CCNP DC · BGP EVPN

Nexus: BGP EVPN control plane for VXLAN

Replace flood-and-learn with a control plane. S1 becomes an iBGP route reflector for the L2VPN EVPN address family; each leaf advertises its VNI (a type-3 route) and its hosts (type-2 routes), and the leaves find each other from those routes.

CCNP Data Center track · Cisco Nexus (NX-OS-style) · 5 objectives

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Objectives

The simulator ticks each one as soon as the network meets it.

On S1 enable feature bgp, feature nv overlay and nv overlay evpn. In router bgp 65000 (router-id 3.3.3.3) add neighbors 1.1.1.1 and 2.2.2.2: remote-as 65000, update-source loopback0, and under address-family l2vpn evpn send-community extended and route-reflector-client.
On L1 and L2 enable feature bgp, feature nv overlay, feature vn-segment-vlan-based and nv overlay evpn; map VLAN 10 to vn-segment 10010; peer with 3.3.3.3 the same way (address-family l2vpn evpn, send-community extended).
On both leaves: interface nve1 with no shutdown, source-interface loopback0, host-reachability protocol bgp and member vni 10010 with ingress-replication protocol bgp; and evpn / vni 10010 l2 with rd auto and route-target import auto, export auto.
show bgp l2vpn evpn on L1: the type-3 route of 2.2.2.2 is there.
Ping PC2 (192.168.10.20) from PC1.

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Before you start

EVPN carries VTEPs and MAC addresses in BGP. The route-target travels as an extended community, so every hop needs send-community extended; route-target auto means ASN:VNI. The route reflector only reflects, so it needs no VNI of its own.

Concept

BGP EVPN: a control plane for VXLAN

BGP EVPN replaces flood-and-learn with BGP routes in the L2VPN EVPN address family. Each VTEP advertises an inclusive-multicast route (type 3) per VNI, so the others know to replicate to it, and a MAC route (type 2) per local host, so remote MACs are known before any traffic flows. A spine is usually the iBGP route reflector.

Concept

VXLAN: a VLAN stretched over a routed fabric

VXLAN puts Ethernet frames inside UDP/IP. Each VTEP (VXLAN tunnel endpoint) maps a VLAN to a 24-bit VNI and sends the VNI’s frames from its loopback to the other VTEPs, so the underlay only has to route between loopbacks. Broadcast and unknown traffic must reach every VTEP with the VNI: by unicast copies to a peer list (ingress replication) or through an underlay multicast group.