Hard Difficulty Questions

IGMPv2 leave messages are received on an interface without active listeners.

Why it fails: Unsolicited or extra leaves do not cause RPF failures.

PIM hello messages are exchanged with an incorrect hold time.

Why it fails: Hold time mismatches affect adjacency timers, not the RPF check.

set routing-options graceful-restart ospf helper

Why it fails: OSPF graceful restart is configured under protocols ospf, not routing-options.

set protocols ospf graceful-restart router-role helper

Why it fails: The router-role keyword is invalid here.

set protocols ospf helper-mode enable

Why it fails: This is not the correct Junos syntax.

captive-portal-profile

Why it fails: Incorrect. Captive portal profiles are configured under access hierarchies, not dot1x.

radius-server-group

Why it fails: Incorrect. RADIUS server groups are configured under access-profile, not dot1x interface.

All participating PEs simultaneously forward BUM traffic to maximize bandwidth utilization.

Why it fails: Simultaneous BUM forwarding by multiple PEs would cause traffic duplication; only the DF forwards BUM traffic.

MAC mobility sequence numbers are reset to zero during the election.

Why it fails: MAC mobility sequence numbers are unaffected by DF elections.

During the initial import processing from EBGP peers before next-hop resolution.

Why it fails: Import policy runs on routes received from EBGP peers, before any BGP route selection, and as-path prepend is an export action applied to advertisements. It is tempting because import processing does precede selection, but this policy is outbound, so it is evaluated after best-path selection.

Before the best path is selected, affecting the local routing table calculation.

Why it fails: Outbound policy is evaluated after the local best path is chosen, when advertising to peers; it cannot alter the local routing table calculation. It is tempting because policy can influence selection via import, but export prepending only affects what neighbours receive.

During the route selection algorithm right after MED comparison.

Why it fails: Route selection completes with best-path determination before any export policy runs; MED comparison is an internal step, not where outbound policy attaches. It is tempting because MED and as-path both influence path preference, but export prepending occurs after selection, not mid-algorithm.

class

Why it fails: In 'class' mode, the switch allocates power based on the detected class of the device (e.g., Class 4 for PoE+). This reserves a fixed amount per class, not the actual consumption. It does not dynamically adjust to real-time power draw, so it may over-allocate and waste budget.

static

Why it fails: In 'static' mode, the switch allocates a fixed amount of power per port regardless of the device's class or consumption. This is the least efficient mode and does not adapt to actual usage. It is not suitable when dynamic allocation based on consumption is desired.

priority

Why it fails: 'Priority' is not a valid PoE management mode on EX Series switches. PoE management modes include 'class', 'consumption', and 'static'. Priority is a separate concept used for power allocation when the budget is exceeded, not a mode itself.

Disable link-state acknowledgement pacing globally.

Why it fails: Disabling link-state acknowledgement pacing globally removes the delay between LSA acknowledgements, but it risks flooding bursts and retransmissions that slow convergence under load. Pacing is tempting because it throttles acknowledgement traffic, yet tuning it per interface, not disabling it globally, is the optimisation.

Convert all backbone areas into completely stubby areas.

Why it fails: Completely stubby areas suppress Type 5 and Type 3 LSAs, but the backbone area 0 cannot be configured as a stub of any kind because it must carry inter-area and external reachability. Stubby areas are tempting because they shrink LSDBs in non-backbone areas, which does aid convergence.

Increase the SPF hold-down timer to allow network stabilization before running computations.

Why it fails: Increasing the SPF hold-down timer delays route computation after a topology change, lengthening convergence rather than optimising it. Hold-down is tempting because damping frequent SPF runs reduces CPU load in unstable networks, but the stem asks for faster convergence in a large enterprise.

IGMP snooping querier election redundancy across core switches

Why it fails: IGMP snooping querier redundancy applies to Layer 2 switch ports, not Layer 3 RP redundancy.

Static RP configuration with multiple backup RP IP addresses configured on every router

Why it fails: PIM static RP does not natively support dynamic multi-RP fallback without BSR or Anycast RP.

Use default bridge priority values on all core switches to allow automated root election.

Why it fails: Relying on default priorities (32768) can lead to arbitrary and suboptimal root bridge selection.

Disable Spanning Tree entirely on all access ports to ensure faster convergence.

Why it fails: Disabling spanning tree entirely risks catastrophic loops if a rogue switch is connected.

The switch port must be configured as a BGP peer.

Why it fails: BGP routing has no bearing on physical PoE power delivery.

The IP phone must be running Junos OS.

