Master JN0-352: Juniper Enterprise Routing and Switching, Specialist Exam Success Starts Here

Correct : A, B, E

The show route advertising-protocol bgp command displays exactly what would be transmitted to a specific BGP neighbor after all configured export routing policy has already been evaluated and applied, meaning any prefixes shown in this output have successfully passed through the export policy chain --- confirming the export routing policy has been processed. The command header explicitly states '7 destinations, 7 routes (7 active, ...)' and every listed prefix is preceded by an asterisk, Junos's standard marker for an active route, confirming all seven displayed routes are active in the local routing table. The routing table name shown, XYZ.inet.0, indicates these routes reside in a named routing instance called XYZ rather than the default master routing instance, whose table would instead be labeled simply inet.0; this rules out the statement claiming the routes belong to the default instance. The AS path column shows only the origin code 'I' (IGP) with no AS numbers prepended ahead of it, meaning the AS path is empty, which indicates these prefixes were originated locally within R1's own AS (through redistribution or local origination) rather than having been learned from and passed through an external AS, ruling out that statement as well. Finally, the Nexthop column explicitly shows 'Self' for every route rather than an actual peer or learned address, confirming R1 is rewriting the next-hop attribute to its own address before advertising --- a deliberate next-hop-self policy action typically applied toward IBGP peers. Reference topics: Junos Enterprise Routing -- BGP, Verifying Advertised Routes and Export Policy Effects.

Correct : C

This scenario describes end hosts --- virtualization hosts running software switches or virtual bridging stacks --- unexpectedly generating and transmitting BPDUs on ports that are supposed to be pure edge (host-facing) ports where no BPDUs should ever legitimately be received. BPDU protection (BPDU guard) is the Junos feature purpose-built for exactly this situation: when applied to an edge-designated interface, it continuously monitors that port for any incoming BPDU, and the moment one is detected, it immediately and automatically disables the port, preventing the unexpected BPDU source from ever participating in or influencing the spanning-tree topology calculation, thereby protecting the stable, intended topology from disruption caused by unauthorized or accidental BPDU generation at the access edge. This directly and precisely resolves the described problem at its source, since the root cause is illegitimate BPDUs arriving on ports that were never meant to see them. Increasing the max-age timer only adjusts how long stale topology information is retained before being aged out and has no effect on preventing rogue BPDUs from being processed in the first place. Disabling RSTP outright on access interfaces would eliminate spanning tree's loop-prevention protection on those ports entirely, introducing a much more severe risk of undetected Layer 2 loops. Root protection (root guard) defends specifically against a port attempting to become the root port by receiving a superior BPDU claiming a better path to root; it addresses a different threat model than blocking any BPDU outright on a true edge port. Reference topics: Junos Enterprise Switching -- Spanning Tree Protocols, BPDU Protection on Edge Interfaces.

Correct : A

The Complete Sequence Number PDU (CSNP) is the IS-IS mechanism used to summarize the entire contents of a router's link-state database, listing the LSP ID, sequence number, checksum, and remaining lifetime for every LSP the sending router currently believes should exist in the database for that level. On broadcast (LAN) circuits, the elected Designated Intermediate System periodically transmits CSNPs to all routers on the segment as a database-synchronization mechanism; any receiving router compares the summarized list against its own local database, and any discrepancy --- an LSP it is missing entirely, or one for which it holds an older sequence number --- triggers a targeted request for the specific, updated LSP content. On point-to-point circuits, a single CSNP is exchanged once when the adjacency first comes up, serving the identical synchronization purpose without needing periodic repetition. The Partial Sequence Number PDU (PSNP), by contrast, is used to acknowledge receipt of specific LSPs or to explicitly request specific LSPs identified as missing or outdated after a CSNP comparison, making it a partial, targeted PDU rather than a complete database listing. The LSP itself is the PDU that actually carries the detailed topology and reachability information being advertised, rather than a database summary. The IS-IS Hello PDU (IIH) is used purely for neighbor discovery and adjacency maintenance and carries no link-state database summary information whatsoever. Reference topics: Junos Enterprise Routing -- IS-IS, CSNP and Link-State Database Synchronization.

Correct : B

GRE encapsulation adds a fixed 24 bytes of overhead to every packet it carries --- 4 bytes for the GRE header itself and 20 bytes for the new outer IPv4 delivery header. When a host transmits a full 1500-byte Ethernet payload into a gr- interface, the resulting encapsulated packet becomes 1524 bytes, which exceeds the physical interface's standard 1500-byte MTU and forces fragmentation or drops if the don't-fragment bit is set. The correct remediation is to reduce the effective MTU seen by end hosts so that encapsulated packets never exceed the physical link's transmission limit. Junos automatically applies this logic to gr- logical interfaces, which default to a 1476-byte protocol MTU (1500 minus 24), but when the underlying physical interface or a manually configured path is involved, administrators must explicitly size the interface MTU to 1476 bytes to prevent post-encapsulation oversize packets. Allowing fragmentation with clear-dont-fragment is a workaround that increases CPU load and can degrade performance rather than solving the root cause, BFD addresses link-failure detection rather than MTU sizing, and ToS copying affects only the type-of-service byte, not packet length. Reference topics: Junos Enterprise Routing -- Tunneling, GRE Encapsulation and MTU Considerations; Junos OS Configuring GRE Tunnel Interfaces.

Correct : C

The BGP finite state machine defined in RFC 4271 progresses through Idle, Connect, Active, OpenSent, OpenConfirm, and finally Established. The Active state is entered either directly after Idle, when the local router begins retrying a TCP connection setup toward the configured peer, or after a previous Connect attempt has failed and the ConnectRetry timer has expired, prompting the router to keep trying to complete the underlying TCP three-way handshake. Seeing a peer parked in Active therefore means the local device has a fully valid neighbor configuration and is persistently attempting to reach the remote address on TCP port 179, but the handshake is not succeeding --- common root causes include a firewall or ACL blocking TCP 179 between the two endpoints, an unreachable or incorrect peer IP address, the remote BGP process not running or not listening, or an asymmetric routing path preventing the SYN/ACK from returning. It does not indicate a misconfiguration on the local box in the sense of a missing statement (that would typically leave the session as Idle), nor does it indicate an established, functioning session exchanging UPDATE messages (that state is Established), and it is not a deliberately idle/disabled condition, which Junos reports plainly as Idle. Recognizing Active as 'trying to connect' rather than 'connected' is essential for correct BGP troubleshooting sequencing. Reference topics: Junos Enterprise Routing -- BGP Fundamentals, BGP Finite State Machine and Session Verification.