Layer 3 Technologies

ENARSI · 105 questions

• A housing authority edge router learns the same parks subnet from a manually configured static route and from OSPF. By default, which path does the router install in the RIB?
• A library consortium edge learns the same court VLAN prefix as an internal EIGRP route and as an eBGP route. Which source wins by default administrative distance?
• A county courts team adds a floating static toward a backup MPLS circuit while OSPF remains the primary path to the justice complex. How should the floating static’s administrative distance be chosen?
• A city clerk’s office sees both an external EIGRP route and an OSPF route for the same water-SCADA prefix. Which path does IOS prefer by default, and why?
• A parks department wants a known-good OSPF path to city hall to remain preferred over an iBGP-learned copy of the same prefix. What AD relationship makes that outcome correct by default?
• During a sanitation-department migration drill, a lab router learns the same township prefix via RIP and via OSPF. Which protocol’s route is installed by default?
• An emergency-management office redistributes library prefixes into the core and wants those routes marked so later filters can recognize them. Which route-map action best tags the redistributed prefixes for that policy?
• A school-district WAN team must stop advertising only police-camera prefixes outbound while leaving other OSPF routes intact. Which route-map approach achieves that selective filter?
• A fire-district IT team redistributes static routes for fire-station WANs into EIGRP and must assign a controlled composite metric. Which route-map capability provides that metric during redistribution?
• A police records bureau wants inbound BGP updates for citizen-portal prefixes from ISP-A preferred over ISP-B inside the AS. Which route-map set action on the ISP-A neighbor best expresses that preference?
• An assessor’s office needs redistributed transit routes that match a prefix-list to receive both a new metric and a route tag in one policy pass. How should the route-map be built?
• A building-permits office must block redistribution of an incorrect summary while still allowing more-specific civic prefixes into the target protocol. Which route-map logic is correct?
• A public-health department earlier tagged guest Wi-Fi routes at the edge. Core routers must now drop those tagged prefixes during redistribution. Which match is the right tool?
• A wastewater treatment plant applies a redistribute route-map that permits only a few matched clauses and has no final explicit deny. Why do unexpected prefixes still fail to redistribute?
• A municipal 911 PSAP sees routing loops after mutual redistribution between OSPF and EIGRP at two borders with no route tags. What is the most direct loop-prevention fix using tagging?
• A county elections office runs a hub-and-spoke radio WAN for sanitation sites and relies on split horizon. What does split horizon prevent by default?
• A civic data center withdraws a failed parks summary and uses route poisoning so remote sites stop using the bad path quickly. What is the core idea of route poisoning?
• A regional planning commission wants to stop a BGP↔OSPF redistribution feedback loop toward city hall without depending only on tags. Which mechanism directly supports that loop-prevention goal?
• A municipal fiber consortium removes redistribution route tags that previously blocked feedback between campuses and soon sees loop-like instability return. What does that symptom most strongly indicate?
• A city traffic-operations center must stop the same 911 subnet from feeding back between OSPF and EIGRP. When is a prefix-list deny a better primary control than tag-based policy alone?
• A county jail facilities team redistributes selected OSPF civic prefixes into BGP so the Internet edge can advertise public services. Which verification cue best confirms those OSPF routes were successfully injected into BGP?
• A public-library branch network injects a static null0 summary into OSPF so remote counties learn an aggregate for the city supernet. Why is redistributing that discard static useful?
• After a department merger, a municipal hospital campus mutually redistributes EIGRP and OSPF at a single border. What seed-metric consideration is most important to avoid unusable or surprising external paths?
• A city IT team must advertise VRF-connected court case-management subnets into BGP for a cloud handoff. Which redistribution pattern correctly injects those connected prefixes?
• A county network team redistributes a classless routing source into OSPF but only classful-looking major networks appear. What missing keyword commonly causes that symptom?
• A township public works team redistributes OSPF into EIGRP for parks and roads VLANs and must set a seed metric so operators are not surprised by unequal-cost candidates. Which action correctly supplies the EIGRP composite seed metric on redistribution?
