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Nokia IS-IS Routing Protocol study materials
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Nokia IS-IS Routing Protocol practice questions

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Question 1IS-IS Routing Protocol

In IS-IS, which protocol data unit is used to carry link-state information about routers and their attached prefixes within a single area?

  1. Hello PDU
  2. Link State PDU (LSP) Correct answer.
  3. Partial Sequence Number PDU (PSNP)
  4. Complete Sequence Number PDU (CSNP)

Explanation

The Link State PDU is the IS-IS carrier of link-state advertisements; each LSP contains TLVs describing the originating router, its neighbors, and reachable IP prefixes. CSNP and PSNP only describe which LSPs a router holds, and Hello PDUs establish and maintain adjacencies.

Question 2IS-IS Routing Protocol

Which IS-IS PDU type is used to establish and maintain adjacencies on a point-to-point link?

  1. Level 1 LAN Hello
  2. Level 2 LAN Hello
  3. Point-to-Point Hello Correct answer.
  4. Link State PDU

Explanation

IS-IS defines a dedicated Point-to-Point Hello PDU for broadcast-less links, while LAN Hello PDUs are used on broadcast and non-broadcast multi-access circuits. The point-to-point Hello carries the adjacency state and the three-way handshake options.

Question 3IS-IS Routing Protocol

What is the default IS-IS metric value assigned to an interface when no metric is explicitly configured on a Nokia router?

  1. 10 Correct answer.
  2. 100
  3. 63
  4. 1

Explanation

Nokia's IS-IS implementation assigns a default interface metric of 10 when the metric is not set, and the wide-metrics TLV supports values up to 16777215. The narrow metric field allows only 6 bits, so 63 is the maximum narrow metric rather than a default.

Question 4IS-IS Routing Protocol

Which IS-IS router type forms adjacencies in both Level 1 and Level 2 and can therefore bridge intra-area and inter-area topologies?

  1. Level 1/2 router Correct answer.
  2. Level 1 router
  3. Level 2 router
  4. Level 1-only designated intermediate system

Explanation

A Level 1/2 router runs two separate link-state databases, one per level, and advertises itself into the backbone area through its Level 2 adjacencies. This dual-level behavior allows it to leak and forward reachability between an area and the backbone.

Question 5IS-IS Routing Protocol

On a broadcast IS-IS circuit, which router generates the pseudonode LSP for that LAN?

  1. The Designated Intermediate System Correct answer.
  2. The Level 2 router with the highest priority
  3. The lowest interface metric router
  4. The highest system ID on the segment

Explanation

The Designated Intermediate System represents the broadcast segment as a pseudonode and originates a pseudonode LSP describing all routers attached to that LAN. This reduces the number of adjacencies and LSPs needed to model the multi-access segment.

Question 6IS-IS Routing Protocol

Which TLV in an IS-IS LSP is used to advertise IPv4 interface addresses and reachable prefixes?

  1. TLV 10 (Authentication)
  2. TLV 1 (Area Addresses)
  3. TLV 22 (Extended IS Reachability)
  4. TLV 128 (IP Internal Reachability Information) Correct answer.

Explanation

TLV 128 carries internal IPv4 reachability information, while TLV 130 carries external IPv4 reachability. TLV 22 describes extended IS neighbors and TLV 1 describes area addresses.

Question 7IS-IS Routing Protocol

What does the System ID portion of an IS-IS NET identify?

  1. The routing domain of the backbone
  2. The AFI and authority format of the address
  3. The specific IS-IS router within an area Correct answer.
  4. The area to which the router belongs

Explanation

A NET is composed of an area address, a System ID, and an NSEL. The System ID uniquely identifies an IS-IS router within its area, while the area address identifies the area and the NSEL must be zero for a router NET.

Question 8IS-IS Routing Protocol

Which Nokia command displays the IS-IS link-state database for Level 2?

