07-25-2011 06:02 AM - edited 03-07-2019 01:23 AM
Hi
We have a WS-C2960S-48TS-L switch with QoS .
I have configured 1 ports and 1 trunk port.
interface GigabitEthernet1/0/34
description
switchport access vlan 104
mls qos trust dscp
!
interface GigabitEthernet1/0/52
description
switchport mode trunk
logging event trunk-status
logging event spanning-tree
udld port
mls qos trust dscp
storm-control broadcast level 30.00
storm-control multicast level 30.00
On port Gi 1/0/34 I see incomming DSCP traffic
GigabitEthernet1/0/34 (All statistics are in packets)
dscp: incoming
-------------------------------
0 - 4 : 374 0 0 0 0
5 - 9 : 0 0 0 0 0
10 - 14 : 0 0 0 0 0
15 - 19 : 0 0 0 0 0
20 - 24 : 0 0 0 0 0
25 - 29 : 0 3203 0 0 0
30 - 34 : 0 0 0 0 0
35 - 39 : 0 0 0 0 0
40 - 44 : 0 0 0 0 0
45 - 49 : 0 1574189 0 0 0
50 - 54 : 0 0 0 0 0
55 - 59 : 0 0 0 0 0
60 - 64 :
cos: incoming
-------------------------------
0 - 4 : 1102822 0 0 0 0
5 - 7 : 477688 0 0
But I see no outgoing DSCP traffic on the trunk.
dscp: outgoing
-------------------------------
0 - 4 : 13528641 0 0 0 0
5 - 9 : 0 0 0 0 0
10 - 14 : 0 0 0 0 0
15 - 19 : 0 0 0 0 0
20 - 24 : 0 0 0 0 0
25 - 29 : 0 0 0 0 0
30 - 34 : 0 0 0 0 0
35 - 39 : 0 0 0 0 0
40 - 44 : 0 0 0 0 0
45 - 49 : 0 0 0 6519 0
50 - 54 : 0 0 0 0 0
55 - 59 : 0 0 0 0 0
60 - 64 : 0 0 0 0
What could be wrong ?
Solved! Go to Solution.
07-30-2011 10:31 AM
Edison,
I am perhaps stealing the thread, but you just hinted on an issue I wanted to ask about for a long time.
As the Catalysts can ben configured to trust either CoS or DSCP, you have to ultimately select just one of them and the second value will be rewritten accordingly. I have recommended people to go for DSCP trust because of these reasons:
Considering the fact that all recent Catalyst switches understand DSCP and for those which do not, the DSCP-to-CoS mapping table can modify the resulting CoS to administrator's - and those switches' - liking, I personally do not see any compelling reason to use CoS trust. But am I thinking correctly here? Please correct me - or confirm my thoughts!
Thank you!
Best regards,
Peter
07-30-2011 07:49 AM
Hello,
Did you activate the QoS on the global configuration level? On recent Catalyst switches, the QoS support has to be enabled first in the global configuration mode using the command
mls qos
If you did use that command then please include the output of the following commands:
show mls qos interface gi1/0/34
show mls qos interface gi1/0/52
Best regards,
Peter
07-30-2011 08:59 AM
On the trunk port, I suggest trusting COS instead of DSCP and make sure to modify the cos-dsp values with the following command:
mls qos map cos-dscp 0 8 16 24 32 46 48 56
07-30-2011 10:31 AM
Edison,
I am perhaps stealing the thread, but you just hinted on an issue I wanted to ask about for a long time.
As the Catalysts can ben configured to trust either CoS or DSCP, you have to ultimately select just one of them and the second value will be rewritten accordingly. I have recommended people to go for DSCP trust because of these reasons:
Considering the fact that all recent Catalyst switches understand DSCP and for those which do not, the DSCP-to-CoS mapping table can modify the resulting CoS to administrator's - and those switches' - liking, I personally do not see any compelling reason to use CoS trust. But am I thinking correctly here? Please correct me - or confirm my thoughts!
Thank you!
Best regards,
Peter
07-30-2011 05:26 PM
Hi Peter,
just to share some knowledge with you here
as i know about the 3750 you have the ability to do what yo mentioned about having all the trust, mapping and queuing based on DSCP and it dose work if you want more details you could refer to the SRND of Telepresence QoS LAN section for more detail about this
but again if you have the trust CoS you know the DSCP will be rewritten unless you use a Command that enforce the switch to ignore re writing the DSCP even if you change the CoS
HTH
07-31-2011 01:27 PM
Hello Peter,
You are 100% correct in your assessment of why trusting DSCP is perfectly fine on Catalyst switches because they all support DSCP these days. The only condition where trust COS is preferred is when you have a situation where you have a phone with a PC connected to the phone and you want to conditionally trust the phone but not the PC. If you trust COS then the tagged traffic from the phone will be trusted and the PC's traffic never will.
This is pretty much the only scenario I can think of where you would want to do this. Since there are many places where you want ip phones but don't trust the users this is the way they want do things.
-Matt
07-31-2011 01:34 PM
Hi Matt,
Thanks so much for answering!
Just a thought: Cisco IP phones are currently capable of rewriting the CoS value in frames sent by the PC. Would it be possible to enhance the IP phones' functionality so that they are capable of rewriting the DSCP value as well? Again, this is an enhancement request which is, in my opinion, quite logical considering the fact that CoS marking imposed by the PC is a rare thing as we've discussed earlier.
Best regards,
Peter
07-31-2011 01:55 PM
Hello Peter,
I think that is a very reasonable enhancement request and will look into getting that submitted if it does not already exist.
-Matt
07-31-2011 03:18 PM
Peter,
You are correct. The DSCP-to-COS mappings will take care of having dscp trusted everywhere. The caveat is the correct mappings are entered in the switch else the translation will produce odd results.
An old fashioned and since I know the trunk will see COS values, not DSCP on the header - I don't really want to rely on the translation. However, if your customer isn't network savvy, it's best to recommend DSCP on all ports.
Regards,
Edison.
08-30-2011 12:35 AM
Hi Peter
Thanks for your answer.
I have fixed the problem with remove the auto MLS QOS settings and configure manualy the mls QOS dscp settings on the switch. And now it works fine.
You are 100 % correct about the statement of the DSCP field. Because I see on the LAn's more and more softphones on the PC's ?Laptop. And than you can not use the COS field on layer-2.
Regards Rene
@ The answer is a littlebit late because I'am just back from my holoday.
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