NAME 名稱

icmp, IPPROTO_ICMP - Linux IPv4 ICMP 核心模塊.  

DESCRIPTION 描述

本網(wǎng)絡(luò)核心協(xié)議模塊實(shí)現(xiàn)了基于 RFC792 協(xié)議中定義的《互聯(lián)網(wǎng)控制報(bào)文協(xié)議》。它針對(duì)網(wǎng)絡(luò)主機(jī)間通訊出錯(cuò)的情況作出回應(yīng)并給出診斷信息。用戶不能直接使用本模塊。相反本模塊需與核心中的其他協(xié)議進(jìn)行通訊，而這些協(xié)議將 ICMP 出錯(cuò)信息返回到網(wǎng)絡(luò)協(xié)議的應(yīng)用層。ICMP 核心模塊也回應(yīng) ICMP 請(qǐng)求。

如果用 IPPROTP_ICMP 打開原始套接字（raw socket）時(shí)，用戶協(xié)議有可以收到任意本地套接字 ICMP 包。 IPPROTO_ICMP. 請(qǐng)參閱 raw(7) 傳遞到套接字的 ICMP 包可以用 ICMP_FILTER 套接字選項(xiàng)進(jìn)行過濾。核心會(huì)處理所有 ICMP 包，包括傳遞到用戶的套接字去的。

Linux 對(duì)可以到達(dá)每個(gè)目標(biāo)主機(jī)出錯(cuò)信息包的比率設(shè)立了限制。 ICMP_REDIRECT 及 ICMP_DEST_UNREACH 也受進(jìn)入包的目標(biāo)路由的限制。

SYSCTLS

ICMP 支持通過 sysctl 接口來設(shè)置一些全局 IP 參數(shù)。對(duì) Sysctl 的訪問可以通過讀、寫 /proc/sys/net/ipv4/* 下的文件通過 sysctl(2) 接口進(jìn)行. 大多數(shù)這些 sysctls 對(duì)特定 ICMP 類型的數(shù)據(jù)包數(shù)量進(jìn)行了限制。 Linux 2.2 使用記號(hào)單元過濾器對(duì) ICMP 包進(jìn)行限制。 此值表示超時(shí)錯(cuò)誤，以秒計(jì)，直到到頂后記號(hào)單元過濾器被清除為止。

icmp_destunreach_rate

發(fā)送目的地不可到達(dá) ICMP 消息包的***數(shù)據(jù)包比率。這限制了發(fā)送到任意一個(gè)路由或目的地的數(shù)據(jù)包的比率。這個(gè)限制不影響發(fā)送用來發(fā)現(xiàn)數(shù)據(jù)鏈路***傳送單位（MTU）的 ICMP_FRAG_NEEDED包 數(shù)據(jù)包。

icmp_echo_ignore_all

如果該值不為零,Linux將忽略所有的 ICMP_ECHO 請(qǐng)求。

icmp_echo_ignore_broadcasts

如果該值不為零,Linux將忽略所有發(fā)送到廣播地址的 ICMP_ECHO 數(shù)據(jù)包。

icmp_echoreply_rate

發(fā)送響應(yīng) ICMP_ECHOREQUEST 請(qǐng)求的 ICMP_ECHOREPLY 數(shù)據(jù)包比率的***值。

icmp_paramprob_rate

發(fā)送 ICMP_PARAMETERPROB 數(shù)據(jù)包比率的***值。當(dāng)一個(gè)具有非法 IP 報(bào)頭數(shù)據(jù)包到達(dá)時(shí)將發(fā)送這些包。

icmp_timeexceed_rate

發(fā)送 ICMP_TIME_EXCEEDED 包比率的***值。當(dāng)一個(gè)數(shù)據(jù)包通過太多網(wǎng)段時(shí)，這些包用作防止路由回環(huán)。

