BGP Labeled Unicast
As well as distributing routes, BGP with Multiprotocol Extensions (MP-BGP) can advertise MPLS label mappings that are mapped to routes. BGP Labeled Unicast (BGP-LU) attaches an MPLS label to an advertised IGP prefix and distributes the MPLS label mapped to the prefix to its peers.
With BGP-LU, a network can be divided into multiple regions to limit the total number of LSPs and enable failures to be contained and restored in a single region These regions operate separate instances of the IGP and use BGP-LU to advertise route information between inter-region routers.
A configuration for BGP-LU uses these type of nodes:
| • | Provider Edge (PE) nodes advertise label bindings to remote PEs in other regions. These advertisements only affect the PE routers and the ABRs and not provider routers (“P”) in the core network. |
| • | Area Border Router (ABR) nodes advertise the label bindings to remote PEs in other regions. |
| • | Default route advertisement is not supported in BGP Labeled Unicast. Because BGP-LU operates as both a service and transport layer, default routes at the LU level in MPLS can create ambiguity in route resolution and dependency tracking. OcNOS prevents such configurations to maintain routing consistency. To avoid this, do not advertise the default route in LU, or apply a route map to filter it (deny default route using route map) on LU neighbors. |
| • | The default behavior in BGP LU for all connected or local IPv4 unicast routes advertised in labeled-unicast address-family mode is modified to assign implicit null label. For more information, refer to BGP Labeled Unicast with Implicit Null Label for Local Routes . |
Hierarchical BGP LU: BGP Labeled Unicast (LU) deployment is not supported as both transport or underlay and service or overlay within a single OcNOS node. This refers to configuring an LU LSP to utilize another LU LSP as its service transport. The MPLS service manager in OcNOS restricts LU FTN over LU FTN. However, hierarchical Labeled BGP is supported, allowing for L3VPN, 6PE, or 6VPE LSPs over LU LSPs. LU LSPs can function as a service or transport and are compatible with various underlay labeling protocols.