Basic IP addressing: Classful IP addresses and special addresses

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Unit 2 IP addressing Subnetting Supernetting
CIDR. Delivery and routing of packets

• Basic IP addressing Classful IP addresses and
  special addresses
• Subnetting and subnet masks
• Supernetting and CIDR (Classless Interdomain
  Routing)
• Delivery and routing of packets
• Routing table organizations
• Dynamic v.s. static routing

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A host is assigned a host number unique within a
network
A router assigned an IP address per interface
Each network assigned an IP network number
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Figure 4.1 Dotted Decimal Notation
Class A Large networks Class B Medium
networks Class C Small networks Hostid with all
0s or all 1s are special.
Figure 4.6 Classful IP Addresses
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Figure 4.5
00000000 0 0
01111111 1 1
10000000 0 0
10111111 1 1
11000000 0 0
11011111 1 1
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Figure 4.12 Multihomed devices
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Figure 4.13 Network addresses Network ID All
0s hostid is commonly referred to as a network
address
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Figure 4.14 Direct broadcast address
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Figure 4.15 limited broadcast address
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Figure 4.16 this host on this network
address
Provide initial configuration information
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Figure 4.17 Specific host on this network
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Figure 4.18 Loopback address
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Private Networks

• 10.0.0.0 - 10.255.255.255
• 172.16.0.0 - 172.31.255.255
• 192.168.0.0 - 192.168.255.255
• Note the above addresses should not be used on
  the Internet.

Network Address Translation (NAT)
Private addresses
Global IP addresses
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Similar to Figure 5.2 subnetting (Three levels
of hierarchy)
Usable addresses 141.14.2.1 to 141.14.2. 254
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Figure 5.3 Addresses in a network with and
without subnetting
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Figure 5.5 Subnet mask
Host id part all 0s
The rest all 1s
The host part of the address becomes all 0s
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A simple example
Logical AND
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Special addresses in subnetting
IMPORTANT These can never be assigned to a host
Restrictions can be relaxed so that these numbers
may be assigned to subnets
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Example 2 An organization with a class B address
needs at least 12 subnetworks.
24 16. Even if restrictions not relaxed. 14
subnetids available
of bits needed in the subnet id part?
23 8, not enough
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Range of addresses in example 2
X Y 00000000 00000000
X Y 00001111 11111111
X Y 00010000 00000000
X Y 00011111 11111111
X Y 00010000 00000001
X Y 00101111 11111111
X Y 00100000 00000000
X Y 00110000 00000000
X.Y.48.0
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Subnetworks in example 2
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00000000 0
X.Y.Z.0
Figure 5.10 Variable-length subnetting
01000000 64
X.Y.Z.64
10000000 128
X.Y.Z. 128
11000000 192
X.Y.Z. 192
11100000 224
X.Y.Z. 224
And the last two subnets must have 11 as the
leading 2 bits in the 4th byte. The 3rd bit can
varies between 0 and 1. Therefore the last two
subnets have addresses of the following format in
the 4th byte 110xxxxx and 111xxxxx
255.255.255.192 11111111 11111111 11111111
11000000 so the first mask uses the first 2
bits of the 4th byte as the subnet ID
So the last byte can be 00xxxxxx, 01xxxxxx,
10xxxxxx, 11xxxxxx. 3 of these can be chosen to
label the first 3 subnets. Let say we pick the
first 3
255.255.255.224 11111111 11111111 11111111
11100000 so the second mask uses the first 3 bits
of the 4th byte as the subnet ID
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Figure 5.11 Supernetwork
32 00100000
33 00100001
Reduce routing table entries. Advertise 1
supernet instead of 4 networks
34 00100010
35 00100011
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Similar to Figure 5.12 Subnet mask vs Supernet
mask
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Two ways of defining a supernet
Figure 5-21 Example of supernetting. Which
address belong to supernet X.Y.32.0?
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Classless Interdomain Routing (CIDR)
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Table 5.1
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Figure 6.1 Direct and Indirect delivery
Same network/subnet/ supernet address
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Figure 6.3 Next-hop routing
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Figure 6.4 Network-specific routing
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Figure 6.5 Host-specific routing
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Figure 6.6 Default routing
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Figure 6.7 Routing module and routing table
Routing tables static v.s. dynamic
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Figure 6.9 Example routing table is in Table 6.1
on p. 156