User Interfaces practice questions

Use the 'commit and-quit' command to apply changes.

Why wrong: The 'commit and-quit' command commits the candidate configuration and immediately exits configuration mode, but it does not schedule any rollback. If the change disrupts access, the device will retain the new config until a human manually intervenes. Unlike 'commit confirmed', it offers no safety net for remote administrators who might get locked out.

Use the 'commit check' command before committing.

Why wrong: 'commit check' validates the syntax and logical semantics of the candidate configuration without activating it. Passing the check does not guarantee the change is safe, and after a normal subsequent commit there is no automatic rollback available. It is a pre-flight validation tool, not a safeguard against unsuccessful remote changes.

Use the 'rollback 0' command after committing.

Why wrong: 'rollback 0' in configuration mode loads the currently committed configuration as the candidate, effectively discarding uncommitted changes. After a commit, using 'rollback 0' then committing would manually revert to the previous config, but this requires outside access and does not happen automatically on a timeout. It is a manual recovery tool, not an automatic confirm mechanism.

show configuration interfaces ge-0/0/1

Why wrong: This command renders the stored interface configuration, such as the logical unit number, family addressing, speed, and description, from the configuration database rather than from the live router's kernel or forwarding planes. It will not report carrier presence, link flaps, or current protocol adjacency state, so it cannot answer the question of whether ge-0/0/1 is actually operational. A configuration can look correct even when the interface is down due to external causes like a disconnected cable or remote fault.

monitor interface ge-0/0/1

Why wrong: The monitor interface command enters an interactive, real-time display that refreshes counter values and status details every few seconds, making it suitable for watching trends over time but not for a one-shot current-state check. Because it remains active until the administrator presses Ctrl-C, it does not give the clean, single snapshot that the question requests. Also, without specifying ge-0/0/1 it monitors all interfaces, and even with the interface argument, the output format differs from terse operational status.

show interface ge-0/0/1

Why wrong: In Junos, the operational show command uses the plural keyword 'interfaces'; the singular 'show interface' is not a valid CLI syntax and will be rejected by the management daemon with an error or a 'syntax error' message. This singular form is a common trap for administrators coming from other devices, but it is not a synonym for 'show interfaces'. The correct query must use 'show interfaces terse ge-0/0/1' to get concise operational status.

show route table inet6.0

Why wrong: The `show route table inet6.0` command is incorrect for this scenario because it displays only the IPv6 unicast routing table. If the routing issue involves IPv4 destinations, which is almost always implied by a generic 'routing issue' unless IPv6 is explicitly mentioned, filtering to `inet6.0` would omit the very routes the engineer needs to inspect. This command is useful only when troubleshooting IPv6 connectivity, such as missing RA-learned routes or BGP IPv6 prefixes, but it would not show IPv4 entries like `10.0.0.0/8` or `192.168.1.0/24`. Running it for an IPv4 problem would produce an empty or irrelevant table, leading the engineer to mistakenly conclude that routing is down when the issue is actually in the IPv4 table.

show route forwarding-table

Why wrong: The `show route forwarding-table` command is incorrect because it displays the forwarding table (also known as the FIB or PFE forwarding table), not the route table (RIB). The forwarding table is derived from the route table and contains only the active next-hops that are programmed into the Packet Forwarding Engine, with no protocol preference or route origin information. It is used to verify what is actually being forwarded in hardware or software, but it does not show all candidate routes, hidden routes, or secondary paths that the routing table holds. For troubleshooting why a route is not being selected or why a specific path is preferred, the engineer must examine the route table (`inet.0`), because it shows the routing decision process before the FIB is populated.

show route protocol bgp

Why wrong: The `show route protocol bgp` command is incorrect because it filters the route table to display only routes learned or advertised by the BGP protocol. A generic routing issue could be caused by an OSPF, IS-IS, static, or directly connected route problem, and this command would hide those entries entirely. Even if the root cause involves BGP, this command shows only BGP-route entries and does not reveal the full routing table context, such as how a BGP route competes with a static or IGP route for the same prefix. To troubleshoot comprehensively, the engineer should view the complete IPv4 routing table in `inet.0` and apply protocol filters only after narrowing down the suspected source, not at the outset.

