4500 remarking dscp value 1 to 0

[Hemant Kumar]

Hi,

I am getting a very strange problem where 4500 switch is remarking the packet with dscp 1 to 0.

Let me explaint the setup.  I have two PCs connected on same switch but on different modules. PC1 is conencted to Gi4/19 and PC2 is connected to

Gi2/43. Both the ports has been configured to trust the dscp. Below are the configuration:

interface GigabitEthernet4/19

switchport access vlan 6

switchport mode access

qos trust dscp

no snmp trap link-status

spanning-tree portfast

interface GigabitEthernet2/43

switchport access vlan 6

switchport mode access

qos trust dscp

no snmp trap link-status

spanning-tree portfast

When I set the DSCP value 1 on PC1, it reaches PC2 as 0. When I mark the traffic with AF21 or AF11, it reaches PC2 with correct value.

Below the hardware details:

Chassis Type : WS-C4506

Mod Ports Card Type                              Model              .

---+-----+--------------------------------------+------------------+-----------

1     2  Supervisor IV 1000BaseX (GBIC)         WS-X4515         

2    48  10/100/1000BaseT (RJ45)                WS-X4448-GB-RJ45  

4    48  10/100/1000BaseT (RJ45)                WS-X4448-GB-RJ45  

[Hemant Kumar]

Forgot to mention IOS:

cat4500-ipbasek9-mz.122-31.SGA1.bin

[sgouldbo]

Could you please include the following output

show run | i qos or your global qos configurations.

Regards,

Sony

[Hemant Kumar]

Thanks for your reply.Below are the output:

Switch#show run | in qos

qos

qos trust dscp

qos trust dscp

qos trust dscp

qos trust dscp

qos trust dscp

qos trust dscp

[paul driver]

Hello

On a 3750, By default dscp rewrite is enabled when mls qos is enabled on the switch, So what your are seeing  may have to do with the default internal dscp mutation maps  to that switch which rewrites the incoming dscp value to the outgoing dscp value

sh mls qos maps dscp-mutation

Dscp-dscp mutation map:

   Default DSCP Mutation Map:

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

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

      0 :    00 01 02 03 04 05 06 07 08 09

      1 :    10 11 12 13 14 15 16 17 18 19

      2 :    20 21 22 23 24 25 26 27 28 29

      3 :    30 31 32 33 34 35 36 37 38 39

      4 :    40 41 42 43 44 45 46 47 48 49

      5 :    50 51 52 53 54 55 56 57 58 59

      6 :    60 61 62 63

D1 - Most significant digit of the DSCP value

D2 - Least significant digit of the DSCP value

So a here on the 3750:
DSCP of  01  is rewritten to a dscp value of 1

DSCP of 10 (af11) is rewritten to a dscp value of 10

DSCP of 18 (af21) is rewritten to a dscp value of 18

Note:

I dont know if these values are the same on a 4500.

res

Paul

Please don't forget to rate any posts that have been helpful.

Thanks.

[Hemant Kumar]

It is same on 4500 as well:

switch#show qos maps dscp policed

Policed DSCP Mapping Table (dscp = d1d2)

d1 : d2  0  1  2  3  4  5  6  7  8  9

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

0 :    00 01 02 03 04 05 06 07 08 09

1 :    10 11 12 13 14 15 16 17 18 19

2 :    20 21 22 23 24 25 26 27 28 29

3 :    30 31 32 33 34 35 36 37 38 39

4 :    40 41 42 43 44 45 46 47 48 49

5 :    50 51 52 53 54 55 56 57 58 59

6 :    60 61 62 63

[Hemant Kumar]

stfo-db-s01#show qos maps dscp

DSCP-TxQueue Mapping Table (dscp = d1d2)

d1 : d2  0  1  2  3  4  5  6  7  8  9

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

0 :    01 01 01 01 01 01 01 01 01 01

1 :    01 01 01 01 01 01 02 02 02 02

2 :    02 02 02 02 02 02 02 02 02 02

3 :    02 02 03 03 03 03 03 03 03 03

4 :    03 03 03 03 03 03 03 03 04 04

5 :    04 04 04 04 04 04 04 04 04 04

6 :    04 04 04 04

DSCP-CoS Mapping Table (dscp = d1d2)

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

Policed DSCP Mapping Table (dscp = d1d2)

d1 : d2  0  1  2  3  4  5  6  7  8  9

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

0 :    00 01 02 03 04 05 06 07 08 09

1 :    10 11 12 13 14 15 16 17 18 19

2 :    20 21 22 23 24 25 26 27 28 29

3 :    30 31 32 33 34 35 36 37 38 39

4 :    40 41 42 43 44 45 46 47 48 49

5 :    50 51 52 53 54 55 56 57 58 59

6 :    60 61 62 63

[Hemant Kumar]

Used the command no qos rewrite ip dscp on both interfaces and now getting the correct values. But still not sure why only it is impacting the non standard dscp values. Investigating more and will update the post after getting the solution