What is the difference between LDP and RSVP ?

LDP (Label Distribution Protocol) and RSVP (Resource Reservation Protocol) are both signaling protocols used in MPLS (Multiprotocol Label Switching) networks, but they serve different purposes. Here are the differences between LDP and RSVP:

Function:

LDP: LDP is primarily responsible for the distribution and allocation of labels used in MPLS forwarding. It establishes label bindings between routers, allowing them to create label-switched paths (LSPs) for forwarding packets.

RSVP: RSVP is a signaling protocol used for resource reservation in network traffic. It is primarily used for establishing Quality of Service (QoS) paths and reserving bandwidth along a network path.

Label Distribution:

LDP: LDP uses a hop-by-hop approach for label distribution. It distributes labels to each individual hop or router along the path, without considering the specific traffic requirements or available resources.

RSVP: RSVP supports explicit routing and allows for the reservation of specific resources along a path. It provides end-to-end signaling, enabling routers to exchange information about the required resources and QoS parameters for a particular flow.

Traffic Engineering:

LDP: LDP does not provide explicit traffic engineering capabilities. It is primarily focused on label distribution for MPLS forwarding.

RSVP: RSVP supports traffic engineering by allowing routers to reserve and allocate network resources based on specific QoS requirements. It enables the creation of explicit paths for traffic based on the desired QoS parameters.

Resource Reservation:

LDP: LDP does not provide explicit resource reservation mechanisms. It assumes that sufficient resources are available in the network for forwarding packets based on the allocated labels.

RSVP: RSVP enables the reservation of network resources along a path, ensuring that sufficient bandwidth and other resources are available to meet the QoS requirements of the traffic.

Application:

LDP: LDP is commonly used for label distribution in MPLS networks, where the primary goal is to establish label-switched paths for efficient packet forwarding.

RSVP: RSVP is often used in scenarios where QoS and resource reservation are critical, such as in real-time multimedia applications or network environments with strict bandwidth requirements.

In summary, LDP and RSVP serve different functions in MPLS networks. LDP is focused on label distribution for MPLS forwarding, while RSVP is used for resource reservation and QoS provisioning. LDP is more suitable for general MPLS forwarding, while RSVP is beneficial for applications that require specific QoS guarantees and traffic engineering capabilities.

 

PARAMETER	LDP	RSVP
Abbreviation for	Label Distribution protocol	Resource Reservation Protocol
Provisioning	Easy to configure. We just need to enable on interfaces. Label bindings automatically established for specific FECs	Complex configuration
Topology	LSPs from multiple ingresses use the same label to reach the egress (multi-point to point LSP)	RSVP sets up independent point to point LSPs.
QoS	Limited	Guaranteed resources
LSP setup initiation	Egress initiates the LSP setup	Ingress initiates the LSP setup.
Requirement	If primarily LSPs need to be set up, LDP should be used	If you require traffic engineering and resources reservations, use RSVP (-TE).
Scalability	High	Low
ECMP	Possible	Not Possible
Fast Reroute (FRR) support	No	Yes
IGP based decision making	LDP follows IGP for decision making	RSVP does not follow the IGP, and take independent decisions on the reserved traffic