• A municipal water utility redistributes selected BGP SaaS prefixes used by the permits office into OSPF on the edge ASBR. How do those redistributed BGP prefixes typically appear inside OSPF?
• A transit authority wants only utility-SCADA prefixes that already carry a specific route tag to enter the global routing table when redistributing from a SCADA VRF IGP. Which approach enforces that conditional redistribution?
• A port authority redistributes the same static civic prefix at two border routers without filtering and operators report duplicate or unstable paths. What is the most appropriate remediation at ENARSI depth?
• An airport authority needs to confirm that a redistributed parks prefix is actually owned by the intended protocol in the routing table after a change window. Which verification approach best proves RIB ownership versus merely seeing the prefix in a protocol database?
• A housing authority manually summarizes many /24 library-branch networks into a /16 at an ABR to shrink the core LSDB. What behavior should operators expect for that OSPF area range summarization?
• A library consortium briefly enables EIGRP auto-summary in a lab that uses non-contiguous civic addressing across branches. What is the primary risk of that auto-summary behavior?
• A county courts network team advertises a BGP aggregate for public civic services while still leaking more-specific prefixes for a dual-homed PSAP. Which design element supports that pattern?
• A city clerk’s office summarizes a parks address range, but some component subnets were never present and users to those holes are blackholed. What mechanism most directly explains that symptom?
• A parks department advertises an OSPF summary toward a partner county and must stop the individual component routes from also being advertised into that area. What is the expected summarization behavior?
• A sanitation department runs EIGRP named mode across township hubs with non-uniform addressing and must choose a summarization approach. When is manual summarization safer than EIGRP auto-summary?
• An emergency-management office wants guest Wi-Fi Internet traffic to exit a cheaper circuit while staff applications keep using the primary MPLS path based on the normal routing table. Which feature implements that selective override?
• A school district WAN team applies PBR with set ip next-hop for selected student-portal traffic on an IOS XE border. What should verification focus on?
• A fire-district IT team must send backup-camera streams to a forensic collector without changing how other traffic to the same destination prefixes is routed in the global table. Which approach fits?
• A police records bureau configures PBR on a border router’s ingress interface so only ACL-permitted packets are policy-routed to an alternate next hop. Which combination is required?
• An assessor’s office uses PBR with set ip next-hop toward a preferred exit. When that next hop becomes unreachable, what is the typical default behavior for matched packets?
• A building-permits office wants citizen-portal traffic steered by PBR to fail over when the preferred exit dies. Which design combines resilience with PBR?
• A public-health department must keep utility SCADA routing separate from corporate office routing on the same edge router without deploying MPLS. Which technology fits that ENARSI requirement?
• A wastewater treatment plant places SCADA and office interfaces into different VRFs on one IOS XE router. What must operators remember when finishing that VRF-Lite build?
• A municipal 911 PSAP needs a shared DNS prefix reachable from two VRF-Lite instances without merging the entire tables. What approach matches controlled leaking at VRF-Lite depth?
• A county elections office runs OSPF for courts inside a VRF while city-hall networks remain in the global table on the same chassis. How should OSPF be applied for the courts VRF?
• A civic data center engineer troubleshoots missing SCADA routes and used only show ip route without a VRF name on a VRF-Lite edge. What was most likely wrong with that verification method?
• A regional planning commission co-locates two agencies that both use overlapping RFC1918 space on shared WAN routers. Which VRF-Lite outcome is the design trying to achieve?
• A municipal fiber consortium needs much faster detection of a dark-fiber failure between campuses than IGP hello timers alone provide. What is BFD’s primary role in that design?
• A city traffic-operations center wants OSPF adjacency to drop quickly when a link fails silently between signal-ops routers. How does BFD integrate with OSPF for that outcome?
• A county jail facilities IT team wants faster failure detection on a latency-sensitive 911 backhaul than default EIGRP hellos provide. Why prefer enabling BFD for the EIGRP neighbors over simply lowering EIGRP hello and hold timers aggressively?
• A public-library branch network is dual-homed at regional hubs and staff ask how BFD echo mode differs from asynchronous mode at a describe level. Which statement is accurate?
