JN0-364 Exam Dumps : Service Provider Routing and Switching - Specialist (JNCIS-SP)

In Juniper Networks Junos OS, a "hidden" route in the BGP table typically signifies that the router has received the prefix but cannot install it into the active routing table because theBGP next hop is unreachable. This is a common occurrence in service provider environments when transitioning betweenExternal BGP (EBGP)andInternal BGP (IBGP).

According to Juniper technical documentation, when an EBGP speaker (R1) advertises a prefix to its peer (R2), it sets the next hop to its own interface IP address ($172.16.10.1$). By default, when R2 re-advertises that prefix to its IBGP peer (R3), itpreserves the original EBGP next-hop address. Unless R3 has a specific route in its Interior Gateway Protocol (IGP) or a static route to reach the $172.16.10.1$ subnet, it will mark the route as unusable (hidden).

In the exhibit, the show route output onR3explicitly shows the nexthop for $203.0.113.0/24$ as $172.16.10.1$. Since this route is marked "hidden," we can conclude R3 does not know how to reach R2's external peering link. To resolve this, the network administrator must modify the next-hop attribute before the route is sent to R3.

By adding the statementset policy-options policy-statement export-to-ibgp then next-hop self(Option B) on routerR2, R2 will replace the external next-hop ($172.16.10.1$) with its own internal peering address ($172.16.20.1$) before advertising the route to R3. Because R3 already has a direct or IGP connection to R2's internal address, it will successfully resolve the next hop, and the route will transition from "hidden" to "active."

Option A is unnecessary because the route is already being exported; Option C is redundant as the policy is already applied to the IBGP group; and Option D changes path preference but does not solve the underlying reachability problem.

In theIS-IS (Intermediate System to Intermediate System)protocol, the process of forming an adjacency between two neighbors follows a specific sequence of states. While OSPF uses states like "Init," "Two-Way," and "Full," IS-IS uses a slightly different nomenclature within its state machine.

According to Juniper Networks technical documentation, when a router first sends anIS-IS Hello (IIH) PDUand receives one back from a neighbor, but has not yet confirmed that the neighbor "sees" it back, the adjacency enters theInitializingstate. Specifically, on a point-to-point link, the state transitions fromDowntoInitializingas soon as the first PDU is received. On a broadcast network (like Ethernet), the Initializing state indicates that the local router has received a Hello PDU from the neighbor, but the local router's own System ID is not yet listed in the neighbor's list of "seen" neighbors (the neighbor's Hello PDU does not yet contain the local router's MAC address).

The adjacency only moves to theUpstate (Option C) once bi-directional communication is confirmed—meaning both routers have seen each other's System IDs in the incoming Hello PDUs.

Why other options are incorrect:

Loading (Option A):This is an OSPF state, not an IS-IS state. In IS-IS, database synchronization happens after the adjacency is Up.

Two-Way (Option D):While functionally similar to the state IS-IS is achieving, "Two-Way" is the specific terminology for OSPF. In IS-IS, the intermediate step between knowing a neighbor exists and having a fully functional adjacency is strictly calledInitializing.

In theOSPF (Open Shortest Path First)protocol, ensuring that all routers within an area have a synchronizedLink-State Database (LSDB)is fundamental to building a consistent loop-free topology. During the adjacency formation process—specifically when transitioning from theExStartstate to theExchangestate—routers must determine what information they are missing from their neighbors without sending the entire database at once, which would be highly inefficient.

TheDatabase Description (DBD)packet, also known as a DDP, is the mechanism used for this summary exchange. According to Juniper Networks technical documentation, the DBD packet does not contain full Link-State Advertisements (LSAs). Instead, it contains only theLSA headers, which include the LSA type, the ID of the advertising router, and the sequence number.

By exchanging these headers, a Juniper router can compare the neighbor's database summary against its own local LSDB. If the router identifies a header in the DBD packet that represents a newer or missing entry, it records that LSA in its "Link-State Request List." This collaborative "handshake" ensures that only the necessary, updated information is requested in the subsequentLink-State Request (LSR)phase. It is important to distinguish this from theLink-State PDU (LSP)mentioned in Option D, which is actually the term used in the IS-IS protocol, not OSPF. In OSPF, the functional unit is the LSA, and the transport vehicle for the initial summary is the DBD packet. This methodical synchronization is what allows OSPF to scale effectively in large service provider environments.