EVPN-based VXLAN Layer 3 gateway on LVTEP

This section discusses the Layer 3 functionality support on such a logical VTEP (LVTEP).

The following figure illustrates a VXLAN LVTEP topology.

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VXLAN LVTEP topology

The LVTEP is formed through MCT peering (spoke-PW-peer) between Leaf-1 and its peer node, Leaf-12-peer, to provide redundancy for a VXLAN leaf node.

A VXLAN tunnel is created between such an LVTEP leaf and a remote leaf. The source IP address of the VXLAN tunnel is the same on both nodes. Therefore, the tunnel has a single tunnel representation on the remote leaf (Leaf-2 in the figure ). The logical connection of the tunnel is shown as the dotted red line.

The single tunnel on Leaf-2 has two underlay paths to reach Leaf-1 and the Leaf-1 peer. Any traffic southbound from Leaf-2 is load balanced and can end up in either of the LVTEP peers.

IP-MAC routes on LVTEP

Similar to the single-VTEP case, the normal MAC-IP routes are exported and installed by EVPN BGP extensions on LVTEP between the leaf nodes, providing for the following behavior:

A BGP MAC/IP route represents L3-to-L2 mapping, which is basically ARP or ND. Static and dynamic ARP/ND entries are exported to remote PEs and get installed as host routes. IPv4/IPv6 addresses that are configured on VE interfaces are also exported.

Upon ARP learning/gleaning/snooping on a local PE, ARP/ND information is exported to its EVPN BGP peers. The information mainly includes the following: MAC, IP/IPv6, L2-VNI, L3-VNI, and ESI segment. (In VXLAN, the ESI segment ID is always 0.)

Such imported ARP/ND routes are installed or withdrawn as host routes in the hardware on the remote nodes. In the control plane they are available through the ARP suppression cache, which can be further used to reply for further ARP requests from hosts that are attached to the remote PE.

The packet path is as follows:

On the nondefault VRF, the ARP/ND exports can have two subscenarios, depending on whether L2-VNI is extended on that PE or not:

On the default VRF, normal host IP forwarding always occurs.

L3-VNI on LVTEP

Similar to the single-VTEP case, the IP prefix routes are also exported and installed by EVPN BGP extensions on LVTEP between the leaf nodes (with Type-5 routes), providing for the following:

BGP IP prefix routes on VRFs are exported to the remote PE over EVPN (Type-5). The information mainly includes the following: Egress-PE-GW-MAC, IP/IPv6 Prefix route, L3-VNI, ESI segment. (In VXLAN, the ESI segment ID is always 0.)

Such imported IP prefix routes are imported to VRFs and installed as VRF routes, with the VXLAN tunnel having L3-VNI as the outgoing port and remote PE-GW-MAC as the destination MAC with in the Inner Payload L2 header.

The packet path is as follows: