The Internet Control Message Protocol (ICMP) is one of the core protocols of the Internet protocol suite. It is chiefly used by networked computers' operating systems to send error messages—indicating, for instance, that a requested service is not available or that a host or router could not be reached. In computing and telecommunications, the transport layer is the second highest layer in the four and five layer TCP/IP reference models, where it responds to service requests from the application layer and issues service requests to the Internet layer. ... The Transmission Control Protocol (TCP) is one of the core protocols of the Internet protocol suite. ... User Datagram Protocol (UDP) is one of the core protocols of the Internet protocol suite. ... The Datagram Congestion Control Protocol (DCCP) is a message-oriented transport layer protocol that is currently under development in the IETF. Applications that might make use of DCCP include those with timingconstraints on the delivery of data such that reliable in-order delivery, when combined with congestion control, is likely... In the field of computer networking, the IETF Signaling Transport (SIGTRAN) working group defined the Stream Control Transmission Protocol (SCTP) as a transport layer protocol in 2002. ... The Real-time Transport Protocol (or RTP) defines a standardized packet format for delivering audio and video over the Internet. ... The Resource ReSerVation Protocol (RSVP), described in RFC 2205, is a transport layer protocol designed to reserve resources across a network for an integrated services Internet. ... The Internet Group Management Protocol (IGMP) is a communications protocol used to manage the membership of Internet Protocol multicast groups. ... The Point-to-Point Tunneling Protocol (PPTP) is a method for implementing virtual private networks. ... The network layer is third layer out of seven in OSI model and it is the third layer out of five in TCP/IP model. ... The Internet Protocol (IP) is a data-oriented protocol used for communicating data across a packet-switched internetwork. ... Internet Protocol version 4 is the fourth iteration of the Internet Protocol (IP) and it is the first version of the protocol to be widely deployed. ... Internet Protocol version 6 (IPv6) is a network layer protocol for packet-switched internetworks. ... The Open Shortest Path First (OSPF) protocol is a hierarchical interior gateway protocol (IGP) for routing in Internet Protocol, using a link-state in the individual areas that make up the hierarchy. ... Is Is is Yeah Yeah Yeahs third EP, to be released on July 24, 2007. ... The Border Gateway Protocol (BGP) is the core routing protocol of the Internet. ... IPsec (IP security) is a suite of protocols for securing Internet Protocol (IP) communications by authenticating and/or encrypting each IP packet in a data stream. ... In computer networking, the Address Resolution Protocol (ARP) is the standard method for finding a hosts hardware address when only its network layer address is known. ... Reverse Address Resolution Protocol (RARP) is a network layer protocol used to obtain an IP address for a given hardware address (such as an Ethernet address). ... This article is chiefly about the Routing Information Protocol (RIP) for the Internet Protocol, but also discusses some other routing information protocols. ... The ICMP for IPv6 (Internet Control Message Protocol Version 6) is an integral part of the IPv6 architecture and must be completely supported by all IPv6 implementations. ... This article does not cite any references or sources. ... IEEE 802. ... The IEEE 802. ... Official Wi-Fi logo Wi-Fi (pronounced wye-fye, IPA: ), also unofficially known as Wireless Fidelity, is a wireless technology brand owned by the Wi-Fi Alliance intended to improve the interoperability of wireless local area network products based on the IEEE 802. ... Official WiMax logo WiMAX, the Worldwide Interoperability for Microwave Access, is a telecommunications technology aimed at providing wireless data over long distances in a variety of ways, from point-to-point links to full mobile cellular type access. ... Asynchronous Transfer Mode (ATM) is a cell relay, packet switching network and data link layer protocol which encodes data traffic into small (53 bytes; 48 bytes of data and 5 bytes of header information) fixed-sized cells. ... Dynamic synchronous Transfer Mode , or DTM for short, is a network protocol. ... Token-Ring local area network (LAN) technology was developed and promoted by IBM in the early 1980s and standardised as IEEE 802. ... Ethernet is a large, diverse family of frame-based computer networking technologies that operate at many speeds for local area networks (LANs). ... In computer networking, fiber-distributed data interface (FDDI) is a standard for data transmission in a local area network that can extend in range up to 200 km (124 miles). ... In the context of computer networking, frame relay consists of an efficient data transmission technique used to send digital information quickly and cheaply in a relay of frames to one or many destinations from one or many end-points. ... General Packet Radio Service (GPRS) is a Mobile Data Service available to users of Global System for Mobile Communications (GSM) and IS-136 mobile phones. ... Evolution-Data Optimized or Evolution-Data only, abbreviated as EV-DO or EVDO and often EV, is one telecommunications standard for the wireless transmission of data through radio signals, typically for broadband Internet access. ... High-Speed Packet Access (HSPA) is a collection of mobile telephony protocols that extend and improve the performance of existing UMTS protocols. ... High-Level Data Link Control (HDLC) is a bit-oriented synchronous data link layer protocol developed by the International Organization for Standardization (ISO). ... In computing, the Point-to-Point Protocol, or PPP, is commonly used to establish a direct connection between two nodes. ... In computer networking, the Layer 2 Tunneling Protocol (L2TP) is a tunneling protocol used to support virtual private networks (VPNs). ... ISDN redirects here. ... This article does not cite any references or sources. ... IEEE photograph of a diagram with the original terms for describing Ethernet drawn by Robert M. Metcalfe around 1976. ... For other uses, see Modem (disambiguation). ... For other uses, see Power band. ... It has been suggested that this article be split into articles entitled Synchronous optical networking, SONET and Synchronous digital hierarchy. ... There are very few or no other articles that link to this one. ... Optical fibers An optical fiber (or fibre) is a glass or plastic fiber designed to guide light along its length. ... Coaxial Cable For the weapon, see coaxial weapon. ... 25 Pair Color Code Chart 10BASE-T UTP Cable Twisted pair cabling is a common form of wiring in which two conductors are wound around each other for the purposes of cancelling out electromagnetic interference known as crosstalk. ... The Internet protocol suite is the set of communications protocols that implement the protocol stack on which the Internet and most commercial networks run. ... An operating system (OS) is the software that manages the sharing of the resources of a computer and provides programmers with an interface used to access those resources. ...

