Overlay Transport Virtualization (OTV) provides an overlay that enables Layer 2 connectivity between separate Layer 2 domains, while keeping these domains independent and preserving the fault isolation, resiliency, and load-balancing benefits of an IP-based interconnection.
Which statements are true about OTV Adjacency Server? (Choose two.)
A. Adjacency Server is required when OTV is deployed with unicast-only transport.
B. Adjacency Server is required when OTV is deployed with multicast-enabled transport.
C. Each OTV device wishing to join a specific OTV logical overlay needs to first register with the Adjacency Server.
D. Each OTV device trying to join a specific OTV logical overlay needs to be configured as an Adjacency Server.
Correct Answer: AC
Explanation/Reference:
Explanation:
Starting with NX-OS 5.2(1) release, OTV can be deployed with unicast-only transport. As previously described, a multicast enabled transport infrastructure lets a single OTV update or Hello packet reach all other OTV devices by virtue of leveraging a specific multicast control group address.
The OTV control plane over a unicast-only transport works exactly the same way as OTV with multicast mode. The only difference is that each OTV devices would need to create multiple copies of each control plane packet and unicast them to each remote OTV device part of the same logical overlay. Because of this head-end replication behavior, leveraging a multicast enabled transport remains the recommended way of deploying OTV in cases where several DC sites are involved. At the same time, the operational simplification brought by the unicast-only model (removing the need for multicast deployment) can make this deployment option very appealing in scenarios where LAN extension connectivity is required only between few (2-3) DC sites.
To be able to communicate with all the remote OTV devices, each OTV node needs to know a list of neighbors to replicate the control packets to. Rather than statically configuring in each OTV node the list of all neighbors, a simple dynamic means is used to provide this information. This is achieved by designating one (or more) OTV Edge device to perform a specific role, named Adjacency Server. Every OTV device wishing to join a specific OTV logical overlay, needs to first “register” with the Adjacency Server (by start sending OTV Hello messages to it). All other OTV neighbor addresses are discovered dynamically through the Adjacency Server. Thereby, when the OTV service needs to be extended to a new DC site, only the OTV edge devices for the new site need to be configured with the Adjacency Server addresses. No other sites need additional configuration.
Reference: http://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/Data_Center/DCI/whitepaper/DCI3_OTV_Intro/DCI_1.html