commit

Why wrong: The 'commit' command immediately activates the candidate configuration and makes it the active configuration on the device. It does not perform any pre-validation; if there is a syntax or semantic error, the commit will fail and may leave the device in an uncertain state, requiring manual rollback. Because it applies changes rather than merely checking them, it is wrong for this scenario.

commit confirmed

Why wrong: The 'commit confirmed' command applies the candidate configuration immediately but starts a countdown timer, rolling back to the previous configuration if the operator does not issue 'commit confirm' within the default 10 minutes. While this offers a safety net, it does not provide a pre-validation step—the configuration is applied first and only later reverted if unconfirmed. Therefore, it is not a substitute for a syntax check.

show | compare

Why wrong: The 'show | compare' command displays the differences between the candidate configuration and the active configuration, but it performs no validation whatsoever. It only outputs a textual diff, so it cannot detect syntax errors, invalid statements, or missing mandatory configuration blocks. Thus, while useful for reviewing changes, it does not verify that the configuration is correct and is not a replacement for 'commit check'.

set

Why wrong: The 'set' command is a configuration-mode directive used to add or modify parameter values within the active configuration hierarchy, such as 'set interfaces ge-0/0/0 unit 0 family inet address 192.0.2.1/24'. It cannot be executed from operational mode to transition into configuration mode; attempting to do so yields a 'syntax error' or 'command not found' because 'set' only has meaning after the CLI has already entered the configuration context. Therefore, 'set' is incorrect for this task.

edit

Why wrong: The 'edit' command is a configuration-mode navigation utility that moves you between hierarchy levels in the configuration tree, for example, 'edit interfaces' or 'edit system syslog'. It presupposes that you are already inside configuration mode and does not itself perform the mode transition from operational mode to configuration mode. While 'edit' may appear in operational mode in some contexts, it does not invoke the 'configure' functionality that opens the configuration database, making it the wrong choice.

cli

Why wrong: The 'cli' command is a shell-level command that starts the Junos CLI from a Unix shell or login session, not a command used within the CLI itself to enter configuration mode. In the operational mode of the CLI, typing 'cli' produces an error because it is not a recognized operational command, and it has no effect on transitioning to configuration mode. Since the administrator is already in the CLI and wants to reach configuration mode, 'cli' is irrelevant and incorrect.

rollback 0

Why wrong: Rollback 0 copies the currently active committed configuration into the candidate configuration, effectively discarding any uncommitted modifications. It does not retrieve a historical configuration; rather, it resets the candidate to the state that is already running on the device. Because the engineer needs the configuration from before the current commit, rollback 0 would not accomplish that task and is therefore incorrect.

load override

Why wrong: load override is a configuration-mode directive that replaces the entire candidate configuration with the contents of a specified local file or remote URL. It does not tap into Junos's committed configuration history and requires an existing file that contains the desired configuration. Unless such a file was previously saved, load override cannot revert to the previous committed configuration, making it an unsuitable choice here.

revert

Why wrong: revert is not a recognized command in Junos for configuration rollback; it is likely a confusion with the rollback operation. Junos offers rollback with a numerical argument to select a past committed configuration, but there is no generic revert command in operational or configuration mode. Attempting to use revert would produce an error because the system would not interpret it as a valid instruction, so it cannot be the correct answer.

show | display set

Why wrong: Piping the output of `show` through `display set` reformats the candidate configuration into `set` commands, but it does not perform any comparison against the active configuration. This transformation is useful for generating scriptable configuration snippets or for viewing the candidate in a loadable format, yet it fails the administrator's need to see what has changed. Since no diff is produced, this option cannot reveal the differences between candidate and active configurations.

run show configuration

Why wrong: The `run` prefix at the configuration-mode prompt executes a command in operational mode, so `run show configuration` simply displays the active committed configuration. This is functionally identical to executing `show configuration` directly in configuration mode, showing only the running configuration with no reference to uncommitted candidate changes. Because it does not compare candidate to active, it cannot show any differences the administrator is trying to identify.

show configuration

Why wrong: The plain `show configuration` command displays the entire active committed configuration in hierarchical text format. It does not include any uncommitted changes sitting in the candidate configuration, and it provides no delta or comparison mechanism. The administrator would see only the current running configuration, not the differences between what is active and what has been staged, so this option fails the stated requirement.

