JN0-106 practice questions
Juniper · JN0-106 · 200 questions
Original practice questions for the JNCIA-Junos (JN0-106) exam, covering networking fundamentals, Junos OS fundamentals, user interfaces, configuration basics, operational monitoring and maintenance, routing fundamentals, and routing policy and firewall filters — framed inside a regional ISP / rural broadband cooperative building out POPs, subscriber aggregation, transit and peering, and rural fiber networks.
This course contains the use of artificial intelligence.
About the JN0-106 exam
- Time allowed
- 1 hour 30 minutes
- Questions
- 65 multiple-choice
- Format
- Proctored, Pearson VUE
Exam details published by the vendor, checked 26 August 2026. Vendors change fees and formats without notice — confirm on the vendor's own page before you book.
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Networking Fundamentals · 36 questions
- A subscriber's video-streaming complaint reaches a rural cooperative's NOC, and the on-call tech traces the traffic path from the head-end's web application down through the TCP/IP stack toward the physical fiber uplink. As the data moves down through each layer of the stack, what happens to it?
- A field technician wiring a new subscriber aggregation switch at a rural cooperative's point of presence needs to know which layer of the OSI model is responsible for physical addressing and for delivering frames between devices on the same local segment. Which layer is that?
- At a small rural head-end, a cooperative still connects four legacy DSLAMs to a single unmanaged hub before uplinking to the core switch. Two DSLAMs transmit at the same instant and their electrical signals collide on the shared hub segment. Which term describes the set of ports where a collision like this can occur?
- A cooperative's network engineer segments subscribers in a small town into two VLANs on the same aggregation switch, specifically so that an ARP broadcast sent by a customer in VLAN 10 does not reach devices in VLAN 20. What has effectively been created between the two VLANs?
- A new subscriber's router sends its first Ethernet frame through a rural cooperative's access switch. The switch has never seen that device's source MAC address before. What does the switch do with that address as part of its normal learning behavior?
- A cooperative's NOC notices that a frame destined for a subscriber's set-top box is being sent out every port on an access switch except the one it arrived on, even though the box has been online and streaming for weeks without issue. What is the most likely explanation for this flooding behavior?
- A rural ISP's access switch periodically removes MAC address table entries for ports that have not sent traffic for a while. What is this behavior called, and why does it matter operationally?
- A rural cooperative wants to deliver a live IPTV channel to every subscriber set-top box that has tuned in across a town, without sending a separate copy of the stream to each individual subscriber and without sending it to devices that never asked for it. Which traffic delivery type best fits this requirement?
- A cooperative's engineer is choosing transport behavior for a live voice call between two rural offices, where a small amount of dropped audio is acceptable but delay caused by session setup or retransmissions is not. Which category of transport protocol behavior best fits this requirement?
- A rural ISP's billing server and its remote-monitoring server both send traffic to the same head-end router at the same time. What allows the receiving system to correctly sort the arriving segments and deliver each stream to the right application?
- A subscriber's laptop at a rural cooperative receives an Ethernet frame carrying a web page from a regional data center. As that frame moves up through the receiving device's protocol stack toward the browser, what happens to it?
- A cooperative's new hire is studying networking fundamentals and needs to understand how the four-layer TCP/IP model relates to the seven-layer OSI model. Which statement correctly describes that relationship?
- A technician auditing a rural cooperative's newly upgraded access layer notes that every subscriber port now connects to a dedicated switch port running full-duplex, with the old shared hubs removed entirely. What effect does this have on collisions for those links?
- A rural cooperative's regional hub site connects two separate towns through a router, with each town's subscribers on its own switched network behind that router. When a subscriber in Town A sends an ARP broadcast, what happens to it at the router?
- A junior technician at a cooperative's NOC sees an access switch send a frame out every port for an unknown destination MAC address, and separately sees a subscriber's DHCP discover frame also go out every port. The technician assumes these are the same behavior. Why are they actually different?
- A rural ISP's back-office application requires guaranteed, in-order delivery of every byte between two servers exchanging subscriber billing records, including automatic retransmission of anything lost in transit. Which transport behavior category provides this?
- A cooperative's engineer needs to double-check a hand-written subnet mask octet before typing it into a router, and the paper shows the binary value 11111000. What is this value in decimal?
- While training a new NOC hire, a senior technician at a rural cooperative draws the path a subscriber's file download takes: the data is handed to the transport layer, then the network layer, then the data link layer, before going out on the fiber. The new hire asks what the unit of data is called at each of those layers. In order, what should the technician say?
- A rural broadband cooperative has been allocated the 10.20.0.0/22 block for a new fiber build and wants to give each of its 16 villages its own separate subnet with room for up to 60 subscriber devices per village. Which subnet mask satisfies both requirements with no wasted subnets?
- A regional ISP's four contiguous head-end blocks — 192.168.4.0/24, 192.168.5.0/24, 192.168.6.0/24, and 192.168.7.0/24 — are all reachable through the same upstream transit router. Which single summary route advertises exactly this address range and nothing more, letting the ISP send one route to its peering partner instead of four?
- A subscriber-aggregation router at a co-op's POP holds three routes toward a destination address of 203.0.113.45: 203.0.113.0/24, 203.0.113.32/27, and a default route of 0.0.0.0/0 pointing to the transit provider. Which route does the router actually use to forward the packet?
- A cooperative's regional office assigns the subnet 172.16.14.96/27 to its NOC workstations. A technician needs to configure a new monitoring server at 172.16.14.110. Which statement correctly describes this address's position within the subnet?