  1. show router isis database detail level 2 Correct answer.
  2. show router isis adjacency
  3. show router isis interface
  4. show router isis statistics

Explanation

The IS-IS database command displays LSPs held in the link-state database, and the level keyword restricts output to Level 1 or Level 2. Adjacency, interface, and statistics commands report operational state rather than LSP contents.

Question 9IS-IS Routing Protocol

A router's Level 1 LSP has a remaining lifetime of zero. What does this indicate to receiving routers?

  1. The LSP is valid but has the highest sequence number
  2. The LSP is purged and should be removed from the database Correct answer.
  3. The LSP is awaiting authentication verification
  4. The LSP is newly originated and must be re-flooded

Explanation

A remaining lifetime of zero marks an LSP as purged, which instructs neighbors to remove it from their databases and stop using it for SPF. The originating router sets the lifetime to zero to withdraw the LSP.

Question 10IS-IS Routing Protocol

Which condition causes an IS-IS adjacency to remain in the Initializing state on a point-to-point link?

  1. The local router has not yet received a Hello listing its own system ID Correct answer.
  2. The LSP sequence number has wrapped
  3. The interface metric exceeds the narrow metric maximum
  4. The remote router has a different area address

Explanation

In the three-way handshake, a point-to-point adjacency stays Initializing until the local router receives a Hello from the peer that lists the local system ID as a neighbor. Only then does the adjacency move to Up.

Question 11IS-IS Routing Protocol

Two Nokia routers are connected by a broadcast Ethernet segment and both are configured as Level 2. How many Level 2 adjacencies exist on that segment after DIS election?

  1. One adjacency per router pair on the segment
  2. One adjacency from each non-DIS router to the DIS Correct answer.
  3. One full mesh adjacency between all routers
  4. Two adjacencies per router for redundancy

Explanation

On a broadcast circuit, non-DIS routers form an adjacency only with the DIS, which represents the segment as a pseudonode. This avoids a full mesh of adjacencies and keeps the topology representation scalable.

Question 12IS-IS Routing Protocol

What is the purpose of the overload bit in an IS-IS LSP?

  1. To disable authentication on the originating interface
  2. To prevent the router from being used as a transit node in SPF calculations Correct answer.
  3. To force the router to originate a new pseudonode LSP
  4. To increase the metric of all attached prefixes by one

Explanation

When the overload bit is set, other routers exclude the advertising router from transit paths in their SPF trees while still allowing traffic destined to its directly attached prefixes. Nokia sets this bit automatically during certain startup or resource-exhaustion conditions.

Question 13IS-IS Routing Protocol

Which IS-IS feature allows a Level 1/2 router to advertise selected Level 2 prefixes into a Level 1 area?

  1. Route leaking Correct answer.
  2. Graceful restart
  3. Wide metrics
  4. LSP fragmentation

Explanation

Route leaking lets a Level 1/2 router inject selected inter-area or external prefixes into its Level 1 LSPs so that Level 1 routers can reach them without a default route. It is typically controlled by route policies on Nokia platforms.

Question 14IS-IS Routing Protocol

Which authentication method in IS-IS uses a key chain with HMAC-MD5 and supports key rollover?

  1. Clear-text password authentication
  2. HMAC-MD5 authentication using a keychain Correct answer.
  3. Null authentication
  4. Simple password authentication

Explanation

HMAC-MD5 authentication can be configured with a keychain, allowing multiple keys with lifetimes so that keys can be rotated without breaking adjacencies. Clear-text and simple password methods send credentials in the PDU without a cryptographic hash.

Question 15IS-IS Routing Protocol

What is the effect of configuring the IS-IS interface type as point-to-point on an Ethernet interface that connects to a single neighbor?

  1. It forces the interface to operate only at Level 1
  2. It eliminates the DIS election and pseudonode on that link Correct answer.
  3. It disables SPF computation for that interface
  4. It suppresses all Hello PDUs on the interface

Explanation

Declaring an interface point-to-point removes the need for DIS election and pseudonode LSP origination, which speeds convergence and simplifies the topology. Hello PDUs are still exchanged using the point-to-point Hello format.

