ICMP protocol http://91mail.51.net provides, to translate detailed drawings, please download to http://91mail.51.net to download the Internet control information protocol objective and feature is schematically described in RFC 792, If the method of sending error information is provided as a non-short error condition, and a means of exploring the network in order to determine the general characteristics of the network. Later, RFC 1122, and RFC 1812 clarified the characteristics of some ICMP protocols. In order to reliably and consistent with other ICMP protocols, we need to merge RFC 792, RFC 1122, and RFC 1812. Other RFCs define other functionality for ICMP protocol: RFC 896-Source Routing Failed RFC 950-Address Mask Extended RFC 1191- MTU Path Discovery RFC 1256-Router Discovery RFC 1349 - Service in the Internet Protocol Group 1 Types a more correct definition of the target, and features of the Internet Control information protocol, and features that it can be used: When a router or a destination owner needs to inform the wrong source host in a datagram At the time, network assay requests and reply information used in order to determine the general characteristics of the network. 1 ICMP specification ICMP information is transmitted in IP datagram. Although ICMP uses IP to do its underlying support, it seems that it is a high-level protocol, and in fact it is part of IP and must be implemented by other IP modules. IP is not designed to be desirable to be absolutely reliable, the purpose of this protocol is to return control information when the network has problems, rather than making the IP protocol absolutely reliable, and does not guarantee the data report or control information to return. Some datagrams will still be lost without any reports. The upper protocol must use its own error control program to determine if the communication is correct. RFC 792 is 1 for ICMP Defining IP protocols. It also specifies the value of the IP type-service domain value and priority status should be equal to zero. In accordance with RFC 1812, the router will use ICMP error information to use ICMP error information using the value of 6 or 7, such as their IP. 1.1 Special circumstances regarding ICMP information For transient error messages, ICMP error messages should not be sent. For the next case, the ICMP protocol has the strict rules of internal operations defined in RFC 792:. To avoid unlimited repetitions, ICMP error messages will not be sent after ICMP error message returning .. For the fragmentation IP datagram, just zero Send the wrong ICMP information on the debris. (First fragment) .ICMP error message is sent from the data report response from the broadcast or multi-point transmission address. .ICMP error message Send from the data reported as a joint layer broadcast ..icmp error message from the source address does not represent the only host - the source IP address is not possible to zero, loop addresses, a broadcast address or more points The data report response of the broadcast address is sent. .ICMP error message is not sent in any type of IGMP information response. When an ICMP information of an unknown type is received, it must be discarded silently. In addition to the information reaches the host, the router will almost always generate ICMP information (s), and the number of ICMP information generated is determined by execution. From a relatively close range of different rules, we can draw an idea about the "network storm", and additional network traffic is after special conditions for the vast majority of ICMP protocols. 2 ICMP information ICMP habits are used for two types of operations:. Report the condition of non-transient errors. . In order to determine the test network for request and response information about the general feature of the network. A digital code as "information type" is assigned to each ICMP information; it detail the type of information. Another number of code is the descriptive ICMP type "code". It is used as a subtype, and its description depends on the information type. The ICMP protocol has two types of operations; therefore, its information is also divided into two types: ICMP error message ICMP Query Information Internet Assignment Digital Administration (IANA) has a list of defined ICMP information types that have been registered. It lists RFCs that define ICMP information. The list query URL: http://www.isi.edu/in- Note / IANA / Specified / ICMP- number. Table 1 defines a variety of different ICMP types and code. 1 ICMP error message ICMP error information is used to report a problem that hinders transmission. The nature of the problem should be a non-transitory transmission issue. Some of the domains in ICMP error messages are always transmitted: ICMP error message general format.
