Understanding Multitopology in cRPD
cRPD enables BGP multiple RIBs functionality to support Multitopology routing (MTR) based on the routing policy with Linux FIBs (routes in forwarding plane). The applications can select required routing table based on the routing policy from the Linux FIB in cRPD for different types of traffic. Each type of traffic is defined by a topology that is used to create a new routing table for that topology. Each topology uses the unified control plane to make routing decisions for traffic associated with that topology. In addition, each topology has a separate forwarding table and, in effect, a dedicated forwarding plane for each topology.
Service providers and enterprises can use multitopology routing (MTR) to engineer traffic flow across a network. MTR can be used with direct and static routes, IS-IS, OSPF, and BGP. In a network carrying multiple traffic types, you often need to direct different types of application traffic over multiple links depending on their link characteristics. Communities are used for BGP when exporting routes to multitopology. OSPFv3 does not support MTR. MTR discovers IGP routes and able to resolve BGP routes against the custom topologies with static and OSPF. .
You can configure separate topologies to share the same network links as needed. MTR uses a combination of control plane (routing) and forwarding plane filters.
MTR provides the ability to generate forwarding tables based on the resolved entries in the routing tables for the topologies you create. MTR and forwarding is available only on master routing instance. A dedicated RIB is created for storing the Multitopology routes. BGP multipath is not enabled on topologies.
When routing topologies are configured under routing-options, a new routing table for each topology is created. Each routing protocol creates a routing table based on the topology name, the instance name, and the purpose of the table.