RSVP-TE CSPF

IGPs use the Shortest Path First (SPF) algorithm to determine how traffic is routed within a network, whereas RSVP uses the Constrained Shortest Path First (CSPF) algorithm to calculate traffic paths that are subject to the following constraints: * LSP attributes-Administrative groups such as link coloring, bandwidth requirements, and EROs * Link attributes-Colors on a particular link and available bandwidth These constraints are maintained in the traffic engineering database (TED). The database provides CSPF with up-to-date topology information, the current reservable bandwidth of links, and the link colors. In determining which path to select, CSPF follows these rules: * Computes LSPs one at a time, beginning with the highest priority LSP-the one with the lowest setup priority value. Among LSPs of equal priority, CSPF starts with those that have the highest bandwidth requirement. * Prunes the traffic engineering database of links that are not full duplex and do not have sufficient reservable bandwidth. * If the LSP configuration includes the include statement, prunes all links that do not share any included colors. * If the LSP configuration includes the exclude statement, prunes all links that contain excluded colors. If a link does not have a color, it is accepted. * Finds the shortest path toward the LSP's outbound router, taking into account any EROs. For example, if the path must pass through Router A, two separate SPF algorithms are computed: one from the inbound router to Router A and one from Router A to the outbound router. * If several paths have equal cost, chooses the one with the same last-hop address as the LSP's destination. * If several equal-cost paths remain, selects the path with the least number of hops. * If several equal-cost paths remain, applies CSPF load-balancing rules configured on the LSP.