ICMP error message length Each ICMP error message includes an IP header (20 to 60 bits) and at least the first eight data bytes that cause errors,; more than 8 bid bytes can be transmitted; received data packets This header and data are necessarily changed. Therefore, an ICMP error message should be between 36 to 72 bile bytes. ICMP error message destination cannot reach (Type 3) source address loss (Type 4) Direct (Type 5) Timeout (Type 11) Number of questions (Type 12) Table 3: ICMP error message
RFC 792 The IP protocol ID number defined for ICMP is 1. It also illustrates the IP type-service domain value and priority value should be equal to zero. According to RFC 1812, the router will use the value of 6 or 7 as the value of the IP flag of ICMP error information they send. The ICMP protocol is the provisions of ICMP error information:. To avoid unlimited ICMP error messages, the ICMP error message is not transmitted from another ICMP error message. .ICMP error message is sent from the data report response to a broad address or a multi-point transfer site. .ICMP error message The data reported from the connection layer broadcast is sent ..IICMP error message is sent from the root source site does not represent the only host's datagram response, that is, the source IP address cannot be zero, loopback Address, a broadcast address or a multi-point transmission address. ICMP error message is sent from any type of IGMP response from any type of error information that is not uniform in the router and host (s). So I will separately describe the conditions for issuing error messages. 1.1 Cannot Arrival (Type 3) The ICMP information type of the host that cannot be reached by the target host: a message that a destination host issues a destination cannot be reached. When the protocol specifies the original digital domain, the packet is not The destination host is active, otherwise the specified port is not active. The information type that ICMP destination cannot be reached is released by a router: a router is not able to reach a destination in response to packet responses that cannot be reached by destination (or next jump). Information. Code Meaning Note 012345 Network Cannot Arrival The host cannot reach the protocol cannot reach the port cannot reach the split is a must, and the DF bit fixed source routing fails to reach the destination network route is invisible. If it is in a network directly connected to the network A line of the host is not available, generated by a router (not to react to ARP). If, the transportation layer specified in the transport protocol in a packet is not supported in the final destination. If the specified transport protocol (e.g., UDP) is generated, the multi-channel output signal cannot be notified of the transport layer of the last destination but no protocol mechanism notifies the sender. If a router needs to be fragments but since the DF flag is fixed without being set. If a router cannot submit a package to the next one, generate a selection jump in the source line
1.1.1 Destination cannot reach-debris is a must, but the fragmented unit is a fixed-unique ICMP error information type that cannot be reached. It has some slightly with other destination that cannot be reached by other destination. Different, this is the type 3 code 4 - fragment is necessary but the fragmented unit is fixed. In this type of information, the unused domain is a length of 16-bit bytes instead of 32-bit bytes. The 16-bit bytes will be used to carry the MTU (maximum transfer unit) for coupling, that is, since the packet is too large, and cannot be delivered to the next connection to use the jump (or destination). Since the datagram cannot be chopped (DF byte is fixed), it should be sent to the sender an error message including the indication of the lower MTU and the next jump link number. 1.1.2 Destination cannot arrive - the communication that is prohibited from the destination network is an error message that can be managed indicating the destination system configured to a rejected datagram from the transmission system. This error message is used in a datagram that is filtered by a secure filtering measures based on filtering devices (firewall / router / other person filtering) or other secure filtration measures. We can conclude that although the filtering device is blocking our packets, and is instructing us to stop sending data, our destination owner is extended and flowing, we cannot reach it. With the next example, a router has a bundled request information format for all from the Internet, and the target port number 53 of the destination machine is fixed to the application ACL at: 1.2 Source Routing Failed (Type 4) ICMP source routing failed information The type is released by a router: if a router sends this information, it means that the router does not need buffer space to store the output data report sequence of the next network on the path of the destination network. RFC 1812 specifically stated that a router should not generate a source of failure information, but restricts the source of the router by failure information (because it consumes bandwidth, and it is an invalid correction method for congestion) A router received ICMP Source Routing Failure Information Type: A router receives possible ignore information: The ICMP source routing failed by the host: If a destination host sends this information (it may be implemented), it means that the Data report is too fast Not being processed. The ICMP source failed information is a request for a reduction rate for the host to send traffic to the Internet. The ICMP information header will always zero. With the next example HPUX B.11.0, the machine-released ICMP source failed error message: Host failure message type received by ICMP Source: ICMP source failed message must be reported to transportation layer, udp or tcp, host should be in one Inhibition of your own circulation during the period, then gradually increase the amount of transmission. 1.3 Redirect (Type 5) A router ICMP redirection message type: If a router generates this message, it means that the host should send future packets to the router of the network, his IP address is in the ICMP message Be given. The router should always be on the same subnet as a router that transmits a packet host and generating an ICMP redirect message. When the router IP address matches the IP address of the original data header, a routing ring is generated. The router cannot generate a redirection message unless there is all the following conditions:. The packet is being forwarded from the same physical interface from it being received, and the IP source address of the packet and the network as the next hop IP address The logical IP address is the same, and. Do not include IP source routing selection. IP redirect message format A router receives an ICMP redirection message type: If the router is running a routing protocol, or redirects on the router and is enabled on the interface on which the package is being sent. When the router is generated for the router, the router can ignore the ICMP. 4 different codes that can appear in code domain: redirect code from the host's ICMP redirection type message: a host should not send ICMP Directional messages, redirection information is only sent by the router 9. Redirect message type by the host received by the host: The host that receives a redirect message must be updated to update its routing information. Each host must be ready to accept host and network redirection. Redirection messages should be quietly discarded under the following conditions: It is not allowed to reach the same network as the new gateway address.