- While documenting the co-op's new IPv6 rollout, an engineer captures three addresses in use on a POP router: fe80::1, ff02::1, and 2001:db8:abcd::1. Which statement correctly matches each address to its IPv6 address type?
- A new POP needs four subscriber VLANs carved out of 10.10.8.0/24: one for 100 residential subscribers, one for 50 business subscribers, and two management VLANs needing 25 hosts each. Using VLSM, which mask set correctly provides just enough usable addresses for each group without unnecessary waste?
- A cooperative's operations team receives a single 10.30.0.0/20 block to allocate across its rural fiber region and plans to hand each of its distribution cabinets a full /24 subnet. How many separate /24 subnets can be carved out of this /20 allocation?
- Two POPs in a rural fiber ring are connected by a dedicated point-to-point fiber link that only ever needs to number two router interfaces, one at each end. Which subnet mask is the most address-efficient choice for this link?
- A cooperative's IPv6 planning team receives a single 2001:db8:abcd::/48 allocation from its upstream provider and wants to give every village in its territory its own separate /64 subnet, the standard size for a single IPv6 LAN segment. How many distinct /64 subnets can this /48 allocation support?
- A distribution cabinet is being planned to serve approximately 400 subscriber CPE devices on a single flat subnet, drawn from a spare 10.5.0.0/16 block. Which subnet mask correctly provides enough usable addresses for this cabinet without requiring the subnet to be split further?
- A cooperative is designing IPv6 addressing for its internal back-office network — device management interfaces, NOC servers, and internal monitoring links that must never be reachable from the public internet. Which type of IPv6 address is the appropriate choice for this internal-only addressing plan?
- A cooperative's back-office workstations use private 10.x addresses internally, but a technician notices that when one of those workstations reaches a public website, the site's server sees a completely different, publicly routable source address in the arriving packets. Which function performed this address change?
- A cooperative's shared uplink occasionally gets busy enough that a live voice call's audio packets and a subscriber's large file download are both waiting to leave the same interface at once. Which general networking concept lets time-sensitive voice packets get serviced ahead of the bulk transfer instead of waiting in strict arrival order?
- A regional ISP owns three head-end blocks for route advertisement to its upstream peer: 192.168.8.0/24, 192.168.9.0/24, and 192.168.11.0/24. The block in between, 192.168.10.0/24, belongs to a different provider and is not part of this ISP's allocation. Which route advertisement correctly summarizes what the ISP can safely send upstream?
- An engineer is documenting a POP router's loopback address for the NOC runbook and has the fully expanded IPv6 address 2001:0db8:0000:0000:0000:0000:0000:0001. Which of the following is the correctly compressed form of this same address?
- A NOC technician is assigned the subnet 10.50.5.64/26 for a new equipment cabinet and needs to confirm the subnet's usable address boundaries before assigning device addresses. Which pair of addresses correctly marks the first and last usable host addresses in this subnet?
- At a small-town head-end, a technician needs to connect a printer and a workstation that both sit on the same subnet, and separately needs to let a NOC server on a different subnet reach a monitoring host on yet another subnet across the POP. Which statement correctly matches each need to the right forwarding function?
- A cooperative's engineering team wants to divide its 10.60.0.0/22 rural fiber allocation into eight equally sized subnets, one for each village PoP along a new fiber ring, with each village needing up to 100 subscriber addresses. Which mask correctly creates exactly eight equal subnets from this /22 block while still meeting the per-village host requirement?
Junos OS Fundamentals · 16 questions
- A rural broadband cooperative's network team is evaluating why Junos runs the same OS image, with the same daemons and command structure, on the co-op's core routers, aggregation switches, and CPE gateways alike. Which benefit best describes this one-software-track design?
- A regional ISP's core router in its main POP experiences a Routing Engine process restart during a routine software patch, but subscribers report no interruption to traffic already flowing through existing sessions. Which aspect of Junos architecture best explains this behavior?
- A rural fiber cooperative's network engineer is asked which Junos component is responsible for actually switching subscriber traffic from an incoming interface to the correct outgoing interface at line rate, on a core aggregation router. Which component performs this function?
- A cooperative's network operations team wants to know which Junos component is responsible for running the dynamic routing protocol sessions to the co-op's upstream transit provider and building the master routing table from the routes it learns. Which component performs this role?
- While explaining Junos concepts to a new hire, a senior engineer at a regional ISP describes traffic entering one interface of a core router and leaving through another interface toward its final destination, without the router itself being the source or destination. What category of traffic is this?
- A network technician at a rural broadband cooperative learns that some packets arriving at a core router cannot simply be switched by the forwarding hardware and instead get sent up to the Routing Engine for special handling. What is this category of traffic called in Junos, and what is a defining trait of it?
- An engineer at a regional ISP is troubleshooting why a router's routing table shows several candidate paths to a subscriber aggregation subnet, while only one specific next hop is actually used to forward live traffic toward that subnet. What explains this difference?
- A rural ISP's senior engineer explains that a specific Junos process running on the Routing Engine is responsible for establishing protocol adjacencies with the co-op's peering routers and computing the best paths that populate the routing table. Which Junos daemon performs this role?
- During a hardware alarm review, a network engineer at a regional ISP's carrier-hotel POP is told that a particular Junos daemon on the Routing Engine tracks the operational status of power supplies, fan trays, and other physical chassis components and raises alarms when something fails. Which daemon is responsible for this?
