Supported Protocols
This section explains the protocols supported for unicast routing.
OMP Routing Protocol
The Cisco SD-WAN Overlay Management Protocol (OMP) is the protocol responsible for establishing and maintaining the Cisco SD-WAN control plane. It provides the following services:
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Orchestration of overlay network communication, including connectivity among network sites, service chaining, and VPN or VRF topologies
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Distribution of service-level routing information and related location mappings
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Distribution of data plane security parameters
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Central control and distribution of routing policy
OMP is the control protocol that is used to exchange routing, policy, and management information between Cisco vSmart Controllers and Cisco IOS XE SD-WAN 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.
OMP is an all-encompassing information management and distribution protocol that enables the overlay network by separating services from transport. Services provided in a typical VRF setting are usually located within a VRF domain, and they are protected so that they are not visible outside the VRF. In such a traditional architecture, it is a challenge to extend VRF domains and service connectivity.
OMP addresses these scalability challenges by providing an efficient way to manage service traffic based on the location of logical transport end points. This method extends the data plane and control plane separation concept from within routers to across the network. OMP distributes control plane information along with related policies. A central Cisco vSmart Controller makes all decisions related to routing and access policies for the overlay routing domain. OMP is then used to propagate routing, security, services, and policies that are used by edge devices for data plane connectivity and transport.
OMP Route Advertisements
On Cisco vSmart Controllers and Cisco IOS XE SD-WAN devices, OMP advertises to its peers the routes and services that it has learned from its local site, along with their corresponding transport location mappings, which are called TLOCs. These routes are called OMP routes or vRoutes to distinguish them from standard IP routes. The routes advertised are actually a tuple consisting of the route and the TLOC associated with that route. It is through OMP routes that the Cisco vSmart Controllers learn the topology of the overlay network and the services available in the network.
OMP interacts with traditional routing at local sites in the overlay network. It imports information from traditional routing protocols, such as OSPF and BGP, and this routing information provides reachability within the local site. The importing of routing information from traditional routing protocols is subject to user-defined policies.
Because OMP operates in an overlay networking environment, the notion of routing peers is different from a traditional network environment. From a logical point of view, the overlay environment consists of a centralized controller and a number of edge devices. Each edge device advertises its imported routes to the centralized controller and based on policy decisions, this controller distributes the overlay routing information to other edge devices in the network. Edge devices never advertise routing information to each other, either using OMP or any other method. The OMP peering sessions between the centralized controller and the edge devices are used exclusively to exchange control plane traffic; they are never, in any situation, used for data traffic.
Registered edge devices automatically collect routes from directly connected networks as well as static routes and routes learned from IGP protocols. The edge devices can also be configured to collect routes learned from BGP.
Route map AS path and community configuration, for example, AS path prepend, are not supported when route-maps are configured for protocol redistribution. The AS path for redistributed OMP routes can be configured and applied by using a route map on the BGP neighbor outbound policy.
OMP performs path selection, loop avoidance, and policy implementation on each local device to decide which routes are installed in the local routing table of any edge device.
OMP advertises the following types of routes:
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OMP routes (also called vRoutes)—Prefixes that establish reachability between end points that use the OMP-orchestrated transport network. OMP routes can represent services in a central data center, services at a branch office, or collections of hosts and other end points in any location of the overlay network. OMP routes require and resolve into TLOCs for functional forwarding. In comparison with BGP, an OMP route is the equivalent of a prefix carried in any of the BGP AFI/SAFI fields.
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Transport locations (TLOCs)—Identifiers that tie an OMP route to a physical location. The TLOC is the only entity of the OMP routing domain that is visible to the underlying network, and it must be reachable via routing in the underlying network. A TLOC can be directly reachable via an entry in the routing table of the physical network, or it must be represented by a prefix residing on the outside of a NAT device and must be included in the routing table. In comparison with BGP, the TLOC acts as the next hop for OMP routes.
The following figure illustrates the two types of OMP routes.
OMP Routes
Each device at a branch or local site advertises OMP routes to the Cisco vSmart Controllers in its domain. These routes contain routing information that the device has learned from its site-local network.
