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ICMP : Internet Control Message Protocol

ICMP : Internet Control Message Protocol. Introduction. ICMP is often considered part of the IP layer. It communicates error messages and other conditions that require attention. ICMP messages are usually acted on by either IP layer or the higher layer protocol. IP header (20 byte).

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ICMP : Internet Control Message Protocol

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  1. ICMP : Internet Control Message Protocol

  2. Introduction • ICMP is often considered part of the IP layer. • It communicates error messages and other conditions that require attention. • ICMP messages are usually acted on by either IP layer or the higher layer protocol. IP header (20 byte) ICMP message IP datagram

  3. ICMP Message • The first 4 bytes have the same format for all messages, but the remainder differs from one message to the next. 0 7 8 15 16 31 8-bit type 8-bit code 16-bit checksum (contents depends on type and code)

  4. ICMP Message Types

  5. ICMP Echo Request and Reply • ICMP echo is a message to send and receive the specified echo data packet between two TCP/IP nodes. 0 7 8 15 16 31 Type(0 or 8) Code(0) checksum identifier sequence number Echo data (variable length)

  6. ICMP Addr Mask Request and Reply • The ICMP Address mask request is intended for a diskless system to obtain its subnet mask at bootstrap time. 0 7 8 15 16 31 Type(17 or 18) Code(0) checksum identifier sequence number 32-bit subnet mask

  7. ICMP Addr Mask • We can write a simple program that issues an ICMP address mask request and prints all replies. % icmpaddrmask 140.252.13.63 Received mask = ffffffe0, from 140.252.13.33 Received mask = ffffffe0, from 140.252.13.35 Received mask = ffff0000, from 140.252.13.34

  8. ICMP Timestamp Request and Reply • The ICMP timestamp request allows a system to query another for the current time. • The recommended value to be returned is the number of milliseconds since midnight, Coordinated Universal Time (UTC). 0 7 8 15 16 31 Type(13 or 14) Code(0) checksum identifier sequence number 32-bit originate timestamp 32-bit receive timestamp 32-bit transmit timestamp

  9. ICMP Timestamp Request and Reply • The requestor fills in the originate timestamp and sends the request. • The replying system fills in the receive timestamp when it receives the request. • The transmit timestamp when it send the reply. 0 7 8 15 16 31 Type(13 or 14) Code(0) checksum identifier sequence number 32-bit originate timestamp 32-bit receive timestamp 32-bit transmit timestamp

  10. ICMP Unreachable Message • It is an error message sent back to the transmission origin when the packet cannot be sent to service. • It is likely to reply from a machine on the way of routing (router), and it might reply from the machine (target host). 0 7 8 15 16 31 Type(3) Code(0-15) checksum Unused (must be 0) IP header + first 8 bytes of original IP datagram data

  11. ICMP Message Types

  12. Exercises • If your system provides the netstat command, use it to see what types of ICMP messages are received and sent.

  13. Ping Program

  14. Introduction • The name “ping” is taken from the sonar operation to locate objects. • The program sends an ICMP echo request message to a host, expecting an ICMP echo reply to be returned. • Ping also measures the round-trip time to the host, giving us some indication of how “far away” that host is.

  15. (1) (2) (3)

  16. Ping Options -

  17. Ping HOST B 192.168.1.2 HOST A 192.168.1.1 - Ping 192.168.1.2 Please return the sent data. I return the data as it is. - Reply from 192.168.1.2 : bytes = 32 time < 10ms TTL = 128

  18. Format of ICMP message • We call the ping program that sends the echo requests the client, and the host being pinged the server. 0 7 8 15 16 31 Type(0 or 8) Code(0) checksum identifier sequence number Optional data

  19. From the result • The network communication with the object host must be normal. • Own host's network setting and operation. • The object host's network setting and operation. • Setting and operation of network/router. • Network performance • The throughput of the network can guess from the display of statistics.

  20. Case of failure • The routing to Internet Protocol address cannot be done. C:\>ping 192.168.10.1Pinging 192.168.10.1 with 32 bytes of data:Reply from 203.100.100.49: Destination net unreachable.Reply from 203.100.100.49: Destination net unreachable.Reply from 203.100.100.49: Destination net unreachable.:

  21. Case of failure • Loop by routing setting mistake. C:\>ping 150.224.XXX.XXXPinging 150.224.XXX.XXX with 32 bytes of data:Reply from 130.XXX.76.17: TTL expired in transit.Reply from 130.XXX.76.17: TTL expired in transit.Reply from 130.XXX.76.17: TTL expired in transit.Reply from 130.XXX.76.17: TTL expired in transit.Ping statistics for 150.224.XXX.XXX:    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),Approximate round trip times in milli-seconds:    Minimum = 0ms, Maximum =  0ms, Average =  0ms

  22. Case of failure • Failure of host name resolution. • The host's stop. C:\>ping www.unknown.netUnknown host www.unknown.net. C:\>ping host1.example.netPinging host1.example.net [211.XXX.XXX.190] with 32 bytes of data:Request timed out.Request timed out.:

  23. Summary • The ping program is the basic connectivity test between two systems running TCP/IP. • It uses the ICMP echo request and echo reply messages and does not use a transport layer. • Ping also let us examine and use the IP record route option.

  24. Exercises • Calculate the RTT if the SLIP link between bsdi and slip is set to 9600 bits/sec. Assume the default of 56 bytes of data.

  25. Normal Access IP ICMP HOST X HOST A Because of router Couldn’t find Host X, router send a Error Message Destination unreachable Echo Request ICMP ICMP HOST Y HOST B Echo Reply

  26. ICMP Message Types • When an ICMP error message is sent, the message always contains the IP header and the first 8 bytes of the IP datagram that caused the ICMP error to be generated. • This lets the receiving ICMP module associate the message with one particular protocol and one particular user process.

  27. ICMP Message Types • An ICMP error message is never generated in response to • An ICMP error message • A datagram destined to an IP broadcast address or an IP multicast address. • A datagram sent as a link-layer broadcast. • A fragment other than the first. • A datagram whose source address does not define a single host.

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