JNCIS-ENT · domain
High Availability
This domain covers high availability on Juniper EX Series and Junos devices, focusing on Link Aggregation Groups, Virtual Chassis, and Routing Engine election. Questions test configuration requirements, operational commands, and failover behavior. You must know how LAG modes interact with server settings and how Virtual Chassis roles are determined and verified.
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Start 20-question practice test →What this domain covers
What to know about High Availability
Be able to configure and verify LAGs and Virtual Chassis on Junos EX switches. Know that static LAG requires no LACP on the switch interface, and that Virtual Chassis primary election uses priority, member ID, and role. Use show virtual-chassis to confirm member IDs, priorities, and roles.
Watch out for
Common High Availability exam traps
- ▸Assuming LACP is required for all LAGs; static LAG mode needs no LACP but must match server settings.
- ▸Confusing Virtual Chassis election criteria, such as mixing up priority, member ID, and role.
- ▸Using the wrong show command for Virtual Chassis status, like show chassis instead of show virtual-chassis.
Question index
All High Availability questions (43)
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You are configuring VRRP on an EX4300 switch acting as the master for VLAN 100. You want the master to immediately relinquish its role if its uplink toward the core fails, so that the backup can take over without waiting for the default VRRP advertisement timer to expire. Which VRRP feature should you configure?
Medium2Which THREE actions occur when a Junos router with GRES and NSR enabled performs a manual Routing Engine switchover while running OSPF and BGP? (Choose three)
Hard3Which THREE conditions can cause a Virtual Chassis primary Routing Engine election or switchover to occur unexpectedly? (Choose three)
Hard4An engineer is preparing to perform an In-Service Software Upgrade (ISSU) on a pair of dual-RE MX240 routers. Which condition must be met to ensure the ISSU succeeds without dropping traffic?
Hard5An engineer configures a Virtual Chassis using EX4300 switches. To ensure member IDs are assigned consistently even if physical positions change, how should the administrator provision the member IDs?
Medium6When configuring a Link Aggregation Group (LAG) on a Juniper switch, what is the naming convention used for the aggregated interface in the Junos CLI?
Easy7You are performing a pre-check for an ISSU on an MX series router. You execute 'request system software in-service check' and the system reports an error indicating that graceful restart or NSR is not properly configured for active routing protocols. How do you resolve this?
Hard8You are troubleshooting a Virtual Chassis where member 0 has failed completely. The replacement switch arrives. Before inserting it into the running Virtual Chassis ring, what critical precaution must be taken regarding Junos OS software versions?
Hard9An administrator is configuring Graceful Restart on a pair of Juniper MX series routers running OSPF. What is the primary purpose of Graceful Restart in this scenario?
Easy10An engineer wants to configure Nonstop Active Routing (NSR) alongside GRES on an MX204 router running OSPF. What is the primary operational benefit of enabling NSR compared to running GRES alone?
Medium11An engineer needs to configure a Link Aggregation Group (LAG) between two Juniper EX4300 switches to provide redundant uplinks to a core router. Which statements regarding the LACP configuration requirements on the EX4300 switch must be met?
Medium12You are configuring VRRP between two EX4600 switches to provide a default gateway for a VLAN. To ensure that the switch with the higher physical interface capacity assumes the master role, what parameter should you adjust?
Medium13Which THREE conditions must be met to successfully execute an In-Service Software Upgrade (ISSU) on a dual-RE Juniper routing platform? (Choose three)
Medium14Which CLI command is used to manually initiate a Routing Engine switchover on an MX series router configured with GRES?
Easy15An administrator is configuring VRRP on an EX4300 switch and wants to ensure that when the primary router recovers from a failure, it immediately reclaims the master role from the backup router. Which VRRP configuration parameter controls this behavior?
Medium16An EX4300 Virtual Chassis has GRES enabled. During a primary Routing Engine failure, what happens to the backup Routing Engine?
Medium17Which CLI command displays the operational status and roles of all members in a Juniper EX Series Virtual Chassis?
Easy18Which operational command allows you to view the real-time status of LACP packet exchanges and partner system IDs for an aggregated interface on a Junos switch?
Easy19An EX4300 Virtual Chassis experiences a split-brain condition due to a failure of all stacking cables between members 0/1 and members 2/3. How does Junos handle this scenario by default?
Medium20Which THREE statements accurately describe the behavior and configuration of VRRP tracking on Junos devices? (Choose three)
Hard21When configuring VRRP on a Juniper router, what IP address must be assigned as the virtual IP address for the group?
