Label Distribution Protocols LDP: hop-by-hop routing RSVP-TE: explicit routing CR-LDP: another explicit routing protocol, no longer under development.

LDP –LDP peers: two LSRs that use LDP to exchange label/FRC mapping information. –Four types of LDP messages: Discovery messages for announcing and maintaining the presence of an LSR in a network. Session message for establishing, maintaining, or terminating session between LDP peers. Advertisement messages for creating, changing, or deleting label mapping for FEC. Notification messages for distributing advisory information and error information. –Discovery messages are sent as UDP packets to LDP port at the all-router-on-this-subnet group multicast address. After a session is established, all messages are exchanged using TCP.

LDP discovery: two mechanisms –Discover LSR neighbors that are directed connected Send LDP Link Hello messages on each interface. UDP packets addressed to LDP discovery port with the all- routers-on-this-subnet group multicast address. – Discover LSR neighbors that are remotely connected. Send Targeted Hello messages to a specific IP address at the LDP discovery port. –When a LSR want to establish a peer relationship, it will reply. –The exchanges of Hello messages establish the adacency.

LDP session management –After two LSRs establishes the adjacency, they can set up TCP connections and start the initialization process. Negotiation of protocol version. Label distribution method, timer values, VPI/VCI ranges for label-controlled ATM. –Hello and Keepalive messages are sent periodically. Label distribution and management –downstream on demand and downstream unsolicited. –Configurable options: Independent LSPs setup or in order LSP setup. Independent LSP setup: LSRs may advertise label mappings to its neighbors at any time In order LSP setup: LSP setup from egress to ingress. An LSR may send a label mapping for a FEC only when (1) the LSR has a label mapping for the FEC for the nexthop, or (2) the LSR is the egress for the FEC.

FEC to LSP mapping –A LSR requests a label mapping from a neighboring LSR when it needs one and advertise the label mapping when I wants the neighbor to use a label. –Two types of FECs in LDP: address prefix and host address. –Special things must be done to deal with loops. LDP identifiers: –An LSR may have multiple label spaces (one for each interface). It must identify the label spaces with LDP identifiers.

RSVP-TE: –How RSVP works? the difference between the paths setup by RSVP and LSP –Forward based on IP header, path associated with a distination and a transport-layer protocol. –LSP: packets are opaque to the intermediate nodes. LSP tunnel. –New features added to the original RSVP: Label distribution, Explicit routing, Bandwidth reservation for LSPs, Rerouting LSPs after failures, Tracking of the actual route of an LSP, The concept of Nodal abstraction, Preemption options. –New objects in RSVP-TE: LABEL_REQUEST PATH LABEL RESV EXPLICIT_ROUTE PATH RECORD_ROUTE PATH, RESV SESSION_ATTRIBUTE PATH

An Example PATH: LSP_TUNNEL: LABEL_REQEUST EXPLICIT_ROUTE(B,C) RECORD_ROUTE(B) PATH: LSP_TUNNEL: LABEL_REQEUST EXPLICIT_ROUTE(C) RECORD_ROUTE(B,C) LSR ALSR B LSR C RESV: LSP_TUNNEL: LABEL(15) RECORD_ROUTE(B,C) RESV: LSP_TUNNEL: LABEL(12) RECORD_ROUTE(B,C)