High Availability practice questions

The backup Routing Engine must be physically removed from the chassis during the upgrade.

Why wrong: Removing the backup RE would break redundancy and abort the ISSU process.

All physical interfaces must be manually disabled prior to issuing the request system software in-service command.

Why wrong: Disabling physical interfaces would cause an outage, contradicting the purpose of ISSU.

All routing protocols must be migrated from OSPF to IS-IS before starting ISSU.

Why wrong: Protocol choice does not dictate ISSU eligibility as long as graceful restart / NSR is supported.

Decrease the VRRP advertisement interval on the backup switch.

Why wrong: Shorter advertisement intervals increase protocol overhead but do not change master selection priority.

Set the virtual router identifier (VRID) to a lower integer value on the preferred switch.

Why wrong: VRID must match across redundant routers in the same broadcast domain; it does not affect master election.

Disable the VRRP preempt feature on both routers.

Why wrong: Disabling preemption prevents a higher priority router from taking over if a lower priority router is already master.

All member switches across both partitions automatically shut down all data interfaces to prevent loops.

Why wrong: Junos does not automatically shut down all data interfaces across a split unless specific MAC-sec or proprietary scripts are used.

The backup routing engine instantly shuts down its control plane daemon permanently.

Why wrong: The backup RE remains active in its partition unless split-brain mitigation actions kick in.

The entire Virtual Chassis reboots simultaneously until stacking cables are re-seated.

Why wrong: Rebooting without manual or programmatic triggers does not happen automatically upon a cable break.

To instantly drop all adjacencies and force an immediate full SPF recalculation across the network.

Why wrong: Dropping adjacencies defeats the purpose of Graceful Restart, which aims to suppress routing changes.

To automatically upgrade Junos OS images without rebooting the forwarding plane.

Why wrong: In-Service Software Upgrade (ISSU) is responsible for software upgrades without control plane downtime, not Graceful Restart alone.

To synchronize firewall filter counters between primary and backup Routing Engines.

Why wrong: Firewall filter counter sync is handled by GRES and daemon state synchronization, not OSPF Graceful Restart.

Disable Graceful Routing Engine Switchover (GRES) on the backup routing engine.

Why wrong: GRES preserves control plane state during switchover; it does not dictate mastership priority.

Enable preemption globally on all members in the virtual-chassis configuration.

Why wrong: Preemption is enabled by default in Junos Virtual Chassis; priority dictates the primary election.

Configure the non-preferred switch with a routing-engine user account restriction.

Why wrong: User accounts do not impact hardware-level Virtual Chassis mastership elections.

Run 'show chassis routing-engine' to verify that the remote neighbor has updated its local RE priority.

Why wrong: Chassis routing-engine command shows local RE status, not BGP neighbor capabilities.

Run 'show lacp statistics ae0' to see if LACP packets are being suppressed during restart.

Why wrong: LACP statistics show link aggregation health, not BGP protocol restart status.

Run 'show vrrp summary' to check if the BGP neighbor has assumed the master VRRP role.

Why wrong: VRRP is a layer 2 gateway redundancy protocol, unrelated to BGP routing sessions.

The interface will only respond to LACP packets and never transmit them.

Why wrong: That describes LACP passive mode.

Active mode can only be used when connecting Juniper switches to non-Juniper servers.

Why wrong: LACP active mode can be used with any standards-compliant LACP peer.

LACP active mode requires static pinning of member links and disables dynamic hash selection.

Why wrong: LACP dynamically negotiates member links and does not require static pinning.

LAG interfaces do not require explicit definition under the chassis stanza.

Why wrong: You must define the aggregated-devices Ethernet device-count under the chassis hierarchy before configuring 'ae' interfaces.

LACP multi-chassis mode must be enabled for a single switch LAG.

Why wrong: Multi-chassis LACP (MC-LAG) is only required when aggregating links across two separate physical routing devices.

LACP heartbeat intervals are strictly hardcoded to 1 second and cannot be modified.

Why wrong: Junos allows tuning LACP intervals between slow (30 seconds) and fast (1 second).

Configure 'set protocols lacp minimum-active-ports 2'.

Why wrong: LACP configuration parameters for aggregated Ethernet interfaces belong under the [edit interfaces aeX aggregated-ether-options] hierarchy.

Configure 'set chassis aggregated-devices ethernet link-threshold 2'.

Why wrong: Chassis hierarchy only defines device counts, not operational link thresholds.

Configure 'set switch-options lacp threshold 2'.

