46 questions · Interior Gateway Protocols · All types, answers revealed
Which TWO types of OSPF areas allow the generation of Type-7 LSAs? (Choose two)
NSSAs allow ASBRs to inject external routes using Type-7 LSAs.
Why this answer
Type-7 LSAs are exclusively generated within Not-So-Stubby Areas (NSSA) and NSSA totally stubby areas by ASBRs connecting external routes.
You want to filter OSPF Type-3 Summary LSAs leaving Area 1 on an ABR running Junos OS. Where must this export policy be applied?
Type-3 LSA generation for aggregated prefixes can be controlled and filtered using the area-range export policy on the ABR.
Why this answer
To filter Type-3 summary LSAs generated by an ABR as they leave an area, you apply the export policy using the 'set protocols ospf area <area-id> area-range <prefix> export <policy-name>' hierarchy.
Which TWO commands are used to troubleshoot OSPF issues on Junos devices? (Choose two)
Displays OSPF neighbor states and adjacency progress.
Why this answer
Operational commands like 'show ospf neighbor' and 'show ospf database' are standard for troubleshooting OSPF adjacencies and LSDB status.
When configuring OSPFv3 authentication, which mechanism is natively utilized in modern Junos implementations since OSPFv3 relies on IPv6 AH/ESP or OSPFv3 Authentication Trailer (RFC 7166)?
Authentication trailers are configured using the authentication-trailers option in OSPFv3.
Why this answer
Junos supports the OSPFv3 Authentication Trailer defined in RFC 7166, configured via the authentication-trailers command under protocols ospf3.
Which OSPFv3 LSA type is responsible for carrying IPv6 prefix information within the same area, replacing the role of Router and Network LSAs carrying IP addresses in OSPFv2?
Type 9 LSAs are used in OSPFv3 to advertise IPv6 prefixes associated with a router or transit network within the same area.
Why this answer
OSPFv3 separates topology information from IP prefix information. Type-9 (Intra-Area-Prefix-LSA) carries IPv6 prefixes associated with routers or transit networks within the area.
Which Junos command displays the link-state database for OSPFv2, showing router LSAs and network LSAs?
This command outputs the complete OSPF LSDB.
Why this answer
The command 'show ospf database' displays the OSPF link-state database on a Junos device.
How do you examine the specific OSPF routing table entries learned via OSPF on a Junos device?
This command filters the routing table to show only OSPF routes.
Why this answer
The 'show route protocol ospf' command displays routes learned specifically through the OSPF routing protocol.
Which Junos configuration command enables MD5 cryptographic authentication on an OSPFv2 interface?
This is the correct Junos syntax for OSPFv2 MD5 authentication.
Why this answer
MD5 authentication for OSPFv2 in Junos is configured under the interface hierarchy with the 'authentication md5' statement followed by a key ID and password.
When redistributing BGP routes into OSPF, what is the default OSPF metric assigned to the redistributed routes in Junos if no metric is specified in the export policy?
Junos assigns a default metric of 5 for routes redistributed into OSPF when not specified.
Why this answer
When routes are redistributed into OSPF without an explicit metric set in the policy, Junos assigns a default metric of 5 for external routes.
An administrator needs to filter Type-3 LSAs entering an OSPF stub area on a Junos routing device. Which statement under the area hierarchy is required?
The 'restrict' option prevents the summary LSA from being injected into the area.
Why this answer
In Junos OS, you can filter inbound Type-3 LSAs into a stub or NSSA area using the 'area-range' command with the 'restrict' or 'hidden' parameter, or using an import policy at the area level, but specifically for summarization and blocking, the area-range statement with 'restrict' prevents the LSA from being advertised.
Which TWO statements are true regarding Junos OSPF routing policies and policy evaluation? (Choose two)
Junos processes policy terms sequentially until a match and terminal action occur.
Why this answer
Junos routing policies are evaluated top-to-bottom per term, and if no match is found, the default action depends on the context (reject for export policies, accept for import policies in some contexts, but let's review exact Junos behavior: export policies default to reject, import policies default to accept). Also, route filtering can match specific prefixes.
You are configuring OSPF domain-id when redistributing routes between OSPF and BGP (or multiarea setups). Which configuration statement sets the OSPF domain identifier?
