Juniper JN0-650 Practice Test 6
Question 50
A MAC address keeps moving between ports because a physical loop exists. Which technical principle BEST explains the Ethernet MAC learning and flooding decision?
- ESI identifies a shared multihomed Ethernet segment to EVPN control plane.
- Ethernet switches learn source MACs per VLAN and flood unknown destinations until learned.
- Private VLAN community ports have scoped peer reachability and promiscuous ports serve shared resources.
- VLAN delivery requires consistent port roles tags and eligible forwarding state at every hop.
Explanation
Correct Answer
B:Ethernet switches learn source MACs per VLAN and flood unknown destinations until learned. In this situation, the relevant action is to identify MAC learning state and remediate loops or incorrect topology.
Incorrect Answers
A:ESI identifies a shared multihomed Ethernet segment to EVPN control plane. That principle is related to Ethernet segment identifier ESI consistency, not the main Ethernet MAC learning and flooding choice. A loop can cause rapid MAC movement and high broadcast utilization.
C:Private VLAN community ports have scoped peer reachability and promiscuous ports serve shared resources. That principle is related to Private VLAN community and promiscuous roles, not the main Ethernet MAC learning and flooding choice. A loop can cause rapid MAC movement and high broadcast utilization.
D:VLAN delivery requires consistent port roles tags and eligible forwarding state at every hop. That principle is related to Layer 2 trunk VLAN mismatch diagnosis, not the main Ethernet MAC learning and flooding choice. A loop can cause rapid MAC movement and high broadcast utilization.
Question 51
A provider accidentally announces a full internet table into a small branch BGP session. Which configuration or operational step BEST meets the stated requirement?
- Set a policy-based higher local preference for preferred internal BGP paths.
- Apply supported BGP accepted-prefix limits and operational alerts.
- Change one interface description to max-prefix and expect a route-count limit.
- Apply a scoped BGP next-hop-self or next-hop resolution design at the appropriate edge.
Explanation
Correct Answer
B:Apply supported BGP accepted-prefix limits and operational alerts. BGP prefix controls limit received-route scale and safeguard resources. The expected validation is that excessive routes trigger the intended protection without destabilizing unrelated sessions.
Incorrect Answers
A:Set a policy-based higher local preference for preferred internal BGP paths. This addresses BGP LOCAL_PREF outbound exit selection rather than the required BGP prefix-limit peer protection decision. BGP prefix controls limit received-route scale and safeguard resources.
C:Change one interface description to max-prefix and expect a route-count limit. This is a risky or ineffective shortcut for BGP prefix-limit peer protection. No route-count guard can overwhelm route memory or control-plane processing.
D:Apply a scoped BGP next-hop-self or next-hop resolution design at the appropriate edge. This addresses iBGP next-hop-self on edge rather than the required BGP prefix-limit peer protection decision. BGP prefix controls limit received-route scale and safeguard resources.
Question 52
Guest devices must accept a portal workflow before gaining restricted internet access. After deploying the recommended Captive portal web authentication change, which result MOST directly verifies success?
- A compliant supplicant authenticates and the switch authorizes its port policy.
- Outgoing packet captures show the expected DSCP values on the selected interface.
- The guest is redirected appropriately and receives only permitted post-portal access.
- Access-Accept authorizes approved access while explicit rejections remain denied.
Explanation
Correct Answer
C:The guest is redirected appropriately and receives only permitted post-portal access. This is the directly observable outcome for Captive portal web authentication. Captive portal web authentication is not a replacement for cryptographic endpoint supplicant validation.
Incorrect Answers
A:A compliant supplicant authenticates and the switch authorizes its port policy. This validates 802.1X supplicant authenticator RADIUS roles but does not directly demonstrate the required Captive portal web authentication result. Captive portal web authentication is not a replacement for cryptographic endpoint supplicant validation.
