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  ICMP agreement 
  Http://91mail.51.net provided to the attached map detailed translation, please http://91mail.51.net control of the Internet to download information and features of the agreement was to head the speakers in RFC 792, such as the provision non-transient errors send the wrong message, and provide a determination of the network in order to the general characteristics of the network and a means of exploration.    Later, RFC 1122, RFC 1812 and ICMP agreement lays out a number of characteristics.    In order to reliable and consistent use of other ICMP agreement work, we need to merge RFC 792, RFC 1122 and RFC 1812.    Other RFCs for the ICMP agreement defines the functionality of the other: 
  RFC 896 - Source Routing failure 
  RFC 950 - Address hide expansion 
  RFC 1191 - Path MTU Discovery 
  RFC 1256 - found that the router 
  RFC 1349 - Group 1 in the Internet protocol services in a more accurate type of the definition of Internet control message protocol goal, and its features may be used by the operation of two types: When a router or an end and mainframe data in a deal with the need to inform the source of the error mainframe, and determination in order to the general characteristics of the network and use the network of information requests and responses. 
  1 ICMP norms 
  ICMP information in the data reported in the IP transmission.    Although ICMP done in the use of IP underlying support, as if it was a high-level agreement, and in fact it is part of IP, IP modules must be realized by the other.    IP is not designed to be absolutely reliable design, the purpose of this agreement is to appear when the network returned to the issue of control of information, rather than IP protocol becomes absolutely reliable, does not guarantee that the data reported or control information able to return.    Some data will be reported in the absence of any report of the circumstances lost.    Upper agreement must use their own judgement error control procedures for communication is correct. RFC 792 for the definition of ICMP IP protocol ID number is 1.    It also provides IP Type - services domain value and the numerical priority status, and should be equal.    In accordance with RFC 1812, the router will be useful if they are 6 or 7 of the IP priority with a little bit of ICMP error message evaluation. 
  1.1 ICMP information relating to the special circumstances of transient error message should not send ICMP error messages.    The ICMP then the situation in the agreement, which is defined by RFC 792 of the internal work of the strict rules: 
  In order to avoid duplication in the unlimited ICMP error message will not be sent after the return of ICMP error messages. 
  . IP for the fragmented data reported only in piecemeal chip ICMP sent the wrong message. (1 debris) 
  . ICMP error messages destined never to broadcast or multicast addresses sent in response to the data reported. 
  . ICMP error message as a link in the never-broadcast sent in response to the data reported. 
  . ICMP error message never in the source address does not mean that the only mainframe - source IP address, it is not possible, Loop address, or a broadcast address broadcast address more than one point of data sent in response to the report. 
  . ICMP error message is not in any type of IGMP information in response to be sent.    When an unknown type of ICMP message is being received, it must be silent was discarded. 
  . Addition to information destination host, the router will almost always produce ICMP message (s), the ICMP was the number of information by the Executive to decide. 
  From the angle of comparison and around a variety of rules, we can arrive at a "network storm" idea, and the additional network traffic is in the vast majority of the special conditions of the agreement after the ICMP. 
  2 ICMP messages 
  ICMP customary for the two types of operations: 
  .    Report non-transient error conditions. 
  .    Determination of the network in order to the general use of information requests and responses test network. 
  Being as a "type of information" is a code be assigned to each ICMP information; its detailed description of the types of information.    In addition to a number of yards was described ICMP type performance of "Code."    It as a type of use, and it depends on the description of types of information. 
  There are two kinds of agreements ICMP type of operation; the information it has been divided into two kinds: 
  ICMP error message 
  ICMP Internet distribution of digital information for the authorities (IANA) has been a registered now the definition of ICMP a list of types of information.    It also sets out the definition of ICMP information RFC.    Enquiries at the list: http://www.isi.edu/in - Note / iana / designation / icmp-number three.    Table 1 ICMP definition of a variety of types and codes. 
  An ICMP error message 
  ICMP error message used to prevent transmission of the report of a problem.    The nature of the problem should be a non-transient delivery issues. 
  ICMP error in the domain of some inside information always be sent: 

