Interior Gateway Protocols practice questions

set protocols ospf area 0.0.0.0 timers hello-interval 1

Why it fails: Timers keyword is not used at the area level for interface hello intervals.

set interfaces xe-0/0/0.1 ospf hello-interval 1

Why it fails: OSPF parameters are configured under protocols ospf, not under system interfaces.

set protocols ospf hello-interval 1 dead-interval 4

Why it fails: Intervals must be defined per interface, not globally under protocols ospf.

set policy-options policy-statement REDIST-STATIC term 1 from external-type 1

Why it fails: Junos policy terms match on route attributes such as protocol and community; external-type is not a valid from condition, so the LSA metric type is never set. It tempts because redistribution is configured in policy-statements, but the metric type belongs in the OSPF export action.

set protocols ospf export REDIST-STATIC metric-type 1

Why it fails: Junos OSPF export references a policy-statement and accepts no metric-type argument, so the command fails to commit. It tempts because export is where redistribution is enabled, but the external metric type must be set as an action inside the policy term, not on the protocol statement.

set protocols ospf redistribute static metric-type 1

Why it fails: Junos OSPF has no redistribute static hierarchy; redistribution is achieved by referencing a policy-statement under export. It tempts because IOS-style syntax uses redistribute with metric-type, but Junos places that value in a policy action instead.

You must apply an export policy on the ABR blocking Type-4 LSAs.

Why it fails: Area types manage LSA filtering natively; routing policies do not filter Type-4 LSAs directly.

You must use set protocols ospf suppress-fa to remove Type-4 LSAs.

Why it fails: Forwarding address suppression is unrelated to Type-4 LSAs.

You must configure set protocols ospf area <area> stub no-summary-asbr.

Why it fails: This command does not exist.

set routing-options graceful-restart ospf helper

Why it fails: OSPF graceful restart is configured under protocols ospf, not routing-options.

set protocols ospf graceful-restart router-role helper

Why it fails: The router-role keyword is invalid here.

set protocols ospf helper-mode enable

Why it fails: This is not the correct Junos syntax.

set protocols ospf3 area 0.0.0.0 interface xe-0/0/0.0 md5 key 123

Why it fails: MD5 command syntax belongs to OSPFv2, not OSPFv3.

set protocols ospf3 security ipsec spi 256

Why it fails: While IPsec can be used, standard modern Junos uses RFC 7166 authentication trailers.

set protocols ospf3 interface xe-0/0/0.0 password 123

Why it fails: This command does not exist.

set protocols ospf area 0.0.0.0 interface em0.0 silent

Why it fails: 'silent' is not a Junos OSPF keyword.

set protocols ospf passive-interface em0.0

Why it fails: Passive interfaces are configured under the specific area interface hierarchy.

set protocols ospf area 0.0.0.0 interface em0.0 disable-hellos

Why it fails: This command does not exist in Junos.

set protocols ospf area 0.0.0.0 domain-identifier 10.0.0.1

Why it fails: Domain-id is configured globally under protocols ospf, not per area.

set routing-options autonomous-system 65000 ospf-domain 10.0.0.1

Why it fails: This is incorrect syntax.

set protocols ospf bgp-domain-identifier 10.0.0.1

Why it fails: This command does not exist.

set protocols ospf area 0.0.0.2 transit-link neighbor 192.168.10.1

Why it fails: Transit-link is not a valid Junos keyword.

set protocols ospf virtual-link neighbor 192.168.10.1 area 0.0.0.1

Why it fails: This is incorrect Junos syntax.

set protocols ospf virtual-router 192.168.10.1 transit-area 0.0.0.2

Why it fails: Virtual-router is used for logical systems / routing instances, not OSPF virtual links.

set protocols ospf summary 10.10.0.0/16 area 0.0.0.1

Why it fails: Junos OSPF summarisation uses the area-range statement, not a summary statement; this syntax is invalid for generating inter-area summary LSAs. It is tempting because the address and area are specified correctly, but the ABR requires area-range configuration to suppress component routes and advertise the aggregate.

set protocols ospf area 0.0.0.1 aggregate 10.10.0.0/16

Why it fails: Junos OSPF area configuration does not accept an aggregate statement; summarisation is performed with area-range under the area hierarchy. It is tempting because it names the correct area and prefix, but the wrong statement means no summary LSA is generated and component routes remain advertised.

set routing-options aggregate route 10.10.0.0/16 ospf

Why it fails: Aggregate routes are configured under routing-options and apply to the routing table generally, not to OSPF area summarisation on an ABR. It is tempting because aggregates do produce summarised prefixes, but they lack the OSPF area context needed to generate inter-area summary LSAs and suppress internal routes.

set protocols ospf area 0.0.0.0 interface xe-0/0/0.0 disable-dr

Why it fails: This command does not exist.

