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Question 101

Which OSPF LSA type is used to advertise routes from an ASBR into an OSPF autonomous system?

1. Type 1
2. Type 2
3. Type 5
4. Type 7

Correct Answer: 3

Explanation

OSPF Type 5 LSAs are originated by an Autonomous System Boundary Router (ASBR) to advertise external routes into the OSPF autonomous system. These routes may originate from another routing protocol or from static routes redistributed into OSPF. Type 1 LSAs describe router information, while Type 2 LSAs are generated by DRs on multiaccess networks. Type 7 LSAs are used for external routes inside NSSA areas and can later be translated into Type 5 LSAs. Therefore, Type 5 is the appropriate LSA type for general external route advertisement by an ASBR.

Question 102

Which OSPF area type allows external routes to be represented using Type 7 LSAs?

1. Backbone area
2. NSSA
3. Standard area
4. Transit area

Correct Answer: 2

Explanation

A Not-So-Stubby Area (NSSA) allows external routes to be introduced into the area while maintaining restrictions on external LSAs entering from outside. An ASBR inside an NSSA uses Type 7 LSAs to advertise redistributed external routes. These Type 7 LSAs can be translated into Type 5 LSAs by an appropriate NSSA border router before being propagated into other OSPF areas. Standard areas can directly use Type 5 LSAs for external routes. Therefore, NSSA is the correct answer for an OSPF area that supports Type 7 LSAs.

Question 103

In OSPF, which router is responsible for generating Type 2 network LSAs on a broadcast multiaccess network?

1. Designated Router
2. Area Border Router
3. Autonomous System Boundary Router
4. Route Reflector

Correct Answer: 1

Explanation

The OSPF Designated Router (DR) generates the Type 2 Network LSA for a broadcast or multiaccess network segment. The Type 2 LSA describes the routers attached to that particular network and helps reduce the amount of adjacency-related flooding required between all routers. A Backup Designated Router (BDR) is also elected to provide redundancy if the DR fails. An ABR connects different OSPF areas, while an ASBR redistributes routes from another routing source. A Route Reflector is a BGP function. Therefore, the DR is responsible for originating the Type 2 LSA.

Question 104

Which OSPF feature is used to reduce the number of routing entries advertised from one area into another?

1. LSA flooding
2. ECMP
3. DR election
4. Route summarization

Correct Answer: 4

Explanation

OSPF route summarization combines multiple more-specific prefixes into a summarized route, reducing the number of routing entries that need to be advertised across an area boundary. Summarization can improve scalability and reduce the impact of topology changes because individual internal prefixes may remain hidden behind the summary. OSPF supports summarization at appropriate area boundaries, particularly on ABRs, while external route summarization can be performed by ASBRs. LSA flooding, ECMP, and DR election serve different purposes. Therefore, route summarization is the correct answer.

Question 105

Which IS-IS packet is used to acknowledge receipt of Link State PDUs?

1. Hello PDU
2. CSNP
3. PSNP
4. LSP

Correct Answer: 3

Explanation

Partial Sequence Number PDUs (PSNPs) are used in IS-IS to acknowledge specific Link State PDUs and request missing LSP information. They play an important role in maintaining synchronization between IS-IS neighbors. Complete Sequence Number PDUs (CSNPs) provide a summary of the LSP database and help identify missing or outdated information. Hello PDUs establish and maintain adjacencies, while LSPs carry link-state information. Therefore, PSNP is the correct answer when referring to acknowledgment and requests for specific LSP information.

Question 106

Which IS-IS PDU provides a complete summary of the LSP database for a circuit?

1. CSNP
2. PSNP
3. IIH
4. BGP UPDATE

Correct Answer: 1

Explanation

A Complete Sequence Number PDU (CSNP) provides a summary of the LSPs known by an IS-IS router. It contains information that allows neighboring routers to compare their databases and identify missing or outdated LSPs. If a router discovers that it lacks an LSP, it can use PSNP mechanisms to request the required information. IS-IS Hello packets, also known as IIHs, establish and maintain adjacencies, while BGP UPDATE messages belong to BGP rather than IS-IS. Therefore, CSNP is the correct answer.

Question 107

Which BGP attribute is primarily used to prevent routing loops between autonomous systems?

1. MED
2. LOCAL_PREF
3. AS_PATH
4. NEXT_HOP

Correct Answer: 3

Explanation

The BGP AS_PATH attribute records the sequence of autonomous systems through which a route has passed. When a BGP router receives a route containing its own AS number in the AS_PATH, it normally rejects the route because accepting it could create an inter-AS routing loop. AS_PATH can also influence BGP path selection, with shorter paths generally preferred under the applicable decision process. LOCAL_PREF controls path preference within an autonomous system, MED can influence inbound path selection by neighboring ASes, and NEXT_HOP identifies the next-hop address. Therefore, AS_PATH provides the primary inter-AS loop-prevention mechanism.