A Cisco SD-WAN device can advertise one of the following types of site-local routes:
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Connected (also known as direct)
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Static
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BGP
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EIGRP
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LISP
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OSPF (inter-area, intra-area, and external)
OMP routes advertise the following attributes:
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TLOC—Transport location identifier of the next hop for the vRoute. It is similar to the BGP NEXT_HOP attribute. A TLOC consists of three components:
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System IP address of the OMP speaker that originates the OMP route
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Color to identify the link type
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Encapsulation type on the transport tunnel
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Origin—Source of the route, such as BGP, OSPF, connected, and static, and the metric associated with the original route.
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Originator—OMP identifier of the originator of the route, which is the IP address from which the route was learned.
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Preference—Degree of preference for an OMP route. A higher preference value is more preferred.
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Site ID—Identifier of a site within the Cisco SD-WAN overlay network domain to which the OMP route belongs.
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Tag—Optional, transitive path attribute that an OMP speaker can use to control the routing information it accepts, prefers, or redistributes.
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VRF—VRF or network segment to which the OMP route belongs.
You configure some of the OMP route attribute values, including the system IP, color, encapsulation type, carrier, preference, service, site ID, and VRF. You can modify some of the OMP route attributes by provisioning control policy on the Cisco vSmart Controller.
TLOC Routes
TLOC routes identify transport locations. These are locations in the overlay network that connect to physical transport, such as the point at which a WAN interface connects to a carrier. A TLOC is denoted by a 3-tuple that consists of the system IP address of the OMP speaker, a color, and an encapsulation type. OMP advertises each TLOC separately.
TLOC routes advertise the following attributes:
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TLOC private address—Private IP address of the interface associated with the TLOC.
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TLOC public address—NAT-translated address of the TLOC.
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Carrier—An identifier of the carrier type, which is generally used to indicate whether the transport is public or private.
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Color—Identifies the link type.
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Encapsulation type—Tunnel encapsulation type.
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Preference—Degree of preference that is used to differentiate between TLOCs that advertise the same OMP route.
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Site ID—Identifier of a site within the Cisco SD-WAN overlay network domain to which the TLOC belongs.
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Tag—Optional, transitive path attribute that an OMP speaker can use to control the flow of routing information toward a TLOC. When an OMP route is advertised along with its TLOC, both or either can be distributed with a community TAG, to be used to decide how send traffic to or receive traffic from a group of TLOCs.
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Weight—Value that is used to discriminate among multiple entry points if an OMP route is reachable through two or more TLOCs.
The IP address used in the TLOC is the fixed system address of the device itself. The reason for not using an IP address or an interface IP address to denote a TLOC is that IP addresses can move or change; for example, they can be assigned by DHCP, or interface cards can be swapped. Using the system IP address to identify a TLOC ensures that a transport end point can always be identified regardless of IP addressing.
The link color represents the type of WAN interfaces on a device. The Cisco SD-WAN solution offers predefined colors, which are assigned in the configuration of the devices. The color can be one of default, 3g, biz-internet, blue, bronze, custom1, custom2, custom3, gold, green, lte, metro-ethernet, mpls, private1, private2, public-internet, red, and silver.
The encapsulation is that used on the tunnel interface. It can be either IPsec or GRE.
You configure some of the TLOC attributes, including the system IP address, color, and encapsulation, and you can modify some of them by provisioning control policy on the Cisco vSmart Controller. See Centralized Control Policy.
OMP Route Redistribution
OMP automatically redistributes the following types of routes that it learns either locally or from its routing peers:
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Connected
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Static
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OSPF intra-area routes
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OSPF inter-area routes
To avoid routing loops and less than optimal routing, redistribution of following types of routes requires explicit configuration:
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BGP
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OSPF external routes
To avoid propagating excessive routing information from the edge to the access portion of the network, the routes that devices receive via OMP are not automatically redistributed into the other routing protocols running on the routers. If you want to redistribute the routes received via OMP, you must enable this redistribution locally on each device.
OMP sets the origin and sub-origin type in each OMP route to indicate the route's origin (see the table below). When selecting routes, the Cisco vSmart Controllerand the router take the origin type and subtype into consideration.