- A new technician at a rural fiber cooperative asks which Junos daemon on the Routing Engine is responsible for accepting an administrator's CLI session, validating configuration syntax, and committing configuration changes. Which daemon handles this function?
- A rural ISP is bringing up a new subscriber aggregation switch, and an engineer notes that once an interface is configured with an IP address and enabled, a specific Junos daemon is responsible for applying that configuration to the actual interface and bringing it into an operational up state. Which daemon performs this role?
- A subscriber at a rural fiber cooperative runs a traceroute toward a distant website, and one of the core routers along the path needs to generate an ICMP "time exceeded" message back to the subscriber because the packet's TTL reached zero at that hop. Which category of traffic does this generated ICMP message represent from the router's own perspective?
- A regional ISP operates Juniper routers at its core, Juniper switches at subscriber aggregation sites, and a Juniper security platform at its network edge. An engineer new to Junos asks how these different device families relate architecturally. Which statement correctly describes that relationship?
- An engineer at a regional ISP is asked why a core router forwards millions of packets per second for ordinary subscriber traffic, yet a sudden flood of malformed packets requiring Routing Engine processing can noticeably slow the router's control-plane responsiveness. What architectural reason best explains this difference in behavior?
- After a static route is added to a router's configuration at a rural ISP's aggregation site and the configuration is committed, the route needs to actually be used to forward live subscriber traffic. Which sequence correctly describes how that route becomes usable for forwarding?
- A rural ISP's senior engineer explains that on a Junos router, the process handling SNMP polling can crash and restart on its own without taking down the process running BGP or the process handling the CLI. What architectural fact explains this resilience?
User Interfaces · 32 questions
- A technician remotely logs into an aggregation router at a rural cooperative's POP after hours and lands at the default operational-mode prompt. Before they can change any settings for an upcoming subscriber turn-up, which command must they enter first to enter configuration mode?
- During a late-night maintenance window at a small-town head end, a technician types configure at the operational prompt and the session prompt changes from a right angle bracket to a hash mark at the end. What does that hash mark indicate about the session?
- A technician at a rural fiber cooperative is unsure what keywords can legally follow show interfaces ge-0/0/0 on an aggregation switch and types a question mark at that point in the command line. What should Junos do in response?
- While troubleshooting a subscriber-aggregation port from a small-town POP, a technician types show interf and presses the space bar. Junos immediately fills in the rest of the keyword to read show interfaces. What CLI feature just occurred?
- An aggregation router at a rural ISP's POP has dozens of subscriber-facing interfaces. A technician runs show interfaces terse and wants to see only the line for ge-0/0/5 without scrolling through the rest. Which pipe modifier accomplishes this?
- A technician needs to know how many routes in the routing table match a particular community tag while triaging a peering issue overnight at a regional ISP's carrier hotel router, without needing to see each individual route. Which pipe modifier gives just that number?
- A technician monitoring a syslog buffer on a rural cooperative's edge router during a night maintenance window only cares about the most recent entries logged, not the entire buffered history. Which pipe modifier limits the display to just the newest lines?
- A technician is capturing show command output into a session log for a change ticket after a rural ISP's overnight maintenance window and does not want the CLI pausing output with a --More-- prompt partway through a long listing. Which pipe modifier prevents that pagination?
- A technician wants to review a router's saved configuration in flat, one-line-per-statement syntax that matches how commands would be typed to recreate it, rather than the default nested, curly-brace hierarchy view. Which command produces that formatting?
- A cooperative just hired a junior technician who is comfortable with a mouse and browser but not yet confident typing Junos CLI commands. For quick, routine status checks on an aggregation router at a rural POP, which built-in Junos interface best suits that technician while they build CLI skills?
- While inside a configuration session making planned changes to an aggregation router at a rural head end, a technician needs to quickly check current interface counters without abandoning the in-progress, uncommitted edits. Which approach lets them do that from within configuration mode?
- A technician working through a long, repetitive series of similar show commands on an aggregation switch at a rural POP wants to retype an earlier command with a minor variation instead of typing it from scratch each time. Which CLI feature supports that workflow?
- A technician runs show interfaces terse on a switch with dozens of interfaces and wants the output narrowed down to only the lines that mention ge-0/0/5, hiding every other interface's line entirely. Which pipe modifier keeps just the matching lines and drops everything else?
- Reviewing a busy interface log on a subscriber-aggregation router at a rural cooperative, a technician wants to see every logged line except the routine keepalive messages, which are cluttering the view. Which pipe modifier hides only the matching lines while showing everything else?
- Scanning a very long show route output on a peering router at a regional carrier hotel, a technician knows roughly what they're looking for but wants the display to jump straight to the first line containing a specific prefix rather than filtering out everything else. Which pipe modifier does that?
- A cooperative's lead technician needs to apply an identical set of configuration statements to twelve near-identical subscriber-aggregation interfaces in one maintenance window. Which capability makes typing the change at the CLI more efficient here than using J-Web?
- A technician at a rural broadband cooperative is deep in Junos configuration mode and needs to work on statements under the interfaces ge-0/0/5 unit 0 family inet hierarchy without retyping that full path before every command. Which command moves the technician's working context into that hierarchy level?
- At a rural broadband cooperative's NOC, an engineer edits a new SNMP community string into the configuration, but a colleague pings the router from home and confirms the old community string still works over an hour later. Which concept explains why the change hasn't taken effect yet?
