Understanding the Scenario:

In an EVPN-VXLAN environment, when using multi-homing in active/active scenarios, there's a risk that a multihomed server might receive duplicate copies of Broadcast, Unknown unicast, and Multicast (BUM) traffic. This is because multiple VTEPs might forward the same BUM traffic to the server.

EVPN Route Types:

Type 4 Route (Ethernet Segment Route): This route type is used to advertise the Ethernet Segment (ES) to which the device is connected. It is specifically used in multi-homing scenarios to signal the ES and its associated Ethernet Tag to all the remote VTEPs. The Type 4 route includes information that helps prevent BUM traffic duplication in active/active multi-homing by using a split-horizon mechanism, which ensures that traffic sent to a multihomed device does not get looped back.

The Type 4 route is crucial for ensuring that in a multi-homed setup, particularly in an active/active configuration, BUM traffic does not result in duplication at the server. The route helps coordinate which VTEP is responsible for forwarding the BUM traffic to the server, thereby preventing duplicate traffic.

Data Center Reference:

Type 4 routes are essential for managing multi-homing in EVPN to avoid the issues of BUM traffic duplication, which could otherwise lead to inefficiencies and potential network issues.