set protocols ospf area 0.0.0.0 interface xe-0/0/0.0 drother-only

Why it fails: This command does not exist.

set routing-options ospf spf-timers delay 200 hold 1000

Why it fails: SPF timers belong under protocols ospf.

set protocols ospf area 0.0.0.0 timers spf 200 1000

Why it fails: SPF timers are configured globally under protocols ospf, not per area.

set protocols ospf interface xe-0/0/0.0 spf-timer 200

Why it fails: SPF timers are global protocol properties, not interface settings.

set debug ospf packets enable

Why it fails: Junos does not use a global 'debug' command hierarchy.

monitor protocols ospf debug

Why it fails: This command is invalid.

set system tracing ospf enable

Why it fails: Tracing is configured under the specific protocol hierarchy in Junos.

A default metric of 10 is assigned.

Why it fails: Junos assigns redistributed routes a default OSPF metric of 1, not 10, when the export policy omits a metric. A metric of 10 would be tempting if you assumed Junos mirrors the Cisco default of 20 or a common seed value, but the actual default is 1.

A default metric of 0 is assigned.

Why it fails: Junos assigns redistributed routes a default OSPF metric of 1, not 0. Zero is tempting because it resembles a directly connected or default route metric, but OSPF external LSAs require a nonzero seed metric, so Junos uses 1 when the export policy omits one.

A default metric of 20 is assigned.

Why it fails: 20 is the default metric for OSPF redistribution in other vendor implementations, but Junos uses 5.

Identical OSPF reference bandwidths

Why it fails: Reference bandwidth is a local calculation parameter and does not need to match for adjacencies.

Matching process IDs

Why it fails: OSPF process IDs are locally significant and do not need to match between routers.

Routing policies cannot match route prefixes, only protocol types.

Why it fails: Routing policies frequently match route prefixes using 'route-filter'.

OSPF import policies evaluate routing updates before they enter the Junos forwarding table.

Why it fails: OSPF import policies apply to the routing table / link-state database injection, not directly the forwarding table.

Policy evaluation stops immediately upon matching a 'next-term' action.

Why it fails: 'next-term' skips to the next term, it does not stop evaluation entirely.

Interface IP address subnets

Why it fails: Point-to-point links can sometimes have unnumbered configurations or different subnets depending on design, though standard subnets usually match; however, unique router IDs and distinct interface IPs are standard. Wait, let's look at MTU or Area ID. Area ID, Hello/Dead, and Authentication are strict requirements.

Router ID

Why it fails: Router IDs must be unique across the OSPF domain, not identical.

set totally-stubby

Why it fails: The correct Junos statement for a totally stubby area is 'set stub no-summaries'.

set stub default-metric 10

Why it fails: This modifies the cost of the injected default route in a stub area, but the area must first be declared as a stub.

set nssa default-lsa type-7

Why it fails: This applies to NSSA areas, not standard stub areas.

Under [edit protocols ospf area <name> prefix-export]

Why it fails: The prefix-export statement is not a valid Junos OSPF configuration option.

Under [edit protocols ospf lsa-filter]

Why it fails: The lsa-filter statement is used on incoming or outgoing interfaces for specific LSA types, but summary LSA filtering uses area-range configuration.

Under [edit protocols ospf export]

Why it fails: Applying a policy here filters routes being redistributed from other protocols into OSPF, not inter-area summaries.

Disabling IPv6 stateless address autoconfiguration (SLAAC) on the underlying physical interface.

Why it fails: SLAAC operates independently of OSPFv3 adjacency formation and need not be disabled for hellos to be exchanged. Disabling SLAAC is appropriate when you want hosts to obtain addresses solely through DHCPv6 or static configuration rather than router advertisements.

Explicit manual configuration of the Router ID using the global router-id statement.

Why it fails: A router ID is required for OSPFv3 to run, but it can be derived automatically from an interface address; explicit global configuration is not the interface-level requirement that blocks adjacency formation. The router-id statement is the right choice when you must guarantee a stable, unique identifier.

Defining explicit neighbor statements using the neighbor command for all point-to-point links.

Why it fails: OSPFv3 forms adjacencies dynamically over point-to-point links via multicast hellos; static neighbour statements are unnecessary and would not be the mandatory interface requirement. Neighbour statements are correct on NBMA or non-broadcast segments where multicast discovery cannot occur.

from protocol ospf tag <value>

Why it fails: The syntax 'protocol ospf' specifies the protocol, but the tag match condition uses a specific keyword in Junos.

from route-tag <value>

Why it fails: 'route-tag' is used for general routing policies, but OSPF-specific tags use 'ospf-tag'.

term match-tag value <value>

Why it fails: This is not a valid Junos policy match condition.