The 'edit' command is used in operational mode to navigate the hierarchy.

Why wrong: The `edit` command in Junos does not operate in operational mode for hierarchy navigation; it is exclusively a configuration-mode command that moves you into a specific hierarchy level (e.g., `edit interfaces`) or enters configuration mode from operational mode. In operational mode, you navigate by invoking commands directly, and from a hierarchy you would use `exit` or press Ctrl-Z to return to operational mode. Therefore, using `edit` in operational mode would either launch configuration mode or be rejected, not navigate a hierarchy.

The 'set' command is used in operational mode to set parameters.

Why wrong: The `set` command is a configuration-mode directive used to create or modify parameters within the candidate configuration, such as `set interfaces ge-0/0/0 unit 0 family inet address 192.0.2.1/24` — it is not used in operational mode to 'set parameters'. Operational mode is for monitoring and troubleshooting, so parameters are typically changed via configuration commands or `request` operations, not `set`. Attempting to use `set` in operational mode would produce an error because the syntax is not recognized outside the configuration context.

The 'rollback 0' command discards the candidate configuration.

Why wrong: The statement that `rollback 0` discards the candidate configuration is incorrect because `rollback 0` actually reverts the candidate configuration to the most recently committed (active) configuration, thereby discarding *uncommitted changes* but leaving the configuration itself intact. It is a configuration-mode command used to clear edits you have not yet committed; after a commit, `rollback 0` returns you to the current active configuration, which is effectively a no-op. To revert to a previous committed version after committing, you would use `rollback 1` or a higher number. So it does not discard the candidate configuration as a whole — it resets the candidate to the active baseline.

commit check

Why wrong: This command validates the syntax, semantics, and resource limits of the candidate configuration without committing it. It reports errors but does not modify the active configuration and does not leave configuration mode. Therefore, it is useful for testing changes but is not a method to exit configuration mode.

quit

Why wrong: The 'quit' command is not recognized in the Junos CLI; it is a common command in other operating systems and CLIs, but Junos uses 'exit' to leave configuration mode. Typing 'quit' produces an error message such as 'unknown command' and leaves you in configuration mode. Therefore, it is not a valid method.

show log

Why wrong: 'show log' is wrong because it outputs syslog-style messages written by system processes, not a direct query of current interface operational state. Log messages may be delayed, filtered by severity, or even absent for an interface issue if no event triggered a log entry. While logs can help diagnose past link flaps or errors, they cannot reliably report the real-time admin/operational status of an interface, so they are supplementary diagnostics, not an operational state viewer.

show configuration interfaces

Why wrong: 'show configuration interfaces' is wrong because it displays the configured interface hierarchy from the configuration database, including logical units, IP addresses, and settings such as 'disable'. That represents the administrator's intended state after a commit, not the current runtime state; an interface can be configured up with valid addressing yet still be operationally down due to a missing cable, no carrier, or hardware failure. Since it cannot report live link state or interface counters, it does not fulfill the requirement to view current operation.

show route

Why wrong: 'show route' is wrong because it displays the routing table, which lists active routes, protocol preferences, next-hop addresses, and route flags. Although a route learned through an interface can be an indirect clue that the interface is functioning, the command does not directly report the interface's link state, speed, errors, or protocol status. Routes might be stale, aggregated, or reachable through indirect next hops, so this command is not designed to answer 'what is the current operation of this interface?'

The interface is up but the link is down.

Why wrong: The output clearly indicates the physical link is up, so claiming the link is down contradicts the observed state. The interface may be up, but if the link were down, the interface would be operationally down and unable to carry traffic. Since the exhibit shows both the administrative state and the link state as 'up', this option misidentifies the link condition.

The interface has no IP address configured.

