Chapter 14 - Multidomain Networking

Abstract

A domain in the MPLS-TE and GMPLS context is considered to be any collection of network elements within a common sphere of address management or path computational responsibility. Three tools enhance the ability to signal across multiple domains in MPLS-TE and GMPLS. The first allows ingress to specify exclusions from a path. This is useful because, when only a loose hop is used in the explicit path, the ingress has no other way to restrict which links, and nodes are included within the path. The second utility adds support for crankback routing within GMPLS signaling. Hierarchical (nested) and stitched LSPs provide the third building block for support of interdomain LSPs. RSVP-TE signaling allows a user to specify the explicit path of an LSP, and have the control plane establish the LSP through the network. The desired route of an LSP is carried in an Explicit Route Object (ERO) in RSVPTE. The ERO encodes the sequence of hops (network nodes or links) that must be traversed by the LSP. The ERO can state that the hops must be traversed in the specified order without intervening LSRs (strict hops), or it can be a series of links, and nodes that must be traversed in the specified order but which can have intervening hops if the computation algorithm generates them (loose hops).