In the EVPN Route Server mode, the tier-0 service router (SR) hosted on the edge node acts as a BGP route server, establishing BGP control plane sessions with southbound VNFs and external data center routers. ESXi hypervisors exchange the user plane traffic directly with the data center fabric routers using VXLAN encapsulation, bypassing the edge node in the data path.
From the BGP control plane perspective, there are two types of sessions:
|Between hosted VNFs and tier-0 VRF gateway.||
|Between tier-0 SR and DC gateways.||
The NSX EVPN Route Server mode is based on the "Interface-ful IP-VRF-to-IP-VRF with SBD IRB" as defined in the IETF RFC 9136. The RFC 9136 introduces a concept called overlay index in EVPN. A key concept of EVPN RT-5 is the overlay index, which can be a gateway IP address, a MAC, or an ESI. When a node receives an EVPN RT-5 with an overlay index specified, the receiving node performs a recursive route resolution to find the appropriate node to forward the data packets for the corresponding IP prefix.
NSX EVPN Route Server mode implements the gateway IP address as the overlay index. The tier-0 SR also advertises to the external router an additional EVPN type-2 route with the appropriate MAC/IP (gateway IP) binding and the corresponding VXLAN TEP address.
The gateway IP address in this case will be the IPv4 BGP next hop for a given prefix as advertised by the VNF to the tier-0 VRF gateway. The recursive route resolution uses respective RT-2 to learn the ESXi TEP address where the VNF is hosted.
Data Center Gateway Requirements
The data center gateway router connected to the edge node tier-0 SR must support the "Interface-ful IP-VRF-to-IP-VRF with SBD IRB Mode" described in the IETF RFC 9136, section 4.4.2.
Virtual Network Function (VNF) Requirements
A VNF is typically a virtual machine used for some networking function such as a virtual router, firewall, or a Telco 5G core application. In the context of EVPN Route Server mode, the VNF is hosted by an ESXi hypervisor and should support 802.1Q-tagged interfaces and regular BGP protocol with IPv4 and IPv6 unicast address families.