network cisco ccna gns3 certification arteq

network cisco ccna gns3 certification arteq
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Sunday, June 10, 2012

dscp and ip precedence cont...

but arteq, you say, the friggin af numbers don't follow the same logic... i was disappointed also...

look again...

notice that the af numbers follow the cs numbers and increase by 1, hence cs3 contains af's 31, 32 and 33.. for assured forwarding in class 3, 31 is the lowest priority for the class, 33 is the highest... that still prevails, but the ds field values don't... tough shit... life isn't fair...

notice af22's ds field value equals 20 decimal or binary 010100, but also notice the ds field values are a constant increment of 2... some compensation there...

if you remember the class selector, ie, cs4 is decimal 4 x 8 or 32, the corresponding af values beyond the cs increase by 1, and the decimal value increases by 2 each time giving  af41 (4x8) + 2 or 34, af42 is then plus two or 36 decimal...  kinda clunky but it works for me...

there is this formula as well...   afxy = 8x + 2y = decimal value or

af32 = 3 times 8 + 2 times 2 = 24 + 4 = 28

and in a pinch there is also this...

dls1(config)#access-list 101 permit ip any any dscp ?
  <0-63>   Differentiated services codepoint value
  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     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 (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 packets with CS7(precedence 7) dscp (111000)
  default  Match packets with default dscp (000000)
  ef       Match packets with EF dscp (101110)

again, af11 is cs1 plus 1, af12 is cs1 plus 2, af11 = af(8x1 + 2x1) or 10 or 001010

af21 is cs2 plus 1 or 8x2 + 2x1 or 16 plus 2 or 18
although  cs5 is 8x5 or 40 expedited forwarding for voice has a ds field value of 46... you'll have to memorize that... or convert binary to decimal from the above output...

ef       Match packets with EF dscp (101110) = 46

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