Introduction to Cisco SD-WAN OMP: A Guide for Beginners

Vikas Swami's photo
Vikas Swami
·

12 min read

  • What is OMP?

The Cisco Overlay Management Protocol (OMP) is a TCP-based protocol that is used to establish and maintain the Cisco SD-WAN control plane. It is responsible for the following services:

* Orchestration of overlay network communication, including connectivity among network sites, service chaining, and VPN or VRF topologies.
* Distribution of service-level routing information and related location mappings.
* Distribution of data plane security parameters.
* Central control and distribution of routing policy.
  • How does OMP work?

OMP runs between Cisco vSmart Controllers and Cisco vEdge devices in the overlay network. These devices automatically initiate OMP peering sessions between themselves, and the two IP end points of the OMP session are the system IP addresses of the two devices.

Cisco SD-WAN OMP (Overlay Management Protocol) uses various message types to facilitate communication and control between SD-WAN devices in the overlay network. The key OMP message types are:

  1. Hello Message: Used for device discovery and neighbor establishment in the overlay network.

  2. Keepalive Message: Maintains the health and reachability of SD-WAN devices in the overlay network.

  3. Topology Advertisement Message: Exchanges topology information to update routing tables and make informed path selection decisions.

  4. Prefix Advertisement Message: Shares information about available routes and reachable prefixes for efficient traffic forwarding.

  5. Capability Advertisement Message: Shares device capabilities and features to determine optimal path selection options.

  6. Acknowledgment Message: Confirms receipt of critical messages, ensuring message delivery and avoiding loss.

These messages are essential for building and maintaining the overlay network, optimizing data forwarding paths, and ensuring a reliable and efficient networking experience for organizations with distributed networks.

Benefits of OMP

OMP provides a number of benefits for Cisco SD-WAN, including:

* Centralized control and management of the overlay network.
* Scalability: OMP can scale to support large networks with many vEdge devices.
* Flexibility: OMP can be used to support a variety of overlay network topologies.
* Reliability: OMP provides mechanisms to ensure the availability of the control plane.
  • Configuration of OMP

OMP is enabled by default on Cisco vSmart Controllers and vEdge devices. However, you may need to configure some OMP parameters, such as the OMP peering IP address and the OMP hello interval.

Cisco SD-WAN OMP creates three types of routes:

  • OMP routes (also known as vRoutes): These routes are prefixes that are learned from the local site via connected interfaces, static routes, and dynamic routing protocols such as OSPF, EIGRP, and BGP. OMP routes require and resolve into TLOCs for functional forwarding.

  • TLOC routes: These routes are used to represent the physical location of a network service. TLOC routes are created by OMP when a vEdge device advertises a service route to a vSmart controller.

  • Service routes: These routes are used to represent a network service, such as a firewall, load balancer, or VPN gateway. Service routes are created by OMP when a vEdge device advertises a service route to a vSmart controller.

OMP routes are stored in the OMP routing table on the vSmart controllers and vEdge devices. The OMP routing table is used to determine the best path to a destination network or service.

Here is a table summarizing the different types of routes created by Cisco SD-WAN OMP:

Route TypeDescription
OMP routes (vRoutes)Prefixes that are learned from the local site via connected interfaces, static routes, and dynamic routing protocols such as OSPF, EIGRP, and BGP.
TLOC routesUsed to represent the physical location of a network service.
Service routesUsed to represent a network service, such as a firewall, load balancer, or VPN gateway.

here is a more detailed explanation of the different types of routes created by Cisco SD-WAN OMP:

  • OMP routes (vRoutes): OMP routes are prefixes that are learned from the local site via connected interfaces, static routes, and dynamic routing protocols such as OSPF, EIGRP, and BGP. OMP routes require and resolve into TLOCs for functional forwarding.

    An OMP route is a prefix that is learned from the local site and advertised to the vSmart controllers. The prefix can be a connected route, a static route, or a route learned from a dynamic routing protocol. OMP routes are stored in the OMP routing table on the vSmart controllers and vEdge devices.

    When an OMP route is received by a vSmart controller, it is resolved into a TLOC. A TLOC is a transport location identifier that is used to represent the physical location of a network service. The TLOC is used to determine the best path to the destination network or service.

  • TLOC routes: These routes are used to represent the physical location of a network service. TLOC routes are created by OMP when a vEdge device advertises a service route to a vSmart controller.

    A TLOC route is a route that represents the physical location of a network service. The route is created by OMP when a vEdge device advertises a service route to a vSmart controller. The service route contains the IP address of the service, the type of service, and the TLOC of the service.