- While several levels deep editing a firewall filter term at a subscriber-aggregation router, a technician wants to jump straight back to the root of the configuration hierarchy to start editing an unrelated interface stanza, without exiting configuration mode entirely. Which single command accomplishes this?
- An engineer wants to verify that a large batch of edits to a rural cooperative's routing policy will pass Junos's syntax and configuration checks before risking an outage on the production router, but does not want the changes to actually take effect yet. Which command should the engineer run?
- A technician is about to push a routing change to a router at an unstaffed rural POP with no out-of-band access, and is worried a mistake could disconnect the site entirely. Which commit variant lets the change take effect immediately but automatically reverts to the prior configuration if the technician doesn't reconfirm within a set time window?
- A network engineer needs to push a maintenance-window configuration change to a rural cooperative's core router at 2 a.m. Sunday, well after the engineer will have gone home for the night. Which commit variant lets the change be scheduled to take effect at that specific future time?
- After pushing an emergency change to fix a flapping interface at a cooperative's aggregation site, an engineer wants the rollback history to show a plain-language note explaining what the change was for, so a colleague reviewing the commit history later doesn't have to guess. What should the engineer do?
- A change pushed 20 minutes ago to a subscriber-aggregation router at a rural ISP is causing intermittent packet loss for an entire town. The on-call engineer wants to restore the configuration exactly as it was two commits ago. After identifying the correct rollback number, what must the engineer still do to make that older configuration active on the router?
- Before committing a rollback, an engineer at a rural cooperative wants to see precisely which configuration lines will be added or removed compared to what's currently active, rather than trusting memory of what changed. Which command shows that difference?
- An engineer has a small ASCII file containing just a few additional static route statements for a rural cooperative's edge router, and wants to add those routes into the existing candidate configuration without disturbing any of the unrelated statements already there. Which load operation should be used?
- A misconfigured automation script corrupted large portions of a rural ISP's lab router configuration with conflicting and duplicate statements, and an engineer wants to discard the entire candidate configuration and start clean from a known-good saved file, keeping nothing from what's currently there. Which load operation fits?
- An engineer has spent an hour building out a complex candidate configuration for a new rural fiber POP and wants to write the current candidate configuration to an ASCII text file on the router for backup, without committing any of it or affecting the active configuration. Which command does this?
- An engineer wants to email a colleague the exact set commands needed to reproduce a firewall filter configuration on another router, rather than the router's default nested, curly-brace formatted view. Which command produces that flat, copy-pasteable set-command output?
- A senior engineer at a rural cooperative wants to know how far back a Junos router's built-in configuration history can go before older committed configurations simply age out of the rollback list. What should the engineer understand about that limit?
- Two engineers at a rural cooperative's NOC both try to enter configuration mode on the same router during a maintenance window, and the second one wants to guarantee that no one else's edits get mixed into theirs while working on a sensitive routing-policy change. Which approach gives that engineer sole, exclusive editing rights to the candidate configuration?
- After a rural fiber cooperative renumbers its internal naming scheme, an engineer needs to rename an existing routing-instance identifier throughout the candidate configuration without deleting and manually re-typing every statement under that instance. Which Junos configuration-mode command accomplishes a rename in place?
Configuration Basics · 35 questions
- A field technician receives a brand-new Juniper router to commission as a POP node for a rural broadband cooperative. Fresh out of the box, the technician logs in over the console as root with no password prompted and tries to commit a change to enable a management IP address, but the commit is rejected. What must be configured first?
- A technician is commissioning a brand-new POP router for a rural fiber build-out, and no IP address has been configured on the management interface yet. Which access method will let the technician log in and configure the device for the first time?
- A co-op network engineer sets 'host-name pop-fiber-042' on a newly commissioned aggregation router. What is the primary effect of this configuration statement?
- A rural broadband cooperative is onboarding a new field technician who needs to run diagnostic commands on POP routers but should never be able to change the configuration. Which approach best reflects Junos login-class design?
- A co-op wants to give a NOC staffer enough access to run day-to-day operational commands — including clearing interface counters during troubleshooting — without granting any configuration rights. Which built-in Junos login class fits this need?
- A cooperative wants POP routers to first try authenticating administrator logins against a central RADIUS server before falling back to any other method. Which Junos configuration concept controls this sequencing?
- A cooperative centralizes administrator authentication through a RADIUS server at its main office, but POP routers in outlying towns sometimes lose connectivity to that office during fiber cuts. What should the authentication-order configuration include to keep local technicians able to log in during an outage?
- A cooperative's security policy requires that administrators never log in directly as root over the network, so every action can be tied to a named account. Which Junos configuration approach enforces this?
- A co-op operates POP routers across several small towns and wants their system clocks to stay tightly synchronized so that log timestamps line up when correlating an outage across multiple sites. Which configuration accomplishes this?
- A cooperative's monitoring platform needs to poll interface statistics from POP routers but should never be able to push configuration changes through SNMP. How should the SNMP community be configured?
- A rural cooperative wants log messages from every POP router forwarded to a central log server at its NOC so technicians don't have to check each device individually after an outage. Which configuration accomplishes this?
- A co-op engineer wants to reference the NTP and syslog servers by hostname instead of by IP address in a POP router's configuration. What must be configured first for hostname references to resolve correctly?
- A cooperative creates a new local user account for a technician on a POP router but forgets to assign a login class before committing. What is the practical consequence?
