Juniper Enterprise Routing and Switching, Specialist (JNCIS-ENT) JN0-352 Exam Dumps: Updated Questions & Answers (September 2026)

Because root bridge election is decided primarily by comparing bridge priority values — with the switch advertising the numerically lowest priority always winning, and MAC address serving only as a fallback tiebreaker when priorities are tied — the only deterministic, reliable way to guarantee that a specific switch is elected root regardless of any other switch's hardware characteristics is to explicitly configure that switch with a lower bridge priority than every other participating switch in the topology. Relying on MAC address alone, as the first distractor suggests, is fundamentally unreliable: MAC addresses are burned in at the factory, cannot be predicted or controlled by the administrator, and any future hardware replacement or newly introduced switch with a numerically lower MAC address could unexpectedly seize the root role since MAC comparison only comes into play at equal priority in the first place, meaning a 'highest MAC' strategy does not even align with how the tiebreak actually favors the lowest value. Port priority and port cost are entirely separate STP parameters that influence which port on a non-root switch is selected as its root port, or which port is selected as designated versus blocking on a given segment; neither parameter has any bearing whatsoever on which switch is elected root bridge for the whole topology, since that decision is made purely from the Bridge ID comparison, independent of any per-port settings. Explicitly and deliberately lowering Switch 1's configured bridge priority is the only correct, industry-standard method. Reference topics: Junos Enterprise Switching – Spanning Tree Protocols, Guaranteeing Root Bridge Placement via Bridge Priority.

The Backup Designated Router exists specifically to provide immediate failover redundancy for the Designated Router role on a multi-access broadcast or NBMA segment: the BDR maintains full adjacencies with every other router on the segment concurrently with the DR, precisely so that if the DR ever fails or is withdrawn, the BDR can be promoted directly to DR essentially instantaneously, without needing to wait through a fresh, full DR/BDR election process, and a new BDR election then takes place separately among the remaining DROther routers to fill the now-vacant backup role. This immediate promotion behavior confirms the first statement as correct. The Designated Router's other core responsibility on the segment is originating the Type 2 Network LSA, which describes the multi-access network itself as a pseudonode, listing every router attached to that segment; this LSA type exists specifically to avoid the full-mesh explosion of Router LSA adjacency listings that would otherwise be needed to describe a shared broadcast segment, and only the DR — never the BDR, and never any DROther — is responsible for generating and maintaining this particular LSA under normal, stable conditions, which confirms the third statement while directly ruling out the fourth. There is no such thing as the DR 'electing' an area border router; ABR status is instead a role a router acquires organically by having interfaces in more than one OSPF area, entirely independent of any DR/BDR election process on any individual segment. Reference topics: Junos Enterprise Routing – OSPF, DR/BDR Roles and Type 2 Network LSA Origination.

Once the two candidate routes have equal route preference and equal local preference (both defaulting to 100 unless modified by policy), the Junos BGP algorithm proceeds to its third decision step, which compares the length of each candidate's AS path attribute and selects whichever path carries the shortest AS path, since a shorter path is interpreted as traversing fewer autonomous system hops to reach the origin. This step occurs well before the algorithm ever reaches the specific EBGP-over-IBGP preference rule, which is only evaluated later, after local preference, AS path length, origin type, and MED have all already been compared and found equal between the candidates; because an IBGP-learned copy of a route typically retains the identical AS path that was originally received from the external AS (IBGP does not prepend the local AS number the way crossing an AS boundary does), it is entirely possible, and often the deciding scenario, for AS path length to differ between competing paths well before the algorithm would ever need to fall back on the IBGP-versus-EBGP tiebreak. Selecting a route purely because it was 'learned through IBGP' is not a rule that exists anywhere in the algorithm and would in fact typically be the opposite of Junos's later EBGP-preference tiebreak. Neither next-hop IP address value nor router ID value is compared with a 'highest wins' rule at any point in the standard path selection sequence — where router ID is used at all, Junos prefers the lowest value, not the highest, making both of those distractors doubly incorrect. Reference topics: Junos Enterprise Routing – BGP, Path Selection Order: AS Path Length Precedes EBGP/IBGP Preference.