B:Outgoing packet captures show the expected DSCP values on the selected interface. This validates DSCP egress rewrite rules but does not directly demonstrate the required Captive portal web authentication result. Captive portal web authentication is not a replacement for cryptographic endpoint supplicant validation.
D:Access-Accept authorizes approved access while explicit rejections remain denied. This validates RADIUS Access-Accept versus Access-Reject handling but does not directly demonstrate the required Captive portal web authentication result. Captive portal web authentication is not a replacement for cryptographic endpoint supplicant validation.
Question 53
A network team needs to distinguish class-mapping errors from physical link saturation. Which next investigation or correction is MOST appropriate?
- Inspect drop-profile thresholds and queue drop counters under load.
- Gather interface CoS statistics flow captures and per-class latency before modifying rates.
- Measure policer counters and packet loss at below and above configured rate.
- Disable all class-of-service monitoring because one show configuration command succeeded.
Explanation
Correct Answer
B:Gather interface CoS statistics flow captures and per-class latency before modifying rates. This checks whether under controlled load intended voice QoS remains protected while other classes retain service.
Incorrect Answers
A:Inspect drop-profile thresholds and queue drop counters under load. That check applies chiefly to RED WRED drop profile thresholds, not the current CoS end-to-end verification of drop behavior issue. Successful CoS needs consistent ingress classification egress scheduling and congestion management.
C:Measure policer counters and packet loss at below and above configured rate. That check applies chiefly to Junos ingress policer rate limit, not the current CoS end-to-end verification of drop behavior issue. Successful CoS needs consistent ingress classification egress scheduling and congestion management.
D:Disable all class-of-service monitoring because one show configuration command succeeded. That bypass leaves the CoS end-to-end verification of drop behavior issue unresolved. Inspecting only a configured class name can hide actual drops and misclassification.
Question 54
A customer edge inserts stacked tags that an intermediate switch drops as malformed. Which technical principle BEST explains the QinQ tag protocol EtherType compatibility decision?
- L2PT encapsulates selected customer Layer 2 control frames across a provider domain.
- Forwarding classes express per-hop traffic treatment and map to transmission queues.
- VLAN stacking requires compatible tag interpretation and consistent port behavior.
- MSTP can group VLANs into instances with independent root bridge elections.
Explanation
Correct Answer
C:VLAN stacking requires compatible tag interpretation and consistent port behavior. In this situation, the relevant action is to align supported outer-tag TPID and VLAN-stacking configuration across participating devices.
Incorrect Answers
A:L2PT encapsulates selected customer Layer 2 control frames across a provider domain. That principle is related to L2PT customer BPDU tunneling, not the main QinQ tag protocol EtherType compatibility choice. Mismatched TPID assumptions can cause customer frames to be dropped.
B:Forwarding classes express per-hop traffic treatment and map to transmission queues. That principle is related to Junos forwarding class to queue mapping, not the main QinQ tag protocol EtherType compatibility choice. Mismatched TPID assumptions can cause customer frames to be dropped.
D:MSTP can group VLANs into instances with independent root bridge elections. That principle is related to MSTP instance root selection, not the main QinQ tag protocol EtherType compatibility choice. Mismatched TPID assumptions can cause customer frames to be dropped.
Question 55
Four OSPF routers share a multiaccess VLAN and network operators want a predictable DR. Which configuration or operational step BEST meets the stated requirement?
- Use a consistent OSPF reference-bandwidth policy across the intended routing domain.
- Configure compatible supported point-to-point OSPF network types when appropriate.
- Tune eligible OSPF interface priority and plan an explicit election event where required.
- Set the lowest priority to zero and expect that router to win the DR election.
Explanation
Correct Answer
C:Tune eligible OSPF interface priority and plan an explicit election event where required. OSPF DR election on broadcast networks is priority based and nonpreemptive under normal conditions. The expected validation is that the intended eligible DR and BDR appear on the broadcast segment after reelection.