Why wrong: The output includes an IP address of 192.168.1.1/24 assigned to the interface, so the interface is definitely not without an IP configuration. A missing IP address would be indicated by 'unassigned' or '0.0.0.0/24' in the output, which is not the case here. Therefore, this option incorrectly claims a lack of IP addressing.

The interface is administratively down.

Why wrong: The administrative status in the output is 'up', meaning the interface has not been administratively disabled by the operator. An administratively down interface would show 'Admin down' or 'administratively down' and would remain down regardless of the physical link state. Since the admin status is up, this option is false.

The pipe (|) is not supported with 'display set'.

Why wrong: The pipe (|) is not supported with 'display set' is incorrect because Junos CLI pipes are universally supported on all commands, including configuration-mode commands that use 'display set'. The pipe simply filters the output of 'show configuration'; it does not affect whether the command itself is valid. If the interface were configured, the pipe would still allow the 'display set' output to appear (possibly filtered), so the pipe is not the cause of the empty result.

The interface name is misspelled.

Why wrong: The interface name is misspelled is incorrect because ge-0/0/0 follows the standard Junos interface naming convention and contains no typographic error. If the name were invalid, Junos would generate a syntax error or a 'statement not found' warning rather than silently returning no output. A misspelling would also typically invoke the CLI's automatic correction suggestions, which did not occur here, indicating the name is recognized but simply unconfigured.

The command syntax is incorrect.

Why wrong: The command syntax is incorrect is not valid because 'show configuration interfaces ge-0/0/0 | display set' is a syntactically correct Junos CLI command. Junos would emit an error message for an invalid keyword, missing argument, or bad pipe usage; instead, the command runs successfully but produces nothing. Syntax errors prevent the command from executing at all, whereas an empty output signifies that the command executed correctly but found no matching configuration.

show ethernet-switching table

Why wrong: The 'show ethernet-switching table' command displays the Layer 2 MAC address forwarding table, showing learned MAC addresses, their VLANs, and output interfaces. While the IRB interface may have a MAC address and be present in this table, the command provides no information about the IRB's operational state, IP address, or whether it is up/down. This command is purely for switch forwarding decisions, not for validating the health of a routed interface, so it cannot answer questions about IRB status.

show configuration interfaces irb.10

Why wrong: The 'show configuration interfaces irb.10' command displays the configured settings for the IRB interface, such as its IP address, VLAN association, and any firewall filters, but it shows only the intended configuration, not the operational reality. A configuration can be valid yet the IRB remain operationally down due to missing parent VLAN activation, physical link issues, or protocol dependencies. Therefore, this command cannot verify whether the IRB is actually up and passing traffic; only operational commands like 'show interfaces terse' provide that real-time status.

show vlan

Why wrong: The 'show vlan' command provides a list of VLANs, their tags, and member interfaces, but it is limited to Layer 2 information and does not show the operational state or IP configuration of IRB interfaces. While it may confirm that a VLAN exists and is assigned to ports, it cannot tell you if the IRB associated with that VLAN is up, has an active IP address, or is functioning as a gateway. Since the question asks specifically about the IRB interface's operational status, this command is too high-level and Layer 2 oriented to be useful.

The default confirmation timeout is 5 minutes.

Why wrong: The claim that the default confirmation timeout is 5 minutes is incorrect for Junos. The actual default is 10 minutes when `commit confirmed` is issued without an explicit timeout value. This misconception may arise from other networking platforms that use a shorter default timer. An administrator expecting 5 minutes might be caught off guard if an automatic rollback occurs later than anticipated, since the timer is longer than assumed.

It requires a reboot to revert to the previous configuration.

Why wrong: Reverting a configuration after a `commit confirmed` does not require a reboot. When the confirmation timer expires without a confirming commit, Junos automatically rolls back to the previously active configuration in real time. This rollback is handled by the control plane and does not disrupt traffic forwarding on the data plane. A reboot would be unnecessary and would undermine the purpose of the auto-rollback safety mechanism, especially in high-availability designs.

It stages the configuration in the candidate configuration but does not apply it until confirmed.

