Benefits of Configuring the LDP-Over-RSVP Feature
MPLS is a significant technology in the service provider environment and is becoming more relevant to enterprise networks. MPLS enables:
- Virtualization
- Traffic engineering
- Consolidation of different traffic types such as IPv4, IPv6, unicast, and multicast across Layer 2 and Layer 3 VPNs
- Quality of service
- Link and node redundancy
- Compliance with service-level agreements
This shift to MPLS is primarily due to the opportunity to increase revenue and improve management of current network resources.
The Juniper Networks Junos® operating system (Junos OS) provides a standards-based MPLS solution based on BGP, LDP, and RSVP.
Deploying MPLS in a service provider network enables support for IPTV, financial applications, collaboration-based applications, and virtual private LAN service (VPLS).
Deploying MPLS functionality in the aggregation and core layers can provide the flexibility needed for the enterprise to achieve its segmentation and traffic engineering needs.
One MPLS feature that can be deployed in multiple scenarios is LDP over RSVP. LDP over RSVP combines the simplicity and scalability benefits of LDP with RSVP’s traffic engineering and traffic protection capabilities.
Technically, LDP does not run over RSVP-TE, but rather an LDP signaled label-switched path (LSP) runs through a TE tunnel that was set up using RSVP-TE. In this case, LDP can be turned on at the edge, RSVP-TE can be used across the core, and the RSVP-TE LSP acts as the link connecting two LDP peers.
One example of how the LDP-over-RSVP feature is used is in service provider networks where they are interconnecting diverse customer networks across multiple providers.
The benefits to service providers are:
- LDP over RSVP provides convergence of different traffic types such as IPv4, IPv6, unicast, and multicast across Layer 2 and Layer 3 VPNs.
- It enables flexible access connectivity options that can accommodate multiple topologies, different protocols, and multiple administrative boundaries.
- It enables secure interworking among multiple providers.
- RSVP tunnels in the core network provide differentiated services on a per customer basis. RSVP-TE supports traffic engineering, bandwidth guarantees, and link and node redundancy capabilities.
- Using RSVP reduces the number of LSPs required in the core, which reduces the resource requirements of the protocols and routers as well as reducing convergence time.
- LDP over RSVP provides cost-efficient rollouts with minimal network disruption because the LSPs are built using point-to-point TE tunnels to directly attached neighbors. These TE tunnels only go to the next hop, not end to end. Then when LDP is run over those tunnels, the sessions are built to the directly connected neighbor. When there is a change in the network, such as adding a new node, the directly connected neighbors of the new node have RSVP and LDP sessions. Thus, the RSVP LSPs are only to the next hop, and LDP takes care of advertising labels for the new addresses.
Another example is an enterprise network connected to a provider edge (PE) router that supports both LDP and RSVP LSPs. The LDP-over-RSVP feature enables you to establish a full mesh of RSVP LSPs between PE devices and simultaneously deploy LDP for simplicity. RSVP LSPs can be deployed in the MPLS core of a campus network to reap the benefits of traffic engineering. In this case, the PE routers and P routers tunnel LDP LSPs through RSVP LSPs.
The benefits of this approach are:
- It is easier to configure LDP than to configure RSVP.
- LDP uses reliable TCP as the transport protocol for all but the discovery messages.
- RSVP-TE supports traffic engineering.
- RSVP-TE supports quality-of-service capabilities.
- RSVP-TE supports link and node redundancy capabilities.
- Using RSVP can reduce the number of LSPs required in the core, which reduces the resource requirements of the protocols and routers.
- If a PE router does not support RSVP-TE, it can still take advantage of the benefits provided by traffic engineering in the core by using LDP over RSVP.