Question 108

Which BGP attribute is normally propagated throughout an autonomous system and is commonly used to select the preferred exit point?

1. MED
2. LOCAL_PREF
3. ORIGIN
4. AGGREGATOR

Correct Answer: 2

Explanation

LOCAL_PREF is a BGP attribute used within an autonomous system to indicate the preferred exit point for outbound traffic. A higher LOCAL_PREF value is generally preferred during BGP best-path selection. Because it is intended for internal BGP decision-making, the attribute is propagated to other internal BGP peers, subject to the relevant configuration. MED has a different purpose and can influence how neighboring autonomous systems choose an entry point. ORIGIN identifies the route’s origin type, while AGGREGATOR provides aggregation-related information. Therefore, LOCAL_PREF is the correct answer.

Question 109

Which BGP feature allows multiple paths to be installed in the routing table when they satisfy the required multipath conditions?

1. BGP Multipath
2. Route Dampening
3. Route Refresh
4. Maximum Prefix

Correct Answer: 1

Explanation

BGP Multipath allows a router to install multiple eligible BGP paths for the same destination rather than selecting only one path. This can provide load sharing and improve redundancy. The paths must satisfy the configured multipath requirements, which can include factors such as comparable attributes and next-hop characteristics depending on the implementation. Route Dampening is used to reduce instability caused by frequently flapping routes. Route Refresh allows routing information to be requested again, while Maximum Prefix limits the number of prefixes accepted from a neighbor. Therefore, BGP Multipath is correct.

Question 110

Which BGP mechanism allows a router to request updated routing information without resetting the BGP session?

1. AS Override
2. Route Reflector
3. Add-Path
4. Route Refresh

Correct Answer: 4

Explanation

BGP Route Refresh allows a router to request routing information from a BGP neighbor again without tearing down the existing BGP session. This is particularly useful after inbound routing policies have been modified because the router can request updated routes and reapply the new policy. A traditional hard reset would interrupt the BGP session and potentially cause unnecessary route withdrawal and re-establishment. AS Override serves a different purpose in MPLS VPN environments, Route Reflectors improve iBGP scalability, and Add-Path allows multiple paths to be advertised. Therefore, Route Refresh is correct.

Question 111

What is the primary purpose of a BGP Route Reflector?

1. Encrypt BGP updates
2. Replace the IGP
3. Reduce the need for a full-mesh iBGP topology
4. Distribute MPLS labels

Correct Answer: 3

Explanation

A BGP Route Reflector improves iBGP scalability by allowing selected routers to reflect routes between BGP clients. Without route reflection, traditional iBGP requires a full mesh of sessions among routers in the same autonomous system. As the number of routers increases, maintaining such a topology becomes increasingly complex. Route Reflectors reduce the number of required sessions while preserving BGP route distribution. They do not encrypt BGP updates, replace the underlying IGP, or distribute MPLS labels. LDP and Segment Routing mechanisms are associated with label distribution. Therefore, reducing the need for a full-mesh iBGP topology is the correct answer.

Question 112

Which BGP feature allows a router to advertise more than one path for the same prefix to a neighbor?

1. Route Dampening
2. Add-Path
3. Graceful Restart
4. MED

Correct Answer: 2

Explanation

BGP Add-Path allows a BGP speaker to advertise multiple paths for the same destination prefix instead of advertising only its selected best path. This can improve path diversity and help downstream routers maintain alternate paths. It can also be useful in environments where route reflectors might otherwise hide alternative paths. Route Dampening addresses route instability, Graceful Restart helps preserve forwarding during certain control-plane events, and MED is a path-selection attribute. Therefore, Add-Path is the correct BGP feature for advertising multiple paths for the same prefix.

Question 113

Which MPLS operation replaces the top label with another label according to the LFIB entry?

1. Push
2. Pop
3. Swap
4. PHP

Correct Answer: 3

Explanation

MPLS label swapping occurs when an intermediate Label Switch Router receives a packet with an incoming label and replaces that label with an outgoing label according to its Label Forwarding Information Base (LFIB). This is the fundamental forwarding operation performed by many transit MPLS routers. Push adds a label to the label stack, while pop removes a label. Penultimate Hop Popping (PHP) is a specific form of label removal performed before the egress router in many MPLS LSPs. Therefore, swap is the correct operation for replacing one MPLS label with another.

Question 114

Which MPLS mechanism removes the outer label at the penultimate router before traffic reaches the egress router?

