This chapter contains configurations for Path Computation Element Protocol (PCEP) and the BGP Link-State capability.

BGP-LS describes a mechanism by which Link-State (LS) and Traffic Engineering (TE) information from IGPs can be collected from networks and shared with external components using BGP. This is achieved using a new BGP Network Layer Reachability Information (NLRI) encoding format. The mechanism is applicable to physical and virtual links. Applications of this technique include Application-Layer Traffic Optimization (ALTO) servers and Path Computation Elements (PCEs). These components, while external to the network, require network state information on a real time basis. Specifically, they require link-state database information of each IGP node (OSPF) from the entire network. The BGP protocol is used to collect the necessary information and to share with the external components – this is achieved using a NLRI encoding format.

BGP uses AFI (16388) and SAFI (71) for distributing the Link state and Traffic engineering information.

It uses Link State NLRI that describes links, nodes, and prefixes comprised of IGP link-state information. A new BGP path attribute called BGP-LS attribute is defined to carry the link, node, prefix properties, and attributes like link and prefix metric or auxiliary Router-IDs of nodes

A Path Computation Element (PCE) is an entity (component, application, or network node) that is capable of computing a network path or route based on a network graph and applying computational constraints. A Path Computation Client (PCC) is any client application requesting a path computation to be performed by a PCE. A Path Computation Element supports requests for path computation issued by a Path Computation Client.

The PCE operates on a network graph in order to compute paths based on the path computation request(s) issued by the PCC(s). The path computation request will include the source and destination of the paths to be computed and a set of constraints to be applied during the computation, and it may also include an objective function. The PCE response includes the computed paths or the reason for a failed computation.