Why wrong: This option incorrectly depicts `commit confirmed` as a staging process that only applies changes after explicit approval. In reality, the configuration is applied instantly upon executing the command; it does not sit in the candidate configuration waiting for confirmation. The confirmation step simply indicates that the already-active configuration should be kept, thereby canceling the scheduled rollback. Staging without activation is characteristic of `commit check` or merely leaving changes in the candidate configuration, not `commit confirmed`.

lo0

Why wrong: lo0 is a virtual loopback interface that has no hardware dependency; it is always operationally 'up' unless explicitly disabled. Its admin state and operational state are both 'up', which is the expected normal condition. A loopback with both states up is fully operational and cannot indicate a physical problem because it does not rely on any cable or remote peer.

ge-0/0/2

Why wrong: ge-0/0/2 is administratively down, as indicated by the 'down' state in the administrative column. This is a configured condition, often used intentionally for maintenance, decommissioning, or to disable an unused port. Because the interface was deliberately disabled by an administrator, it is not an operational fault; the operational 'down' state matches the intentional admin down state.

ge-0/0/0

Why wrong: ge-0/0/0 shows both administrative and operational states as 'up', meaning the interface is enabled and successfully established a link. This is the ideal status for a physical interface, indicating that the cable is connected, the remote peer is up, and no error conditions such as excessive CRC errors or link flaps are present. There is no operational issue on this interface.

Command options are enclosed in curly braces { }.

Why wrong: In the Junos CLI, curly braces are used in configuration syntax to enclose hierarchical statement blocks (for example, interfaces { ge-0/0/0 { unit 0; } }), not to wrap command-line options. Command options are entered after the command name using flags such as -c, -t, or explicit argument keywords, and they are separated by spaces. Therefore, saying command options are enclosed in curly braces confuses configuration delimiters with operational command syntax.

Commands must be entered in full; abbreviation is not allowed.

Why wrong: Junos commands support unambiguous abbreviation: typing show sys uptime is not required when show system uptime is intended; show sys uptime is accepted. The CLI resolves the shortest unique prefix, and if the prefix is ambiguous, it prompts you to choose among matching commands. This flexibility speeds up administration and is controlled by the CLI's command-completion engine. Consequently, the statement that commands must be entered in full is incorrect.

You can commit configuration changes directly.

Why wrong: The commit operation is a configuration-mode function; from operational mode, an administrator must first run configure (or edit) to enter the configuration hierarchy. After modifying candidate configuration statements, commit validates and activates the changes. Issuing commit directly from operational mode is not a valid action, because operational mode is reserved for show, ping, and similar commands. Thus, the option misrepresents Junos's separation between candidate configuration and operational state.

The engineer used 'commit' instead of 'commit confirmed'.

Why wrong: The error occurs because the 'set' command itself is rejected before any commit is attempted. 'commit confirmed' is a safety feature that automatically rolls back changes if not confirmed within a timeout, but a standard 'commit' is sufficient to apply configuration changes. Since the engineer never successfully entered configuration mode, the commit type is irrelevant; the fatal issue is that 'set' is not available in operational mode.

Junos only allows one IPv6 address per interface.

Why wrong: Junos does not restrict interfaces to a single IPv6 address; it fully supports multiple IPv6 addresses on the same interface by configuring additional 'address' statements under the 'family inet6' hierarchy. The error is not due to an address limit, but rather because the 'set' command was executed outside configuration mode. If the engineer had been in configuration mode, adding a second IPv6 address with a second 'set' command would be perfectly valid.

The 'set' command requires the 'add' keyword to add a second address.

Why wrong: The Junos CLI uses 'set' as the universal keyword to create or modify configuration elements; there is no separate 'add' keyword for appending values such as additional addresses. To add a second IPv6 address, you simply issue another 'set interfaces <interface> unit <unit> family inet6 address <address>' statement. The absence of an 'add' keyword is not the problem here, as Junos does not follow that syntax model.

Enter configuration mode, then commit the configuration, then set the static route under routing-options static, then verify the route with show route.

