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Catalyst 9300 qos

tpahuja
Level 1
Level 1

Folks,

             Looking at 9300 qos document it says that the default behavior of the cat 9300 is to trust DSCP. Does anyone know what is the behavior of the cat 9300 for uplinks(trunks).

 

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2 Accepted Solutions

Accepted Solutions

brselzer
Cisco Employee
Cisco Employee

Hello,

 

It depends on the type of ingress and egress interface:

 

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst9400/software/release/16-6/configuration_guide/qos/b_166_qos_9400_cg/b_166_qos_9400_cg_chapter_01.html

 

Look for the table under "Trust Behavior for Wired Port"

 

1) If you come in a layer 3 interface, and leave a layer 3 interfaced. We will trust DSCP. 

2) If you come in a layer 2 interface and leave a layer 2 interface, we don't alter the packet so DSCP is conserved. Since there is no cos because there is no tag, there will still be no cos.

3) If you come in a trunk and leave a trunk, we will trust both DSCP and CoS

4) If you come in a layer 3 interface and leave a trunk, we will trust DSCP. Since the layer 3 interface doesn't have a cos value, we will set it to 0. 

 

Hope that helps!

 

-Bradley Selzer
CCIE# 60833

View solution in original post

It depends:

 

1) If it is just normal data traffic, we would set cos to 0 since there is no tag on an access port.

2) If it is a phone in a voice vlan, the phone tags traffic even on an access port. We will preserve whatever the tag is. 

 

Essentially, if there is a situation where there is no tag, we will set it to 0. If there is, we will preserve it. However, this is just the default behavior. It can easily be overwritten with a policy-map.

 

Hope that helps!

-Bradley Selzer
CCIE# 60833

View solution in original post

3 Replies 3

brselzer
Cisco Employee
Cisco Employee

Hello,

 

It depends on the type of ingress and egress interface:

 

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst9400/software/release/16-6/configuration_guide/qos/b_166_qos_9400_cg/b_166_qos_9400_cg_chapter_01.html

 

Look for the table under "Trust Behavior for Wired Port"

 

1) If you come in a layer 3 interface, and leave a layer 3 interfaced. We will trust DSCP. 

2) If you come in a layer 2 interface and leave a layer 2 interface, we don't alter the packet so DSCP is conserved. Since there is no cos because there is no tag, there will still be no cos.

3) If you come in a trunk and leave a trunk, we will trust both DSCP and CoS

4) If you come in a layer 3 interface and leave a trunk, we will trust DSCP. Since the layer 3 interface doesn't have a cos value, we will set it to 0. 

 

Hope that helps!

 

-Bradley Selzer
CCIE# 60833

What is your come in as layer 2 and go out through a trunk?

It depends:

 

1) If it is just normal data traffic, we would set cos to 0 since there is no tag on an access port.

2) If it is a phone in a voice vlan, the phone tags traffic even on an access port. We will preserve whatever the tag is. 

 

Essentially, if there is a situation where there is no tag, we will set it to 0. If there is, we will preserve it. However, this is just the default behavior. It can easily be overwritten with a policy-map.

 

Hope that helps!

-Bradley Selzer
CCIE# 60833
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