ip addressing - the computer networks...
TRANSCRIPT
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IP ADDRESSING
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Outline
à Network architecture à Address format à Netmask
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NETWORK ARCHITECTURE
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Network Architecture
H2 H3
IP net 1
IP net 3 IP net 6
IP net 7
IP net 9 ATM CDN
H4
Ethernet
R5
R4
R3 xDSL
xDSL
Ethernet WIFI
Host
Logical subnet
R1
Router (Gateway)
Physical network
R2
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Logical IP Subnet (LIS)
Set of interfaces with common address prefix
Prefix
1 physical network
1 logical IP network
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Logical and Physical Networks à All interfaces with the same address prefix must be connected to the same physical network
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à All interfaces of the same physical network must have the same address prefix
What does this imply?
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A Network Identifier
Host Network
à Network part à Host part
Address prefix is unique to a given (physical/logical) network
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Scalability!
IP net 1
IP net 3 IP net 6
IP net 7
IP net 9
R1
R2
R5
R4
R3
rou<ng are closely related
Addressing and
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Does It Come for Free?
à Address space waste à Addressing efficiency
à Commonly below 25%
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ADDRESS FORMAT
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IP Addresses
à 32 bits (4 bytes) à Represented in dotted
decimal notation
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à Each byte expressed as a decimal number separated by a dot
à 12.4.56.38 193.129.3.215 à Each element from O to 255
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How Large is the Prefix? à Fixed size is too limited à Three sizes:
à Class A: 1 byte à Class B: 2 bytes à Class C: 3 bytes
Check the first byte!
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Class A à E.g., 84.24O.2O.1
à Max 128 network prefixes à Max 16M host addresses
Host 1 7 8 31 Network
0 127
0
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à E.g., 153.24O.2O.1
à Max 16K network prefixes à Max 64K host addresses
2 7 16 31
128 191
Host Network 1 0
Class B
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à E.g., 2O3.24O.2O.1
à Max 2M network prefixes à Max 255 host addresses
2 7 16 31
1 0 1 Host Network 192 223
Class C
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And It Goes On … à Class D à E.g., 225.24O.2O.1
à Used for multicast à Class E: anycast à Not associated to interfaces
2 7 31 Mul<cast Address 1 0 1 1
224 239
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Reserved Host Field Values
à All ones: directed broadcast à E.g., 2O3.24O.2O.255 à Routed à Cannot be associated
to an interface
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à All zeros: the LIS à E.g., 2O3.24O.2O.O à Could be associated to an interface
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Available Host Identifiers
n bit host field ê
2n-2 available identifiers
Possibly 2n-1 if network address is associated to an interface
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Reserved Addresses
à All ones: limited broadcast à 255.255.255.255 à Not received by all stations
à Not routed à This host: O.O.O.O à Loopback: 127.*.*.*
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NETMASK
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Issues With Classful Addressing
à Lack of flexibility à Low addressing efficiency
à Centralized address space assignment
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Netmask and Classless Addressing
à Associated to IP address à Marks boundary of network and host parts
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à Any size network/host part
1 1 0 0 0 0 0 0 . 1 0 1 0 1 0 0 0 . 0 0 0 0 1 0 1 0 . 0 1 0 0 0 1 0 1
1 24 32 2 3 25 27 1 1 1 1 1 1 1 1 . 1 1 1 1 1 1 1 1 . 1 1 1 1 1 1 1 1 . 1 1 0 0 0 0 0 0 255 . 255 . 255 . 192
Netmask
192 . 168 . 10 . 69 Address
Network part Host part
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Valid Netmask Byte Values
à 0 0000 0000 à 128 1000 0000 à 192 1100 0000 à 224 1110 0000 à 240 1111 0000 à 248 1111 1000 à 252 1111 1100 à 254 1111 1110 à 255 1111 1111
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Natural Netmaks/Prefixes
à Class A è 255.O.O.O à Class B è 255.255.O.O à Class C è 255.255.255.O
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à Subnetting: prefix shorter than natural one
à Supernetting: prefix longer than natural one
Subnetting and Supernetting
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SubneKng Examples 0 1 23 24 31 2 3
Host 1 Network 0 1 25
From 129
to 190
1 0 0 0 0 0 0 1
1 0 1 1 1 1 1 0
From 65
to 126
1 1 0 0 0 0 0 0 . 1 0 1 0 1 0 0 0 . 0 0 0 0 1 0 1 0 . 0 1 0 0 0 0 0 1 0 1 1 1 1 1 1 0 192 . 168 . 10 .
Network field
26
Host
255 . 255 . 255 . 192
1 1 1 1 1 1 1 1 . 1 1 1 1 1 1 1 1 . 1 1 ì1 1 1 1 1 1 . 1 1 0 0 0 0 0 0 Netmask
Net (natural prefix)
Subnet
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Subnetting and Centralized Address Assignment à Addresses assigned to organization in natural prefixes
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à One large set of addresses à Organizations use subnetting to devise a prefixes for each network