The adoption of server virtualization has been increasing rapidly. Server virtualization provides flexibility and agility in provisioning and placement of computing workloads. However, network connectivity has not kept pace with such innovations in the computing environment, although it still offers a rigid approach to provisioning transport services.
As a solution, network overlays abstract the details of the physical network, making it much faster to connect virtual machines (VMs) and other devices. Rather than provision paths on physical devices, overlays encapsulate traffic using protocols such as Overlay Transport Virtualization (OTV) or Virtual Extensible LAN (VXLAN) across the physical network. These newer protocols allow operators to move beyond the limitations of VLANs, which support only 4096 virtual networks, so that they can better support multitenant services.
This chapter covers the following key topics:
Overlay Transport Virtualization (OTV): This section provides an overview of overlay transportation, including Layer 2 MAC address routing along with a configuration example.
Virtual Extensible LAN (VXLAN) Overview: This section discusses the Layer 2 VLAN extension to provide multitenant flexibility, high segment scalability, and Layer 2 spanning tree improvement, along with a configuration example.
“Do I Know This Already?” Quiz
The “Do I Know This Already?” quiz enables you to assess whether you should read this entire chapter thoroughly or jump to the “Exam Preparation Tasks” section. If you are in doubt about your answers to these questions or your own assessment of your knowledge of the topics, read the entire chapter. Table 3-1 lists the major headings in this chapter and their corresponding “Do I Know This Already?” quiz questions. You can find the answers in Appendix A, “Answers to the ‘Do I Know This Already?’ Quizzes.”
Table 3-1 “Do I Know This Already?” Section-to-Question Mapping
Foundation Topics Section
Overlay Transport Virtualization (OTV)
Virtual Extensible LAN (VXLAN) Overview
1. Which statement about Cisco Overlay Transport Virtualization is true?
OTV is a “MAC in IP” technique for supporting Layer 2 VLANs over any transport.
OTV is core and site transparent. Changes to the Layer 2 design of the sites are needed.
OTV cannot support multiple concurrent overlays.
OTV transport must support multicast.
2. What is an OTV joined interface?
A Layer 2 access or trunk interface
A logical multiaccess and multicast-capable interface
An interface to form OTV adjacencies with the other OTV edge devices belonging to the same VPN
A Layer 3 interface that uses multicast only to forward OTV traffic
3. How does OTV exchange MAC reachability information?
Uses OSPF as an internal control plane
Uses BGP as an internal control plane
Uses EIGRP as an internal control plane
Use IS-IS as an internal control plane
4. In current data center networking architecture, which network layer is used to transmit VXLAN packets or other overlay packets?
5. How many available IDs can be assigned to a VXLAN at any given time?
6. Which statement about VXLAN high availability is correct?
For an anycast IP address, vPC VTEP switches can use the same VTEP IP address.
For an anycast IP address, vPC VTEP switches must use a secondary IP address on the loopback interface.
Distributed anycast gateways must be connected with vPC.
VTEP high availability will use unicast instead of multicast communications.