Cisco Cisco Virtual Topology System 1.5 White Paper

 

 

© 2015 Cisco and/or its affiliates. All rights reserved. This document is Cisco Public Information. 

Page 14 of 16 

Figure 7.    Data Center Virtualization Using Software Overlay with Cisco Virtual Topology System 

 

Bare-metal integration is the other main use case that the Virtual Topology System solution supports (Figure 9). 

This use case can be used as a baseline for building network connectivity between physical and virtual workloads 

in the data center. A MP-BGP EVPN based control plane from Virtual Topology System and ToR switches such as 

Cisco Nexus 9000 Series Switches can be used for this scenario, and a VXLAN-based software overlay can be 

used in the data plane. The VXLAN overlay solution allows physical VTEPs for both virtualized and bare-metal 

servers through the use of physical and virtual integrated overlays and allows DCI and services integration. 

VXLAN-based software overlay supports two variants of the solution: a VXLAN overlay with a BGP EVPN control 

plane and a VXLAN overlay with the IP Multicast flood-and-learn mechanism. 

One topology supported for this solution deploys distributed Layer 2 and 3 gateways. In this case, the Layer 2 and 

3 boundary for the server or virtual machines resides on the overlay network gateways that are directly attached to 

the physical servers. In the physical topology, these reside on the ToR switches in each server rack. Each ToR 

switch then becomes the Layer 2 and 3 gateway for the virtual machines that are directly attached to it. Virtual 

machines belonging to the same subnet may also span racks, so the Layer 3 gateway functions for these subnets 

will be distributed across the ToR switches (anycast gateway). This overlay network extends between the 

distributed gateways across the spine and aggregation switches. 

The ToR switches also provide VXLAN physical gateway termination. Examples of use cases for physical gateway 

overlay termination include: 

● 

Physical gateway for virtualized servers: In this case, the server has a Layer 2 vSwitch and uses VLANs to 

segment traffic belonging to different tenants. Traffic for the different tenants is tagged with the required 

VLANs and terminates on the physical gateway. 

● 

Physical gateway for bare-metal servers: In this case, each VLAN or group of VLANs is assigned to a 

specific bare-metal endpoint or access network. 

● 

Physical gateway stitching: This case provides the functions that are needed to stitch the overlay into the 

physical network for the Internet, VPNs, or services in scenarios such as a DCI or border-services leaf.