3Com Router 3000 Ethernet FamilyConfiguration GuideChapter 1 MPLS Architecture3Com Corporation1-7II. LDP SessionAn LDP session is to exchange label and release messages between LSRs. There aretwo types of LDP session:zLocal LDP Session: an LDP session between two directly connecting LSRs.zRemote LDP Session: an LDP session between two indirectly connecting LSRs.III. LDP MessageThere are four types of message involved in the LDP.zDiscovery message: used to notify or maintain the existing LSRs in the network;zSession message: used to establish, maintain or terminate a session betweenLDP peers;zAdvertisement message: used to establish, modify or delete a flag, that is, an FECbinding;zNotification message: used to provide suggestive messages or error notifications.IV. Label Space and LDP IdentifierA label space refers to the range of labels that can be allocated to LDP peers. You canspecify a label space for each interface of an LSR or for the entire LSR.An LDP identifier is to identify a special LSR label space. It is a six-byte value in thefollowing format: : Here the IP address of four bytes is the LSR IP address and the remaining two bytes isthe label space number.1.4.2 LDP Working ProcessFigure 1-5 illustrates the LDP label distribution.MPLS LERLSP1MPLS LSRIngressEgressLSP2Label RequestLabel MappingLDP SessionABCDEFGHFigure 1-5Label distribution process