Why wrong: Switch-options does not control LACP link thresholds.

show system backup-router

Why wrong: This command shows fallback gateway configurations.

show virtual-chassis gres

Why wrong: Virtual-chassis gres is not a valid operational command string.

show gres statistics

Why wrong: There is no 'show gres statistics' command in Junos OS.

Both Routing Engines are rebooted simultaneously, relying entirely on OSPF Graceful Restart helper mode.

Why wrong: Rebooting both REs simultaneously would cause a total control plane outage; ISSU specifically avoids this.

The forwarding plane is restarted first, followed by a simultaneous upgrade of the dual REs.

Why wrong: The forwarding plane remains operational throughout an ISSU.

The primary Routing Engine is wiped and reloaded while data traffic is redirected through the console port.

Why wrong: Console ports are management interfaces and cannot carry production data traffic.

Disable Virtual Chassis on both switches to allow VRRP to function properly.

Why wrong: VRRP can run across Virtual Chassis interfaces without disabling the Virtual Chassis architecture.

Remove LACP from all aggregated interfaces connected to the VRRP routers.

Why wrong: LACP does not interfere with VRRP advertisement transmission.

Configure Nonstop Active Routing (NSR) under the VRRP hierarchy.

Why wrong: NSR is an interior gateway protocol feature, not a configurable parameter directly under VRRP.

Mixed speed links automatically drop to 1G to maintain backward compatibility without administrative intervention.

Why wrong: VCPs do not auto-negotiate down like standard Ethernet access links unless explicitly supported by the optic type.

Junos automatically load-balances stacking traffic across 1G and 10G links using weighted round-robin.

Why wrong: Stacking ports operate at fixed configured speeds and do not dynamically load-balance like data LAGs.

Only the 10G ports will carry control plane traffic while 1G ports are restricted to data transit.

Why wrong: Stacking links carry both control plane and member data traffic indiscriminately.

A loopback IP address configured on the master Routing Engine.

Why wrong: Loopback addresses are typically host-specific (/32) and not part of the client broadcast subnet.

A public IP address provided by your upstream Internet Service Provider.

Why wrong: Virtual gateway IPs are typically private internal subnet gateways, though they can be public if the subnet requires it; however, subnet matching is the core rule.

A reserved multicast address in the 224.0.0.18 range.

Why wrong: 224.0.0.18 is the destination IP for VRRP control packets, not the virtual gateway IP assigned to clients.

show lacp statistics

Why wrong: This command displays LACP packet counters for aggregated interfaces.

show vrrp summary

Why wrong: This command shows VRRP router groups and their active master states.

NSR automatically configures VRRP tracking on all local VLAN interfaces.

Why wrong: VRRP tracking must be configured manually.

NSR allows software upgrades to be performed without ever rebooting either Routing Engine.

Why wrong: Software upgrades still require rebooting the REs sequentially; NSR does not eliminate reboots.

NSR replaces LACP negotiation with static member pinning during link failures.

Why wrong: NSR is a routing protocol high-availability feature, unrelated to LACP.

show lacp vrrp-status

Why wrong: This command does not exist in Junos OS.

show spanning-tree vrrp

Why wrong: Spanning tree and VRRP are distinct protocols; this command is invalid.

show chassis vrrp

Why wrong: VRRP is a routing/layer 3 protocol, not a chassis component.

Rely on automatic plug-and-play assignment, which permanently locks member IDs based on initial boot order.

Why wrong: Auto-assignment can change if switches are booted out of order or replaced, making pre-provisioning necessary for stability.

Disable GRES so that member IDs do not synchronize across the stack.

Why wrong: GRES has no impact on Virtual Chassis member ID assignment.

Configure the MAC address of each switch under the [edit chassis vrrp] hierarchy.

Why wrong: Chassis vrrp hierarchy does not exist; VRRP is configured under interfaces.

The Virtual Chassis primary routing engine priority is set too low.

Why wrong: VC priority affects mastership election, not LACP packet exchanges on individual physical ports.

VRRP preemption is enabled on the aggregated interface.

Why wrong: VRRP cannot be configured directly on an 'ae' interface in the same manner as standard routed VLAN interfaces.

GRES is disabled on the EX4300 switch.

Why wrong: GRES affects Routing Engine failover, not interface-level LACP protocol timers.

The Virtual Chassis stacking cable was disconnected during the switchover.

Why wrong: MX series routers use redundant Routing Engines in a modular chassis, not Virtual Chassis stacking cables.

VRRP preemption caused the default gateway IP to shift to the backup engine.

Why wrong: VRRP operates at Layer 3 on interfaces and is independent of BGP daemon state synchronization.

The LACP timeout on the aggregated uplink was set to slow mode.

Why wrong: LACP timeout does not affect BGP routing engine switchover states.