16.3 OTV over DWDM and Dark Fibre
Overlay Transport Virtualization (OTV) is an IP-based mechanism developed by Cisco to provide Layer 2 extension capabilities over any sort of WAN-based transport infrastructure. Cisco OTV’s only requirement from the network infrastructure is IP connectivity between the data centers. Cisco OTV also provides an overlay that enables Layer 2 extension between separate Layer 2 domains while at the same time keeping these domains independent and preserving the fault isolation, resiliency, and load balancing benefits of an IP-based interconnect.
Cisco OTV employs the concept of MAC routing, meaning a control plane protocol is used to exchange MAC location information between different network devices, thus providing LAN extension capabilities. Cisco OTV also uses dynamic encapsulation for Layer 2 traffic flows that must be sent to the remote location. Every Ethernet frame is individually encapsulated into an IP packet so they can be delivered across the transport network. Finally, Cisco OTV provides a built-in multi-homing capability with automatic detection that is critical to improving high availability of the overall architecture.
The following figure outlines the deployment of Cisco OTV over Rainpole.com’s DWDM point-to-point connection.
Figure 19. OTV Deployment over DWDM and Dark Fibre
Note The grey links in the figure represent logical links to the OTV overlay and not physical connections.
In Rainpole.com’s implementation example, the Nexus 7710s enforce the separation between SVI routing and Cisco OTV encapsulation for any given VLAN. This is a critical consideration for Rainpole.com’s topology because the Nexus 7710s switches perform both functions. This separation can best be achieved through the use of virtual device contexts, a feature available on the Nexus 7700 platform.
For this design, two virtual device contexts would be deployed:
• A Cisco OTV virtual device context dedicated to perform OTV functions
• A routing virtual device context to provide SVI routing support
The use of OTV over DWDM or dark fibre provides several design advantages over the previously described Cisco vPC-based solution:
• Cisco OTV allows for the provisioning of Layer 2 and Layer 3 connectivity that can leverage the same DWDM or dark fibre connections. This is made possible because Cisco OTV encapsulates all traffic generated from the Cisco OTV virtual device context as if it was normal IP traffic that can be exchanged between sites leveraging a Layer 3 routed connection.
• Cisco OTV’s native failure domain isolation technology means there is no requirement to explicitly configure BPDU filtering to prevent the creation of a cross-site STP domain. In addition, ARP optimization is provided to limit the amount of ARP broadcast frames exchanged across the data center interconnect.
• Cisco OTV’s Layer 2 data plane isolation means that storm-control configuration is simplified during deployment due to the native suppression of unknown unicast frames.
• Cisco OTV’s native multi-homing LAN extension capability allows extending the service to additional remote data centers in a simple manner.
