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VXLAN Tunnel DSCP Operations

Cumulus Linux provides configuration options to control DSCP operations during VXLAN encapsulation and decapsulation, specifically for solutions that require end-to-end quality of service, such as RDMA over Converged Ethernet.

The configuration options propagate ECN between the underlay and overlay according to RFC 6040, which describes how to construct the IP header of an ECN field on both ingress to and egress from an IP-in-IP tunnel.

Configure DSCP Operations

You can set the following DSCP operations:

  • The VXLAN encapsulation DSCP action. The action can be copy if the inner packet is IP, set to configure a specific value, or derive to derive the value from the switch priority. The default setting is derive.
  • The VXLAN decapsulation DSCP or COS action. The action can be copy to copy the DSCP value from the outer packet (underlay), preserve to keep the values configured in the inner packet (overlay), or derive to derive the value from the switch priority. The default setting is derive.

The following example sets the VXLAN encapsulation DSCP action to copy.

cumulus@switch:~$ nv set nve vxlan encapsulation dscp action copy
cumulus@switch:~$ nv config apply

The following example sets the VXLAN encapsulation DSCP value to 16.

cumulus@switch:~$ nv set nve vxlan encapsulation dscp action set
cumulus@switch:~$ nv set nve vxlan encapsulation dscp value 16
cumulus@switch:~$ nv config apply

The following example sets the VXLAN decapsulation DSCP value to preserve.

cumulus@switch:~$ nv set nve vxlan decapsulation dscp action preserve
cumulus@switch:~$ nv config apply

Edit the /etc/cumulus/switchd.conf file, then restart switchd.

The following example sets the VXLAN encapsulation DSCP action to copy.

cumulus@switch:~$ sudo nano /etc/cumulus/switchd.conf
...
# vxlan encapsulation update
vxlan.def_encap_dscp_action = copy
# default vxlan encap dscp value, only applicable if action is 'set'
#vxlan.def_encap_dscp_value =

# vxlan decapsulation update
#vxlan.def_decap_dscp_action = derive

The following example sets the VXLAN encapsulation DSCP value to 16.

cumulus@switch:~$ sudo nano /etc/cumulus/switchd.conf
...
# vxlan encapsulation update
vxlan.def_encap_dscp_action = set
# default vxlan encap dscp value, only applicable if action is 'set'
vxlan.def_encap_dscp_value = 16

# vxlan decapsulation update
#vxlan.def_decap_dscp_action = derive

The following example sets the VXLAN decapsulation DSCP value to preserve.

cumulus@switch:~$ sudo nano /etc/cumulus/switchd.conf
...
# vxlan encapsulation update
#vxlan.def_encap_dscp_action = derive
# default vxlan encap dscp value, only applicable if action is 'set'
#vxlan.def_encap_dscp_value =

# vxlan decapsulation update
vxlan.def_decap_dscp_action = preserve
...

After you modify /etc/cumulus/switchd.conf file, you must restart switchd for the changes to take effect.

cumulus@switch:~$ sudo systemctl restart switchd.service

Restarting the switchd service causes all network ports to reset, interrupting network services, in addition to resetting the switch hardware configuration.

Show the DSCP Setting

To show the VXLAN encapsulation DSCP setting, run the nv show nve vxlan encapsulation dscp command:

cumulus@switch:~$ nv show nve vxlan encapsulation dscp 
       operational  applied
------  -----------  -------
action  copy         copy

To show the VXLAN decapsulation DSCP setting, run the nv show nve vxlan decapsulation dscp command.

cumulus@switch:~$ nv show nve vxlan decapsulation dscp
        operational  applied
------  -----------  --------
action  preserve     preserve

Considerations

You can only set the VXLAN encapsulation and decapsulation DSCP actions globally. Cumulus Linux does not support per-VXLAN or per-tunnel settings.