Incorrect Answers
A:Use a consistent OSPF reference-bandwidth policy across the intended routing domain. This addresses OSPF reference bandwidth and high-speed links rather than the required OSPF designated router election broadcast LAN decision. OSPF DR election on broadcast networks is priority based and nonpreemptive under normal conditions.
B:Configure compatible supported point-to-point OSPF network types when appropriate. This addresses OSPF point-to-point network type rather than the required OSPF designated router election broadcast LAN decision. OSPF DR election on broadcast networks is priority based and nonpreemptive under normal conditions.
D:Set the lowest priority to zero and expect that router to win the DR election. This is a risky or ineffective shortcut for OSPF designated router election broadcast LAN. Assuming every high-priority router instantly replaces the current DR leads to wrong operational expectations.
Question 56
An enterprise must avoid installing an unwanted OSPF route in the local routing table. After deploying the recommended OSPF routing policy import filtering change, which result MOST directly verifies success?
- The preferred external route follows correct E1 total metric or E2 selection rules.
- The local route table follows documented acceptance policy while LSDB visibility is understood.
- Critical VLAN stays present and dynamic VLANs appear only when advertised.
- Remote IPv6 routers receive only the intended OSPFv3 external destinations.
Explanation
Correct Answer
B:The local route table follows documented acceptance policy while LSDB visibility is understood. This is the directly observable outcome for OSPF routing policy import filtering. Local route preference or policy and OSPF flooding are distinct decisions.
Incorrect Answers
A:The preferred external route follows correct E1 total metric or E2 selection rules. This validates OSPF external type-one versus type-two metrics but does not directly demonstrate the required OSPF routing policy import filtering result. Local route preference or policy and OSPF flooding are distinct decisions.
C:Critical VLAN stays present and dynamic VLANs appear only when advertised. This validates MVRP static versus dynamic registration but does not directly demonstrate the required OSPF routing policy import filtering result. Local route preference or policy and OSPF flooding are distinct decisions.
D:Remote IPv6 routers receive only the intended OSPFv3 external destinations. This validates OSPFv3 routing policy for external IPv6 but does not directly demonstrate the required OSPF routing policy import filtering result. Local route preference or policy and OSPF flooding are distinct decisions.
Question 57
A carrier-prepend policy makes one available route look less attractive to remote ASes. Select TWO statements that correctly combine the BGP AS_PATH loop prevention and length implementation, its evidence, or its governing principle.
- Add approved BGP community tags and match them in explicit import or export policies.
- Remove all route-target communities and claim an AS_PATH loop has been resolved.
- Selected routes have expected AS sequence and no local-AS loop.
- Implement ordered Junos policy terms with prefix match and explicit accept or reject decisions.
- Use deliberate AS-path policy without bypassing loop-prevention safeguards.
Explanation
Correct Answers
C:Selected routes have expected AS sequence and no local-AS loop. This is direct observable evidence for BGP AS_PATH loop prevention and length.
E:Use deliberate AS-path policy without bypassing loop-prevention safeguards. This is the intended implementation action for BGP AS_PATH loop prevention and length.
Incorrect Answers
A:Add approved BGP community tags and match them in explicit import or export policies. This belongs to BGP communities tagging routing intent, not the specified BGP AS_PATH loop prevention and length operation. BGP AS_PATH records AS traversal and participates in loop prevention and path selection.
B:Remove all route-target communities and claim an AS_PATH loop has been resolved. This would not be an appropriate BGP AS_PATH loop prevention and length decision. Ignoring the local-AS loop check can introduce unstable routing behavior.
D:Implement ordered Junos policy terms with prefix match and explicit accept or reject decisions. This belongs to Junos BGP policy term matching, not the specified BGP AS_PATH loop prevention and length operation. BGP AS_PATH records AS traversal and participates in loop prevention and path selection.
Question 58
A prepending policy unexpectedly modifies inbound routes rather than outbound announcements. Which technical principle BEST explains the BGP AS path prepend outbound advertisement decision?
- eBGP multihop and local-address controls align transport endpoints and TTL.