Question 16IS-IS Routing Protocol

Which PDU does a router send to request a specific missing LSP from a neighbor?

  1. Partial Sequence Number PDU Correct answer.
  2. Complete Sequence Number PDU
  3. Level 1 LAN Hello
  4. Link State PDU

Explanation

A Partial Sequence Number PDU lists specific LSP identifiers that the sender needs or acknowledges, prompting the neighbor to send the missing LSPs. The Complete Sequence Number PDU instead summarizes the entire database for synchronization.

Question 17IS-IS Routing Protocol

On a Nokia router, which command displays the IS-IS adjacencies and their current state?

  1. show router isis database
  2. show router isis interface
  3. show router isis adjacency Correct answer.
  4. show router isis routes

Explanation

The adjacency command lists IS-IS neighbors, their levels, and their state, which is useful for verifying that adjacencies have reached Up. The database command shows LSPs, the routes command shows the IS-IS routing table, and the interface command shows per-interface parameters.

Question 18IS-IS Routing Protocol

What happens when a Nokia IS-IS router receives an LSP with a sequence number higher than the one in its database?

  1. It discards the LSP as a duplicate
  2. It waits for the LSP lifetime to expire before installing it
  3. It installs the newer LSP and floods it to other adjacencies Correct answer.
  4. It requests the LSP again using a CSNP

Explanation

A higher sequence number indicates a newer version of the LSP, so the router replaces the stored copy, runs SPF if the topology changed, and floods the LSP onward. Duplicate detection applies only when the sequence number matches the stored value.

Question 19IS-IS Routing Protocol

Which metric type does Nokia recommend enabling to support interface metrics greater than 63?

  1. Narrow metrics
  2. Delay metrics
  3. Wide metrics Correct answer.
  4. Error metrics

Explanation

Wide metrics use a 24-bit field carried in extended TLVs, allowing interface metrics up to 16777215. Narrow metrics are limited to 6 bits, so values above 63 cannot be represented without wide metrics.

Question 20IS-IS Routing Protocol

A Level 1 router needs to reach a prefix outside its area. What does it use by default to forward such traffic?

  1. An LSP with the overload bit set
  2. A Level 2 LSP flooded into the area
  3. A leaked external prefix in its Level 1 LSP
  4. A default route advertised by the nearest Level 1/2 router Correct answer.

Explanation

By default, a Level 1/2 router sets the attached bit and advertises a default route into the Level 1 area, so Level 1 routers forward inter-area traffic to it. Leaked prefixes are optional and are not present unless route leaking is configured.

Question 21IS-IS Routing Protocol

Which Nokia command enables IS-IS on an interface within a router isis context?

  1. interface "toR2" Correct answer.
  2. enable isis "toR2"
  3. isis interface "toR2"
  4. add interface "toR2"

Explanation

Within the IS-IS context on Nokia SR OS, the interface command associates a configured interface with IS-IS and enters the interface context for further parameters. The other forms are not valid SR OS IS-IS configuration syntax.

Question 22IS-IS Routing Protocol

Which IS-IS mechanism reduces the number of LSPs generated for a broadcast segment with many routers?

  1. LSP fragmentation
  2. Per-neighbor point-to-point LSPs
  3. Pseudonode LSP generated by the DIS Correct answer.
  4. LSP purging

Explanation

The DIS represents the broadcast segment as a pseudonode and originates a single pseudonode LSP listing all attached routers. Without it, each router would need to advertise a full mesh of adjacencies, greatly increasing LSP count and SPF complexity.

Question 23IS-IS Routing Protocol

An engineer wants Level 1 routers to reach a specific external prefix without a default route. Which Nokia configuration achieves this?