Why it fails: IP phones run their own vendor operating systems, not Junos OS.

show spanning-tree interface

Why it fails: Displays STP port states, not LLDP or PoE status.

show chassis routing-engine

Why it fails: Displays routing engine CPU and memory, unrelated to LLDP/PoE.

set protocols ospf area 0.0.0.0 interface xe-0/0/0.0 disable-dr

Why it fails: This command does not exist.

set protocols ospf area 0.0.0.0 interface xe-0/0/0.0 drother-only

Why it fails: This command does not exist.

set poe power-budget-threshold 80

Why it fails: Threshold statements trigger SNMP traps or syslog warnings, they do not control port shedding order.

set poe management-mode class-based

Why it fails: Management-mode determines how power is calculated (class vs consumption), not shedding priority.

set interfaces all poe shutdown-on-overload

Why it fails: This is not a valid Junos interface PoE statement.

Applying multiple rewrite rules causes an automatic system kernel crash

Why it fails: Junos accepts multiple rewrite rules on one interface without crashing; the kernel enforces one rule per rewrite type, so a DSCP and an 802.1p rule coexist. The crash claim is tempting as a dramatic explanation for misremarking, but the real cause is per-type rule interaction, not instability.

Only one rewrite rule total can be applied per logical interface regardless of type

Why it fails: Junos allows one rewrite rule per type per logical interface — a DSCP rule and an 802.1p rule can coexist, each remarking its own field. The single-rule claim is tempting because it sounds like a clean simplification, but it contradicts the per-type granularity that explains the observed remarking.

Only Layer 2 rewrite rules are permitted on trunk ports

Why it fails: Junos permits both a DSCP rewrite and an IEEE 802.1p rewrite on the same interface, each operating on its own header field; restricting Layer 2 rewrites to trunk ports misstates the rule. It tempts because 802.1p rewriting is commonly configured on trunk interfaces carrying tagged traffic.

forwarding-class

Why it fails: Forwarding-class assigns a new class to the packet.

transmit

Why it fails: Transmit allows the packet to pass.

mark-action

Why it fails: Mark-action is used to remark the packet header.

Junos rejects configurations where both BA and MF classifiers are applied to the same interface

Why it fails: Junos permits both classifier types on one interface and resolves them by precedence, so the configuration is accepted. It is tempting because some platforms restrict combining classifier types, but on Junos the documented behaviour is ordered evaluation, not rejection.

Both classifiers are executed simultaneously in hardware without precedence

Why it fails: Junos applies a defined precedence between the two classifier types rather than running them concurrently; hardware evaluates them in a fixed sequence. It is tempting because both classifiers do operate in hardware, but that shared execution plane does not mean simultaneous, order-independent processing.

Multi-field classification is evaluated first, followed by behavior aggregate classification

Why it fails: Junos evaluates the behaviour aggregate classifier first, then the multi-field classifier, so this reverses the documented order. It is tempting because multi-field classifiers are more granular and appear logically prior, but granularity does not determine processing sequence on ingress.

Reconfigure the port from access mode to trunk mode.

Why it fails: Trunk versus access mode affects VLAN tagging of traffic, not Power over Ethernet detection or delivery. A hardware error is a physical-layer PoE fault, so changing the link mode cannot resolve it; trunk reconfiguration is correct when a phone needs multiple VLANs, such as voice and data separation.

Modify the LLDP-MED network policy timeout value to allow longer initialization.

Why it fails: LLDP-MED network policy timeout governs how long a phone waits for VLAN and QoS policy information, not power negotiation. A hardware error points to the PoE controller or port hardware, so extending the timeout would not clear it; LLDP-MED tuning suits phones that power up but fail to receive voice VLAN settings.

Disable spanning tree protocol on the interface.

Why it fails: Spanning tree operates at Layer 2 and has no bearing on Power over Ethernet delivery; a hardware error indicates a physical or controller fault. Disabling STP is relevant when resolving Layer 2 loops or topology convergence issues, not power faults.

show igmp bsr

Why it fails: IGMP does not manage PIM BSR functions.

show msdp bsr-state

Why it fails: BSR is a PIM function, not MSDP.

show multicast bsr

Why it fails: This is an invalid operational command.

It removes the Originator ID and replaces the Cluster List with its own cluster ID.

Why it fails: The original Originator ID must be preserved so the internal sender can detect loops.

It increments the Originator ID value by one and clears the Cluster List.

Why it fails: Originator ID is an IP address representing the router ID and is not incremented.

It clears both the Originator ID and Cluster List to reset loop detection for the local cluster.

Why it fails: Clearing these attributes would reintroduce the risk of internal BGP routing loops.

Configure 'set access-profile captive-portal multiple-logins per-port'.

Why it fails: Incorrect. Captive portal profiles do not manage dot1x supplicant limits.

Set the port mode to trunk and enable voice-vlan stacking.

Why it fails: Incorrect. Trunk mode alone does not bypass supplicant limits.

Configure the interface with 'set protocols dot1x interface ge-0/0/1 mac-radius multiple-clients'.

Why it fails: Incorrect. This command does not exist in Junos OS.