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.

The described symptom — excessive packet drops specifically attributed to exceeding the MTU on a GRE tunnel carrying full-size video streaming traffic across default-MTU gigabit Ethernet interfaces — is a direct consequence of the 24 bytes of GRE encapsulation overhead pushing packets that were already at or near the standard 1500-byte Ethernet MTU past the physical interface's transmission limit once the outer GRE and IP headers are added. The most durable fix is to proactively increase the physical member interfaces' MTU beyond the 1500-byte default — to 1524 bytes or higher — which provides sufficient headroom to absorb the full GRE encapsulation overhead without ever causing the fully encapsulated packet to exceed the interface's transmission capability, allowing full-size 1500-byte payloads to pass through the tunnel intact and without fragmentation or drops. As a complementary measure, configuring the clear-dont-fragment-bit option on the tunnel or member interfaces instructs Junos to clear the DF (don't fragment) bit on oversized packets rather than dropping them outright when they do exceed the available MTU, allowing the Packet Forwarding Engine to fragment and later reassemble the traffic instead of silently discarding it, which directly addresses the reported packet loss even under transient conditions. Simply raising the MTU only to 1500 bytes fails to account for the 24-byte GRE overhead and would not resolve the underlying oversize condition. Routing the tunnel over a higher-bandwidth link addresses potential congestion but does nothing to correct an MTU-based packet-size violation, which is the root cause explicitly identified in this scenario. Reference topics: Junos Enterprise Routing – Tunneling, GRE MTU Sizing and Fragmentation Handling for High-Throughput Applications.

On EX Series switches, aggregated Ethernet (ae) interfaces do not exist by default; before any ae interface can be created, referenced, or brought into service, an administrator must first reserve the desired number of aggregated Ethernet device slots by configuring set chassis aggregated-devices ethernet device-count number at the [edit chassis] hierarchy. This statement allocates the internal resources needed for that many ae interfaces to exist as valid, configurable objects; until it is committed, any interface-level configuration referencing ae0 (such as the aggregated-ether-options and family ethernet-switching stanzas shown in the exhibit) is accepted syntactically by the CLI but never actually instantiates a live ae0 device, which is exactly why show interfaces ae0.0 returns 'device ae0 not found' despite the interface appearing fully configured. Increasing the device-count to at least 1 (or higher, to cover the number of LAG bundles planned) immediately resolves this and allows ae0 to appear as an operational interface once its member links are also associated with it. This is a foundational and frequently overlooked prerequisite step in LAG deployment on Juniper switches. There is no separate licensing requirement for aggregated Ethernet functionality on EX Series switches, a reboot is not needed since the chassis statement takes effect upon commit, and the LACP mode (active versus passive) is unrelated to whether the ae interface object itself exists in the first place. Reference topics: Junos Enterprise Switching – Link Aggregation, Configuring the Aggregated Ethernet Device Count.

Root bridge election is based on comparing each switch's full Bridge Identifier, which combines the bridge priority value with the switch's MAC address, with priority always evaluated first and MAC address serving strictly as a tiebreaker when two or more switches present identical priority values. In this scenario, the network has been left entirely at the default spanning-tree configuration, meaning every switch is operating at the standard IEEE and Junos default bridge priority of 32768; since all three switches share the exact same priority value, the comparison necessarily falls through to the MAC address tiebreak, where the switch with the numerically lowest MAC address wins the election. Comparing the three addresses shown — 00:1a:2b:3c:4d:01, 00:1a:2b:3c:4d:02, and 00:1a:2b:3c:4d:03 — Switch A's address is the lowest, since only the final octet differs and 01 is less than both 02 and 03, making Switch A the elected root bridge. RSTP uses the identical Bridge ID comparison mechanism as legacy STP for root election, so there is no special 'median MAC address' rule that applies uniquely under RSTP, making that distractor factually invalid regardless of protocol version. The election process also does not require any manual bridge priority configuration to complete; the default priority value is entirely sufficient on its own to allow a deterministic election to occur, since default priorities are still numerically comparable Bridge IDs. Reference topics: Junos Enterprise Switching – Spanning Tree Protocols, Default Priority and MAC Address Tiebreaking.