  1. Disable the attached bit on the Level 1/2 router
  2. Enable wide metrics on all Level 1 interfaces
  3. Configure route leaking with a policy that matches the prefix Correct answer.
  4. Set the overload bit on the Level 1/2 router

Explanation

Route leaking uses a route policy to select prefixes from the Level 2 database and advertise them into Level 1 LSPs, giving Level 1 routers explicit reachability. Wide metrics, the overload bit, and the attached bit do not inject specific prefixes into the area.

Question 24IS-IS Routing Protocol

During database synchronization on a point-to-point link, when does a router send a CSNP to its neighbor?

  1. Only when the LSP lifetime expires
  2. Only when the neighbor requests one with a PSNP
  3. Immediately after the adjacency reaches Up Correct answer.
  4. After every SPF run completes

Explanation

On point-to-point links, routers exchange CSNPs once the adjacency transitions to Up so each side can compare databases and request missing LSPs with PSNPs. Periodic CSNPs are sent on broadcast circuits by the DIS instead.

Question 25IS-IS Routing Protocol

A Nokia router's Level 2 LSP shows the overload bit set after a restart. What is the most likely cause?

  1. The router's interface metric exceeds the wide metric maximum
  2. The router's authentication key has expired
  3. The router has an area address mismatch with its neighbor
  4. The router is waiting for the IS-IS database to converge before clearing the bit Correct answer.

Explanation

A router may set the overload bit temporarily during startup or after a restart so that other routers do not use it as a transit node until its database is fully synchronized. Once convergence completes, the bit is cleared and normal transit forwarding resumes.

Question 26IS-IS Routing Protocol

In an IS-IS NET, which component is the Area Identifier that must match on every router in the same Level 1 area?

  1. The 6-octet System ID
  2. The variable-length selector byte
  3. The leading bytes before the System ID Correct answer.
  4. The 802.1Q VLAN tag carried in the hello

Explanation

An IS-IS NET is composed of an area identifier, a fixed 6-octet System ID, and a 1-octet NSAP selector. The area portion is the leading bytes, and routers must share it to form Level 1 adjacencies. The System ID is unique per router, while the selector is normally 00.

Question 27IS-IS Routing Protocol

Which IS-IS PDU type is used to send a complete list of LSP headers so a neighbor can detect missing or outdated database entries?

  1. IS-IS Hello PDU
  2. Complete Sequence Number PDU Correct answer.
  3. Link State PDU
  4. Partial Sequence Number PDU

Explanation

A Complete Sequence Number PDU carries the sequence numbers and lifetimes of all LSPs in the sender's database for a level. The receiver compares them with its own database to identify missing or newer entries. Partial Sequence Number PDUs request or acknowledge individual LSPs instead.

Question 28IS-IS Routing Protocol

What is the default behavior of a Nokia IS-IS router configured at Level 1/2 when forwarding traffic to a destination outside its own Level 1 area?

  1. It converts the packet into a Level 1 LSP for redistribution.
  2. It floods the packet to all Level 1 neighbors simultaneously.
  3. It forwards the packet toward the nearest Level 2 router using its default route. Correct answer.
  4. It drops the packet because Level 1 prefixes are never leaked.

Explanation

A Level 1 router installs a default route pointing to the closest attached Level 1/2 router. Traffic for inter-area or external destinations is forwarded to that router, which then uses its Level 2 database. Level 1 routers do not hold Level 2 topology information.

Question 29IS-IS Routing Protocol

Which Nokia command changes the IS-IS interface type to point-to-point on a router port?

  1. configure router isis interface "toR2" mesh-group 1
  2. configure router isis interface "toR2" level 2
  3. configure router isis interface "toR2" passive
  4. configure router isis interface "toR2" interface-type point-to-point Correct answer.

Explanation

The interface-type point-to-point command sets the interface to form point-to-point adjacencies and skip DIS election. This is appropriate for links that are logically point-to-point even if the media is Ethernet. The passive keyword disables adjacency formation entirely.