OMP Route Origin Type |
OMP Route Origin Subtype |
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BGP |
External Internal |
Connected |
— |
OSPF |
External-1 External-2 Intra-area Inter-area and NSSA-External-1, NSSA-External-2 |
Static |
— |
EIGRP |
|
LISP |
— |
OMP also carries the metric of the original route. A metric of 0 indicates a connected route.
Administrative Distance
Administrative distance is the measure used to select the best path when there are two or more different routes to the same destination from multiple routing protocols. When the Cisco vSmart Controller or the router is selecting the OMP route to a destination, it prefers the one with the lower or lowest administrative distance value.
The following table lists the default administrative distances used by the Cisco SD-WAN devices:
Protocol |
Administrative Distance |
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Connected |
0 |
Static |
1 |
NAT (NAT and static routes cannot coexist in the same VPN; NAT overwrites static routes) |
1 |
Learned from DHCP |
1 |
GRE |
5 |
EBGP |
20 |
OSPF |
110 |
IBGP |
200 |
OMP |
250 |
EIGRP |
Internal: 90, External: 170 |
OMP Best-Path Algorithm and Loop Avoidance
Cisco SD-WAN devices advertise their local routes to the Cisco vSmart Controller using OMP. Depending on the network topology, some routes might be advertised from multiple devices. Cisco SD-WAN devices use the following algorithm to choose the best route:
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Select an ACTIVE route. An ACTIVE route is preferred over a STALE route. An active route is a route from a peer with which an OMP session is UP. A stale route is a route from a peer with which an OMP session is in Graceful Restart mode.
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Check whether the OMP route is valid. If not, ignore it.
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If the OMP route is valid and if it has been learned from the same Cisco SD-WAN device, select the OMP route with the lower administrative distance.
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If the administrative distances are equal, select the OMP route with the higher OMP route preference value.
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If the TLOC preference values are equal, compare the origin type, and select one in the following order (select the first match): Connected Static EBGP OSFP intra-area OSPF inter-area OSPF external EIGRP internal EIGRP external IBGP Unknown
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If the origin type is the same, select the OMP route that has the lower origin metric.
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If the router IDs are equal, a Cisco IOS XE SD-WAN device selects the OMP route with the lower private IP address. If a Cisco vSmart Controller receives the same prefix from two different sites and if all attributes are equal, it chooses both of them.
Here are some examples of choosing the best route:
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A Cisco vSmart Controller receives an OMP route to 10.10.10.0/24 via OMP from a Cisco vEdge device Cisco IOS XE SD-WAN device with an origin code of OSPF, and it also receives the same route from another Cisco vSmart Controller, also with an origin code of OSPF. If all other things are equal, the best-path algorithm chooses the route that came from the Cisco IOS XE SD-WAN device.
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A Cisco vSmart Controller learns the same OMP route, 10.10.10.0/24, from two Cisco IOS XE SD-WAN devicesin the same site. If all other parameters are the same, both routes are chosen and advertised to other OMP peers. By default, up to four equal-cost routes are selected and advertised.
A Cisco IOS XE SD-WAN device installs an OMP route in its forwarding table (FIB) only if the TLOC to which it points is active. For a TLOC to be active, an active BFD session must be associated with that TLOC. BFD sessions are established by each device which creates a separate BFD session with each of the remote TLOCs. If a BFD session becomes inactive, the Cisco vSmart Controller removes from the forwarding table all the OMP routes that point to that TLOC.
OMP Graceful Restart
Graceful restart for OMP allows the data plane in the Cisco SD-WAN overlay network to continue functioning if the control plane stops functioning or becomes unavailable. With graceful restart, if the vSmart controller in the network goes down, or if multiple vSmart controllers go down simultaneously, Cisco IOS XE SD-WAN devices and Cisco vEdge devices can continue forwarding data traffic. They do this using the last known good information that they received from the vSmart controller. When a vSmart controller is again available, its DTLS connection to the device is re-established, and the device then receives updated, current network information from the vSmart controller.
