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dscp values not passing between port channel interfaces on 3750's

stogyman_
Level 1
Level 1

Greetings,

I have two stacks of 3750's trunked together over an 8gig etherchannel.  My ip phones on the second stack of switches are not passing dscp values across the port

channel.  I have mls qos trust dscp on each of the trunk ports associated with the port channel.  The command set does not allow me to add mls qos trust dscp ton

the port channel interface.  I tried setting up a quick and dirty policy map and apply the service policy to the port channel interface but got an error message stating

can not apply servfice policy to a virtual interface.  I have some snipets of the config below.  What am I missing here? Thank you.

class-map match-any VoIP
  match ip dscp ef
!
!
policy-map VoIP_QoS
  class VoIP
    trust dscp
!
!
interface Port-channel1
switchport trunk encapsulation dot1q
switchport mode trunk
switchport nonegotiate

interface GigabitEthernet1/0/2
switchport trunk encapsulation dot1q
switchport mode trunk
switchport nonegotiate
mls qos trust dscp
channel-group 1 mode on

interface GigabitEthernet1/0/2
switchport trunk encapsulation dot1q
switchport mode trunk
switchport nonegotiate
mls qos trust dscp
channel-group 1 mode on

System image file is "flash:c3750-ipbase-mz.122-35.SE5/c3750-ipbase-mz.122-35.SE
5.bin"

5 Replies 5

Edison Ortiz
Hall of Fame
Hall of Fame

QoS must only be applied on the physical ports that are member of the etherchannel, not on the port-channel interface.

If DSCP value aren't being sent/received, verify you have 'mls qos' and 'mls qos trust dscp' at both ends of the links

You also must make sure you have the correct dscp-cos maps in both switches.

By default, the mapping is incorrect and there isn't any correlation between DSCP 46 and COS 5. COS 5 maps to DSCP 40.

Regards

Edison

mls qos command is issued globally on both stacks and when I issue the show

mls qos command they both return with:

WHINYXC3750_STACK2-8#sh mls qos
QoS is enabled
QoS ip packet dscp rewrite is enabled

also my mapping is:

mls qos map cos-dscp 0 8 16 26 32 46 48 56

it has to be something with the port channel, because I have other stacks of 3750's who are trunked by single links and they pass dscp values across the

trunk port fine.  I guess I will have to remvoe the port channel and run them over a single trunk link to verify.  All dscp vlaues are coming across the wan fine from

devices plugged into the first stack that does not traverse the port channel to the other stack of 3750's.  I appreciate the input, thank you.

Just found something interesting on all my trunk ports that are part of my port channel on that second stack of switches:

even though you can see I have the command set mls qos trust dscp on my individual trunk links:

interface GigabitEthernet1/0/2
switchport trunk encapsulation dot1q
switchport mode trunk
switchport nonegotiate
mls qos trust dscp
channel-group 1 mode on

when I issue the
sh mls qos int gi1/0/2 it returns the following:

GigabitEthernet1/0/2
trust state: not trusted
trust mode: trust dscp
trust enabled flag: dis
COS override: dis
default COS: 0
DSCP Mutation Map: Default DSCP Mutation Map
Trust device: none
qos mode: port-based

trust state: not trusted..........now I just need to figure out why that would be.

David Williams
Level 1
Level 1

Did anyone ever find a solution to this problem?  We seem to be running into the same issue with a stack of 3750s.

No, not yet. I have a tac case open but they are having a difficult recreating the issue. Once a solution is reached, I will make sure to post to the forum.

Date: Wed, 23 Dec 2009 13:19:01 -0700

From: supportforums-donotreply@cisco.com

To: stogyman@hotmail.com

Subject: New message: "dscp values not passing between port channel interfaces on 3750's"

stogyman_,

A new message was posted in the Discussion thread "dscp values not passing between port channel interfaces on 3750's":

https://supportforums.cisco.com/message/2009318#2009318

Author : Dave Williams

Profile : https://supportforums.cisco.com/people/dwilliams1979

Message:

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