Question 30IS-IS Routing Protocol

Which IS-IS timer governs how long a receiving router considers an LSP valid before it must be purged?

  1. The hello interval
  2. The CSNP interval
  3. The LSP transmit interval
  4. The remaining lifetime field in the LSP header Correct answer.

Explanation

Each LSP carries a remaining lifetime that counts down on every router. When it reaches zero, the LSP is considered expired and is purged from the database. The originating router refreshes the LSP before expiration.

Question 31IS-IS Routing Protocol

Which IS-IS feature reduces the number of LSPs flooded when many routers share a broadcast segment?

  1. Mesh groups
  2. Designated Intermediate System election Correct answer.
  3. Wide metrics
  4. Passive interfaces

Explanation

On a broadcast segment, routers elect a Designated Intermediate System that represents the segment in the topology. This creates a pseudonode LSP so each router need only advertise a link to the DIS rather than to every peer. Mesh groups and passive interfaces affect flooding and adjacency differently.

Question 32IS-IS Routing Protocol

Which Nokia command displays the IS-IS link-state database entries for Level 1 only?

  1. show router isis database level 1 Correct answer.
  2. show router isis interface
  3. show router isis database detail
  4. show router isis adjacency

Explanation

The show router isis database command accepts a level keyword to filter output to Level 1 or Level 2. Adding level 1 restricts the display to Level 1 LSPs. The adjacency and interface commands show operational state rather than database contents.

Question 33IS-IS Routing Protocol

Which field in an IS-IS Hello PDU carries the set of area addresses that the sending router supports?

  1. The Area Addresses TLV Correct answer.
  2. The Protocols Supported TLV
  3. The IP Interface Address TLV
  4. The Extended IS Reachability TLV

Explanation

The Area Addresses TLV in the Hello PDU lists the area addresses configured on the sending router. Neighbors compare this list to confirm they share an area before forming a Level 1 adjacency. The Protocols Supported TLV advertises which network protocols the router supports.

Question 34IS-IS Routing Protocol

Two Nokia routers are connected by a point-to-point link and both are configured at Level 2 only. Which condition must be satisfied before they form a Level 2 adjacency?

  1. Their DIS priorities must be equal.
  2. Their System IDs must be identical.
  3. Their area addresses must differ.
  4. Their Level 2 hello PDUs must be successfully exchanged and accepted. Correct answer.

Explanation

Level 2 adjacencies are formed when both sides exchange valid Level 2 hello PDUs with compatible parameters such as authentication and protocol support. Area addresses do not need to match for Level 2. System IDs must be unique and DIS election does not apply on point-to-point links.

Question 35IS-IS Routing Protocol

An engineer wants a Level 1/2 router to advertise a specific Level 2 prefix into its Level 1 area without advertising a default route. Which Nokia configuration accomplishes this?

  1. configure router isis export-policy Correct answer.
  2. configure router isis level-capability level-1
  3. configure router isis summary-address
  4. configure router isis interface "toR2" passive

Explanation

An export policy attached to the IS-IS instance can leak selected Level 2 prefixes into Level 1 using the appropriate level match and action. This provides granular reachability without a blanket default route. The other commands change level capability, summarization, or adjacency behavior.

Question 36IS-IS Routing Protocol

A Nokia IS-IS router receives an LSP with a sequence number lower than the one already stored in its database. What action does it take?

  1. It discards the LSP and sends a PSNP with the newer entry. Correct answer.
  2. It purges its own database entry.
  3. It installs the lower sequence number and floods it.
  4. It resets the adjacency with the sender.

Explanation

IS-IS uses sequence numbers to determine which version of an LSP is newest. A lower sequence number indicates stale information, so the router discards it and may send a PSNP to inform the sender of the newer entry. The adjacency is not affected by this database-level event.

Question 37IS-IS Routing Protocol

Which authentication method in IS-IS uses a key chain and supports HMAC-MD5 with key rollover?

