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OSI Network Layer
Network Fundamentals – Chapter 5
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Network Layer Protocols and Internet Protocol (IP)
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Network Layer Protocols & Internet Protocol (IP):
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Network Layer Protocols and Internet Protocol (IP)
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Network Layer Protocol Implications
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Network Layer Protocol is Media Independent
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Network Layer Protocol Encapsulation
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Internet Protocol (IP) Packet Header
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IP Addressing Groups Nodes into “Subnets”
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Grouping Devices into Networks with Hierarchical Addressing
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Dividing Large Networks is a Security Strategy
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Hierarchical Addressing
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Subnet Address Structure:
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Routers “route” based on Next Hop Addresses
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Route Tables:
1. Directly Connected Networks
2. Static Routes
3. Routes Learned via Routing Protocol
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Let’s Review Binary Math! 1
28
64
32
16
8
4
2
1
. 255
1 1 1 1 1 1 1 1
Bit Value by Position:
8 Bits = 1 Byte or “octet”
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Lets’ Review v4 IP Addresses:
32 bit address
4 octets (or bytes)
“dotted decimal” format
128
64
32
16
8
4
2
1
128
64
32
16
8
4
2
1
128
64
32
16
8
4
2
1
128
64
32
16
8
4
2
1
IP Address:
224 . 168 . 155 . 224
1 1 1 0 0 0 0 0 . 1 0 1 0 1 0 0 0 . 1 0 0 1 1 0 1 1 . 1 1 1 0 0 0 0 0
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IP Address is part of a “Class”:
12
8
64
32
16
8
4
2
1
12
8
64
32
16
8
4
2
1
Class A 0 126 0 0 0 0 0 0 0 0 . 0 1 1 1 1 1 1 0
Class B 128 191 1 0 0 0 0 0 0 0 . 1 0 1 1 1 1 1 1
Class C 192 223 1 1 0 0 0 0 0 0 . 1 1 0 1 1 1 1 1
The Rest 224 254 1 1 1 0 0 0 0 0 . 1 1 1 1 1 1 1 0
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All IP Addresses have two components:
The Network Address (to the left)
The Host ID (to the right)
Combination is a unique address 1
28
64
32
16
8 4 2 1 12
8 64
32
16
8 4 2 1 12
8 64
32
16
8 4 2 1 12
8 64
32
16
8 4 2 1
Mask: 255 . 255 . 255 . 0
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 0 0
128
64
32
16
8 4 2 1 128
64
32
16
8 4 2 1 128
64
32
16
8 4 2 1 128
64
32
16
8 4 2 1
IP Address:
192 . 168 . 155 . 224
1 1 0 0 0 0 0 0 . 1 0 1 0 1 0 0 0 . 1 0 0 1 1 0 1 1 . 1 1 1 0 0 0 0 0
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Default Subnet Mask
128
64
32
16 8 4 2 1 128
64
32
16 8 4 2 1 128
64
32
16 8 4 2 1 128
64
32
16 8 4 2 1
Class A 255 0 . 0 . 0
1 1 1 1 1 1 1 1 . 0 0 0 0 0 0 0 0 . 0 0 0 0 0 0 0 0 . 0 0 0 0 0 0 0 0
Class B 255 255 . 0 . 0
1 1 1 1 1 1 1 1 . 1 1 1 1 1 1 1 1 . 0 0 0 0 0 0 0 0 . 0 0 0 0 0 0 0 0
Class C 255 255 . 255 . 0
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 0 0
• A = 126 Networks, 16,777,214 hosts
• B = > 16,000 Networks, 65,534 hosts
• C = > 2,000,000 Networks, 254 hosts
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A “Network” is a range of addresses:
Example: 192.168.101.0 to 192.168.101.255 The first number in the range (host = all zero) is the Network Number = 192.168.101.0
The last number in the range (host = all ones) is the broadcast address = 192.168.101.255
The middle of the range can be used for identifying individual hosts.
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Subnet Mask: A subnet mask is used to identify the Network ID portion of
the address range:
A = 255.0.0.0
B = 255.255.0.0
C = 255.255.255.0
Three methods of identifying the Subnet Mask:
Default Subnet Mask
Subnet Mask for the Enterprise
CIDR /number notation
We extract the Network ID using a binary logical “trick” … the “and logic”.
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