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New Member

DSCP getting remapped on Catalyst 3750

Hi,

My incoming DSCP value 24 packets are getting remapped...I'm not sure why. Here is my config :

class-map match-all ef-traffic

match ip dscp ef

class-map match-all cs3-traffic

match ip dscp cs3

!

policy-map voip

class ef-traffic

police 100000 8000 exceed-action drop

trust dscp

class cs3-traffic

police 32000 8000 exceed-action drop

trust dscp

interface FastEthernet1/0/3

service-policy input voip

My DSCP map is :

Dscp-cos map:

d1 : d2 0 1 2 3 4 5 6 7 8 9

---------------------------------------

0 : 00 00 00 00 00 00 00 00 01 01

1 : 01 01 01 01 01 01 02 02 02 02

2 : 02 02 02 02 03 03 03 03 03 03

3 : 03 03 04 04 04 04 04 04 04 04

4 : 05 05 05 05 05 05 05 05 06 06

5 : 06 06 06 06 06 06 07 07 07 07

6 : 07 07 07 07

Cos-dscp map:

cos: 0 1 2 3 4 5 6 7

--------------------------------

dscp: 0 8 16 26 32 46 48 56

The output of my :

"show mls qos interface fastEthernet 1/0/3 statistics"

command shows that the 24 packets are getting changed to something in the region of "30 - 34".

Any help would be appreciated.

Thanks,

Ellis

4 REPLIES

Re: DSCP getting remapped on Catalyst 3750

the switch will only alter packets at egress. What is the trust state when the traffic is leaving the switch?

New Member

Re: DSCP getting remapped on Catalyst 3750

Hi Mark, thanks very much for your reply.

I have just tried setting the uplink port (from the switch to the core) to trust DSCP, it makes no difference.

Would this make any difference? Doesn't each port have it's own egress queues, so therefore the results I'm seeing from the "show mlq qos interface XXX statistics" command show me the DSCP values of packets going out of the egress port that connects to the device (VoiP phone)......these figures have nothing to do with the egress queue of the uplink port? Or am I missing something ? (probably!)

New Member

Re: DSCP getting remapped on Catalyst 3750

Sorry, may be obvious but

Have you configured dscp (or 'device' if you have cisco phone) trust on the port that connects to the device? What does the output of show mls qos int fa1/0/2 show?

Also, does your IpPrecedence-dscp map map 3 to 24?

New Member

Re: DSCP getting remapped on Catalyst 3750

Thanks for your help everyone, but I now understand whats going on.

I was mis-interpreting the meaning of the stats from "show mls qos interface x/x/x statistics"

"DSCP incoming" appears to be traffic coming from the device into the interface.

"DSCP outgoing" appears to be traffic coming from the interface to the device" and not DSCP values coming out of the port onto the backplane as I had imagined.

Thanks all for your help.

Ellis

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