  1. MD5 with a single static key only
  2. HMAC-MD5 with a key chain Correct answer.
  3. Simple password with a static string
  4. Clear-text password authentication

Explanation

IS-IS supports HMAC-MD5 authentication using a key chain, which allows multiple keys with lifetimes for graceful rollover. This is configured at the interface or area level depending on the level. Static MD5 keys without a chain do not provide rollover.

Question 38IS-IS Routing Protocol

After a Nokia router restarts and sets the overload bit in its LSPs, what is the intended effect on transit traffic?

  1. Other routers purge its LSPs immediately.
  2. Other routers ignore its directly connected prefixes entirely.
  3. Other routers form only Level 1 adjacencies with it.
  4. Other routers avoid using it as a transit next hop until the bit clears. Correct answer.

Explanation

The overload bit signals that a router is not ready to carry transit traffic, typically during startup while databases synchronize. Neighbors still reach prefixes directly attached to the overloaded router but avoid using it as an intermediate hop. The bit clears once the router is fully operational.

Question 39IS-IS Routing Protocol

Which IS-IS metric encoding should be enabled to advertise interface metrics greater than 63?

  1. Transition metrics
  2. Wide metrics Correct answer.
  3. Narrow metrics
  4. Default metrics

Explanation

Narrow metrics use a 6-bit field limiting values to 63, while wide metrics use a 24-bit field allowing much larger values. Enabling wide metrics is required for high-bandwidth links that need metrics above 63. Transition mode can advertise both formats during migration.

Question 40IS-IS Routing Protocol

On a broadcast Ethernet segment, how does IS-IS represent the multi-access link in the topology?

  1. The segment is omitted from the topology entirely.
  2. The DIS generates a pseudonode LSP representing the segment. Correct answer.
  3. Each router advertises a full mesh of point-to-point links.
  4. Only the highest-priority router advertises the segment.

Explanation

The elected DIS creates a pseudonode LSP that represents the broadcast segment as a virtual node. Each router on the segment advertises a link to the pseudonode rather than to every other router. This keeps the topology representation compact.

Question 41IS-IS Routing Protocol

A Level 1 router needs to reach a prefix in another area, but the network administrator wants to avoid a default route. Which approach provides the needed reachability?

  1. Setting the overload bit on the border router
  2. Leaking the specific Level 2 prefix into Level 1 via an export policy Correct answer.
  3. Configuring the Level 1 router as passive
  4. Disabling Level 2 on the border router

Explanation

Prefix leaking allows selected Level 2 prefixes to be advertised into Level 1, giving Level 1 routers specific reachability without a default route. This is configured with an export policy on the border router. Disabling Level 2 or setting overload would break inter-area forwarding.

Question 42IS-IS Routing Protocol

A Nokia IS-IS adjacency on a point-to-point link remains in the Initializing state. Which condition most likely explains this?

  1. The local router is receiving hellos but the neighbor is not receiving the local hellos. Correct answer.
  2. The router is configured as Level 1/2.
  3. The interface metric is set to 10.
  4. The LSP database is fully synchronized.

Explanation

The Initializing state indicates that the local router sees the neighbor's hellos but the neighbor does not yet see the local router's hellos. This is commonly caused by a one-way link, a filtering issue, or a mismatch in hello parameters. Once hellos are exchanged bidirectionally, the adjacency moves to Up.

Question 43IS-IS Routing Protocol

Which IS-IS PDU is used by a router to request a specific missing LSP from a neighbor?

  1. Partial Sequence Number PDU Correct answer.
  2. Complete Sequence Number PDU
  3. Level 1 LAN Hello PDU
  4. Level 2 LAN Hello PDU

Explanation

A Partial Sequence Number PDU references specific LSPs and is used to request missing entries or acknowledge receipt. Complete Sequence Number PDUs summarize the entire database rather than individual LSPs. Hello PDUs maintain adjacencies.

Question 44IS-IS Routing Protocol

A Nokia router's Level 2 LSP shows the overload bit set after a restart. Which condition is the most likely cause?

