Priority Code Point (PCP)ΒΆ

Priority Code Point (PCP) is a means of classifying and managing network traffic and of providing quality of service (QoS) in modern Layer 2 Ethernet networks. It uses the 3-bit PCP field in the VLAN header for the purpose of packet classification.

The PCP field was introduced by the IEEE P802.1p working group.


When a Test Agent Application attempts to configure PCP settings in outgoing IP packets, it cannot be guaranteed that the settings are indeed carried through. This is because the Test Agent Application does not control the host it is running on and its interface configurations.

To ensure that PCP settings are applied as intended when using a Test Agent Application, you need to manually map (on the host OS) the SO_PRIORITY bits set on the socket to the PCP bits in the VLAN header. Below is an example of a command doing this mapping for VLAN 123 on interface eth0:

ip link set eth0.123 type vlan egress 0:0 1:1 2:2 3:3 4:4 5:5 6:6 7:7


Making this kind of changes may cause malfunctions on the host. You need to be fully aware of the consequences of the command you intend to run.

Read more about how to use ip link set here:

To learn more about SO_PRIORITY, see this article: