RSVP LSP Tunnels Overview
A Resource Reservation Protocol (RSVP) label-switched path (LSP) tunnel enables you to send RSVP LSPs inside other RSVP LSPs. This enables a network administrator to provide traffic engineering from one end of the network to the other. A useful application for this feature is to connect customer edge (CE) routers with provider edge (PE) routers by using an RSVP LSP, and then tunnel this edge LSP inside a second RSVP LSP traveling across the network core.
You should have a general understanding of MPLS and label switching concepts. For more information about MPLS, see the Junos MPLS Applications Configuration Guide.
An RSVP LSP tunnel adds the concept of a forwarding adjacency, similar to the one used for generalized Multiprotocol Label Switching (GMPLS). (For more information about GMPLS, see GMPLS Overview.)
The forwarding adjacency creates a tunneled path for sending data between peer devices in an RSVP LSP network. Once a forwarding adjacency LSP (FA-LSP) has been established, other LSPs can be sent over the FA-LSP by using Constrained Shortest Path First (CSPF), Link Management Protocol (LMP), Open Shortest Path First (OSPF), and RSVP.
To enable an RSVP LSP tunnel, the Junos OS uses the following mechanisms:
- LMP—Originally designed for GMPLS, LMP establishes forwarding adjacencies between RSVP LSP tunnel peers, and maintains and allocates resources for traffic engineering links.
- OSPF extensions—OSPF was designed to route packets to physical and logical interfaces related to a Physical Interface Card (PIC). This protocol has been extended to route packets to virtual peer interfaces defined in an LMP configuration.
- RSVP-TE extensions—RSVP-TE was designed to signal the setup of packet LSPs to physical interfaces. The protocol has been extended to request path setup for packet LSPs traveling to virtual peer interfaces defined in an LMP configuration.
The following limitations exist for LSP hierarchies:
- Circuit cross-connect (CCC)-based LSPs are not supported.
- Graceful restart is not supported.
- Link protection is not available for FA-LSPs or at the egress point of the forwarding adjacency.
- Point-to-multipoint LSPs are not supported across FA-LSPs.