  1. The router's System ID has been duplicated.
  2. The router has lost its Level 1 area configuration.
  3. The router is still synchronizing its database and has not yet cleared the bit. Correct answer.
  4. The router's authentication key has expired.

Explanation

Routers commonly set the overload bit during startup so that neighbors avoid using them for transit while databases synchronize. The bit clears automatically once the router is fully operational. Duplicate System IDs or expired authentication would produce different symptoms.

Question 45IS-IS Routing Protocol

A Nokia router configured with wide metrics interoperates with a neighbor that supports only narrow metrics. Which statement describes the resulting behavior?

  1. The router must disable IS-IS on the interface.
  2. The neighbor automatically upgrades to wide metrics.
  3. The neighbor rejects the adjacency because metric formats differ.
  4. The router can use transition mode to advertise both narrow and wide metrics during migration. Correct answer.

Explanation

Transition mode allows a router to advertise both narrow and wide metric TLVs so that older neighbors can still interpret the topology. Once all routers support wide metrics, transition mode can be removed. Adjacency formation is not blocked by differing metric formats.

Question 46IS-IS Routing Protocol

Which Nokia command displays IS-IS adjacencies and their current state?

  1. show router isis statistics
  2. show router isis adjacency Correct answer.
  3. show router isis interface
  4. show router isis database

Explanation

The show router isis adjacency command lists neighbors with their system IDs, levels, and states such as Up or Initializing. It is the primary tool for verifying adjacency health. The database and interface commands show different aspects of IS-IS operation.

Question 47IS-IS Routing Protocol

A network designer wants to reduce LSP flooding on a large broadcast segment where many routers are attached. Which IS-IS mechanism limits flooding of LSPs among routers on that segment?

  1. Passive interfaces
  2. Wide metrics
  3. Mesh groups Correct answer.
  4. Overload bit

Explanation

Mesh groups restrict the flooding of LSPs within a group of routers on a broadcast segment, reducing unnecessary flooding. This is useful in highly meshed topologies such as full-mesh VPNs. Passive interfaces, overload, and wide metrics address different concerns.

Question 48IS-IS Routing Protocol

A Level 1/2 router has an export policy that leaks a Level 2 prefix into Level 1. Which condition must be true for the leaked prefix to appear in Level 1 LSPs?

  1. The prefix must be advertised with narrow metrics.
  2. The prefix must be directly connected to the router.
  3. The prefix must be summarized first.
  4. The prefix must be present in the Level 2 database and match the policy. Correct answer.

Explanation

Prefix leaking selects routes from the Level 2 database that match the export policy and advertises them into Level 1. Directly connected status or summarization is not required. Metric encoding format does not determine whether leaking occurs.

Question 49IS-IS Routing Protocol

Which statement accurately describes the role of the System ID in an IS-IS network?

  1. It specifies the authentication key used by the router.
  2. It defines the metric encoding format used by the router.
  3. It uniquely identifies the router within the IS-IS domain. Correct answer.
  4. It identifies the area to which the router belongs.

Explanation

The System ID is a fixed 6-octet field within the NET that uniquely identifies each router in the IS-IS domain. The area portion identifies the area, while authentication and metric encoding are configured separately. Duplicate System IDs cause serious database conflicts.

Question 50IS-IS Routing Protocol

Which IS-IS PDU type is used by a router to report the state of its own links and reachable prefixes to other routers in the same area?

  1. Complete Sequence Number PDU (CSNP)
  2. Intermediate System to Intermediate System Hello PDU (IIH)
  3. Link State PDU (LSP) Correct answer.
  4. Partial Sequence Number PDU (PSNP)

Explanation

LSPs carry the router's own link-state information, including neighbor adjacencies, IP prefixes, and metric values, and they are flooded throughout the area. Hellos only establish and maintain adjacencies, while CSNP and PSNP are used to synchronize databases, not to originate topology data.