In OpenStack, VXLAN (Virtual Extensible LAN) is a network virtualization technology used to create overlay networks. It encapsulates the original Ethernet frames within UDP packets and adds a VXLAN header to enable communication between virtual machines across different physical networks.

The “egress_pkt_mark” is a configuration parameter used in OpenStack Neutron, the networking component of OpenStack, specifically for VXLAN tunnels. The egress_pkt_mark value is used to mark the outer UDP packets with a specific value when they leave the OpenStack network node and are forwarded to the physical network.

This marking is often used by the physical network devices, such as switches or routers, to apply specific policies like Quality of Service (QoS) or traffic shaping based on the marked packets. The egress_pkt_mark can be set to a specific value using the OpenStack Neutron configuration file to differentiate VXLAN traffic from other types of network traffic.

By configuring the egress_pkt_mark value, network administrators can have more granular control over the behavior of VXLAN traffic as it leaves the OpenStack network node and is transmitted over the physical network infrastructure.