- A co-op assigns a technician to a custom login class that includes view and network permissions but not configure. What happens when that technician attempts to enter configuration mode on a POP router?
- A technician unboxes a new POP router for a rural fiber build-out and connects only the management interface to a switch port that hands out DHCP leases, without touching the console. What is a technician relying on to get an initial address this way?
- A co-op engineer types the root-authentication plain-text-password command and enters a password at the prompt. What does Junos do with that password in the resulting configuration?
- After a POP router is fully commissioned with a management IP address and SSH enabled, a co-op still keeps a console cable connected to it in the equipment rack. What operational purpose does that console connection continue to serve?
- A cooperative's centralized syslog server is getting flooded with routine informational messages from dozens of POP routers, making real problems hard to spot. How should the syslog configuration on each router be adjusted?
- At a rural fiber cooperative's regional POP, a technician reviewing the aggregation router's interface list sees the name ge-0/0/2. In the Junos physical interface naming convention, what does the "0/0/2" portion identify?
- A field engineer for a rural broadband cooperative is bringing up a new fiber transit uplink. She needs to set the port's link speed and framing, and separately assign an IP address for routing to the upstream carrier. Which pairing correctly matches each property to the level where Junos expects it configured?
- A regional ISP is provisioning a new subscriber VLAN on aggregation port ge-1/0/5. Logical unit 100 needs the address 10.20.30.1/24 so subscriber CPE devices can route through it. Which configuration statement correctly assigns that address?
- A rural ISP's network team configures a stable address on lo0.0 for every core and edge router, and uses that address as the source for routing protocol sessions and remote management. What makes the loopback interface well-suited for that role?
- An engineer is assigning the address on lo0.0 for a POP router that will serve as the router ID and management anchor for that site. Which subnet mask is the correct choice for that loopback address, and why?
- A cooperative's aggregation router has three subscriber ports, ge-0/0/4, ge-0/0/6, and ge-0/0/9, that all need the identical family inet and MTU settings applied at once instead of being configured one interface at a time. Which Junos feature is built for exactly this?
- Inside an interface-range block, an engineer needs to add ge-0/0/10 through ge-0/0/23 as a contiguous block of subscriber ports, separately from a handful of individually named interfaces elsewhere in the network. What is the functional difference between the member and member-range statements available inside that block?
- A rural broadband cooperative operates 40 small POPs, each running an identical block of NTP and syslog configuration on its router. Maintaining that block by hand in 40 separate candidate configurations is error-prone whenever a setting needs to change. What is the Junos-recommended way to keep that shared block consistent across every POP router?
- An engineer wants a configuration group to apply a common MTU setting to every Gigabit Ethernet subscriber port on a router without listing each ge- interface name individually inside the group. How should the group's interface stanza be written to achieve that?
- An engineer defines a group named pop-common under the groups hierarchy with shared NTP and syslog settings, and commits the change. On the router itself, though, neither service reflects any of the new settings. What is the most likely explanation?
- A subscriber aggregation interface inherits an MTU value from a configuration group applied router-wide with apply-groups, but the same interface also has an explicit MTU value configured directly on it. Which value takes effect on that interface?
- A cooperative's compliance policy requires that every committed router configuration be automatically copied off the device to a central archive, without relying on a technician to remember to do it manually. Which Junos feature is designed for this?
- An engineer wants a POP router's configuration to be transferred to the central archive server automatically every time a commit succeeds, rather than only on a fixed periodic schedule. Which statement under the archival configuration hierarchy triggers that commit-driven behavior?
- Ahead of a large maintenance window at a regional POP, an engineer wants to snapshot the currently active, known-good configuration as a dedicated safety net, separate from the router's normal rollback history. Which action accomplishes that?
- A change during a maintenance window breaks IP reachability to a POP router, leaving only console access available. A rescue configuration was saved earlier that day. What is the correct way to restore the router to that known-good baseline?
- An aggregation router administrator numbers each subscriber logical unit to match the VLAN ID it carries, for example unit 210 for VLAN 210, purely to make the configuration easier to read. Which statement about Junos logical unit numbering is accurate?
- An engineer configuring a new transit uplink at a carrier interconnect point sets an encapsulation type on the physical interface, then separately configures VLAN tagging and an IP address on a logical unit beneath it. Which statement correctly describes why these properties are split across those two levels?
Operational Monitoring and Maintenance · 23 questions
- A technician at a rural fiber cooperative's head-end needs a fast overview of every interface's administrative and link status on an aggregation router before a scheduled maintenance window. Which command gives that summary in one screen without digging into per-interface detail?
- While reviewing show interfaces ge-0/0/2 extensive on a subscriber-aggregation switch feeding a small-town fiber node, a technician sees the Input errors counter climbing with framing errors accounting for most of the count. What does this most likely indicate?
- A cooperative's core router shows a steadily increasing Output drops counter on the interface uplinked to a subscriber-aggregation switch, while Output errors stays at zero. What does that pattern point to?
- A NOC engineer at a rural telecom cooperative notices the Carrier transitions counter on a POP's uplink interface has climbed into the hundreds over the past hour, while the link currently shows up. What does that counter tell the engineer?
- A technician runs show interfaces terse on a subscriber-aggregation switch and finds a port listed as down, even though a colleague swears the fiber patch and optic on that port were both replaced and tested earlier that day. What should the technician check first before assuming a new physical fault has appeared?