ICMP differs in purpose from TCP and UDP in that it is usually not used directly by user network applications. One exception is the ping tool, which sends ICMP Echo Request messages (and receives Echo Response messages) to determine whether a host is reachable and how long packets take to get to and from that host. The Transmission Control Protocol (TCP) is one of the core protocols of the Internet protocol suite. ... User Datagram Protocol (UDP) is one of the core protocols of the Internet protocol suite. ... For other uses, see Ping (disambiguation). ... The Echo Request is an ICMP message which sends a packet of data to the host and expects that data to be sent in return in a Echo Reply. ...

Technical Details

Internet control message protocol is part of the Internet protocol suite as defined in RFC 792. ICMP messages are typically generated in response to errors in IP datagrams (as specified in RFC 1122) or for diagnostic or routing purposes. The Internet protocol suite is the set of communications protocols that implement the protocol stack on which the Internet and most commercial networks run. ... The Internet Protocol (IP) is a data-oriented protocol used for communicating data across a packet-switched internetwork. ... A packet is the fundamental unit of information carriage in all modern computer networks. ...

The version of ICMP for Internet Protocol version 4 is also known as ICMPv4, as it is part of IPv4. IPv6 has an equivalent protocol, ICMPv6. Internet Protocol version 4 is the fourth iteration of the Internet Protocol (IP) and it is the first version of the protocol to be widely deployed. ... Internet Protocol version 4 is the fourth iteration of the Internet Protocol (IP) and it is the first version of the protocol to be widely deployed. ... Internet Protocol version 6 (IPv6) is a network layer protocol for packet-switched internetworks. ... The ICMP for IPv6 (Internet Control Message Protocol Version 6) is an integral part of the IPv6 architecture and must be completely supported by all IPv6 implementations. ...