  • Service routes: These routes are used to represent a network service, such as a firewall, load balancer, or VPN gateway. Service routes are created by OMP when a vEdge device advertises a service route to a vSmart controller.

    A service route is a route that represents a network service. The route contains the IP address of the service, the type of service, and the location of the service. The location of the service is represented by a TLOC.

  • Scenario 1: A vEdge device learns a route to the 10.1.1.0/24 network via a connected interface. The vEdge device advertises the route to the vSmart controller as an OMP route. The vSmart controller resolves the OMP route to a TLOC, and the route is stored in the OMP routing table on the vSmart controller and vEdge device. This is vroute.

  • Scenario 2: A vEdge device learns a route to the 10.2.2.0/24 network via OSPF. The vEdge device advertises the route to the vSmart controller as an OMP route. The vSmart controller resolves the OMP route to a TLOC, and the route is stored in the OMP routing table on the vSmart controller and vEdge device. This is Tloc Route.

  • Scenario 3: A vEdge device advertises a service route to the vSmart controller. The service route represents a firewall that is located at the 10.3.3.0/24 network. The service route contains the IP address of the firewall, the type of service, and the TLOC of the firewall. This is service route.

  • Some of the Cisco OMP commands that you can use:

    • show omp peers

This command displays the list of OMP peers that the device is connected to.

  • show omp status

This command displays the status of the OMP control plane.

  • clear omp routes

This command clears the OMP routing table.

  • sdwan omp graceful-restart

This command enables or disables OMP graceful restart.

  • sdwan omp timers

This command configures the OMP timers.

  • Now detailed working

  • OMP (Overlay Management Protocol) uses various message types to facilitate communication and control between SD-WAN devices in the overlay network. These messages play a crucial role in establishing and maintaining the overlay network's health and performance. Below are some of the key OMP message types used in Cisco SD-WAN:

    1. Hello Message:

      • Purpose: The Hello message is used for device discovery and neighbor establishment in the overlay network.

      • Function: When a new SD-WAN device joins the network or when devices reboot, they send Hello messages to discover and establish connections with neighboring SD-WAN devices.

      • Usage Example: When a new edge device is added to a branch office, it sends Hello messages to other SD-WAN devices in the overlay, identifying and forming adjacency with its neighbors.

    2. Keepalive Message:

      • Purpose: The Keepalive message is used to maintain the health and reachability of the SD-WAN devices in the overlay network.

      • Function: SD-WAN devices periodically exchange Keepalive messages to indicate that they are active and reachable.

      • Usage Example: SD-WAN devices send Keepalive messages at regular intervals to ensure their neighbors are alive and functional.

    3. Topology Advertisement Message:

      • Purpose: The Topology Advertisement message is used to exchange topology information within the overlay network.

      • Function: When changes occur in the network topology, such as link status or device reachability, SD-WAN devices exchange Topology Advertisement messages to update their routing tables and make informed path selection decisions.

      • Usage Example: If a link between two SD-WAN devices becomes unavailable, the device sends a Topology Advertisement message to notify other devices about the link failure, prompting rerouting of traffic.

    4. Prefix Advertisement Message:

      • Purpose: The Prefix Advertisement message is used to exchange information about available routes and prefixes within the overlay network.

      • Function: SD-WAN devices share information about reachable prefixes, ensuring efficient traffic forwarding within the overlay.

      • Usage Example: When a new network segment is added or an existing segment becomes reachable through a different path, SD-WAN devices send Prefix Advertisement messages to announce the updated route information.

    5. Capability Advertisement Message:

      • Purpose: The Capability Advertisement message is used to share information about a device's capabilities and supported features.

      • Function: When SD-WAN devices discover new neighbors, they exchange Capability Advertisement messages to understand each other's capabilities, such as encryption support, QoS settings, and tunneling capabilities.

      • Usage Example: SD-WAN devices exchange Capability Advertisement messages during device discovery to determine the best path selection options based on their respective capabilities.

    6. Acknowledgment Message:

      • Purpose: The Acknowledgment message is used to confirm the receipt of critical messages in the overlay network.

      • Function: When a device receives critical messages, such as Topology Advertisement or Prefix Advertisement messages, it sends Acknowledgment messages to confirm receipt, ensuring message delivery and avoiding message loss.

      • Usage Example: After receiving a Topology Advertisement message indicating a link failure, the receiving device sends an Acknowledgment message back to the sender to confirm the receipt of the message.