- A technician troubleshooting a slow subscriber link wants to watch live, continuously-updating traffic statistics (bits per second, packets per second) for one interface directly from the Junos CLI, without generating a static, one-time report. Which operational-mode command provides that live view?
- An engineer at a rural ISP's carrier-hotel POP needs to inspect the actual packet headers crossing an interface in real time, similar to a lightweight packet sniffer, to confirm a subscriber's DHCP requests are actually reaching the router. Which Junos CLI command is built for that?
- A field technician needs to quickly confirm basic IP reachability to a subscriber's CPE at a remote village site without waiting a full second between each probe. Which Junos ping option is built for that fast check?
- A subscriber several hops downstream from a cooperative's core reports intermittent connectivity to the internet. Running traceroute from the core router toward the subscriber's CPE shows normal replies through the fourth hop, then asterisks for every hop after that. What does this output tell the engineer?
- A cooperative's network team is deciding how field techs should remotely access routers at unmanned rural POPs for day-to-day monitoring. Why should SSH be chosen over Telnet for this access?
- After a brief outage at a POP overnight, an engineer wants to review the general system log for events like interface flaps or process restarts that occurred around the time of the outage. Which command displays that log?
- A NOC engineer wants to watch a specific log file update in real time on the terminal, similar to tailing a log on a Linux server, while reproducing an intermittent issue at a POP. Which Junos operational-mode command does that?
- A router at a cooperative's regional hub seems sluggish to respond to CLI input, and the engineer suspects the routing engine's CPU is overloaded. Which command lets the engineer see which processes are consuming the most CPU, similar to a Unix top view?
- Before ordering a replacement part for a router at a remote POP, an engineer needs to confirm the exact model, serial number, and installed FPCs/PICs currently in the chassis. Which command provides that hardware inventory?
- Before pushing a Junos OS upgrade to a router at a rural head-end, an engineer wants to confirm there's enough free space on the device's local storage to hold the new software image. Which command checks that?
- A router at a small-town POP is nearly out of local storage, mostly from old log files and unused software images accumulated over years of operation. Which command helps an engineer identify and optionally remove those unneeded files to reclaim space?
- Before starting a scheduled Junos OS upgrade on a POP router, an engineer wants to confirm the exact software version currently running so the correct upgrade path can be chosen. Which command shows that?
- Before installing a new Junos OS package on a production router at a rural cooperative's core, an engineer wants to check that the package is compatible with the router's current configuration and hardware without actually installing it yet. Which command performs that check?
- An engineer has already validated a new Junos OS package against a POP router's configuration and is ready to actually install it and have the router come up on the new version after a single maintenance-window reboot. Which command accomplishes both the install and the reboot in one step?
- Before upgrading Junos OS on a POP router that has no on-site spare, a cautious engineer wants a bootable backup copy of the current, known-working software and configuration on backup storage media, so the router can be recovered quickly if the upgrade goes wrong. Which command creates that backup?
- A cooperative is scheduling generator maintenance at an unmanned POP that will briefly cut power to a router. To avoid filesystem corruption, an engineer wants to gracefully halt the Junos OS before power is physically removed. Which command should be run first?
- A technician inherits a router at a decommissioned rural POP with an unknown root password and no other configured administrative accounts. What is the general Junos procedure for regaining administrative access?
- A newly hired field tech at a small cooperative office is more comfortable with a graphical interface than the CLI, but still needs a quick read on interface status, system health, and recent log entries for a POP router. What does J-Web's Monitor section provide?
Routing Fundamentals · 23 questions
- A rural fiber cooperative's edge router learns three different paths toward the regional data center's /24 subnet: one from a directly connected interface, one from a manually entered static route, and one from OSPF. Which structure does Junos consult first to decide which of these candidate paths gets used to actually forward subscriber traffic?
- After Junos on a subscriber-aggregation router chooses the single best path to a village's DSL access switch, that path needs to reach the Packet Forwarding Engine so subscriber traffic actually moves. Which table receives just that one active, forwarding-ready path?
- Two different sources — a manually configured static route and OSPF — both offer the aggregation router at a rural exchange point a path to the same downstream /24. Junos has to pick one as active. What general rule governs that choice when multiple protocols offer a route to the identical destination?
- A co-op's edge router has three routes sitting in inet.0 for the exact same prefix: one from a directly connected interface, one static route an engineer configured, and one learned via OSPF. Assuming none of the preference values were manually changed from their Junos defaults, which of these three is generally the most trusted and becomes the active route?
- An engineer runs a route lookup on a co-op's core router and sees two entries for the same downstream /24, but only one of them is marked as the route Junos is actually using to forward subscriber traffic right now. What is that in-use route called?
- A NOC technician at a regional ISP notices a static route to a backup POP still listed under show route even though OSPF is currently supplying the preferred, active path to that same destination. What best describes the static route's current status?
- A small telecom cooperative has one router with a single upstream transit provider and no dynamic routing protocol running toward that provider. The network engineer wants to guarantee a specific, predictable path out of the network without relying on any protocol adjacency. Which routing mechanism directly fits this need?
- A rural ISP wants traffic destined for a retired subscriber block to be dropped immediately at the aggregation router without sending any notification back to the sender, to avoid generating extra traffic toward customers who are still probing that old range. Which static route next-hop option produces this silent-drop behavior?
- An engineer configures a static route for a decommissioned subnet at a co-op's head-end and wants the router to actively notify any sender that the destination is unreachable, rather than dropping packets without a trace. Which next-hop keyword accomplishes this?