Why wrong: This order is invalid because 'commit' is executed before the static route has been added to the candidate configuration. The commit command in Junos copies the current candidate configuration to the 'active' configuration; since the static route hasn't been defined, no change takes effect. After the commit, adding the route via 'set' only updates the candidate configuration, leaving the active configuration untouched, so the routing table never receives the static route and 'show route' will not display it. In short, all configuration changes must be staged before the commit that activates them.

Set the static route under routing-options static, then enter configuration mode, then commit the configuration, then verify the route with show route.

Why wrong: Static route configuration must be performed inside configuration mode, not from the operational prompt. The 'set' command for editing routing-options is only available after you enter configuration mode (for instance, by typing 'configure' or 'edit'). Attempting to issue 'set routing-options static route ...' directly at the operational prompt results in an error or is simply ignored, because the device interprets commands against its operational state, not its configuration database. Therefore, entering configuration mode is necessarily the first step before any 'set' command can modify the candidate configuration.

Enter configuration mode, then set the static route under routing-options static, then verify the route with show route, then commit the configuration.

Why wrong: This order places verification ('show route') before the 'commit', but 'show route' displays the active routing tables that reflect only the committed configuration. Even though the static route has been added to the candidate configuration, it has no effect on the routing table until a commit makes it active. As a result, the verification command will fail to see the route, giving a false negative. Therefore, the commit must always precede any verification that checks the operational routing state.

Step 1: Connect to the device. Step 2: Execute 'request system snapshot'. Step 3: Enter operational mode. Step 4: Confirm the operation.

Why wrong: This order is wrong because it attempts to execute 'request system snapshot' before entering operational mode. In the Junos CLI, 'request system snapshot' is an operational-mode command; it is not valid in configuration mode, and your session only enters operational mode after connecting. If you issue the command while still in configuration mode, the CLI returns an error such as 'error: command unknown'. Therefore, step 3 must occur before step 2, and you must explicitly ensure you are in operational mode (the default top-level prompt) before running the command.

Step 1: Execute 'request system snapshot'. Step 2: Connect to the device. Step 3: Enter operational mode. Step 4: Confirm the operation.

Why wrong: This sequence is fundamentally flawed because it places 'request system snapshot' as the very first step, but you cannot execute any Junos CLI command without an active connection to the device. Commands are typed into a terminal session that must be established by physically connecting to the console port or via a network protocol like SSH or telnet. Without a connection, there is no device to receive the command, and the 'request system snapshot' operation cannot even begin. Thus, connecting to the device is an absolute prerequisite for any subsequent CLI interaction, including entering operational mode and running the snapshot command.

Step 1: Enter operational mode. Step 2: Execute 'request system snapshot'. Step 3: Confirm the operation. Step 4: Connect to the device.

Why wrong: This order is incorrect because it claims you can enter operational mode before connecting to the device, which is impossible. Operational mode is a state within an active Junos CLI session; you cannot be in any mode without first establishing a connection to the device via console, SSH, or another access method. Additionally, even if you somehow entered operational mode, the final step of connecting would be redundant and out of order, as you would already need a connection to run the snapshot command in step 2. The correct workflow mandates connecting first, then entering operational mode, then executing the command, and finally confirming.

show interface terse: Displays detailed interface statistics

Why wrong: This mapping is incorrect because 'show interface terse' outputs only a concise one-line status per interface, showing administrative and operational state plus IP addresses, not detailed statistics. Comprehensive interface statistics such as input/output byte counts, packet errors, discards, and queue depths are only shown by 'show interfaces detail' or 'show interfaces extensive'. Thus, the command listed here is a summary tool, not a statistics tool.

show route: Displays the configuration of routing protocols

Why wrong: This mapping misidentifies the purpose of 'show route': it displays the routing tables, i.e., the set of active routes and their attributes, not the configuration parameters of routing protocols. Information about OSPF areas, BGP neighbors, or IS-IS levels is stored in the configuration hierarchy and viewed using 'show protocols <protocol>' or 'show configuration protocols'. Therefore, 'show route' cannot be used to troubleshoot protocol-level configuration errors; it only reflects the result of their operation.