Which RSVP object allows LSRs to influence path selection?

The Explicit Route Object (ERO) is used in RSVP Path messages to specify a particular path that a Label-Switched Path (LSP) must take. The ingress Label Switching Router (LSR) includes the ERO, which contains a list of specific routers (hops) for the path. This allows network administrators to explicitly control the route, overriding the path that would otherwise be selected by the Interior Gateway Protocol (IGP). This capability is fundamental to MPLS Traffic Engineering (TE).

A. The record route object (RRO) is used to record the actual path that an LSP traverses, not to influence its selection beforehand.

C. The hop object (PHOP/NHOP) identifies the previous or next hop router in the path for message processing, but does not define the entire explicit route.

D. The session object identifies the specific data flow (e.g., destination address, protocol) for which a reservation is being made, not the network path.

---

1. Juniper Networks TechLibrary, MPLS Applications User Guide, "RSVP Traffic Engineering." This guide states, "To establish a TE LSP, the ingress router must determine the path to the egress router. The path can be explicit. An explicit path is a list of routers, specified in the ERO, that the LSP must traverse." This directly links the ERO to path selection.

2. Juniper Networks TechLibrary, Junos OS Routing Protocols Library for Routing Devices, "RSVP Objects." This document defines the key RSVP objects. It describes the Explicit Route Object (ERO) as being "carried in Path messages. It consists of a sequence of hops that the LSP must traverse." It also defines the Record Route Object (RRO) as being used to "record the actual route taken by the LSP," clearly distinguishing its function from the ERO.

3. Juniper Networks Day One, "This Week: An Expert Packet Walkthrough on the Junos OS," Chapter 4: MPLS. This book explains, "The ingress LER will insert an Explicit Route Object (ERO) into the RSVP Path message... The ERO contains the list of hops that the LSP must traverse." This reinforces the ERO's role in dictating the path.