The 'domain-id' command defines the OSPF domain identifier.
Why this answer
The domain-identifier for OSPF (often used in MPLS VPNs or inter-AS scenarios) is configured under protocols ospf using the domain-id statement.
You are configuring OSPFv2 on a Junos device and need to inject default routes into an OSPF NSSA area. Which configuration command under protocols ospf area should be used?
This command correctly generates a Type 7 default LSA into the NSSA area with the specified metric.
Why this answer
To inject a default route into an NSSA area in Junos OSPF, the stub default-metric command or nssa no-summarize with default-metric is configured under the specific area. Specifically, 'nssa default-metric' generates a Type 7 default LSA.
You are redistributing BGP routes into OSPF on an MX Series router. By default, what metric type and cost are assigned to these redistributed routes when they enter the OSPF domain?
Junos assigns external metric-type 2 and a cost of 1 by default to all routes redistributed into OSPF.
Why this answer
By default, routes redistributed into OSPF are assigned metric-type 2 (E2) and a default metric value of 1.
Which TWO statements are correct regarding OSPF NSSA (Not-So-Stubby Area) behavior and configuration in Junos OS? (Choose two)
Type-7 LSAs are specifically designed for NSSAs to originate external routes without accepting Type-5 LSAs from the backbone.
Why this answer
NSSA areas allow external routes to be injected via Type-7 LSAs. By default, an NSSA does not flood default routes unless explicitly configured with 'default-lsa'.
Which THREE parameters must match between two OSPF routers on a shared broadcast segment for an adjacency to successfully form? (Choose three)
Duplicate Router IDs will prevent adjacencies from forming, and they must be unique within the OSPF domain.
Why this answer
OSPF hello/dead timers, area ID, and authentication parameters must match between neighbors to establish an adjacency.
What is the default OSPF reference bandwidth in Junos OS?
100 Mbps is the standard default reference bandwidth for OSPF.
Why this answer
The default OSPF reference bandwidth in Junos OS is 100 Mbps (100,000,000 bps).
Which command allows you to view the real-time tracing of OSPF packet exchanges and state changes on a Junos device?
Traceoptions logging for OSPF debugging is configured via this hierarchy.
Why this answer
OSPF tracing is configured and viewed using standard Junos traceoptions, and operational debugging is viewed using 'clear' or 'show log' or real-time tracing commands. For checking active traces or running traces, traceoptions are configured under protocols ospf.
Which THREE configuration tasks are required when implementing OSPFv3 on Junos devices? (Choose three)
OSPFv3 is configured under protocols ospf3.
Why this answer
Configuring OSPFv3 requires specifying protocols ospf3, configuring areas, and enabling OSPFv3 on specific interfaces (IPv6 enabled).
You want to tune the speed at which OSPF processes link-state updates by modifying the SPF calculation delay and hold timers. Where are these timers configured?
SPF timers are tuned globally under protocols ospf.
Why this answer
SPF calculation timers (delay and hold) are configured under the protocols ospf hierarchy using the spf-delay and spf-holdtime statements.
You need to modify the priority of a Junos OSPF interface to ensure it becomes the designated router (DR). Which command accomplishes this?
The 'priority' command sets the OSPF interface priority (default is 1, higher wins).
Why this answer
OSPF interface priority is configured under the interface level within protocols ospf using the 'priority' command.
Which statement correctly describes the function of an OSPF Stub Area?
Stub areas do not accept external LSAs; ABRs inject a default route to reach external destinations.
Why this answer
Stub areas block external Type-5 LSAs and instead rely on a default route injected by the ABR.
Which Junos configuration hierarchy is used to disable the generation of OSPF Type-7 to Type-5 LSA translation on an NSSA Area Border Router (ABR)?
The 'translator-role never' command disables the NSSA ABR from performing Type-7 to Type-5 translation.
Why this answer
To prevent an NSSA ABR from translating Type-7 LSAs into Type-5 LSAs, you use the 'no-summaries' or 'nssa translator never' commands. Specifically, disabling translation is done via 'set protocols ospf area <name> nssa translator-role never'.
Which TWO actions can you take in Junos OS to optimize OSPF convergence times in a large enterprise network? (Choose two)
Lowering hello and dead timers allows routers to detect link failures more rapidly.