• A municipal hospital campus WAN is migrating from classic EIGRP to named mode so township hubs share a consistent address-family configuration model. What is the primary operational difference named mode introduces?
• A city IT team enables EIGRP for dual-stack parks cameras and must keep IPv4 and IPv6 routing logically separate inside the same named process. Which approach matches EIGRP address-family behavior?
• After a change window, a county network team finds EIGRP adjacencies down between two civic hubs. Show commands reveal mismatched K-values. What is the expected result?
• A township public-works department configures EIGRP authentication with a key chain on WAN interfaces so a rogue device plugged into a spare circuit cannot join the AS. What symptom typically appears when authentication fails between two otherwise valid neighbors?
• A municipal water utility explains backup path selection for a court VLAN. When does EIGRP install a neighbor’s path as a feasible successor?
• A transit authority sees Stuck-in-Active after a summary flap on the civic WAN. What does SIA indicate for operators?
• A port authority configures EIGRP stub routing at remote fire stations. What primary problem does the stub feature address?
• An airport authority has two circuits toward a landfill site with unequal EIGRP metrics and wants both paths to carry traffic. Which feature enables that unequal-cost load balancing?
• A housing authority has two identical MetroE links into city hall running EIGRP with matching metrics. What behavior provides equal-cost multipath?
• A library consortium wants traffic to prefer one WAN exit by influencing the EIGRP composite metric on an interface. Which inputs most directly feed that classic composite metric?
• A county courts network runs EIGRP for SCADA inside a VRF while a separate global EIGRP process serves office VLANs on the same router. What does this separation provide?
• A city clerk’s office cannot form an EIGRP neighbor on the WAN link to a partner county. Investigation shows passive-interface was left enabled on that WAN interface. What is the impact?
• Before a planned fiber cut, a parks department reviews the EIGRP topology table for a critical prefix. How should operators distinguish the successor from a feasible successor?
• A sanitation department configures a remote site as an EIGRP stub but still needs that site to advertise one critical local prefix upstream. Which concept addresses that need?
• An emergency-management office configures EIGRP on two civic hubs but adjacency never forms. The hubs use different autonomous-system numbers. What is the correct conclusion?
• After migrating to EIGRP named mode, a school-district WAN team notices metric values in show outputs look different from classic scaled metrics. What should troubleshooters understand?
• A fire-district IT team sees two feasible successors for a prefix, yet only one path is installed in the routing table. Variance is still at the default of 1. What explains this?
• A police records bureau plans a weekend EIGRP authentication key rollover across library WAN edges. What practice best preserves adjacency continuity during the rollover?
• An assessor’s office enables OSPFv3 for IPv6 campus edges while continuing OSPFv2 for IPv4. Which statement correctly describes their roles?
• A building-permits office sees OSPF neighbors stuck in 2-Way on a broadcast Ethernet segment that already has a DR and BDR. What is the correct interpretation for non-DR/BDR routers?
• A public-health department’s OSPF adjacency to a PSAP link drops after a MetroE change. Which mismatch is a classic cause that prevents neighbors from forming?
• A wastewater treatment plant enables OSPF authentication with MD5 keys so unauthorized routers cannot inject LSAs into the plant area. What is the typical symptom when authentication fails?
• A municipal 911 PSAP configures an Ethernet WAN between two civic hubs and wants to avoid DR/BDR election on that link. Which OSPF network type choice achieves that?
• A county elections office runs OSPF over a hub-and-spoke radio WAN to landfill sites where spoke-to-spoke multicast is unreliable. Which OSPF network type best fits that design and what must the engineers plan for?
• A civic data center designs OSPF with area 0 at the core, normal areas for city departments, and stub areas for remote libraries. What roles do those area types play?
• A regional planning commission converts a remote fire-district OSPF area to totally stubby so the LSDB stays tiny. What routes should routers in that area keep after the ABR is configured correctly?
• A municipal fiber consortium needs a remote area that can still inject a limited set of external routes while blocking most Type-5 flooding from the core. Which OSPF area type should they choose and why?
