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Core switch 3750G & QoS

Cat3750G:

interface GigabitEthernet1/0/1

description Link to 3560-1

switchport trunk encapsulation dot1q

switchport mode trunk

load-interval 30

mls qos trust dscp

!

interface GigabitEthernet1/0/3

description Link to SRC

switchport access vlan 15

switchport mode access

load-interval 30

duplex full

speed 100

mls qos trust cos

!

Gi1/0/3 - connected to Voice Gateway Cisco3745

Gi1/0/1 - connected to Catalyst 3560

=========================

When i saw traffic at port Gi1/0/3 using SPAN - i saw packets from Cisco3745 with IP DSCP EF.

But if i saw saw traffic at port Gi1/0/1 using SPAN - i saw packets from Cisco3745 with IP DSCP 0.

From that i made desicion that packet from Cisco3745 input into Cat3750G( port gi1/0/3) with DSCP EF and exit from Cat3750G( port gi1/0/1) with DSCP 0

Is't right behavior?

1 ACCEPTED SOLUTION

Accepted Solutions

Re: Core switch 3750G & QoS

As this link is no trunk, frames that are sent over it carry no 802.1p info. The switch will have to examine dscp and set the cos accordingly.

You have to trust dscp instead of cos on int gi1/0/3.

Regards,

Leo

5 REPLIES
Purple

Re: Core switch 3750G & QoS

Hi,

What CoS values do the packets coming in to port Gi1/0/3 have ? Since you are trusting CoS, a CoS of 0 will be mapped to DSCP 0 by default...

Hope that helps - pls rate posts that help.

Regards,

Paresh

New Member

Re: Core switch 3750G & QoS

The packets from VoiceGataway where policy on interface looked into gi1/0/3

policy-map Samara

class RTP

priority 2500

set dscp ef

class CCAPP

bandwidth 500

set precedence 3

Strange things that a saw packets on input gi1/0/3 with DSCP EF and same packets on output gi1/0/1 with DSCP 0

Re: Core switch 3750G & QoS

What class-map are you using to define class RDP?

Just naming the policy-map RDP will not suffice to make it work as intended.

Regards,

Leo

Re: Core switch 3750G & QoS

As this link is no trunk, frames that are sent over it carry no 802.1p info. The switch will have to examine dscp and set the cos accordingly.

You have to trust dscp instead of cos on int gi1/0/3.

Regards,

Leo

New Member

Re: Core switch 3750G & QoS

Excellent! It's helped!

Best regards!

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