Setting COS on egress in Linux
In order to set COS (802.1Q Priority Code Point) on outgoing frames, you first need to set the VLAN interface's egress-qos-map to match the kernel's internal SKB priorities. According to the man page:
defines a mapping of Linux internal packet priority to VLAN header prio field but for outgoing frames
Because the COS has 8 distinct values, let's map internal priorities one to one up to 7:
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The mapping can also be set with NetworkManager (field vlan.egress-priority-map). At time of this writing, newer
kernels and versions of NetworkManager seem to have a bug, though:
https://issues.redhat.com/browse/RHEL-72475
Next, if the packet originates from the local node, instruct it to set the internal priority class in the OUTPUT chain of the mangle table. For example, to set all ICMP packets that leave this node to SKB priority 6 and subsequently COS 6, you can use the following command:
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