Exam JN0-364 Topic 1 Question 151 Discussion

In a Juniper Networks environment, deployingRSVP-signaled LSPsrequires a functionalTraffic Engineering Database (TED). This database is populated by the Interior Gateway Protocol (IGP) using specific extensions that carry link-state information beyond simple reachability, such as available bandwidth, administrative groups (link coloring), and Maximum Reservable Bandwidth.
The behavior of these extensions differs betweenOSPFandIS-ISin Junos OS:
* OSPF (Option C):By default, OSPF is a "pure" routing protocol. To support RSVP-TE, it must carry Opaque LSAs (Type 10). According to Juniper documentation, you mustexplicitly configuretraffic engineering within the OSPF protocol hierarchy using the set protocols ospf traffic-engineering command. Without this command, OSPF will not flood the TE information required by the Constrained Shortest Path First (CSPF) algorithm, and LSPs will fail to establish.
* IS-IS (Option D):IS-IS was designed to be extensible through the use of TLVs (Type, Length, Value).
In Junos OS,IS-IS traffic engineering extensions are enabled by defaultonce the protocol is active.
As soon as you enable IS-IS on an interface, it begins to advertise the wide metrics and TE TLVs (like TLV 22 and 135) necessary for building the TED.
This distinction is a common design consideration for network architects. While IS-IS simplifies the rollout of MPLS by having TE enabled "out of the box," OSPF requires that extra configuration step to transition from a standard IGP to a TE-aware protocol.