1322 CHAPTER 76: MPLS B ASICS CONFIGURATIONA label space ID of 1 means per interface, a label space ID of 0 means perplatform.n Currently, only per platform label space is supported.LDP Label Distribution Figure 383 illustrates how LDP distribute labels.Figure 383 Label distributionIn Figure 383, B is the upstream LSR of C on LSP1.As described previously, there are two label advertisement modes. The maindifference between them is whether the downstream advertises the bindingsunsolicitedly or on demand.The following details the advertisement process for each of the two modes.DoD modeIn DoD mode, an upstream LSR sends a label request message containing thedescription of a FEC to its downstream LSR, which assigns a label to the FEC,encapsulates the binding information in a label mapping message and sends themessage back to it.When the downstream LSR responds with label binding information depends onthe label distribution control mode used by the LSR:■ In ordered mode, an LSR responds to its upstream LSR with label bindinginformation only when it receives that of its downstream LSR.■ In independent mode, an LSR immediately responds to its upstream LSR withlabel binding information no matter whether it receives that of its downstreamLSR or not.Usually, an upstream LSR selects its downstream LSR based on the information inits routing table. In Figure 383, all LSRs on LSP1 work in ordered mode, while LSRF on LSP2 works in independent mode.LERLSR A LSR B LSR DLSR CLSR E LSR F LSR GLSR HIngress EgressLabel requestLSP1LSP2Label mapping