NOTES

由于在許多其他實(shí)現(xiàn)中不支持 IPPROTO_ICMP 原始套接字（raw socket），可移植程序不能依靠這一特性。

當(dāng)Linux不作為路由器時(shí)，將不被發(fā)送 ICMP_REDIRECT 包。內(nèi)核也只有在路由表中的舊網(wǎng)關(guān)和路由重新定向超時(shí)時(shí)才接受這些包。

ICMP_TIMESTAMP 返回的 64 位毫秒為單位的時(shí)間戳是自1970年1月1日以來的時(shí)間．

Linux 的 ICMP 在內(nèi)部使用原始套接字（raw socket）來發(fā)送ICMP包。這個(gè)原始套接字可能在 netstat(8) 消息輸出中出現(xiàn)，帶著一個(gè)“zero inode”信息。

VERSIONS

在2.2版本中將再不支持 ICMP_ADDRESS 請(qǐng)求。

在2.2版本中將不再支持 ICMP_SOURCE_QUENCH  

參見

ip(7)

RFC792 對(duì)ICMP協(xié)議進(jìn)行了詳細(xì)的敘述。

#p#

NAME

icmp, IPPROTO_ICMP - Linux IPv4 ICMP kernel module.  

DESCRIPTION

This kernel protocol module implements the Internet Control Message Protocol defined in RFC792. It is used to signal error conditions and for diagnosis. The user doesn't interact directly with this module; instead it communicates with the other protocols in the kernel and these pass the ICMP errors to the application layers. The kernel ICMP module also answers ICMP requests.

A user protocol may receive ICMP packets for all local sockets by opening a raw socket with the protocol IPPROTO_ICMP. See raw(7) for more information. The types of ICMP packets passed to the socket can be filtered using the ICMP_FILTER socket option. ICMP packets are always processed by the kernel too, even when passed to a user socket.

Linux limits the rate of ICMP error packets to each destination. ICMP_REDIRECT and ICMP_DEST_UNREACH are also limited by the destination route of the incoming packets.  

SYSCTLS

ICMP supports a sysctl interface to configure some global IP parameters. The sysctls can be accessed by reading or writing the /proc/sys/net/ipv4/* files or with the sysctl(2) interface. Most of these sysctls are rate limitations for specific ICMP types. Linux 2.2 uses a token bucket filter to limit ICMPs. The value is the timeout in jiffies until the token bucket filter is cleared after a burst. A jiffy is a system dependent unit, usually 10ms on x86 and about 1ms on alpha and IA64.

icmp_destunreach_rate

Maximum rate to send ICMP Destination Unreachable packets. This limits the rate at which packets are sent to any individual route or destination. The limit does not affect sending of ICMP_FRAG_NEEDED packets needed for path MTU discovery.

icmp_echo_ignore_all

If this value is non-zero, Linux will ignore all ICMP_ECHO requests.

icmp_echo_ignore_broadcasts

If this value is non-zero, Linux will ignore all ICMP_ECHO packets sent to broadcast addresses.

icmp_echoreply_rate

Maximum rate for sending ICMP_ECHOREPLY packets in response to ICMP_ECHOREQUEST packets.

icmp_paramprob_rate

Maximum rate for sending ICMP_PARAMETERPROB packets. These packets are sent when a packet arrives with an invalid IP header.

icmp_timeexceed_rate

Maximum rate for sending ICMP_TIME_EXCEEDED packets. These packets are sent to prevent loops when a packet has crossed too many hops.

NOTES

As many other implementations don't support IPPROTO_ICMP raw sockets, this feature should not be relied on in portable programs.

ICMP_REDIRECT packets are not sent when Linux is not acting as a router. They are also only accepted from the old gateway defined in the routing table and the redirect routes are expired after some time.

The 64-bit timestamp returned by ICMP_TIMESTAMP is in milliseconds since January 1, 1970.

Linux ICMP internally uses a raw socket to send ICMPs. This raw socket may appear in netstat(8) output with a zero inode.

VERSIONS

Support for the ICMP_ADDRESS request was removed in 2.2.

Support for ICMP_SOURCE_QUENCH was removed in Linux 2.2.  

SEE ALSO

ip(7)

RFC792 for a description of the ICMP protocol.