- A network engineer at a regional ISP is deciding whether to use discard or reject for a static route covering an aggregate summary block that includes some currently unassigned subscriber subnets. Silent discard risks packets vanishing without any diagnostic clue if a legitimate customer is accidentally caught in the summary. Which factor should most directly drive the choice between discard and reject here?
- A co-op wants a static route to its regional data center to normally use the primary fiber path, but automatically fail over to a secondary microwave link if the primary next-hop becomes unusable, without running a dynamic routing protocol. Which static route feature is designed for assigning a distinct preference value to each of several next-hops for the same destination?
- A cooperative configures its regional data center route with a primary next-hop toward its main transit provider and a qualified next-hop toward a secondary transit provider carrying a higher (less preferred) preference value. What common name describes this overall static routing design, where the backup path only becomes active if the primary disappears from the routing table?
- A router at a small cooperative's head-end needs a single routing table entry that matches any destination not covered by a more specific route, so subscriber traffic bound for the wider internet has somewhere to go. Which route accomplishes this?
- An engineer configures a static route on a co-op's aggregation router, but the next-hop IP address typed in isn't on any subnet directly attached to that router, it's only reachable through another route already sitting in the table. What must happen before this static route can actually be used to forward traffic?
- A network engineer explains that Junos can maintain more than one independent routing table on the same device, each with its own set of routes, entirely separate from the default inet.0 table. What is this general capability called at an introductory level?
- A regional cooperative offers wholesale broadband service to several smaller downstream providers over the same core routers, and wants each downstream provider's routes kept completely separate from the co-op's own internal backbone routes on the same device. Which routing concept most directly supports this kind of separation?
- A network engineer describes a dynamic routing protocol category where each router periodically advertises its entire routing table, along with a simple metric like hop count, to its directly connected neighbors, without any router building a full map of the network topology. What category of protocol is being described?
- An engineer at a regional carrier explains that instead of trusting secondhand summaries from neighbors, every router in this protocol's area independently floods information about its own directly connected links, so each router ends up building its own complete map of the topology before computing the best paths. Which protocol category does this describe?
- A regional ISP runs one routing protocol among its own routers inside its single autonomous system, and a different protocol to exchange reachability information with its separate upstream transit provider's autonomous system. Which pair of terms correctly labels these two protocol roles?
- A regional ISP is growing quickly, adding new aggregation sites and backup links every quarter, and the network engineer is tired of manually updating static routes across a dozen routers every time the topology changes. What is the main advantage of adopting a dynamic routing protocol in this situation?
- A small rural cooperative operates a single router with exactly one upstream transit connection and no plans to add a second one. The engineer is deciding whether to run a dynamic routing protocol toward that upstream or simply configure a static default route. Which factor most strongly favors the static route in this specific case?
- A co-op's edge router faces the public internet, and the engineer wants it to drop any incoming packet whose source address doesn't have a matching route pointing back out the same interface it arrived on, catching spoofed traffic using the router's own routing table rather than a separately written filter. Which mechanism does this?
- A subscriber-facing interface on a co-op's aggregation router goes physically down. The router had a directly connected route to that interface's subnet, which had been the active route in the forwarding table. What happens to that route once the interface is down?
Routing Policy and Firewall Filters · 35 questions
- Prairie Broadband Cooperative's engineers want to control which routes get installed in the routing table or advertised to a neighboring carrier, without changing how the routing protocol itself calculates best paths. Which Junos mechanism is built for this job?
- A technician at Ridgeline Fiber Cooperative is reviewing policy applied where routes learned from a BGP peering session are evaluated before Junos decides whether to place them into the routing table. Which type of routing policy does this describe?
- At a cooperative's aggregation router, a policy is applied where routes already sitting in the routing table are evaluated before Junos decides whether to advertise them out to an upstream transit provider. Which type of routing policy does this describe?
- A cooperative's edge router learns a subscriber-aggregation route from OSPF and also has a matching static route toward the same subnet. No export policy has been configured on the BGP session to its transit provider. By Junos's default BGP export behavior, what happens to these routes?
- A cooperative runs OSPF across its internal aggregation network and has several static routes pointing to subscriber DSL pools. With no export policy configured on OSPF, what happens to those static routes with respect to OSPF advertisement?
- While writing a routing-policy term, an engineer at a regional ISP needs to match on the source protocol and prefix of incoming routes, separately from matching on which neighbor or protocol the route is being sent toward. Which two match-condition keywords in a Junos policy term correspond to these two directions?
- A term in an export policy matches routes destined for a specific transit neighbor and includes the action accept. What effect does this accept action have on policy evaluation for a matching route?
- An engineer adds a term near the top of an export policy toward an upstream peer with the action reject, intended to withhold one subscriber block from that peer. What is the effect of reject on evaluation of a matching route?
- A policy term at a cooperative's border router does not match the current route, but the policy has additional terms below it that might. Which flow-control action would Junos apply by default in this situation?
- An engineer wants a route that matches an early term in one export policy to stop being evaluated in that policy and instead be evaluated against a completely separate policy further down the export chain. Which then action accomplishes this?
- A cooperative's BGP export statement lists three policies in order: FILTER-MARTIANS, LIMIT-SUBSCRIBER-BLOCKS, then ADVERTISE-DEFAULT. A route matches a terminating term in LIMIT-SUBSCRIBER-BLOCKS. What happens to that route with respect to ADVERTISE-DEFAULT?