  ICMP error message the general format.    ICMP error message length of each ICMP error messages including IP header (from 20 to 60 bytes) from the wrong and at least the initial eight data bytes; more than 8 bytes can be transmitted; received data packets in the table of data from the first and certainly for the change.    Therefore, an ICMP error message length should be in the 36 to 72 bytes between. 
  ICMP error message destination inaccessible (type 3) loss of the source address (type 4) to direct (type 5) overtime (type 11) number three (type 12) 

  Table 3: ICMP error message 

  RFC 792 for the definition of ICMP IP protocol ID number is 1.    It also explains the types of IP - services domain median values and priorities should be zero.    In accordance with RFC 1812, the router will use numerical 6 or 7 as they send the wrong message to the ICMP IP signs of value.    ICMP agreement for the ICMP error message states: 
  In order to avoid duplication of unlimited never ICMP error message to other ICMP error messages sent a response. 
  . ICMP error message to never doomed to a broadcast address or a multicast address sent in response to the data reported. 
  . ICMP error messages never sent by radio link layer data on response to be sent. 
  . ICMP error message never address the root causes does not mean that the only mainframe data sent in response to the report, the source IP addresses can not be zero, loop-back addresses, a broadcast address or a multicast address.    ICMP error message never routers and host (s) issued by the wrong message to the conditions inconsistent IGMP any type of a response is sent.    Therefore, I will briefly separated from the error message stating the conditions. 
  1.1 inaccessible destinations (type 3) 
  Released by the purpose mainframe inaccessible purpose mainframe ICMP types of information: a purpose mainframe issued a destination inaccessible when the news of the agreement specified in the original agreement digital domain, data packets on the mainframe purpose is not active, otherwise specified The port is inactive.    ICMP destination of the information inaccessible through a router issue: a router in the destination (or the next jump-) inaccessible or services can be obtained without forwarding data packets issued in response to a destination inaccessible information. 
  Notes significance code 
  012345 network inaccessible mainframe inaccessible agreement can not be reached port inaccessible to the split is fixed and DF-Source Routing Network Routing failure destination is not in the foreseeable If a direct link has been the destination host on the network is not the availability of a line from a router produced (not to respond to ARP).    If, in a designated data packets in the transport agreements not in the final destination of the transport layer supported.    If, had a designated transport protocol (such as UDP) on the multi-channel output signal can not be the final destination of the packet transport layer protocol mechanism but did not notify the sender.    If a router needs to debris However, since the DF flag can be set up without being fixed.    If a router can not bring a package to the next, had a line in the source selection jump 

  1.1.1 inaccessible destinations - debris is necessary but debris unit is the only fixed destination inaccessible types of ICMP error message, it inaccessible to other destinations the ICMP error message format of the data reported some minor the differences, this is the type 3 code 4 — debris is necessary but debris unit is fixed.    In this type of information, the domain is not the length of 16 bytes, rather than 32 bytes.    The remaining 16 bytes will be used to carry the association for MTU (maximum transmission unit) because that is too large data packets can not be shipped to link the use of a jump (or destination).    Since the data was not being chopped (DF bytes are fixed), it should be sent to the sender includes instructions should be a relatively low MTU, and under the direction of a jump-link serial number wrong message. 
  1.1.2 inaccessible destinations - with the aim of prohibiting network communications can be directed destination management system is the wrong message was sent from the system to configure the data was rejected.    This error message is used in the filtration devices based on use (firewall / router / filter other people) restrictions or other security measures standards and filtration filters on the data reported.    We can come to the conclusion, despite the filter is blocking our data packets, and we are instructed to stop sending data, but our destination is the extension of the mainframe and mobile, we are not able to reach it.    By the next example to illustrate a router on the Internet from all the congestion request information on the format to the target machine, 53 ports in the application was fixed applications in the ACL: 
  1.2 Source Routing failure (type 4) 
  ICMP Source Routing failure types of information from a router issue: If a router sending this message, it need not mean that the router buffer storage space to the purpose of the network on the path of the output data network reported sequence.    Special note RFC 1812 Router should not generate a source of land from the failure information, but the source of the router land from the failure to restrict information (because it is depleting bandwidth, and it is an invalid Congestion correction methods) a Router received ICMP Source Routing failure types of information: 
  Receive a router may be overlooked: from the host the ICMP Source Routing failure types of information: if a purpose mainframe send this message (which may be realized), which means that data can not be too fast to reach deal with .    Internet communication sent to the destination volume ICMP source of information on the failure of a mainframe reduce the rate request.    ICMP header will always zero.    By the next HPUX B.11.0 example, the issuance of a machine based on ICMP error message source of failure: 

