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Icmp

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Principal,Guru Nanak Institute of Technology, Nagpur
Principal,Guru Nanak Institute of Technology, Nagpur

ICMP is a helper protocol that supports IP by providing error reporting and simple queries. ICMP messages are encapsulated as IP datagrams with a 4 byte header containing the type, code, and checksum. Common ICMP error messages include Destination Unreachable (sent when a datagram cannot be forwarded), Redirect (informs about a better route), and Time Exceeded (sent when the TTL reaches zero).

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1 Internet Control Message Protocol • The Internet Control Message Protocol (ICMP) is a helper protocol that supports IP with facility for – Error reporting – Simple queries • ICMP messages are encapsulated as IP datagram: DR. SUDHIR SHELKE
2 ICMP message format additional information or 0x00000000 type code checksum bit # 0 15 23 248 317 16 4 byte header: • Type (1 byte): type of ICMP message • Code (1 byte): subtype of ICMP message • Checksum (2 bytes): similar to IP header checksum. Checksum is calculated over entire ICMP message If there is no additional data, there are 4 bytes set to zero.
3 ICMP Error message • ICMP error messages include the complete IP header and the first 8 bytes of the payload (typically: UDP, TCP) Unused (0x00000000) IP header ICMP header IP header 8 bytes of payload ICMP Message from IP datagram that triggered the error type code checksum
4 ICMP Error message • ICMP error messages report error conditions • Typically sent when a datagram is discarded • Error message is often passed from ICMP to the application program Host IP datagram Host or router ICMP Error Message IP datagram is discarded
5 Frequent ICMP Error message Type Code Description 3 0–15 Destination unreachable Notification that an IP datagram could not be forwarded and was dropped. The code field contains an explanation. 5 0–3 Redirect Informs about an alternative route for the datagram and should result in a routing table update. The code field explains the reason for the route change. 11 0, 1 Time exceeded Sent when the TTL field has reached zero (Code 0) or when there is a timeout for the reassembly of segments (Code 1) 12 0, 1 Parameter problem Sent when the IP header is invalid (Code 0) or when an IP header option is missing (Code 1) DR. SUDHIR SHELKE
6 Some subtypes of the “Destination Unreachable” Code Description Reason for Sending 0 Network Unreachable No routing table entry is available for the destination network. 1 Host Unreachable Destination host should be directly reachable, but does not respond to ARP Requests. 2 Protocol Unreachable The protocol in the protocol field of the IP header is not supported at the destination. 3 Port Unreachable The transport protocol at the destination host cannot pass the datagram to an application. 4 Fragmentation Needed and DF Bit Set IP datagram must be fragmented, but the DF bit in the IP header is set. DR. SUDHIR SHELKE

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Icmp

  • 1. 1 Internet Control Message Protocol • The Internet Control Message Protocol (ICMP) is a helper protocol that supports IP with facility for – Error reporting – Simple queries • ICMP messages are encapsulated as IP datagram: DR. SUDHIR SHELKE
  • 2. 2 ICMP message format additional information or 0x00000000 type code checksum bit # 0 15 23 248 317 16 4 byte header: • Type (1 byte): type of ICMP message • Code (1 byte): subtype of ICMP message • Checksum (2 bytes): similar to IP header checksum. Checksum is calculated over entire ICMP message If there is no additional data, there are 4 bytes set to zero.
  • 3. 3 ICMP Error message • ICMP error messages include the complete IP header and the first 8 bytes of the payload (typically: UDP, TCP) Unused (0x00000000) IP header ICMP header IP header 8 bytes of payload ICMP Message from IP datagram that triggered the error type code checksum
  • 4. 4 ICMP Error message • ICMP error messages report error conditions • Typically sent when a datagram is discarded • Error message is often passed from ICMP to the application program Host IP datagram Host or router ICMP Error Message IP datagram is discarded
  • 5. 5 Frequent ICMP Error message Type Code Description 3 0–15 Destination unreachable Notification that an IP datagram could not be forwarded and was dropped. The code field contains an explanation. 5 0–3 Redirect Informs about an alternative route for the datagram and should result in a routing table update. The code field explains the reason for the route change. 11 0, 1 Time exceeded Sent when the TTL field has reached zero (Code 0) or when there is a timeout for the reassembly of segments (Code 1) 12 0, 1 Parameter problem Sent when the IP header is invalid (Code 0) or when an IP header option is missing (Code 1) DR. SUDHIR SHELKE
  • 6. 6 Some subtypes of the “Destination Unreachable” Code Description Reason for Sending 0 Network Unreachable No routing table entry is available for the destination network. 1 Host Unreachable Destination host should be directly reachable, but does not respond to ARP Requests. 2 Protocol Unreachable The protocol in the protocol field of the IP header is not supported at the destination. 3 Port Unreachable The transport protocol at the destination host cannot pass the datagram to an application. 4 Fragmentation Needed and DF Bit Set IP datagram must be fragmented, but the DF bit in the IP header is set. DR. SUDHIR SHELKE