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1、由于最近要用到tos，ipprecedence和dscp，找了一些資料，現(xiàn)在明白了tos，ipprecedence和dscp這三者的關(guān)系。網(wǎng)上流傳的版本眾多，其實都是正確的，只是分別被不同的標(biāo)準定義，因而讓人莫名其妙。IPPrecedence和ToS都位于IP頭中，共占一個字節(jié)，8bits，關(guān)于這幾個字節(jié)的作用被不同的標(biāo)準定義過，分別是RFC791，RFC1122，RFC1349；RFC1349廢除了之前兩個RFC的定義，現(xiàn)在大多設(shè)備都使用RFC1349中的定義，所以對于tos，有如下版本，分別說明如下
2、；?下面是RFC1349中的原話：InthepasttherehasbeensomeconfusionaboutthesizeoftheTOSfield.RFC-791defineditasathreebitfield,includingbits3-5inthefigureabove.Itincludedbit6intheMBZfield.RFC-1122addedbits6and7totheTOSfield,eliminatingtheMBZfield.This?memo?redefinestheTO
3、Sfieldtobethefourbitsshowninthefigureabove.?一、RFC1349中的TOS、IPprecedenceRFC1349中定義的ToS格式如下：TypeofService(TOS)XXXXXXX076543210?可表示如下：?????????0????????????????1????????????????2????????????????3????????????????4????????????????5????????????????6???????????
4、?????7+------------+-----------+------------+------------+------------+-----------+-----------+------------+
5、?????PRECEDENCE???????????????????????
6、???????????????????????????????????????????????????????????????????
7、?????????????????
8、
9、???????優(yōu)先權(quán)?????????
10、???????????????????????
11、??????????????????????????TOS??????????????????????????????????
12、??MBZ?????
13、
14、?????????????????????????????????????????????????????
15、???????????????????????????????????????????????????????????????????
16、?????????????????
17、+------------+
18、-----------+------------+------------+------------+-----------+-----------+------------+（MBZ：mustbezero）?對應(yīng)的優(yōu)先級如下：BitsMeaning7-5IPPrecedence:111NetworkControl110InternetworkControl101Critic/ECP100FlashOverride011Flash010Immediate001Priority000Routine41=L
19、owDelay;0=NormalDelay31=HighThroughput;0=NormalThroughput21=HighReliability;0=NormalReliability11=Minimisemonetarycost(RFC1349)0Mustbe0整理成表格為：PROPERTYCLIENTVIEWSETTINGBITMASK/BINARYVALUEPrecedenceROUTINE(DEFAULT)000?PRIORITY001?IMMEDIATE010?FLASH011?FLAS
20、HOVERRIDE100DelayNormalLow01ThroughputNormalHigh01ReliabilityNormalHigh01CostNormalLow01CongestionN/A0?二、RFC791中的TOS、IPprecedenceTheIPTypeofServiceByte:Bits0-2:Precedence.Bit3:Delay(0=NormalDelay,1=LowDelay)Bit4:Throughput
