Network Layer Part 6

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Network Layer Part 6

  1. 1. 4 Tutun Juhana Telecommunication Engineering Network Layer (Part 6) School of Electrical Engineering & Informatics Institut Teknologi Bandung Computer Networks
  2. 2. INTERNET CONTROL MESSAGE PROTOCOL VERSION 4 (ICMPV4)
  3. 3. The value of the protocol field in the IP datagram is 1 to indicate that the IP data is an ICMP message 3
  4. 4. Messages includes the IP header of the original datagram + the first 8 bytes of data in that datagram 4
  5. 5. Provides port numbers (UDP and TCP) and sequence number (TCP). 5
  6. 6. ERROR REPORTING MESSAGES 6
  7. 7. Error Reporting Messages • No ICMP error message will be generated in response to a datagram carrying an ICMP error message. • No ICMP error message will be generated for a fragmented datagram that is not the first fragment. • No ICMP error message will be generated for a datagram having a multicast address. • No ICMP error message will be generated for a datagram having a special address such as 127.0.0.0 or 0.0.0.0 7
  8. 8. Destination Unreachable Note: For codes, please refer to Forouzan’s 8
  9. 9. Source Quench 9
  10. 10. Time Exceeded   10
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  12. 12. Parameter Problem If a router or the destination host discovers an ambiguous or missing value in any field of the datagram, it discards the datagram and sends a parameter-problem message back to the source 12
  13. 13. Redirection 13
  14. 14. QUERY MESSAGES 14
  15. 15. Query Messages • ICMP can also diagnose some network problems  accomplished through the query messages 15
  16. 16. Echo Request and Reply • The echo-request and echo-reply messages are designed for diagnostic purposes • Network managers and users utilize this pair of messages to identify network problems. • The combination of echo-request and echo-reply messages determines whether two systems (hosts or routers) can communicate with each other. 16
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  18. 18. Timestamp Request and Reply • Two machines (hosts or routers) can use the timestamp-request and timestamp-reply messages to: – determine the round-trip time needed for an IP datagram to travel between them – synchronize the clocks in two machines 18
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  23. 23. CHECKSUM 23
  24. 24. • In ICMP the checksum is calculated over the entire message (header and data) 24
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  27. 27. DEBUGGING TOOLS 27
  28. 28. Ping • We can use the ping program to find if a host is alive and responding • The source host sends ICMP echo request messages (type: 8, code: 0); the destination, if alive, responds with ICMP echo reply messages • The ping program sets the identifier field in the echo request and reply message and starts the sequence number from 0; this number is incremented by one each time a new message is sent • Note that ping can calculate the round-trip time. It inserts the sending time in the data section of the message. When the packet arrives it subtracts the arrival time from the departure time to get the round-trip time (RTT). 28
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  30. 30. Traceroute • The traceroute program in UNIX or tracert in Windows can be used to trace the route of a packet from the source to the destination 30
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