  ICMP received information on the source of failure of mainframe type: 
  ICMP source of failure information must be reported to the transport layer, TCP or UDP, the host should be in a period inhibit their liquidity, and then gradually increase throughput. 
  1.3 redirect (type 5) 
  A router issued by the ICMP redirect news type: 
  If a router have this news, it means that the future host should send data packets to the network router, the IP address he is in the ICMP message to be determined.    Router should always transmitted as data packets generated ICMP redirect mainframe and routers news of the same online.    When the router IP address to the original data at the IP address of the first match, a routing loop is generated. 
  Unless all of the following conditions have otherwise not have router redirect: 
  . Data packets are being received from it was the same physical interface transponders out, 
  . Data packets in the IP source address and IP address as the next leap network IP address the same logic, and 
  . Do not contain IP source routing. 

  IP router redirect a message format received an ICMP redirect news type: 
  If the router is running a routing protocol, or redirect the router and the package is being rushed in its interface was on the opening.    When the router on the data path selection, ICMP Router can be ignored. 
  To appear in the code domain of the four different types of code: 

  Redirect code issued by the ICMP redirect mainframe types of information: 
  A host should not be sent ICMP redirect news, redirects information is only sent from the router 9. 
  Received from the host of ICMP redirect news type: 
  Redirect news received a host must therefore update its routing information. 
  Each console must be ready to accept the mainframe and network redirection. 
  Under the following conditions should be redirected news quietly discarded: 
  It designated the new gateway address is not adopted by the network redirection at the same online. 
  If not for the source of redirect designated as a destination for the current first jump Gateway. 
  1.4 overrun error (type 11) 
  In the transport error message, more than the survival of the ICMP error issued by a router: 
  Transfer operating systems (or applications) will be real-time value on the time domain IP header, it represents a data packet was allowed to travel on the Internet in the largest of time.    In the time domain of the first Internet (IP header) was dealing with each node was reduced.    RFC 791 provides data on the time spent dealing with the domain reduction process.    Domain value of the second measurement units.    RFC also said that the value of real-time greatest time to 255 seconds can be set up, it is 4.25 minutes.    RFC also provides the greatest time domain can be set to 255 seconds, equivalent to 4.25 minutes.    If this domain value zero, data packets must arrive at the destination before it was discarded.    As a measure linked to the field assessment is somewhat specious.    Some of the data processing speed routers may be relatively long, and some routers can handle fast data packets (heavy burden status).    True to the wishes of the life span of data on a threshold, so not out of the infinite loop data packets will not plug the Internet. 
  Data on life expectancy is limited is to help us stop the old copy of After some time after arrival.    So when we re-broadcast, we can be assured not previously delivered a message, a copy of the old has been abandoned and will not hinder the process. 
  If he found a router with a data packet IP header of a domain, such as the life-cycle, and he would have discarded packets and ICMP an overtime information code 0 - in the transmission process in excess of the life-cycle (which may also be a routing loop issues signs). 
  A router must generate an ICMP time exceeded the news because of the code 0 when it expires TTL domain discarded when a data packet.    Each router can be an interface option at that interface on the origin of the information was suspended, but that information must be allowed to choose the origin of the default. 
  The next one example, in the 'ping' an IP (yyyy) attempts, we received to the destination IP address from one to another routing error message routing the transmission of information in overtime.    Life-cycle has been exhausted: 

  Router issued reassembled debris overtime wrong message: 
  When the router regrouped be doomed to a router package, which is the Internet as a host.    Are acting as host router received overtime when news mainframe rules are equally applicable. 

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