Re: QoS verification on the exam

Hi Sud,

I have seen your previous e-mail on GS, but I was a bit lazy and was
waiting for others to reply ;-)

QoS verification is not very time consuming if you know the tools and
have the right formulas in mind. I would definetly verify it in the
lab.

To generate test traffic you can just use telnet, ping or traceroute.
All those commands allow you to set the value of the ToS field.
However for telnet you need to set it in global config mode.

"ip telnet tos B8" would mark all outgoing telnet packets with DSCP
46/EF. Please be aware that this command requires the number to be in
hex.

These are the formulas to calculate the ToS value:

  IP Precedence to ToS: IP_Precedence_Value * 32
  AF to ToS: FIRST_DIGIT * 8 + SECOND_DIGIT * 2 * 4
  DSCP to ToS: DSCP_VALUE * 4

Here are some examples for calculating the ToS value:

Convert IP Precedence to ToS
----------------------------

IP Precedence 4
ToS = 4 * 32 = 128
ToS in Hex = 80

Convert AF values to ToS
------------------------

AF31
DSCP = FIRST_DIGIT * 8 + SECOND_DIGIT * 2
DSCP = 3 * 8 + 1 * 2
DSCP = 26
ToS = 26 * 4 = 104
ToS in Hex = 68

Convert a DSCP value to ToS
---------------------------

DSCP 46 (EF)
ToS = 46 * 4 = 184
ToS in Hex = B8

For verification of the markings you can use "show policy-map
interface x/y" on routers and "show mls qos interface x/y statistics"
on switches.

Best regards,

Jochen

On Tue, Apr 10, 2012 at 10:25 AM, Sud <mitsuie2_at_gmail.com> wrote:
> Hello friends,
>
> Just wondering whether the group received my mail.
>
> Please can you give me some light.
>
> Cheers!
> Sud
>
> Sent from my iPad
>
> On Apr 6, 2012, at 10:40 PM, Sud Mu <mitsuie2_at_gmail.com> wrote:
>
>> Hi all,
>>
>> These days I'm going through QoS technologies.
>>
>> I'm wondering whether it will be practical to verify the QoS configs in the actual lab based on the time limit we have.
>>
>> It's true that the more I verify the more marks I'm sure about. But would like to know whether i should verify that section generating traffic by trying various possibilities.
>>
>> I feel like I should be virtually 100% sure about what I configure and leave it not verified.
>>
>> Sud
>>
>> Sent from my iPad
>
>
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Received on Tue Apr 10 2012 - 12:25:56 ART