qos部分乾頤堂qos03-差分服務(wù)和phb

1、乾頤堂網(wǎng)絡(luò)實驗室QoS 服務(wù)質(zhì)量差分服務(wù)的類基礎(chǔ)Understanding the Differentiated Services Model-PHB每一跳行為Differentiated Services ModelThe Differentiated Services model describes services associated with traffic classes.差分服務(wù)模型描述了不同的流量分類Complex traffic classification and conditioning is performed at the network edge, resultin

2、g in a per-packet復(fù)雜的流量分類和條件可以在網(wǎng)絡(luò)邊界實施No per-flow state in the core.-核心沒有基于流的狀態(tài)The core only performs simple “per-hop behaviors” on traffic aggregates.核心僅僅基于簡單的PHBThe goal is scalability.分類和標(biāo)記分類工具通過檢查數(shù)據(jù)幀、信元和數(shù)據(jù)包頭將數(shù)據(jù)包分類，同時QoS工具的分類功能還可以修改包頭的字段，便于分類很多QoS工具都依靠分類功能用以決定該為哪種流量應(yīng)用該工具標(biāo)記功能將一個值放入數(shù)據(jù)幀、數(shù)據(jù)包或者信元頭部中的一個字

3、段，該字段是轉(zhuǎn)為QoS標(biāo)記功能設(shè)計的，通過標(biāo)記數(shù)據(jù)包，其他的QoS功能可以根據(jù)頭部內(nèi)的標(biāo)記字段來執(zhí)行數(shù)據(jù)包分類。標(biāo)記功能簡化了網(wǎng)絡(luò)的QoS設(shè)計，簡化了其他QoS工具的配置分類和標(biāo)記不直接影響網(wǎng)絡(luò)流量的帶寬、演示、抖動和丟包，但他們卻是應(yīng)用其他QoS工具的前提可以被擴展ACL匹配的字段可以被CB直接匹配的字段分類標(biāo)準(zhǔn)CB的一些例子按照（所謂的）1層特性來給數(shù)據(jù)分類，比如來自某個接口的數(shù)據(jù)R2(config)#class-map A-定義一個class-map名為A，默認為匹配所有（match-all）R2(config-cmap)#match input-interface e0/0-匹配來e0

4、/0接口的流量根據(jù)二層特征來給數(shù)據(jù)分類R3(config)#class-map BR3(config-cmap)#match source-address mac cc00.41fc.0000匹配三層特性來分類R3(config)#class-map TestR3(config-cmap)#match ip precedence 1 2 3 4-這里需要特別指出的是，在這里，和route-map的邏輯相同，在同一行中是任意的意思，即或的關(guān)系，匹配1-4的任意一個ip優(yōu)先級分類標(biāo)準(zhǔn)CB依賴四層或者高層信息R4(config)#class-map match-any Ender-這里我們匹配的是任

5、意一個條件，即匹配TCP或者UDP的流量R4(config-cmap)#match access-group name TCPR4(config-cmap)#match access-group name UDP!R4(config)#ip access-list extended TCPR4(config-ext-nacl)#permit tcp any host 44.1.1.1 eq 23IP包頭中用于QoS的字段接下來的部分列出了您可以標(biāo)記的頭部字段，并且說明了該字段最適合用于何種場景QoS中最常用的兩個標(biāo)識字段是IP優(yōu)先級和DSCPDSCP EncodingDiffServ fiel

6、d: The IP version 4 header ToS octet or the IPv6 traffic class octet, when interpreted in conformance with the definition given in RFC 2474 . IPv4中取出三位作為IP優(yōu)先級位IP優(yōu)先級舉例：101(000XX)=160（5*32）DSCP: The first six bits of the DiffServ field, used to select a PHB (forwarding and queuing method)-六位的DSCP，用于選擇

7、PHB（即在每一個設(shè)備所受的服務(wù)，轉(zhuǎn)發(fā)和隊列方法）優(yōu)先級字段優(yōu)先級字段的值應(yīng)該隨著重要性而增長，對QoS行為來說值越大越重要DSCP與此不同，在定義逐跳行為的RFC中，建議使用的DSCP值并不是越大越好IP precedencenetwork control precedence (7)網(wǎng)絡(luò)控制internetwork control precedence (6)網(wǎng)間控制critical precedence (5，101)，voice關(guān)鍵flash override precedence (4)，video疾速flash precedence (3)，voice control閃速immed

8、iate precedence (2)，data快速priority precedence (1)，data優(yōu)先routine precedence (0)普通IP Precedence bit settings 6 and 7 are reserved for network control information such as routing updates.優(yōu)先級6和7保留給網(wǎng)絡(luò)控制信息Per-Hop BehaviorsDSCP selects PHB throughout the network.四類PHBDefault PHB (FIFO, tail drop)EF Expedit