- Ethernet switches learn source MACs per VLAN and flood unknown destinations until learned.
- AS_PATH prepending may influence remote inbound selection but is not guaranteed to override peer policy.
- Import changes received-route eligibility while export governs what is sent to peers.
Explanation
Correct Answer
C:AS_PATH prepending may influence remote inbound selection but is not guaranteed to override peer policy. In this situation, the relevant action is to apply controlled AS_PATH prepending in export policy to appropriate external neighbors.
Incorrect Answers
A:EBGP multihop and local-address controls align transport endpoints and TTL. That principle is related to BGP loopback peering and multihop, not the main BGP AS path prepend outbound advertisement choice. Inserting prepends into all paths can cause unexpected global traffic shifts.
B:Ethernet switches learn source MACs per VLAN and flood unknown destinations until learned. That principle is related to Ethernet MAC learning and flooding, not the main BGP AS path prepend outbound advertisement choice. Inserting prepends into all paths can cause unexpected global traffic shifts.
D:Import changes received-route eligibility while export governs what is sent to peers. That principle is related to BGP import versus export policy direction, not the main BGP AS path prepend outbound advertisement choice. Inserting prepends into all paths can cause unexpected global traffic shifts.
Question 59
A user connects an unmanaged bridge that starts sending spanning-tree BPDUs. After deploying the recommended BPDU protection on access edges change, which result MOST directly verifies success?
- Active routes prefer the expected lowest cumulative OSPF metric.
- Isolated endpoints reach the intended shared gateway but not peer isolated ports.
- Rogue bridge BPDUs trigger the intended guard action without affecting valid trunks.
- Intended guest frames match their rule and general traffic uses the appropriate default.
Explanation
Correct Answer
C:Rogue bridge BPDUs trigger the intended guard action without affecting valid trunks. This is the directly observable outcome for BPDU protection on access edges. BPDU protection blocks unexpected spanning-tree participation at designated access edges.
Incorrect Answers
A:Active routes prefer the expected lowest cumulative OSPF metric. This validates OSPF path cost selection but does not directly demonstrate the required BPDU protection on access edges result. BPDU protection blocks unexpected spanning-tree participation at designated access edges.
B:Isolated endpoints reach the intended shared gateway but not peer isolated ports. This validates Private VLAN isolated port separation but does not directly demonstrate the required BPDU protection on access edges result. BPDU protection blocks unexpected spanning-tree participation at designated access edges.
D:Intended guest frames match their rule and general traffic uses the appropriate default. This validates Filter-based VLAN rule precedence but does not directly demonstrate the required BPDU protection on access edges result. BPDU protection blocks unexpected spanning-tree participation at designated access edges.
Question 60
During an operational risk review, this situation is reported: A provider changes its ASN and a previously stable BGP session stops opening. If the underlying control is neglected, which failure would MOST directly follow?
- Mis-scoped multicast can leak too far or fail to reach authorized hosts.
- Confusing local preference with Junos route preference can produce wrong active-route reasoning.
- Wrong peer-AS values cause BGP OPEN rejection despite TCP connectivity.
- Merely seeing multiple BGP routes does not prove load balancing occurs.
Explanation
Correct Answer
C:Wrong peer-AS values cause BGP OPEN rejection despite TCP connectivity. BGP OPEN exchange checks autonomous-system identity and capability compatibility. A useful corrective investigation is to inspect show bgp neighbor last error and BGP OPEN notification fields.
Incorrect Answers
A:BGP OPEN exchange checks autonomous-system identity and capability compatibility. Mis-scoped multicast can leak too far or fail to reach authorized hosts.
B:BGP OPEN exchange checks autonomous-system identity and capability compatibility. Confusing local preference with Junos route preference can produce wrong active-route reasoning.
D:BGP OPEN exchange checks autonomous-system identity and capability compatibility. Merely seeing multiple BGP routes does not prove load balancing occurs.