Why this answer
OSPF convergence can be accelerated by tuning SPF schedule delays (spf-options) and adjusting interface-specific hello and dead intervals.
You need to prevent an OSPF interface from participating in Designated Router (DR) election, forcing it to always act as a DROTHER, even if it has the highest priority. How is this achieved in Junos?
Wait, 'no-dr-election' is not a valid Junos command; priority 0 is the correct method. Let's make sure the option text reflects correct evaluation. Actually, setting priority 0 is the correct method.
Why this answer
Setting the OSPF interface priority to 0 prevents the router from participating in DR/BDR elections and forces it to become a DROTHER.
Which THREE types of LSAs are blocked from entering an OSPF Totally Stubby Area? (Choose three)
Type 4 LSAs are blocked in totally stubby areas.
Why this answer
Totally stubby areas block summary LSAs (Type 3), ASBR summary LSAs (Type 4), and AS external LSAs (Type 5). Router (Type 1) and Network (Type 2) LSAs are allowed within the area.
When configuring OSPF sham-links in Junos to support MPLS VPN back-door links, which TWO characteristics apply? (Choose two)
Sham-links use /32 source and destination addresses inside the VPN routing instance.
Why this answer
Sham-links are treated as intra-area links between PE routers and require a separate /32 IP address configured under the loopback or routing instance, appearing as unnumbered or numbered point-to-point links.
Which TWO actions can be performed by an OSPF routing policy export filter when redistributing routes into OSPF? (Choose two)
Export policies can assign a specific metric to redistributed routes.
Why this answer
Routing policies when exporting into OSPF can set metric types (Type 1 or Type 2) and modify route metrics. They cannot directly change area ID during redistribution without area design changes.
Which THREE mechanisms are utilized by Junos to protect OSPF routing operations and control plane resources? (Choose three)
Cryptographic authentication prevents unauthorized routers from forming adjacencies.
Why this answer
Control plane protection for OSPF includes Routing Engine firewall filters (lo0 filters), OSPF cryptographic authentication (MD5/SHA), and OSPF graceful restart helper mode / overload control.
Which command verifies the OSPF neighbor states and adjacency progress on a Junos device?
This is the correct operational command to check OSPF neighbors.
Why this answer
The 'show ospf neighbor' command displays OSPF neighbor states, interface, and dead timer details.
An engineer is configuring OSPFv3 on Junos OS and notices that adjacencies are failing to form over a point-to-point link. Reviewing the interface configuration, what is a mandatory requirement for OSPFv3 interface configuration that differs fundamentally from OSPFv2?
OSPFv3 runs directly over IPv6 and uses link-local addresses as source addresses for hello packets and neighbor formation.
Why this answer
OSPFv3 relies heavily on IPv6 link-local addresses for neighbor discovery and next-hop resolution, and interfaces must have an IPv6 link-local address assigned.
An engineer needs to prevent Type-5 LSAs from entering an OSPF stub area while still allowing external routes to be reached via a default route. Which configuration statement under [edit protocols ospf area] achieves this on a Juniper device?
The 'stub' command under the area hierarchy defines the area as a stub, blocking external LSAs and injecting a default route.
Why this answer
Configuring 'stub' without the 'no-summaries' keyword makes the area a standard stub area, which blocks Type-5 LSAs and injects a default route (Type-3 summary default).
You are designing a routing policy to tag routes being redistributed from OSPF into BGP. Where in the routing policy should the tag match condition be placed?
In Junos routing policies, 'ospf-tag' is the correct match condition under the 'from' statement to evaluate OSPF route tags.
Why this answer
When matching OSPF route tags in routing policies, the term must include the 'ospf-tag' match condition within the 'from' block.
You need to ensure that an OSPF interface does not send or receive OSPF hellos, but its subnet is still advertised into the OSPF domain. What configuration achieves this in Junos?
The 'passive' keyword configures the OSPF interface as passive.
Why this answer
Configuring an interface as passive prevents OSPF protocol packets from being sent or received on that interface while still including its network prefix in the routing updates.
You want to tune OSPF convergence by reducing the hello and dead intervals on a point-to-point interface. Which configuration is valid?
