Re: QoS

Hi Marten

the confusion is in the syntax of the command .

the set ip tos commands only allows you to set four bits in the TOS
byte of the ip header

by choosing a value of 12 you are setting minimum delay and maximum throughout

so with the config you have above you will have EF , since IPP(3
leftmost bits) is set to 5 or 101 in binary and delay and throughput
bits are set while the remaining bits are clear (11000)

Since dscp bits = 6 most significant bits or leftmost bits

adding this up you have dscp EF(101110)

see command refernce for more info on the set ip tos command
http://www.cisco.com/en/US/docs/ios/qos/command/reference/qos_s1.html#wp1059575

HTH

On 5/12/10, Maarten Vervoorn <mr.vervoorn_at_gmail.com> wrote:
> I have a question about the solution a QoS excersise
>
> Requirement - Router originated telnet traffic should have a dscp
> of EF. Give the neccessary config.
>
> Restrictions:
> Do this without using any interface commands
> Do not use the command -> ip telnet tos xxx
>
> The solution to this is:
> !
> access-list 101 permit tcp any any eq telnet
> !
> route-map telnet permit 10
> match ip address 101
> set ip precedence 5
> set ip tos 12
> !
> ip local policy route-map telnet
>
> Can you explain the TOS bit numbering for me? If i check the configuration
> you are able to select tos 0-15.
>
> What I thought is that TOS is 128 bits (8 caracters). Left 3 are Precedence
> and left 6 are DSCP
> precedence 5 is 101 00000
> DSCP ef is 101110 00
> So if you need to add 00011000 to 1010000 to make 10111000
> if I calculate 00011000 it is 24
> What I understood from a previous post is that a 0 is appended and prepended
> so this maken 01011100. But why is in this case the 0 prepended in front of
> the bits. Normaly DSCP are the left six bits. Now for all of a sudden in a
> route-map the DSCP bits are 7,6,5,4,3,2
> Normaly when you calculate Precedence or DSCP in TOS yoi take bits 8,7,6 for
> precedence and 8,7,6,5,4,3 for DSCP
> Precedence 5 = TOS 160
>
>
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-- 
Warm Regards ,
Beauty
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