Configure QoS

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Packets received at the switch can be classified to a particular class of service based on the filters configured. Certain policies can be applied before forwarding the packets. The following task illustrates the classification of the TCP packets received in the switch and changing the DSCP value in the IP header of the TCP packets to 46.

See Basic SEFOS Topology for the topology of this task. Connect port 25 to host A and port 26 to host B. Host B should have a command to dump traffic over a network interface such as tcpdump or snoop. If not, port 25 and port 26 can be connected to a data capturing device as shown in Basic SEFOS Topology.

Connect to SEFOS.
See Connect to SEFOS.

Enable port 1 and port 2.

SEFOS-1# configure terminal
SEFOS-1(config)# interface xl-ethernet 0/26
SEFOS-1(config-if)# no shutdown
SEFOS-1(config-if)# exit
SEFOS-1(config)# interface xl-ethernet 0/25
SEFOS-1(config-if)# no shutdown
SEFOS-1(config-if)# exit
SEFOS-1(config)# vlan 1
SEFOS-1(config-vlan)# ports xl-ethernet 0/25 xl-ethernet 
0/26 untagged xl-ethernet 0/25 xl-ethernet 0/26

You might see the following message if both interfaces are already in VLAN 1.

% Member Ports cannot be added/deleted on Default VLAN
SEFOS-1(config-vlan)# end

Enable QoS.

SEFOS-1# configure terminal
SEFOS-1(config)# qos enable
SEFOS-1(config)# end

Create an access control list filter for TCP packets.

SEFOS-1# configure terminal
SEFOS-1(config)# ip access-list extended 11
SEFOS-1(config-ext-nacl)# permit tcp any any
SEFOS-1(config-ext-nacl)# exit
SEFOS-1(config)# interface xl-ethernet 0/25
SEFOS-1(config-if)# ip access-group 11 in
SEFOS-1(config-if)# end

Specify the class mapping for the incoming packet and policy mapping for the classified packet.
1. Enter Global Configuration mode.
```
SEFOS-1# configure terminal
```
2. Create a class map and enter Class Map Configuration mode.
```
SEFOS-1(config)# class-map 10
```
3. Configure the match criteria for the class map with the criteria specified by the access list 11 (configured in Step 4 as all TCP packets).
```
SEFOS-1(config-cls-map)# match access-group ip-access-list 11
SEFOS-1(config-cls-map)# set class 100
```
4. Exit Class Map Configuration mode.
```
SEFOS-1(config-cls-map)# exit
```
5. Create a policy map to apply to the packet before forwarding it.
```
SEFOS-1(config)# policy-map 10
```
6. Create a policy map for class 100 packets and set the DSCP value in the IP header for the outgoing packets matched by this class as 46.
```
SEFOS-1(config-ply-map)# set policy class 100 default-priority-type ipdscp 46
SEFOS-1(config-ply-map)# exit
```
  46 (0x2e) is a decimal number. If an 8-bit TOS value is shown, it is shown as 0xb8 because 0x2e must be shifted left 2 bits to get the 6 bits of the DSCP value.

View the configuration details.

SEFOS-1# show access-lists
...
Filter Protocol Type             : TCP
IP address Type                  : IPV4
...
In Port List                     : X10/25
...
 
Filter Action                    : Permit
Status                           : Active...
L3FilterId                   : 11
PriorityMapId                : None
CLASS                        : 100
PolicyMapId                  : 10
...
SEFOS-1# show policy-map 10
QoS Policy Map Entries
----------------------
PolicyMapId  : 10IfIndex      : 0
Class        : 100
DefaultPHB   : IP DSCP 46
...

Verify the functionality of the policy configuration by generating 100 TCP packets.
From host A to host B, send TCP packets to host B and use the host-supported packet dumping command to verify the DSCP value.
```
# tcpdump -xx -n -i eth3 ip
...
16:34:27.979962 IP 12.0.0.100.905 > 12.0.0.17.shell:
...
16:34:27.980163 IP 12.0.0.17.shell > 12.0.0.100.905:
0x0000:  0014 4f6c 7de9 001b 2147 d479 0800 4500
0x0000:  001b 2147 d479 0014 4f6c 7de9 0800 45b8
...
```
These packets are received at port 26 and have a DSCP value 46. In this example, the dump command shows a DSCP value of 0xb8.

Configure QoS

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