EVPN (MAC-VRF) Control Word

EVPN-VPWS is built on an MPLS network, and the transit device's load-balancing hashing algorithm can cause out-of-order delivery of packets. The transit device can incorrectly identify an Ethernet payload as an IPv4 or IPv6 payload if the first nibble of the destination address MAC is 0x4 or 0x6, respectively. By inserting a control word between the label stack and the Layer 2 header of the packet on the MPLS packet-switched network, you can ensure that the top nibble is 0, thus preventing the packet from being identified as an IPv4 or IPv6 packet. When you enable the control word, the PE devices advertise their support in the auto-discovery route for each EVPN instance (EVI). Before the control word is inserted into the data packet, you must configure all the PE devices in an EVI on the EVPN-VPWS service, and all the PE devices in the EVI agree to support the control word. If any PE device in an EVI does not support the control word, then the PE devices will not include the control word in their packet.