1. Penultimate Hop Popping
2. Label Push
3. Label Swap
4. Route Target Import

Correct Answer: 1

Explanation

Penultimate Hop Popping (PHP) removes the top MPLS label at the router immediately before the egress Label Edge Router. This allows the egress router to receive the packet without needing to perform an additional lookup to remove the outer transport label. PHP can reduce label-processing work at the egress and is commonly associated with implicit-null signaling. Label push adds labels, label swap replaces labels, and Route Target import is an MPLS VPN control-plane function. Therefore, Penultimate Hop Popping is the correct answer.

Question 115

Which MPLS table contains label forwarding information used to forward labeled packets?

1. RIB
2. LFIB
3. ARP table
4. DNS table

Correct Answer: 2

Explanation

The Label Forwarding Information Base (LFIB) contains information used to forward MPLS-labeled packets. It associates incoming labels with forwarding actions such as label swap, pop, or other appropriate operations and identifies the outgoing interface or next hop. The Routing Information Base (RIB) contains IP routing information and contributes to forwarding decisions but is not itself the primary table for MPLS label forwarding. ARP stores IPv4-to-MAC mappings, while DNS resolves names to addresses. Therefore, LFIB is the correct table for MPLS label forwarding information.

Question 116

Which MPLS mechanism can be used to test connectivity and diagnose problems along an MPLS LSP?

1. MPLS LSP Ping
2. DHCP
3. ARP
4. NTP

Correct Answer: 1

Explanation

MPLS LSP Ping is an OAM and troubleshooting mechanism used to verify connectivity across an MPLS Label Switched Path. It can help determine whether an LSP is operational and can identify problems affecting label-switched forwarding. MPLS LSP Traceroute can provide additional information about the path through the MPLS network. DHCP provides address configuration, ARP resolves IPv4 addresses to MAC addresses, and NTP provides time synchronization. Therefore, MPLS LSP Ping is the appropriate tool for testing MPLS LSP connectivity.

Question 117

Which Segment Routing identifier represents a specific adjacency between two directly connected nodes?

1. Prefix-SID
2. Node-SID
3. Adjacency-SID
4. Anycast-SID

Correct Answer: 3

Explanation

An Adjacency Segment Identifier (Adj-SID) represents a specific adjacency or link from one Segment Routing node toward a neighboring node. It allows a segment-routing policy to explicitly influence traffic over a particular link rather than simply selecting a destination node. A Prefix-SID generally represents reachability to a prefix, and a Node-SID commonly identifies a node or its loopback prefix. An Anycast-SID can represent a set of nodes sharing the same logical segment. Therefore, Adjacency-SID is the correct identifier for a specific adjacency.

Question 118

What does the Segment Routing Global Block (SRGB) define?

1. BGP community values
2. A range of SIDs used for global segment identifiers
3. OSPF authentication keys
4. MPLS VPN Route Targets

Correct Answer: 2

Explanation

The Segment Routing Global Block (SRGB) defines a range of Segment Identifiers that can be used consistently across a Segment Routing domain. Prefix-SIDs and other globally meaningful SIDs can be mapped into this range according to the Segment Routing configuration. Consistent SRGB allocation simplifies the interpretation of segment identifiers across the network. BGP community values are unrelated to SRGB, OSPF authentication keys provide routing protocol security, and Route Targets control VPN route import and export. Therefore, the SRGB is the range associated with globally significant Segment Routing identifiers.

Question 119

Which Segment Routing protection mechanism provides fast local repair around certain link or node failures without requiring traditional RSVP-TE signaling?

1. LDP
2. BGP PIC
3. TI-LFA
4. VRRP

Correct Answer: 3

Explanation

Topology Independent Loop-Free Alternate (TI-LFA) is a Segment Routing fast-reroute mechanism designed to provide rapid local protection against failures such as link or node failures. It calculates backup paths in advance and can use Segment Routing instructions to steer traffic around the failure. TI-LFA can operate without requiring traditional RSVP-TE signaling for each protected path. LDP is a label distribution protocol, BGP PIC provides rapid BGP convergence through preinstalled paths, and VRRP provides gateway redundancy. Therefore, TI-LFA is the correct answer.

Question 120

Which QoS mechanism places packets into different treatment classes based on characteristics such as DSCP markings?

1. Shaping
2. Classification
3. Policing
4. Fragmentation

Correct Answer: 2

Explanation

QoS classification identifies traffic and places packets into appropriate classes based on characteristics such as DSCP, IP addresses, protocols, ports, or other matching criteria. After classification, additional QoS actions such as marking, queuing, shaping, or policing can be applied. Shaping controls the transmission rate by buffering traffic, while policing enforces a rate by monitoring traffic and potentially dropping or remarking packets. Fragmentation divides packets into smaller pieces and is not a primary QoS classification function. Therefore, classification is the correct answer.