QOS之Classification and Marking

QOS的模型：

Best-Effort Service 盡力而為服務模型

Integrated Service 綜合服務模型，簡稱Intserv

Differentiated Service 區分服務模型，簡稱Diffserv

我們在這主要讨論的是Diffserv，要提供區分服務的QOS，就必須先将資料分為不同的類别，或者将資料設定為不同的優先級。将資料分為不同的類别，稱為分類(classification)，分類并不修改原來的資料包。将資料設定為不同的優先級稱為标記(marking)，而标記會修改原來的資料包。分類和标記是實施QOS的前提，也是基礎。

QOS的流程：

<a target="_blank" href="http://blog.51cto.com/attachment/201104/101332930.png"></a>

Marking is the QOS feather component that colors a packet so it can be identified and distinguished from other packts in QOS treatment 也就是說為資料包打上顔色 以至于QOS可以把它和其他的包分别對待。

CLASSIFICATION:

incoming interface

ip precedence

DSCP

SOURCE dan destination

application

marking方法：

network layer ：（基于資料包tos位）

link layer ：

COS (ISL 802.1P)

MPLS EXP BIT

Frame relay DE bit

vlan

<a target="_blank" href="http://blog.51cto.com/attachment/201104/102901871.png"></a>

Inter-Switch Link (ISL)幀中，預留有1-byte的IEEE 802.1p字段，其中有3 bits可以标記CoS。 

IEEE 802.1Q幀中，預留有2-byte字段，其中同樣隻有3 bits可以标記CoS，

而IEEE 802.1Q幀中，native VLAN是不能被标記的，因為沒有額外封裝。 

CoS中由于隻有3 bit可以标記，是以隻能标記出0-7共8類資料，預設标為0，然而6和7是被保留的，是以隻有0-5共6類可供使用者标記使用。

幀中繼可丢棄名額符（DE）位 在幀中繼資料包中，有額外的一個字段可以用來訓示該資料包的優先級，這個字段被稱為可丢棄名額符Discard eligible (DE)位，預設為0，設定為1表示該資料不重要而優先被丢棄

af11     Match packets with AF11 dscp (001010) 分兩塊001 是1  010 是1

 af12     Match packets with AF12 dscp (001100) 001            100 是2

  af13     Match packets with AF13 dscp (001110)001            110   3

  af21     Match packets with AF21 dscp (010010)010        2   010   1

  af22     Match packets with AF22 dscp (010100)

  af23     Match packets with AF23 dscp (010110)

  af31     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)    在af41 af42 af43中af41的優先級最高             

  af42     Match packets with AF42 dscp (100100)

  af43     Match packets with AF43 dscp (100110)

cs1      Match packets with CS1(precedence 1) dscp (001000)     後三位全部置0相當于ip優先級

  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 packets with CS7(precedence 7) dscp (111000)

  default  Match packets with default dscp (000000)

  ef       Match packets with EF dscp (101110)      

ip 優先級 Precedence

 &lt;0-7&gt;           Precedence value

  critical        Set packets with critical precedence (5)

  flash           Set packets with flash precedence (3)

  flash-override  Set packets with flash override precedence (4)

  immediate       Set packets with immediate precedence (2)

  internet        Set packets with internetwork control precedence (6)

  network         Set packets with network control precedence (7)

  priority        Set packets with priority precedence (1)

  routine         Set packets with routine precedence (0)

我們可以設定ip precedence 或者DSCP 隻是分類方法的不同，标志不同的優先級，DSCP比ip precedence有更加細化了優先級類别，我們看下三者的聯系

<a target="_blank" href="http://blog.51cto.com/attachment/201104/103530958.png"></a>

分類基于 ACL        NBAR

标記 ：PBR  CBMARKING

PBR 可以基于源ip 進行轉發，而路由轉發隻是基于目的ip進行轉發，看個例子

<a target="_blank" href="http://blog.51cto.com/attachment/201104/111438509.png"></a>

由于r4和r3之間是以太網鍊路預設r5的流量走r4到r2

我們在r3上做pbr讓r5的loopback0 5.5.5.5 走R1 loopback1 走r4

access-list 100 permit ip host 5.5.5.5 host 2.2.2.2

access-list 101 permit ip host 9.9.9.9 host 2.2.2.2

route-map PBR permit 10

 match ip address 100

 set interface Serial1/1

route-map PBR permit 20

 match ip address 101

 set ip next-hop 34.1.1.4

interface Serial1/3

 ip address 35.1.1.3 255.255.255.0

 ip policy route-map PBR

在r3開啟debug

*Mar  1 00:24:23.647: IP: s=9.9.9.9 (Serial1/3), d=2.2.2.2, len 100, FIB policy match

*Mar  1 00:24:23.647: IP: s=9.9.9.9 (Serial1/3), d=2.2.2.2, g=34.1.1.4, len 100, FIB policy routed