• A city traffic-operations center must identify which OSPF router is summarizing inter-area prefixes versus which one is redistributing an external routing source at the civic core. Which role mapping is correct?
• A county jail facilities team temporarily loses a contiguous path to area 0 while fiber work isolates a new OSPF area. What is the purpose of configuring an OSPF virtual link in that situation?
• A public-library branch network wants OSPF to prefer one dual-data-center uplink over the other without changing bandwidth references globally. Which mechanism is the primary way to influence that path preference?
• A municipal hospital campus WAN learns the same external prefix as both OSPF External Type-1 and Type-2 toward a cloud breakout. Which preference rule should the engineers expect?
• A city IT team sees an OSPF adjacency stall in ExStart/Exchange between two civic core routers after a WAN circuit change. Which mismatch is the classic cause of that symptom?
• A county network team troubleshoots OSPF on a multipoint tunnel-style segment where they want no DR election and treat the cloud as a collection of point-to-point adjacencies. Which network type behavior matches that goal?
• A township public works LAN connects several agency routers on a multi-access Ethernet transit segment running OSPF broadcast. How is the Designated Router chosen?
• A municipal water utility configures Type-3 filtering at an ABR so guest Wi-Fi prefixes stay local to one OSPF area and do not appear as inter-area routes elsewhere. What is the expected result?
• A transit authority runs OSPF inside a courts VRF-Lite instance while a separate global OSPF process serves parks networks on the same edge router. What operational reality should the team verify?
• A port authority learns the same permit-portal prefix as an intra-area OSPF route, an inter-area route, and an external route. Which preference order should guide troubleshooting?
• An airport authority clones a router template and later sees odd OSPF adjacency and LSA behavior across civic edge devices. Which requirement was most likely violated?
• A housing authority dual-homes citizen-facing prefixes to two ISPs with eBGP while keeping iBGP among civic core routers. What roles do those BGP peering types play?
• A library consortium needs BGP to carry dual-stack public services: IPv6 for modern portals and IPv4 for legacy catalog systems. How should that be structured on the BGP speakers?
• A county courts border router must form eBGP to an ISP using loopback endpoints rather than the directly connected interface addresses. Which feature enables that peering?
• A city clerk's office wants to stop a rogue device from successfully establishing BGP and injecting routes into the city ASN. Which control directly protects the TCP session between legitimate peers?
• A parks department uses private AS numbers internally but must advertise civic prefixes to the public Internet without leaking those private ASNs in the AS path. Which action addresses that requirement on the eBGP edge?
• A sanitation department applies a new inbound BGP filter toward an ISP and needs the policy to take effect without bouncing the TCP session. Which capability supports that approach?
• An emergency-management office peers with two similar ISP transit routers and wants identical outbound policies without duplicating every neighbor statement detail. Which BGP construct helps?
• A school district WAN team sees a BGP session fail to stay up toward an ISP and must interpret neighbor state while troubleshooting. Which statement best matches common state meaning?
• A fire-district IT team wants outbound traffic to prefer ISP-A and wants return traffic from the Internet to prefer the ISP-B path for the same civic prefixes. Which attribute pairing matches those goals?
• A police records bureau compares multiple BGP paths to a SaaS exit and must recall the classic best-path decision order at ENARSI depth. Which early sequence is correct?
• An assessor's office deploys a single BGP route reflector in the civic core so many edge routers no longer need a full iBGP mesh. What primary purpose does that route reflector serve?
• A building-permits office wants to accept only the provider-assigned blocks from its ISP and drop unexpected Internet prefixes. Which inbound BGP policy approach best matches that goal?
• A public-health department advertises eBGP-learned defaults into iBGP toward internal civic routers, but those routers cannot reach the ISP next-hop address. Which BGP neighbor setting on the border router most directly fixes that reachability gap?
• A wastewater treatment plant shares one edge router among multiple agencies and needs separate BGP routing contexts without provider MPLS. Which enterprise pattern fits that requirement at ENARSI depth?
• A municipal 911 PSAP must peer with a modern ISP whose autonomous system number no longer fits in the classic 2-byte ASN space. What capability must the PSAP's BGP implementation support?