VXLAN Underlay Routing - Part I: OSPF and Dijkstra/SPF algorithm

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"Virtual Extensible LAN VXLAN - A Practical guide to VXLAN Solution Part 1. (373 pages)

The role of the Underlay Network

Underlay Network the main job from the EVPN VXLAN Network Virtualization Overlay (NVO) solutions perspective is to offer resilient IP connectivity between the Network Virtualization Edge Interfaces (NVE) on VXLAN Tunnel End Point (VTEP) devices. In addition, the Underlay Network can be used for BUM traffic forwarding (Broadcast, Unknown Unicast, and Multicast) though this solution requires a Multicast Routing enabled on an Underlay Network. The common routing protocols choices for VXLAN Underlay Network are OSPF, IS-IS which are Link State Protocols and BGP which in turn is Path Vector Protocol. The focus of this chapter is the Dijkstra/Shortest Path First (SPF) algorithm that Link State Protocols uses for calculating the Shortest-Path Tree. Figure 1-1 shows the Link type-1 (point-to-point) and Link Lype-3 (Stub Network) Routers LSA originated by Leaf-101, Leaf-102, Spine-11, and Spine-12. In addition, figure 1-1 illustrates how routers form a topology based on received LSAs.

Figure 1-1: Examples of Link type-1 (p2p) and Link-Type 3 (Stub) Router LSAs.