9、ed Forwarding（101110）-快速轉(zhuǎn)發(fā) AF Assured Forwarding 保證轉(zhuǎn)發(fā)Class-Selector (兼容IP Precedence) PHB后三位為0，稱之為CS。兼容ip優(yōu)先級，CS1=P1，類推至cs7默認0沒有QoS機制101110的EFAF保證轉(zhuǎn)發(fā)類選擇器PHB基于差分服務(wù)模型的網(wǎng)絡(luò)，QoS特性無法支持差分服務(wù)是不可想象的DSCP中定義了一個特用于兼容IP優(yōu)先級的CS的PHB（每一跳行為），即CS越高優(yōu)先級越高Backward Compatibility Using the Class Selector用CS向后兼容IP優(yōu)先級Class-Selec

10、tor “xxx000” DSCP Compatibility with current IP Precedence usage (RFC 1812) = maps IP Precedence to DSCP-和ip 優(yōu)先級兼容（后三位等于0）Differentiates probability of timely forwarding 不同的轉(zhuǎn)發(fā)可能(xyz000) = (abc000) if xyz abcIf a packet has DSCP = “011000,” it has a greater probability of timely forwarding than a pac

11、ket with DSCP = “001000.”DSCP example af11 Match packets with AF11 dscp (001010) af12 Match packets with AF12 dscp (001100) af13 Match packets with AF13 dscp (001110) af21 Match packets with AF21 dscp (010010) af22 Match packets with AF22 dscp (010100) af23 Match packets with AF23 dscp (010110) af31

12、 Match packets with AF31 dscp (011010) af32 Match packets with AF32 dscp (011100) af33 Match packets with AF33 dscp (011110) af41 Match packets with AF41 dscp (100010) af42 Match packets with AF42 dscp (100100) af43 Match packets with AF43 dscp (100110) cs1 Match packets with CS1(precedence 1) dscp

13、(001000) cs2 Match packets with CS2(precedence 2) dscp (010000) cs3 Match packets with CS3(precedence 3) dscp (011000) cs4 Match packets with CS4(precedence 4) dscp (100000) cs5 Match packets with CS5(precedence 5) dscp (101000) cs6 Match packets with CS6(precedence 6) dscp (110000) cs7 Match packet

14、s with CS7(precedence 7) dscp (111000) default Match packets with default dscp (000000) ef Match packets with EF dscp (101110)Per-Hop Behaviors (Cont.)EF PHB:Ensures a minimum departure rate-保證最小轉(zhuǎn)發(fā)能力Guarantees bandwidth (The class is guaranteed an amount of bandwidth with prioritized forwarding.)-保證

15、帶寬，優(yōu)先轉(zhuǎn)發(fā)Polices bandwidth (The class is not allowed to exceed the guaranteed amountexcess traffic is dropped.)-管制流量，超過的會被丟棄DSCP value “101110”: looks like IP Precedence 5 to pliant devicesBits 5 to 7: “101” = 5 (Same three bits used for IP Precedence) Bits 3 to 4: “11” = drop probability high 丟棄可能性最大

16、，可以理解為管制后都丟棄Bit 2: Just “0”EF=快速轉(zhuǎn)發(fā)：101110-固定值如果僅僅識別IP優(yōu)先級，則優(yōu)先級5，等同EFPer-Hop Behaviors (Cont.)AF PHB-確保轉(zhuǎn)發(fā):Guarantees bandwidth-帶寬保證Allows access to extra bandwidth, if available-可以占用更多的出接口Four standard classes (af1, af2, af3, and af4；001，010，011，100)DSCP value range: “aaadd0”Where “aaa” is a binary va

17、lue of the classWhere “dd” is drop probability-代表丟棄可能性，值越高，丟棄可能性越大Per-Hop Behaviors (Cont.)Each AF class uses three DSCP values.-每個AF類用三個DSCP值（如AF11，AF12，AF13）Each AF class is independently forwarded with its guaranteed bandwidth.每個AF類依據(jù)保證帶寬獨立的轉(zhuǎn)發(fā)它們數(shù)據(jù)Congestion avoidance is used within each class to

18、prevent congestion within the class.擁塞避免針對不同的AF有不同的待遇AF13丟棄可能性大于AF11;AF43的包對比AF21，更易被丟棄dd位的取值：00，01，10，11;00被CS占用Per-Hop Behaviors (Cont.)A DiffServ node must allocate a configurable, minimum amount of forwarding resources (buffer space and bandwidth) per AF class.Excess resources may be allocated between nonidle classes. The manner must be specified.Reordering of IP packets of the same flow is not allow