Chapter 7 Internet Protocol

Transcription

1 Chapter 7 Internet Protocol Datagram Fragmentation Options Checksum IP Design 7-1 Figure 7-1 IP datagram bytes bytes Header Data VER 4 bits HLEN 4 bits Time to live 8 bits Identification 16 bits Service type 8 bits Protocol 8 bits Flags 3 bits Total length 16 bits Fragmentation offset 13 bits Header checksum 16 bits Source IP address Destination IP address Option 7-2 Forouzan Notes COSC 6377 Fall

2 7 2 Figure 7-2 Service type D: Minimize delay T: Maximize throughput Precedence R: Maximize reliability C: Minimize cost D T R C TOS bits 7-3 Figure 7-3 Encapsulation of a small datagram in an Ethernet frame Length: Minimum 46 bytes Header Data < 46 bytes Padding Trailer 7-4

3 7 3 Figure 7-4 Multiplexing Transport layer TCP UDP ICMP IGMP EGP OSPF Network layer Header 7-5 Figure 7-5 MTU IP datagram Header MTU Maximum length of data that can be encapsulated in a frame Frame Trailer 7-6

4 7 4 Figure 7-6 Flags field D: Do not fragment M: More fragments D M 7-7 Figure 7-7 Fragmentation example... Offset = 0000/8 = ,399 Offset = 0000/8 = Offset = 1,400/8 = 175 1,400 2,799 Byte 0000 Byte 3, Offset = 2,800/8 = 350 2,800 3,

5 7 5 Figure , , Detailed fragmentation example 14, , Bytes ,399 14,567 Fragment 1 1 1, , Bytes 1,400 2,199 Fragment 2.2 Bytes ,999 Original datagram Bytes 1,400 2,799 14,567 Fragment 2 0 1, , Bytes 2,200 2,799 Fragment 2.1 Bytes 2,800 3,999 Fragment Figure 7-9 Option format Code 8 bits Length 8 bits Data Variable length Copy 1 bit Class 2 bits Number 5 bits Copy 0 Copy only in first fragment 1 Copy into all fragments Class 00 Datagram control 01 Reserved 10 Debugging and management 11 Reserved Number End of option No operation Loose source route Timestamp Record route Strict source route 7-10

6 7 6 Figure 7-10 Categories of options Single-byte No operation End of option Options Record route Multiple-byte Strict source route Loose source route Timestamp 7-11 Figure 7-11 No operation option Code: a. No operation option NO-OP A 7-byte option NO-OP An 11-byte option b. Used to align beginning of an option An 8-byte option c. Used to align the next option 7-12

7 7 7 Figure 7-12 End of option option Code: a. End of option Options END-OP Data ~ ~ b. Used for padding 7-13 Figure 7-13 Record route option Code: Length (Total length) Pointer First IP address (Empty when started) Second IP address (Empty when started). Last IP address (Empty when started) 7-14

8 7 8 Figure 7-14 Record route concept Figure 7-15 Strict source route option Code: First IP address (Filled when started) Length (Total length) Pointer Second IP address (Filled when started). Last IP address (Filled when started) 7-16

9 7 9 Figure 7-16 Strict source route concept Figure 7-17 Loose source route option Code: First IP address (Filled when started) Second IP address (Filled when started). Last IP address (Filled when started) Length (Total length) Pointer 7-18

10 7 1 Figure 7-18 Timestamp option Code: Length (Total length) Pointer O-Flow Flags 4 bits 4 bits First IP address Second IP address. Last IP address 7-19 Figure 7-19 Use of flag in timestamp Enter timestamps only Flag: 0 Enter IP addresses and timestamps IP addresses given, enter timestamps Flag: 1 Flag:

11 7 1 Figure 7-20 Timestamp concept Figure 7-21 Checksum concept Sender Receiver Section 1 Section 1 Section 2 Section Checksum All 0s Checksum Section k Section k Sum Checksum Packet Sum Complement Checksum Complement Result If the result is 0, keep; otherwise, discard. 7-22

12 7 1 Figure 7-22 Checksum in one s complement arithmetic Sender T T T T = 0 Receiver 7-23 Figure 7-23 Example of checksum calculation , 5, and and 0 4 and Sum Checksum

13 7 1 Figure 7-24 From upper layer protocol To upper layer protocol IP components IP IP packet Header-adding module Data and dest. address Data Reassembly module Reassembly table Processing module... IP packet IP packet, next hop, interface IP packet Routing table Routing module... Fragmentation module MTU table IP packet From data link layer To data link layer IP packet, next hop 7-25 Figure 7-25 MTU table Interface Number MTU

14 7 1 Figure 7-26 Reassembly table Src Addr: Source Address F: Fragments Dtgm ID: Datagram ID... State Src Addr Dtgm ID Timeout F. 7-27