Part 1 Cisco Viptela SDWAN: Advertise Routes to OMP

Cisco Viptela SDWAN: Advertise Routes to OMP

OMP, which is responsible for vSmarts domain for that vEdge router, advertises connected routes, static routes, and OSPF inter-area and intra-area routes by default. Routers do not advertise external routes to OMP using BGP or OSPF.

You can use the advertise command to have the vEdge router advertise these routes to OMP, and therefore to the vSmart controller that controls the vEdge router.

Fig 1.1- BGP/OSPF to OMP

To configure the routes that the vEdge/cEdge router advertises to OMP for all VPNs configured on the router:

NDNA_vEdge(config-omp)# advertise (bgp | connected | ospf type | static) 

To configure the routes that the vEdge router advertises to OMP for a specific VPN on the router. For OSPF, the route type can be external

NDNA_vEdge(config-vpn-omp)# advertise (aggregate prefix [aggregate-only] | bgp | connected | network prefix | ospf type | static) .

The bgp, connected, ospf, and static options advertise all learned or configured routes of that type to OMP. To advertise a specific route instead of advertising all routes for a protocol, use the network option, specific the prefix of the route to advertise.

You can set route advertisements with the omp advertise command for all VPNs on the router. When you use the vpn OMP advertise command, you can set route advertisements only for specific VPNs. Route advertisements are applied if both commands are configured.

BGP-OMP
In networks that have both overlay and underlay connectivity for example, when vEdge routers are interconnected by both a Viptela overlay network and an MPLS underlay network. you can assign as AS number to OMP itself. For vEdge routers running BGP, this overlay AS number is included in the AS path of BGP route updates. 

If you configure the same overlay AS number on multiple vEdge routers in the overlay network, all these routers are considered to be part of the same AS, and as a result, they do not forward any routes that contain the overlay AS number. 

BGP AS path propagation:
BGP propagates AS path information to routers behind the vEdge router (in the service-side network) that run BGP, and it receives AS path information from these routers. OMP advertises BGP routes with AS path information if you re distribute BGP routes.

The routers on which AS path propagation is not configured receive AS path information but do not forward it to their BGP routers in their local service-side network if some of them have it configured.

BGP routing loops can be avoided by propagating AS path information.