Hello and dead intervals are configured per interface under the OSPF area.
Why this answer
OSPF interface timers such as hello-interval and dead-interval are configured directly under the interface hierarchy within protocols ospf.
Which THREE parameters must match between OSPF routers for an adjacency to successfully form on a point-to-point network? (Choose three)
Authentication keys and type must match if authentication is enabled.
Why this answer
For OSPF neighbors to form adjacencies, area ID, hello/dead intervals, and authentication settings (if enabled) must match. MTU size can also cause stuck in ExStart/Exchange if mismatched and enabled.
You want to change the OSPF reference bandwidth globally on a Junos routing device to accurately calculate costs for high-speed interfaces. Where is this configured?
This command sets the OSPF reference bandwidth globally to 10 Gbps.
Why this answer
The reference bandwidth for OSPF is configured globally under the protocols ospf hierarchy using the reference-bandwidth statement.
You are tasked with summarizing internal OSPF routes on an Area Border Router (ABR). Which configuration statement accomplishes route summarization for an area?
The 'area-range' command summarizes routes advertised from the specified area into the backbone or other areas.
Why this answer
Internal route summarization on an OSPF ABR in Junos is configured using the 'area-range' statement under the specific area hierarchy.
You need to adjust the OSPF cost on a specific interface to manipulate path selection. Which command sets the OSPF cost on an interface?
The 'cost' command explicitly sets the OSPF cost for that interface.
Why this answer
OSPF interface cost is explicitly configured under the interface hierarchy within protocols ospf using the 'cost' statement.
When configuring OSPFv3, which Junos address-family hierarchy is used to enable OSPFv3 on an interface?
OSPFv3 is configured under protocols ospf3 referencing areas and interfaces directly.
Why this answer
OSPFv3 in Junos operates within the IPv6 address family under protocols ospf3.
You are redistributing static routes into OSPF on a Junos device and want to assign a specific metric type to the resulting External LSAs. Where is this metric-type defined?
The 'metric-type' action within a routing policy 'then' clause sets the OSPF external metric type.
Why this answer
External route metric types (Type 1 or Type 2) when redistributing into OSPF are defined under the export policy term's then clause using 'metric-type'.
You are configuring OSPF database overflow protection to prevent a router from running out of memory due to an excessive number of external LSAs in the LSDB. Which configuration enables this feature globally?
This command configures OSPF database overflow protection with a maximum external LSA limit and recovery timer.
Why this answer
Database overflow protection in Junos OSPF is configured using the 'database-overflow' statement under protocols ospf, specifying the limit and external timer.
An OSPF area in your network contains multiple ABRs. You need to suppress the generation of Type-4 summary LSAs into a totally stubby area. How does Junos handle this natively?
Type-4 LSAs (ASBR summaries) are blocked along with Type-3 and Type-5 LSAs in totally stubby areas.
Why this answer
Totally stubby areas automatically block Type-3, Type-4, and Type-5 LSAs. No separate command is needed to suppress Type-4 LSAs once an area is defined as a totally stubby area.
You are configuring an OSPF NSSA and want to suppress the translation of Type-7 LSAs into Type-5 LSAs on one of the ABRs because another ABR is already performing the translation. Which statement is used?
The 'no-translate' option disables Type-7 to Type-5 LSA translation on the NSSA ABR.
Why this answer
To prevent an NSSA ABR from translating Type-7 LSAs into Type-5 LSAs, you configure the 'no-translate' option under the nssa statement.
You need to configure OSPFv2 graceful restart as a helper on a Junos router to assist neighboring routers during their routing engine switchover. Which command enables helper mode?
This command explicitly configures OSPF graceful restart helper behavior.
Why this answer
By default, OSPF graceful restart helper mode is enabled on Junos routers. To explicitly configure or modify it, you use the 'graceful-restart helper' command under protocols ospf.
You are troubleshooting an OSPF network where virtual links are deployed to connect a non-backbone area to Area 0 across a transit area. Which statement is true regarding virtual link configuration in Junos?
This command correctly establishes an OSPF virtual link through a transit area using the neighbor router ID.
Why this answer
Virtual links require you to specify the area ID of the transit area and the router ID of the remote endpoint (the other ABR) under protocols ospf.
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