Easy22Which THREE parameters can be tuned under the VRRP hierarchy in Junos to customize failover timing and behavior? (Choose three)
Medium23When planning an In-Service Software Upgrade (ISSU) on a Juniper routing platform, what is the behavior of the Routing Engines during the execution of the upgrade command?
Hard24You are analyzing a core Juniper MX router after an ISSU upgrade procedure completed. You notice that BGP sessions dropped immediately after the final routing engine rebooted. What post-upgrade verification step should have been performed to prevent unexpected protocol drops during ISSU?
Hard25You are troubleshooting a VRRP deployment where two EX4600 switches are acting as redundant gateways for several VLANs. Clients on VLAN 10 report intermittent gateway unreachability. You notice that VRRP mastership frequently flips between Switch A and Switch B. What is the most effective way to stabilize VRRP mastership?
Hard26Which TWO items are required when configuring VRRP on a Juniper router interface? (Choose two)
Easy27You are troubleshooting a Link Aggregation Group (LAG) between an EX4300 switch and a third-party switch. Member links are flapping intermittently. Examination of system logs reveals LACP timeout errors. What is the most likely cause?
Hard28Which THREE criteria are evaluated by Junos when electing the primary Routing Engine in an EX Series Virtual Chassis? (Choose three)
Medium29You are configuring a Link Aggregation Group (LAG) with LACP on an EX3400 switch. You want to ensure that the interface bundle drops traffic if fewer than two active member links are operational. Which feature configuration achieves this?
Medium30You are troubleshooting an issue where an EX4300 Virtual Chassis fails to boot after adding a new switch member. The system console displays errors regarding incompatible Junos images and hardware mismatch on the Virtual Chassis ports. What is the correct procedure to recover and integrate the new member?
Hard31An administrator is setting up VRRP tracking on an EX4300 switch interface. If the uplink interface monitoring the core network fails, what should happen to the VRRP priority on the gateway interface?
Medium32Which TWO options represent valid benefits of configuring Link Aggregation Groups (LAG)? (Choose two)
Easy33A Juniper EX4300 Virtual Chassis has four members. You want to ensure that if the master Routing Engine fails, the backup takes over and the new master is reachable through the same management IP address without any manual intervention. Which statement describes the correct behavior?
Hard34You are configuring Multi-Chassis Link Aggregation (MC-LAG) across two Juniper switches acting as separate control plane devices. Which protocol is used between the peer switches to synchronize state and ensure MAC address table consistency across the MC-LAG domain?
Hard35Which operational command displays the configured member IDs, priorities, and roles in an EX Series Virtual Chassis?
Easy36Which configuration command enables Graceful Routing Engine Switchover (GRES) globally on a Juniper routing platform?
Easy37An engineer configures a LAG between an EX4300 switch and a server. The server uses static LAG mode (no LACP). How must the Junos switch interface be configured to successfully form the bundle?
Medium38Which TWO commands are used to verify link aggregation and LACP operational status on a Juniper switch? (Choose two)
Easy39You are configuring a Link Aggregation Group (LAG) on an EX series switch. Which statement is correct regarding LACP active mode?
Easy40Which CLI command displays the packet statistics, errors, and drop counters for a Link Aggregation Group (LAG) named ae0?
Easy41You are verifying BGP Graceful Restart helper mode on a Juniper router. A peering router restarts its control plane. What output or verification command confirms that your router is acting as a Graceful Restart helper for the peer?
Hard42An administrator configures a Link Aggregation Group (LAG) using LACP between two EX series switches. The link fails to aggregate, and the log shows 'LACP status: Expired'. What does the 'Expired' state indicate?
Medium43Which TWO methods are used to connect switches in a Juniper EX Series Virtual Chassis? (Choose two)
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Frequently asked questions
- What does the High Availability domain cover on the JNCIS-ENT exam?
- Be able to configure and verify LAGs and Virtual Chassis on Junos EX switches. Know that static LAG requires no LACP on the switch interface, and that Virtual Chassis primary election uses priority, member ID, and role. Use show virtual-chassis to confirm member IDs, priorities, and roles.
- How many questions are in this domain?
- This page lists all 43 High Availability questions in the JNCIS-ENT question bank. The actual exam draws from this domain proportionally to its weighting in the official exam blueprint.
- What is the best way to practise this domain?
- Start with a short focused session (10 questions) to identify gaps, then work through explanations. Repeat with a longer session once the weak areas feel solid.
- Can I practise only High Availability questions?
- Yes — the session launcher on this page filters questions to this domain only. Choose any session length for inline explanations and scoring.