When OMP graceful restart is enabled, Cisco IOS XE SD-WAN devices and Cisco vEdge devicesand a vSmart controller (that is, two OMP peers) cache the OMP information that they learn from their peer. This information includes OMP routes, TLOC routes, service routes, IPsec SA parameters, and centralized data policies. When one of the OMP peers is no longer available, the other peer uses the cached information to continue operating in the network. So, for example, when a device no longer detects the presence of the OMP connection to a vSmart controller, the device continues forwarding data traffic using the cached OMP information. The device also periodically checks whether the vSmart controller has again become available. When it does come back up and the device re-establishes a connection to it, the device flushes its local cache and considers only the new OMP information from the vSmart controller to be valid and reliable. This same scenario occurs when a vSmart controller no longer detects the presence of Cisco IOS XE SD-WAN devices and Cisco vEdge devices.
BGP and OSPF Routing Protocols
The Cisco SD-WAN overlay network supports BGP and OSPF unicast routing protocols. These protocols can be configured on Cisco IOS XE SD-WAN devices in any VRF except for transport and management VRFs to provide reachability to networks at their local sites. Cisco IOS XE SD-WAN device can redistribute route information learned from BGP and OSPF into OMP so that OMP can better choose paths within the overlay network.
When the local site connects to a Layer 3 VPN MPLS WAN cloud, the devices act as an MPLS CE device and establishes a BGP peering session to connect to the PE router in the L3VPN MPLS cloud.
When the devices at a local site do not connect directly to the WAN cloud but are one or more hops from the WAN and connect indirectly through a non-Cisco SD-WAN device, standard routing must be enabled on the devices’ DTLS connections so that they can reach the WAN cloud. Either OSPF or BGP can be the routing protocol.
In both these types of topologies, the BGP or OSPF sessions run over a DTLS connection created on the loopback interface in VRF 0, which is the transport VRF that is responsible for carrying control traffic in the overlay network. The Cisco vBond Orchestrator learns about this DTLS connection via the loopback interface and conveys this information to the Cisco vSmart Controller so that it can track the TLOC-related information. In VRF 0, you also configure the physical interface that connects the Cisco IOS XE SD-WAN device to its neighbor—either the PE router in the MPLS case or the hub or next-hop router in the local site—but you do not establish a DTLS tunnel connection on that physical interface.
BGP Community Propagation
Feature Name |
Release Information |
Description |
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BGP Community Propagation |
Cisco IOS XE Release 17.3.1a Cisco vManage Release 20.3.1 |
This feature enables propagation of BGP communities between routing protocols during route redistribution. One one node, the OMP redistributes routes from BGP and on the other node, the OMP redistributes node into BGP. The BGP AS Path is propagated over OMP so that it can be preserved between Cisco SD-WAN nodes. The BGP community propagation helps in propagating BGP communities between Cisco SD-WAN sites, across VPNs using OMP redistribution. |
Starting from Cisco IOS XE Release 17.3.1a, the community propagation feature is supported. Without this option, no BGP communities are sent to the BGP neighbor, even if they are attached. With this feature, the Cisco IOS XE SD-WAN device can start propagating the communities attached to the BGP entries to the neighbor. The BGP overlay is migrated to a Cisco-SDWAN overlay where BGP route attributes are propagated between Cisco SD-WAN sites across VPNs.
EIGRP
Cisco EIGRP (Enhanced Interior Gateway Routing Protocol) is a Cisco proprietary routing protocol. It is an open-standard Interior Gateway Protocol (IGP). EIGRP is an enhancement to the original Interior Gateway Routing Protocol (IGRP developed) by Cisco. EIGRP does not fully update if there are no changes in the network. This reduces the flooding activities in other IGPs. It also can use both equal cost and unequal cost paths, which is unique among IGPs.
EIGRP is supported only on Cisco IOS XE SD-WAN devices.
See Introduction to EIGRP for more information in EIGRP.
Note |
If your EIGRP network includes Cisco vEdge devices, you may need additional software. Refer to Cisco IOS XE SD-WAN Release 16.11.x and Cisco SD-WAN Release 19.1.x release notes for configuration information. |
Benefits of EIGRP
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Increased network width from 15 to 100 hops
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Fast convergence
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Incremental updates, minimizing bandwidth
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Protocol-independent neighbor discovery
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Easy scaling
Limitations and Restrictions
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EIGRP is not supported on the transport side network on Cisco IOS XE SD-WAN devices.
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EIGRP route match is not supported in vSmart centralized control policy.