These OMP message types play a vital role in establishing communication, maintaining network health, and enabling dynamic path selection within the Cisco SD-WAN overlay network. They ensure efficient data transfer, seamless failover, and overall network performance across geographically distributed locations.

  • In Cisco SD-WAN (Software-Defined Wide Area Networking), the term "neighbor" refers to the neighboring devices that establish connections with each other within the SD-WAN overlay network. SD-WAN neighbors play a crucial role in device discovery, exchanging routing information, and establishing communication paths for data traffic. There are two primary types of neighbors in Cisco SD-WAN:

    1. Control Plane Neighbors:

      • Control plane neighbors are devices that exchange control plane information, such as routing updates, topology changes, and OMP (Overlay Management Protocol) messages.

      • Control plane neighbors are responsible for maintaining the dynamic routing and path selection within the overlay network.

      • Devices communicate control plane information through the control plane protocol, which in Cisco SD-WAN is typically OMP.

      • Control plane neighbors are essential for building and maintaining the overlay network's routing table, enabling efficient data forwarding and failover mechanisms.

      • Example: In a Cisco SD-WAN deployment, edge devices at different branch offices act as control plane neighbors, exchanging OMP messages to discover each other and share routing updates.

    2. Data Plane Neighbors:

      • Data plane neighbors are devices that forward data traffic to each other over established communication paths in the overlay network.

      • Data plane neighbors are responsible for forwarding user data packets between different locations in the SD-WAN deployment.

      • Devices communicate data traffic using data plane protocols and tunneling technologies, such as IPsec or MPLS.

      • Data plane neighbors do not necessarily have to be control plane neighbors, as data forwarding paths can differ from control plane adjacency.

      • Example: In a Cisco SD-WAN deployment, two edge devices at different branches might act as data plane neighbors, forwarding data traffic to each other using IPsec tunnels over the Internet.

It's important to note that in many SD-WAN solutions, the same device can act as both a control plane neighbor and a data plane neighbor. For instance, in a hub-and-spoke SD-WAN architecture, the hub device can act as a control plane neighbor for all the spokes, exchanging routing information, and also serve as a data plane neighbor, forwarding data traffic between the spokes.

  • OMP (Overlay Management Protocol) plays a vital role in exchanging routing information between peers (SD-WAN devices) within the overlay network. OMP is responsible for managing the dynamic routing and path selection, ensuring efficient data forwarding and optimal network performance. Let's explore how OMP routing exchange occurs between peers in Cisco SD-WAN:

    1. Neighbor Discovery:

      • When a new SD-WAN device is added to the network or when devices reboot, they initiate the process of neighbor discovery.

      • SD-WAN devices use the OMP protocol to send Hello messages to discover other devices in the overlay network and establish adjacencies with their neighbors.

    2. Control Plane Peering:

      • Once devices discover each other through the Hello messages, they establish control plane peering.

      • Control plane peering is the establishment of a logical connection between SD-WAN devices for exchanging OMP messages containing routing information.

    3. Topology Advertisement:

      • SD-WAN devices exchange Topology Advertisement messages to share information about the network's topology and reachability.

      • Topology Advertisement messages contain details about links, network segments, and device reachability within the overlay network.

    4. Prefix Advertisement:

      • Prefix Advertisement messages are used to exchange information about available routes and reachable prefixes in the overlay network.

      • SD-WAN devices share information about networks they can reach, ensuring efficient data forwarding.

    5. Path Selection and Optimization:

      • Based on the received Topology and Prefix Advertisement messages, SD-WAN devices analyze the available paths and make informed routing decisions.

      • Path selection takes into account factors such as link quality, available bandwidth, latency, and QoS (Quality of Service) requirements.

    6. Real-Time Network Monitoring:

      • OMP continuously monitors the health and performance of the overlay network.

      • If a link's quality degrades or a device becomes unreachable, OMP detects the changes and updates the routing table accordingly.

    7. Dynamic Path Control:

      • OMP can dynamically reroute traffic in response to network changes or performance issues.

      • If a link fails or experiences congestion, OMP can redirect traffic to alternative paths to maintain optimal data flow.

    8. Traffic Engineering:

      • OMP allows administrators to define policies and rules for traffic prioritization and optimization.

      • Traffic engineering ensures that critical applications receive the required bandwidth and QoS levels, while non-critical traffic is efficiently handled.

    9. Secure Communication:

      • OMP ensures secure communication between peers by encrypting control plane messages.

      • This prevents unauthorized access or tampering of control plane information, enhancing overall network security.