| RSVP – Resource Reservation Protocol | LDP – Label Distribution Protocol | |
| Standard? | RFC3209 | RFC 5036 |
| What configuration steps are required? | You need to enable RSVP and MPLS on the interfaces, create the LSP(s) under protocols MPLS, and depending on LSP configuration an IGP might also be required. set protocols mpls interface set protocols rsvp interface set interface unit family mpls set protocols mpls label-switch-path lsp_name … set protocols ospf/isis … interface | You only need to configure LDP and MPLS on the interfaces. An IGP is also required. LDPs configuration is very simple. I describe it as: “turn it on, let it run! Labels for the address of the loopback interface matching the RID will get advertised by default in Junos. set protocols mpls interface set protocols ldp interface set interface unit family mpls set protocols ospf/isis … interface |
| Does it follow the IGP? | Depends on configuration: If you configure a strict ERO listing the physical interface address of every hop from ingress to egress an IGP is not needed. an IGP is not needed. If you don’t configure an ERO, or the ERO does not list all hops, has loose hops, or includes the address of a loopback interface, then the IGP is needed to complete the path. | YES, a route must be present in the routing table for a label to be advertised. you must enable both LDP and the routing protocol on the same set of interfaces |
| What label assignment method does it follow? | Downstream on demand A router configured with an LSP sends signaling downstream requesting labels to be assigned for the LSP. | Downstream unsolicited A router running LDP, bounds labels to FECs and advertises them. |
| Which device initiates signaling for label assignment? | Ingress | Egress (unsolicited advertisement) by default Unsolicited on demand assignment can be configured |
| Can label assignments be controlled by policy? | NO | YES You can configure the following policy types: – ingress-policy – egress-policy – export-policy – dod-request-policy By default, router only advertises a label for the IP address of the loopback matching the RID |
| Does it support traffic engineering? | YES | NO Thus, no bandwidth reservation. traffic constraints, or specific path. |
| Does it use CSPF? | YES | NO |
| How does it work? | Request/response processing all the way from ingress to egress. – A request (PATH) message is sent from ingress to egress requesting a label to be assigned and requesting attributes such as bandwidth reservation. – A response is sent from egress towards ingress, and each hop along the way assigns a label for the LSP. | Hop by hop processing and mapping of labels to FECs. – At each router running LDP, a label is assigned to each prefix, depending on configuration (only the loopback interface by default in Junos). This makes the router the egress for that particular prefix. Each router does this independently – On the receiving router, the information is locally installed in the LDP database and in the routing table (inet.3). The router becomes the ingress for that prefix. Also, a label is mapped for each received label/prefix and advertised to other routers. The router also becomes the transit for that prefix, for traffic coming from neighbors upstream. |
| Which messages does the protocol use? | LSP SETUP: – PATH – RESV LSP ERRORS – RESVErr – PATHErr LSP TEAR DOWN – PATHTear – RESVTear | DISCOVERY – Hellos ADVERTISEMENT: – Label Request – Label Mapping ERRORS/STATUS – Notification |
| What protocol/port number and DA are used? | IP PROTOCOL = 46 DA=Egress router’s address, or address of next hop. | DISCOVERY (HELLO): – UDP port = 646 – DA=224.0.0.2/Address of target neighbor (extended discovery) SESSION: – TCP port 646 – DA = neighbor address |
| Is authentication supported? | Per interface | Per session |
| Is graceful-restart supported? | YES – helper enabled by default – restart capability enabled when you configure routing-options graceful-restart – when you disable graceful-restart with set protocols rsvp graceful-restart disable, both helper and restarting capabilities are disabled. – You can disable helper-mode only with set protocols rrvp graceful-restart helper-disable | YES – helper enabled by default – restart capabilities enabled when you configure routing-options graceful-restart – When you disable graceful-restart with set protocols ldp graceful-restart disable both helper and restarting capabilities are disabled. – You can disable helper-mode only with set protocols ldp graceful-restart helper-disable |
| Does it support protection? | – Link Protection – Node Protection – Fast Reroute | Link Protection |
| What is the protocol’s preference value? | 7 | 9 |
| What is the benefit? | – Extensible – Provides Traffic Engineering | – Simple – Extremely scalable |
LDP vs. RSVP
2 Thoughts to “LDP vs. RSVP”
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I really appreciate this artice. Is very useful!
ABout RSVP reservation, I would like to understand so deeply the difference between them. Have you ever used Fixed filter, Wildcard filter or shared explicit? About wildcard and shared types I have a lot of doubts and I would like to know some uses cases.
The Fixed filter reservation style is the default reservation style and it means a reservation for each flow.
The Shared Explicit reservation style is enabled when you configure adaptive in Juniper, and it means shared reservation for multiple flows.