LDP Tunneling over RSVP-TE
Overview
LDP-over-RSVP-TE tunneling is a technique used in MPLS networks to combine the strengths of Label Distribution Protocol (LDP) and Resource Reservation Protocol Traffic Engineering (RSVP-TE). This approach allows LDP Label Switched Paths (LSPs) to be encapsulated within RSVP-TE LSPs, providing enhanced traffic engineering capabilities while maintaining operational simplicity.
Feature Characteristics
LDP-over-RSVP-TE facilitates the integration of LDP LSPs within RSVP-TE tunnels, leveraging the strengths of both protocols. It harnesses RSVP-TE's traffic engineering capabilities for path computation, bandwidth reservation, and quality of service (QoS) provisioning. Ingress nodes execute FEC resolution to designate the suitable RSVP-TE tunnel for tunneling LDP LSPs, establishing hierarchical LSPs with RSVP-TE as the outer label and LDP as the inner label.
Benefits
LDP-over-RSVP-TE offers significant benefits are:
| • | Advanced Traffic Engineering: By leveraging RSVP-TE's advanced traffic engineering mechanisms, LDP-over-RSVP-TE enables efficient path computation, bandwidth reservation, and Quality of Service (QoS) provisioning. |
| • | Simplified Network Topology: eliminates the need for a full mesh of intra-area RSVP LSPs (Label Switched Paths) between PE (Provider Edge) nodes. |
| • | Enhanced Resilience with Fast Reroute (FRR): Inherit RSVP-TE's Fast Reroute (FRR) capabilities. This means that in case of link or node failures, the network can quickly reroute traffic along pre-established backup paths |
| • | Flexible Hierarchical LSP Design: Provides flexibility in network design by allowing for hierarchical LSPs (Label Switched Paths) where RSVP-TE serves as the outer label and LDP as the inner label. |
Prerequisites
Before configuring this feature, ensure the following:
| • | A functional MPLS network with support for both LDP and RSVP-TE protocols. |
| • | Network devices (routers or switches) capable of supporting LDP and RSVP-TE functionalities. |
Limitations
The limitations are:
| • | Tunneling over inter-domain IGP area is not supported. |
| • | LDP LSP tunneling over RSVP multipath is not supported. |
| • | MPLS trace route is not supported in LDP-over-RSVP tunneling path. |
| • | Dynamic TLDP sessions are not supported, TLDP session has to be explicitly configured. |
| • | LFA and/or RLFA protection is not supported for LDP-over-RSVP tunnels. |
| • | LDP over RSVP is supported only in a linear topology, where LDP traffic traversing the RSVP domain cannot be looped back toward the source LDP domain due to the presence of an IGP path that would cause such a loop. |
| • | In QMX devices being LSR node, Entropy Label (EL) and Entropy Label Indicator (ELI) cannot be inserted after RSVP label for "LDP over RSVP" use case. |
| • | LDP over RSVP (LoR) FTN updates are not hitless if the RSVP trunk undergoes an MBB sequence. |
| • | LDP over RSVP (LoR) is supported only for OSPF intra-area routes. The Type 3 and Type 5 routes are not considered for LoR. |