ICMP messages are constructed at the IP layer, usually from a normal IP datagram that has generated an ICMP response. IP encapsulates the appropriate ICMP message with a new IP header (to get the ICMP message back to the original sending host) and transmits the resulting datagram in the usual manner. In information technology, Header refers to supplemental data placed at the beginning of a block of data being stored or transmitted, which contain information for the handling of the data block. ...

For example, every machine (such as intermediate routers) that forwards an IP datagram has to decrement the time to live (TTL) field of the IP header by one; if the TTL reaches 0, an ICMP Time to live exceeded in transit message is sent to the source of the datagram. This article is about a computer networking device. ... Time to live (sometimes abbreviated TTL) is a limit on the period of time or number of iterations or transmissions in computer and computer network technology that a unit of data (e. ... The Time Exceeded Message is an ICMP message which is generated by a gateway to inform the source of a datagram that the datagram has been discarded due to the time to live field reaching zero. ...

Each ICMP message is encapsulated directly within a single IP datagram, and thus, like UDP, ICMP is unreliable. User Datagram Protocol (UDP) is one of the core protocols of the Internet protocol suite. ... In computer networking, a reliable protocol is one that ensures data arrival via some internal method, as opposed to an unreliable protocol, which does not guarantee that all the data will arrive intact (or indeed, at all). ...

Although ICMP messages are contained within standard IP datagrams, ICMP messages are usually processed as a special case, distinguished from normal IP processing, rather than processed as a normal sub-protocol of IP. In many cases, it is necessary to inspect the contents of the ICMP message and deliver the appropriate error message to the application that generated the original IP packet, the one that prompted the sending of the ICMP message.

Many commonly-used network utilities are based on ICMP messages. The traceroute command is implemented by transmitting UDP datagrams with specially set IP TTL header fields, and looking for ICMP Time to live exceeded in transit (above) and "Destination unreachable" messages generated in response. The related ping utility is implemented using the ICMP "Echo request" and "Echo reply" messages. traceroute outputs the list of traversed routers in simple text format, together with timing information traceroute is a computer network tool used to determine the route taken by packets across an IP network. ... The Time Exceeded Message is an ICMP message which is generated by a gateway to inform the source of a datagram that the datagram has been discarded due to the time to live field reaching zero. ... For other uses, see Ping (disambiguation). ...

List of permitted control messages (incomplete list)

• 0 - Echo Reply
• 1 - Reserved
• 2 - Reserved
• 3 - Destination Unreachable
• 4 - Source Quench
• 5 - Redirect Message
• 6 - Alternate Host Address
• 7 - Reserved
• 8 - Echo Request
• 9 - Router Advertisement
• 10 - Router Solicitation
• 11 - Time Exceeded
• 12 - Parameter Problem
• 13 - Timestamp
• 14 - Timestamp Reply
• 15 - Information Request
• 16 - Information Reply
• 17 - Address Mask Request
• 18 - Address Mask Reply
• 19 - Reserved for security
• 20-29 - Reserved for robustness experiment
• 30 - Traceroute
• 31 - Datagram Conversion Error
• 32 - Mobile Host Redirect
• 33 - IPv6 Where-Are-You
• 34 - IPv6 Here-I-Am
• 35 - Mobile Registration Request
• 36 - Mobile Registration Reply
• 37 - Domain Name Request
• 38 - Domain Name Reply
• 39 - SKIP Algorithm Discovery Protocol, Simple Key-Management for Internet Protocol
• 40 - Photuris, Security failures
• 41 - ICMP for experimental mobility protocols such as Seamoby [RFC4065]
• 42-255 - Reserved

