05-16-2013 06:18 AM - edited 03-07-2019 01:23 PM
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
05-16-2013 06:29 AM
Forgot to mention IOS:
cat4500-ipbasek9-mz.122-31.SGA1.bin
05-16-2013 06:36 AM
Could you please include the following output
show run | i qos or your global qos configurations.
Regards,
Sony
05-16-2013 06:48 AM
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
05-16-2013 07:08 AM
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.
05-16-2013 07:47 AM
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
05-19-2013 10:36 PM
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
05-24-2013 04:51 AM
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
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