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Figure 3-13: Internet Protocol (IP)

Basic Characteristics

There were already single networks, and many more would come in the future

Developers needed to make a few assumptions about underlying networks

So they kept IP simple

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Figure 3-13: Internet Protocol (IP)

Connection-Oriented Service and Connectionless Service

Connection-oriented services have distinct starts and closes (telephone calls)

Connectionless services merely send messages (postal letters)

IP is connectionless

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IP Packet

PCInternet Process

First RouterInternet Process

IP Packet

ConnectionlessPackets Sent in Isolation

Like Postal Letters

UnreliableNo Error Correction

Discarded by Receiver if Error is DetectedLeaves Error Correction to Transport Layer

Reduces the Cost of Routers

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Figure 3-13: Internet Protocol (IP)(Study Figure)

IP is Unreliable (Checks for Errors but does not Correct Errors) (Figure 3-14) Not doing error correction at each hop between

switches reduces switch work and so switch cost

Does not even guarantee packets will arrive in order

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Figure 3-13: Internet Protocol (IP)(Study Figure)

Hierarchical IP Addresses Postal addresses are hierarchical (state, city,

postal zone, specific address)

Most post offices have to look only at state and city

Only the final post offices have to be concerned with specific addresses

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Figure 3-15: Hierarchical IP Address

Network Part (not always 16 bits)

Subnet Part (not always 8 bits)

Host Part (not always 8 bits)

Total always is 32 bits.

128.171.17.13

Host 13126.171.17.13

CBA Subnet (17)

UH Network (128.171)The Internet

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Figure 3-13: Internet Protocol (IP)(Study Figure)

Hierarchical IP Addresses 32-bit IP addresses are hierarchical (Figure 3-

15)

Network part tells what network host is on

Subnet part tells what subnet host is on within the network

Host part specifies the host on its subnet

Routers have to look only at network or subnet parts, except for the router that delivers the packet to the destination host

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Figure 3-13: Internet Protocol (IP)(Study Figure)

Hierarchical IP Addresses 32-bit IP addresses are hierarchical

Total is 32 bits; part sizes vary

Network mask tells you the size of the network part (Figure 3-16)

Subnet mask tells you the length of the network plus subnet parts combined

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Figure 3-16: IP Address Masking with Network and Subnet Masks

Network Masking Subnet Masking

Mask Represents Tells the size of the network part

Tells the size of the network and the subnet parts combined

Eight ones give the decimal value

255 255

Eight zeros give the decimal value

0 0

Masking gives IP address bit where the mask value is 1; 0 where the mask bit is 0

IP address bit where the mask value is 1; 0 where mask bit is 0

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Figure 3-16: IP Address Masking with Network and Subnet Masks

Example 1 Network Masking Subnet Masking

IP Address 128.171.17.13 128.171.17.13

Mask 255.255.0. 0 255.255.255.0

Result 128.171.0. 0 128.171.17.0

Meaning 16-bit network part is 128.171 Combined 24-bit network plus subnet part are 128.171.17

Example 2

IP Address 60.47.123.7 60.47.123.7

Mask 255.0.0.0 255.255.0.0

Result 60.0.0.0 60.47.0.0

Meaning 8-bit network part is 60 Combined 16-bit network plus subnet parts are 60.47