as 200.11.8.45. Find the number of addresses in the block, the first address, and the last address.
SolutionFigure 5.17 shows a possible configuration of the network that uses this block. 1. The number of addresses in this block is N = 232−n = 256.2. To find the first address, we keep the leftmost 24 bits and set the rightmost 8 bits all to 0s. The first address is 200.11.8.0, in which 24 is the value of n.3. To find the last address, we keep the leftmost 24 bits and set the rightmost 8 bits all to 1s. The last address is 200.11.8.255.
Example 5.15
54
Figure 5.18 Solution to Example 5.15
55
A router receives a packet with the destination address 201.24.67.32. Show how the router finds the network address of the packet.
SolutionSince the class of the address is C, we assume that the router applies the default mask for class C, 255.255.255.0 to find the network address.
Example 5.16 (Note that the book’s solution is incorrect)
255
67
56
Another way to find the first address, the last address, and the number of addresses is to represent the mask as a 32-bit
binary (or 8-digit hexadecimal) number.
a. The first address can be found by ANDing the given addresses with the mask. ANDing here is done bit by bit. The
result of ANDing 2 bits is 1 if both bits are 1s; the result is 0 otherwise.
b. The last address can be found by ORing the given
addresses with the complement of the mask
The complement of a number is found by changing each 1 to 0 and each 0 to 1.
c. The number of addresses can be found by complementing the mask, interpreting it as a decimal number, and adding
1 to it.
Another way to find the first address, last address,
, and the number of addresses
57
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Network Address Translation (NAT) Network Address Translation (NAT): is the process of modifying IP address information in IPv4 headers while in transit across a traffic routing device.
NAT is necessary when the number of IP addresses assigned to you by your ISP is less than the total number of computers that you wish to provideInternet access for.
The simplest type of NAT provides a one-to-one translation of IP addresses. This refers to this type of NAT as basic NAT, which is often also called a one-to-one NAT.
Another way to map an entire network (or networks) to a single IP address (Security wise).
NAT allows you to take advantage of the reserved address blocks.
Figure 19.10 A NAT implementation
59
Figure 19.11 Addresses in a NAT
60
Figure 19.12 NAT address translation
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Table 19.4 Five-column translation table
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Figure 19.13 An ISP and NAT
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