By default, during a swap operation, the IEEE 802.1p bits of the VLAN tag remain unchanged. When the swap-by-poppush operation is enabled on a logical interface, the swap operation is treated as a pop operation followed by push operation. The pop operation removes the existing tag and the associated IEEE 802.1p bits and the push operation copies the inner VLAN IEEE 802.1p bits to the IEEE bits of the VLAN or VLANs being pushed. As a result, the IEEE 802.1p bits are inherited from the incoming transparent tag.
In effect, swap-by-poppush serves as a VLAN operation property and is used along with a swap or swap-push VLAN rewrite operation, indicating the nature of the swap operation being performed.