(Source: IANA ICMP Parameters) The Echo Reply is an ICMP message generated in response to an ICMP Echo Request message, and is mandatory for all hosts and routers. ... The Destination Unreachable message is an ICMP message which is generated by the router to inform the client that the destination host is unreachable. ... The Source Quench is an ICMP message which requests the sender to decrease the traffic rate of messages to a router or host. ... The Redirect Message is an ICMP message which informs a host to redirect its routing information (to send packets on an alternate route). ... The Echo Request is an ICMP message which sends a packet of data to the host and expects that data to be sent in return in a Echo Reply. ... The Time Exceeded Message is an ICMP message which is generated by a gateway to inform the source of a datagram that the datagram has been discarded due to the time to live field reaching zero. ... The Timestamp is an ICMP message which is used for time synchronization. ... The Timestamp Reply is an ICMP message which replies to a Timestamp message. ... Address Mask Request is an ICMP query message, normally sent by a host to a router in order to obtain an appropriate subnet mask. ... Address Mask Reply is an ICMP message, used to reply to an Address Mask Request message with an appropriate subnet mask. ... Internet Protocol version 6 (IPv6) is a network layer protocol for packet-switched internetworks. ... This page may meet Wikipedias criteria for speedy deletion. ... Internet Protocol version 6 (IPv6) is a network layer protocol for packet-switched internetworks. ... Here I Am is the pop rock solo album by former M2M band member, Marion Raven. ... Simple Key-Management for Internet Protocol or SKIP is a protocol developed by the IETF Security Working Group for the sharing of encryption keys. ... In computer networking, Photuris is a session key management protocol laid down in RFC 2522. ... The Seamoby Candidate Access Router Discovery, or CARD, is an experimental protocol outlined by RFC4065. ...

ICMP segment structure

Header

The grey cells describe the IP header. The ICMP header consists of the green cells.

Version 

This would normally be set to '4' to indicate use of ipv4

IHL 

Internet Header Length : The length of the header in 32 bit words. This field is needed since header length might vary.

Type of Service or DSCP

Set to 0 by default.

Total Length 

The length of the header and data in octets

Identification, Flags and Fragment Offset 

Taken from the IP protocol.

Time to live 

How many routing hops this packet may endure.

Protocol 

ICMP version used.

IP Header Checksum 

used for error checking

Source Address 

The source address from whom the packet was sent.

Destination Address 

The destination address of the packet.

Type 

ICMP type as specified above.

Code 

further specification of the ICMP type; e.g. : an ICMP Destination Unreachable might have this field set to 1 through 15 each bearing different meaning.

Checksum 

This field contains error checking data calculated from the ICMP header+data, with value 0 for this field.

ID

This field contains an ID value, should be returned in case of ECHO REPLY.

Sequence

This field contains a sequence value, should be returned in case of ECHO REPLY.

The Internet Protocol (IP) is a data-oriented protocol used for communicating data across a packet-switched internetwork. ... Time to live (sometimes abbreviated TTL) is a limit on the period of time or number of iterations or transmissions in computer and computer network technology that a unit of data (e. ... In telecommunication, a redundancy check is extra data added to a message for the purposes of error detection and error correction. ...

Padding Data

After the ICMP header follows padding data (in octets): In computer technology and networking, an octet is a group of 8 bits. ...

• The LINUX "ping" utility pads ICMP to a total size of 64 in addition to the 8 octet header.
• WINDOWS "ping.exe" pads to a total size of 40 in addition to the 8 octet header.

See also

• PMTUD
• ICMPv6
• IRDP
• Smurf attack
• TCP
• ping
• traceroute

Path MTU discovery (PMTUD) is a technique in computing for determining the maximum transmission unit size on the network path between two IP hosts with a view to avoiding IP fragmentation. ... The ICMP for IPv6 (Internet Control Message Protocol Version 6) is an integral part of the IPv6 architecture and must be completely supported by all IPv6 implementations. ... ICMP Internet Router Discovery Protocol (IRDP) uses Internet Control Message Protocol (ICMP) router advertisements and router solicitation messages to allow a host to discover the addresses of operational routers on the subnet. ... The smurf attack, named after its exploit program, is a denial-of-service attack which uses spoofed broadcast ping messages to flood a target system. ... The Transmission Control Protocol (TCP) is one of the core protocols of the Internet protocol suite. ... For other uses, see Ping (disambiguation). ... traceroute outputs the list of traversed routers in simple text format, together with timing information traceroute is a computer network tool used to determine the route taken by packets across an IP network. ...

External links

• RFC 792, Internet Control Message Protocol
• ICMP Sequence Diagram
• RFC 1122, Requirements for Internet Hosts -- Communication Layers
• Filtering ICMP on firewalls
• IANA