MACsec (IEEE 802.1AE) secures a point-to-point Ethernet link independently of how the logical unit above it is configured for VLAN tagging, so neither trunk mode nor access mode has any bearing on whether the MACsec Key Agreement (MKA) protocol can establish a secure channel. What does determine success is the pre-shared key material: when static CAK security mode is used, the Connectivity Association Key (CAK) and the Connectivity Association Key Name (CKN) must be configured identically on both ends of the link. If they do not match, MKA never completes the exchange, no secure channel is created, and all traffic on that interface is dropped rather than merely left unencrypted. Equally important, and frequently overlooked, is that MACsec adds up to 32 bytes of overhead per frame for the security tag (SecTAG) and integrity check value (ICV); Juniper's official guidance is to ensure the difference between the interface's physical MTU and the protocol MTU is large enough to absorb this overhead, or frames will be silently discarded once encryption is active, producing symptoms that look identical to a failed session. Both the CAK/CKN and MTU checks are documented first-line troubleshooting steps for MACsec on EX Series switches. Reference topics: Junos Enterprise Switching – Layer 2 Security, Configuring and Troubleshooting MACsec on EX Series Switches.

The destination address 172.16.200.5 falls within the 172.16.0.0/16 aggregate's summarized range but does not fall within either of the two active, more-specific contributing routes actually present in the table — 172.16.10.0/24 and 172.16.99.0/24 — meaning no route more specific than the /16 itself exists to cover it. Under Junos's longest-match forwarding logic, the lookup for 172.16.200.5 therefore resolves to the aggregate route itself, and since aggregate routes are installed by default with a reject next hop rather than any real forwarding path, the router drops the packet and simultaneously generates an ICMP destination-unreachable message back to the originating source, explicitly signaling that no valid path exists for that specific destination even though a covering summary is being advertised. This reject behavior is precisely why aggregate routes are valuable for reducing the number of routes advertised upstream while still providing clear, immediate feedback for traffic aimed at address space within the summary that has no genuine underlying route, rather than silently black-holing it or misdirecting it toward an unrelated contributing route's next hop. The aggregate route itself remains active and installed throughout this process — a gap in contributing coverage does not deactivate the aggregate, since the aggregate's activation depends only on at least one contributing route being active, which is satisfied here by both existing /24 blocks. There is also no default route present in this scenario to fall back upon. Reference topics: Junos Enterprise Routing – Protocol Independent Routing, Aggregate Route Reject Behavior for Uncovered Address Space.

OSPF neighbor state progression, as defined in RFC 2328 and displayed by Junos through show ospf neighbor, moves through a well-defined set of named states: Down, Attempt, Init, 2-Way, ExStart, Exchange, Loading, and Full. Down is the initial state, indicating no Hello packets have been recently received from a potential neighbor on that interface; it is a genuine, valid OSPF state and is correctly included here. Init indicates that a Hello packet has been received from the neighbor, but that neighbor has not yet listed the local router's own router ID within its Hello packet, so bidirectional communication has not yet been confirmed; this too is a standard, valid state. Loading occurs after the Exchange state, during which Database Description packets have been fully exchanged and the router is now actively requesting the specific, more-detailed LSAs it identified as missing or outdated from its neighbor via Link State Request packets; it is likewise a standard, valid OSPF neighbor state. 'Established' is not an OSPF state at all — that terminology belongs to BGP's finite state machine, where Established represents the fully operational session state; the OSPF equivalent concept is instead called Full. 'Reject' is not a recognized OSPF neighbor state under any circumstance and does not appear anywhere in the RFC 2328 state machine, making it an invalid distractor as well. Reference topics: Junos Enterprise Routing – OSPF, The OSPF Neighbor State Machine.