- A cooperative's OSPF neighbor advertises a route that does not match any term in the router's configured import policy. With no explicit default action configured, what happens to that route by Junos's built-in default import behavior?
- A cooperative configures an export policy toward its transit provider with a single term that matches only the co-op's own aggregate prefix. A subscriber static route does not match that term. What happens to the subscriber static route with respect to advertisement to the transit provider?
- A cooperative agreed with a peering partner to accept only two specific subscriber blocks over a peering session, nothing else. Which routing-policy match condition lets the import policy match precisely those two prefixes, including any more-specific routes within them, while still not matching a route the peer accidentally advertises for someone else's block?
- A cooperative wants its BGP export policy toward a transit provider to advertise only the static routes representing its subscriber DSL pools, and nothing learned via OSPF or direct interface routes. Which from match condition in the export policy term achieves this source-based selection?
- A policy term is written with a then action of reject but includes no from or to condition at all. Which routes will this term match when evaluation reaches it?
- An engineer needs an export policy term to match a subscriber aggregate block plus every more-specific route contained within it, not just the exact aggregate prefix itself. Which Junos route-filter match type is appropriate?
- A rural cooperative peers separately with Transit-A and Transit-B. Engineers are concerned that if a term is missing, the co-op's router could start forwarding traffic between the two transit providers, effectively becoming unpaid transit itself. Which policy design correctly prevents this?
- A network engineer at a rural broadband cooperative wants to drop management traffic addressed to a POP router unless it comes from the NOC subnet, without changing which routes the router installs in its routing table. Which Junos OS mechanism inspects individual packets against match conditions to make that permit-or-deny decision, rather than influencing route selection?
- A technician at a regional ISP is building a firewall filter with three terms to protect a subscriber aggregation router: term one permits DNS to the resolver, term two permits established management sessions, and term three is a catch-all. When Junos evaluates this filter against an incoming packet, in what order does it check the terms?
- A cooperative's NOC wants a firewall-filter term that tallies how much traffic from a suspicious source address is arriving at a POP router, but still lets that traffic continue to be evaluated against the remaining terms in the filter. Which kind of then action should the term use?
- A rural broadband cooperative applies a firewall filter to a subscriber-facing interface with two terms: one permits DHCP, and one permits DNS. A subscriber's device then sends an ICMP echo request that matches neither term. What happens to that packet?
- A cooperative's engineer needs to filter traffic arriving from subscribers into a POP router's aggregation interface, while leaving traffic the router sends back out to those same subscribers unaffected. Under family inet on that interface, which statement should reference the firewall filter?
- A regional carrier-hotel operator wants to protect a POP router's Routing Engine from unauthorized SSH and SNMP attempts, without affecting the transit customer traffic the router forwards through its packet-forwarding engine. Which interface should the firewall filter be applied to for this purpose?
- A rural fiber cooperative wants a firewall-filter term to cap how much traffic a single residential subscriber's aggregation port can send toward the core, allowing a small burst above the cap for normal web-browsing behavior. Which introductory Junos concept, referenced inside a filter term's then action, is designed for this kind of rate limiting?
- An engineer at a small-town head-end facility writes a firewall-filter term intended to match only inbound TCP traffic destined for port 22 on the POP router from a specific NOC host address. Which part of the term should carry the source address, destination port, and protocol conditions that decide whether a packet matches?
- A co-op's NOC configures a filter term with the then action set to log, matching traffic from an unfamiliar address range hitting a POP router. After that term, the filter has two more terms: one permitting known partner traffic and a final explicit discard-all term. Does the log action by itself stop the matched packet from reaching the later terms?
- A cooperative's filter has four terms applied to a POP router's transit-facing interface. Traffic from a peering partner matches term two, and term two's then action is accept, a terminating action. What happens to terms three and four for that specific packet?
- A rural broadband cooperative notices that one subscriber on a shared aggregation port is consuming enough upstream bandwidth to degrade service for neighboring subscribers on the same port. Which combination of Junos concepts, applied together on that interface, addresses this at an introductory level?
- A new technician at a regional ISP asks why the co-op's POP router evaluates each packet against a firewall filter independently, rather than remembering that a subscriber's device already had an accepted connection a moment earlier. Which characteristic of a Junos firewall filter explains this behavior?
- A carrier-hotel operator applies a firewall filter to a POP router's transit interface that discards packets from a specific bogon range. After the filter is committed, does the router's routing table change as a result of packets from that range being discarded?
- A rural telecom cooperative wants unauthorized SSH attempts hitting its POP router's loopback filter to be dropped without any indication being sent back to the source, so a scanning host gets no useful feedback at all. Which terminating then action fits this requirement better than the alternative that would notify the sender?
- A regional ISP's edge router receives a packet claiming a source address from a private, non-routable range on an interface facing the public internet, which should never legitimately appear there. Which introductory firewall-filter approach addresses this kind of spoofed-source traffic at the network edge?
- A technician configures a POP router's firewall filter with term A first, which broadly discards all TCP traffic, followed by term B, which is meant to permit TCP port 22 from the NOC subnet. After committing, NOC staff can no longer reach the router by SSH. What is the most likely cause?
- A cooperative's NOC is troubleshooting a suspected DDoS-style flood aimed at a POP router and wants to see, in near real time, how much traffic each firewall-filter term is matching without disrupting the accept and discard decisions already configured. Which action should be added to the terms of interest to provide this visibility?
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