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Nexus Switching 2nd Edition

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Chapter 11. Overlay Transport Virtualization (OTV)<br />

This chapter covers the following topics:<br />

• Introduction to OTV<br />

• OTV terminology <strong>and</strong> concepts<br />

• OTV control plane<br />

• OTV data plane<br />

• Multihoming with OTV<br />

• OTV <strong>and</strong> ARP<br />

• FHRP localization<br />

• Ingress routing optimization<br />

Overlay Transport Virtualization (OTV) is an IP-based innovation to provide a Layer 2<br />

extension between data centers. OTV is transport agn<strong>os</strong>tic, meaning that the transport<br />

infrastructure between data centers can be dark fiber, MPLS, IP routed WAN, ATM, Frame<br />

Relay, <strong>and</strong> so on. The only requirement is that the data centers must have IP reachability<br />

between them. OTV enables multipoint services for Layer 2 extension <strong>and</strong> independent<br />

Layer 2 domains between data centers, preserving the fault-isolation, resiliency, <strong>and</strong> loadbalancing<br />

benefits of an IP-based interconnection.<br />

Unlike traditional Layer 2 extension technologies, OTV introduces the concept of Layer 2<br />

MAC routing. The MAC-routing concept enables a control-plane protocol to advertise the<br />

reachability of Layer 2 MAC addresses. The MAC-routing concept has tremendous benefits<br />

over traditional Layer 2 extension technologies that traditionally leveraged data plane<br />

learning, hence, flooding of Layer 2 traffic acr<strong>os</strong>s the transport infrastructure.<br />

As customers consolidate data centers, there is still a driving requirement for multipoint<br />

support, meaning more than two locations sharing the same Layer 2 information. OTV<br />

provides multipoint connectivity <strong>and</strong> IP multicast capabilities to provide optimal multicast<br />

traffic replication to multiple sites. The benefit of multicast replication for multipoint<br />

services is the elimination of head-end replication, which provides suboptimal b<strong>and</strong>width<br />

utilization.<br />

Multihoming has always been a requirement to provide redundancy within a given data<br />

center. Historically, building Layer 2 solutions with multihoming required additional<br />

configuration to provide for end-to-end Layer 2 loop prevention. OTV has a built-in loop<br />

detection <strong>and</strong> suppression mechanism that offers transparent multihoming that does not<br />

require additional configuration.<br />

In addition, OTV offers failure boundary <strong>and</strong> site independence preservation. Because OTV<br />

uses a control-plane protocol to advertise MAC address reachability, OTV does not rely on<br />

traffic flooding to propagate reachability information for MAC addresses. With the controlplane<br />

MAC address learning, OTV does not flood unknown unicast traffic, <strong>and</strong> Address<br />

Resolution Protocol (ARP) traffic is forwarded only in a controlled manner. Because OTV<br />

does not forward or propagate Spanning Tree Bridge Protocol Data Units (BPDUs) acr<strong>os</strong>s

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