*Mar  1 00:24:23.891: IP: s=9.9.9.9 (Serial1/3), d=2.2.2.2, len 100, FIB policy match

*Mar  1 00:24:23.891: IP: s=9.9.9.9 (Serial1/3), d=2.2.2.2, g=34.1.1.4, len 100, FIB policy routed

*Mar  1 00:24:23.991: IP: s=9.9.9.9 (Serial1/3), d=2.2.2.2, len 100, FIB policy match

*Mar  1 00:24:23.991: IP: s=9.9.9.9 (Serial1/3), d=2.2.2.2, g=34.1.1.4, len 100, FIB policy routed

*Mar  1 00:24:24.111: IP: s=9.9.9.9 (Serial1/3), d=2.2.2.2, len 100, FIB policy match

r3#

*Mar  1 00:24:24.111: IP: s=9.9.9.9 (Serial1/3), d=2.2.2.2, g=34.1.1.4, len 100, FIB policy routed

*Mar  1 00:24:24.227: IP: s=9.9.9.9 (Serial1/3), d=2.2.2.2, len 100, FIB policy match

*Mar  1 00:24:24.227: IP: s=9.9.9.9 (Serial1/3), d=2.2.2.2, g=34.1.1.4, len 100, FIB policy routed

*Mar  1 00:22:59.287: IP: s=5.5.5.5 (Serial1/3), d=2.2.2.2, len 100, FIB policy match

*Mar  1 00:22:59.287: fibidb-&gt;namestring: Serial1/1

*Mar  1 00:22:59.287: ipfib_policy_set_interface_lookup: tag_ptr: 0x0

*Mar  1 00:22:59.287: adj 0x0, NULL

*Mar  1 00:22:59.287: IP: s=5.5.5.5 (Serial1/3), d=2.2.2.2 (Serial1/1), len 100, FIB policy routed

*Mar  1 00:22:59.431: IP: s=5.5.5.5 (Serial1/3), d=2.2.2.2, len 100, FIB policy match

*Mar  1 00:22:59.431: fibidb-&gt;namestring: Serial1/1

*Mar  1 00:22:59.431: ipfib_policy_set_interface_lookup: tag_ptr: 0x0

*Mar  1 00:22:59.431: adj 0x0, NULL

我們隻是設定了permit 10 和20 而r5的源流量

*Mar  1 00:21:42.731: IP: s=35.1.1.5 (Serial1/3), d=2.2.2.2, len 100, FIB policy rejected(no match) - normal forwarding

*Mar  1 00:21:42.851: IP: s=35.1.1.5 (Serial1/3), d=2.2.2.2, len 100, FIB policy rejected(no match) - normal forwarding

*Mar  1 00:21:42.919: IP: s=35.1.1.5 (Serial1/3), d=2.2.2.2, len 100, FIB policy rejected(no match) - normal forwarding

*Mar  1 00:21:42.975: IP: s=35.1.1.5 (Serial1/3), d=2.2.2.2, len 100, FIB policy rejected(no match) - normal forwarding

*Mar  1 00:21:43.015: IP: s=35.1.1.5 (Serial1/3), d=2.2.2.2, len 100, FIB policy rejected(no match) - normal forwarding

總結：pbr在資料層面沒有permit正常轉發，而路由層（重分布）面直接deny

pbr打标記隻能基于入口，不能設定DSCP

r3(config)#route-map PBR permit 10

r3(config-route-map)#match ip add 101

r3(config-route-map)#set ip ?

  address     Specify IP address

  default     Set default information

  df          Set DF bit

  next-hop    Next hop address

  precedence  Set precedence field

  qos-group   Set QOS Group ID

  tos         Set type of service field

r3(config-route-map)#set ip tos ?      

  &lt;0-15&gt;             Type of service value

  max-reliability    Set max reliable TOS (2)

  max-throughput     Set max throughput（吞吐量） TOS (4)

  min-delay          Set min delay TOS (8)

  min-monetary-cost  Set min monetary cost TOS (1)

  normal             Set normal TOS (0)

以上是手工指令行的形式打标記，我們還可以基于模版是的打标記就是MQC

ip access-list extended tel

 permit tcp any any eq telnet

ip access-list extended www

 permit tcp any any eq www

class-map match-all（預設） www     class map 調用ACL  what traffic do we care about

 match access-group name www   match all 一個class map 可能比對多個流量隻有都滿足才執行

class-map match-all tel

 match access-group name tel

policy-map CBMARK          polic map 調用class-map   what will be done to this traffic

 class tel

  set dscp af11

 class www

  set dscp af41

interface FastEthernet0/0

service-policy input CBMARK   在接口下調用 （出入口都行）

Router#  show policy-map int f0/0

 本文轉自q狼的誘惑 51CTO部落格，原文連結：http://blog.51cto.com/liangrui/550434，如需轉載請自行聯系原作者