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Question 161

Which OSPF feature allows a router to advertise a default route into an OSPF domain?

1. Route reflection
2. Default-information originate
3. Area filtering
4. LSA throttling

Correct Answer: 2

Explanation

The OSPF default-information originate feature allows a router to advertise a default route into an OSPF domain. This is useful when a router has connectivity toward an external network or Internet and needs to provide other OSPF routers with a default path. Depending on the configuration, the router may require an existing default route before originating the OSPF default route, or the configuration can force advertisement. Route reflection is a BGP mechanism, while area filtering and LSA throttling address different OSPF functions. Therefore, default-information originate is correct.

Question 162

Which OSPF network type is commonly used on an Ethernet broadcast segment?

1. Point-to-point
2. Non-broadcast
3. Broadcast
4. Loopback

Correct Answer: 3

Explanation

OSPF commonly uses the broadcast network type on Ethernet segments. In this environment, OSPF can dynamically discover neighbors using multicast Hello packets and elect a Designated Router and Backup Designated Router. The DR reduces the number of full adjacencies and limits unnecessary LSA exchange on the shared segment. Point-to-point networks are typically used for direct router-to-router links, while non-broadcast networks require different neighbor-discovery behavior. A loopback interface represents a logical interface rather than a shared Ethernet segment. Therefore, broadcast is the correct OSPF network type.

Question 163

Which OSPF mechanism is used to authenticate routing protocol exchanges between neighbors?

1. OSPF authentication
2. Route Target
3. MPLS TC
4. BGP Community

Correct Answer: 1

Explanation

OSPF authentication can be configured to help ensure that routing protocol messages are accepted only from trusted neighbors using the appropriate authentication parameters. Authentication helps protect the routing control plane against unauthorized or malformed routing information. Depending on the OSPF version and implementation, different authentication methods may be supported. Route Targets are used with VPN route import and export, MPLS TC carries traffic-class information, and BGP Communities communicate policy information in BGP. Therefore, OSPF authentication is the correct mechanism for protecting OSPF neighbor exchanges.

Question 164

Which IS-IS level is primarily responsible for routing between different IS-IS areas?

1. Level 1
2. Level 2
3. Level 0
4. Level 3

Correct Answer: 2

Explanation

IS-IS Level 2 routers provide routing between different IS-IS areas and form the backbone of an IS-IS domain. Level 1 routers primarily provide intra-area routing and generally rely on Level 2 connectivity to reach destinations outside their local area. A router can operate as both Level 1 and Level 2, depending on the network design. IS-IS does not use Level 0 or Level 3 in its standard hierarchical routing model. Therefore, Level 2 is the correct answer for inter-area routing.

Question 165

What is the primary purpose of the IS-IS overload bit?

1. Prevent a router from being used as a transit path
2. Encrypt IS-IS packets
3. Create BGP sessions
4. Allocate MPLS labels

Correct Answer: 1

Explanation

The IS-IS overload bit indicates that a router should generally not be used as a transit router for certain traffic while it completes tasks such as database synchronization or route installation. This can be useful during startup or when a router does not have sufficient routing information to safely carry transit traffic. Other routers can recognize the overload condition and avoid selecting the affected router as a transit path where appropriate. The overload bit does not provide encryption, establish BGP sessions, or distribute MPLS labels. Therefore, preventing transit use is the correct purpose.

Question 166

Which IS-IS packet is used to establish and maintain neighbor adjacencies?

1. LSP
2. CSNP
3. IIH
4. PSNP

Correct Answer: 3

Explanation

IS-IS Intermediate System-to-Intermediate System Hello packets, commonly called IIHs, are used to establish and maintain adjacencies between neighboring IS-IS routers. These packets allow routers to exchange information required to determine whether a neighboring device is reachable and whether an adjacency can be formed. LSPs carry link-state information, CSNPs provide database summaries, and PSNPs acknowledge or request specific LSP information. Therefore, IIH is the correct packet type for IS-IS neighbor establishment and maintenance.

Question 167

Which BGP attribute is commonly used to influence how neighboring autonomous systems choose an entry point into your network?

1. MED
2. LOCAL_PREF
3. Weight
4. Cluster List

Correct Answer: 1

Explanation

The Multi-Exit Discriminator (MED) attribute can be used to communicate a preference to a neighboring autonomous system regarding which entry point should be selected for reaching advertised prefixes. A lower MED is generally preferred when comparing routes from the same neighboring AS under the applicable BGP decision process. LOCAL_PREF is primarily used within an autonomous system to influence outbound path selection. Weight is a Cisco-specific local attribute, while the Cluster List is associated with BGP route reflection. Therefore, MED is the correct attribute for influencing inbound path selection by a neighboring AS.

Question 168

Which BGP attribute is locally significant and is commonly preferred first on Cisco routers during best-path selection?

1. MED
2. Weight
3. AS_PATH
4. ORIGIN

Correct Answer: 2

Explanation

Cisco’s BGP Weight attribute is locally significant and can influence route selection on an individual router. A higher Weight is preferred over a lower Weight when comparing otherwise eligible paths. Weight is not propagated to BGP neighbors, making it useful when an administrator wants to influence route selection only on a particular router. AS_PATH, ORIGIN, and MED are other BGP path attributes considered at different stages of the best-path process. Therefore, Weight is the correct answer for a Cisco-specific local preference mechanism used early in the decision process.

Question 169

Which BGP configuration can make an internal BGP router advertise itself as the next hop for routes learned from an external BGP neighbor?

1. Route Reflector
2. Next-Hop-Self
3. Add-Path
4. AS Override

Correct Answer: 2

Explanation

The BGP next-hop-self function changes the next-hop attribute when advertising routes to another BGP peer, commonly making the advertising router itself the next hop. This is especially useful in iBGP designs where an internal router needs to provide a reachable next hop for routes learned from an external BGP neighbor. Route Reflectors address iBGP scalability, Add-Path allows multiple paths to be advertised, and AS Override is commonly associated with MPLS VPN scenarios involving overlapping autonomous system numbers. Therefore, Next-Hop-Self is correct.

Question 170

Which BGP feature can prevent a customer AS number from causing a loop when the same AS is used on both sides of an MPLS VPN service provider?

1. AS Override
2. MED
3. Route Refresh
4. Graceful Restart

Correct Answer: 1

Explanation

BGP AS Override is commonly used in MPLS Layer 3 VPN environments when the same customer autonomous system number appears at multiple customer sites. Normally, receiving a route containing the local AS number would cause the route to be rejected as a potential loop. With AS Override, the PE router can replace occurrences of the customer’s AS number before advertising the route toward another customer site. MED influences path selection, Route Refresh requests updated routes, and Graceful Restart helps maintain forwarding during certain restarts. Therefore, AS Override is correct.

Question 171

Which MPLS label value is commonly used to request explicit-null behavior for IPv4?

1. Label 0
2. Label 1
3. Label 2
4. Label 3

Correct Answer: 1

Explanation

MPLS label value 0 is the IPv4 Explicit Null label. When explicit null is used, the penultimate router does not simply remove the MPLS label; instead, it can replace the label with the explicit-null value so that the egress router receives information that preserves the MPLS label context, including the Traffic Class field. This can be useful for QoS-related processing. Label 1 is associated with the Router Alert label, while label 3 represents Implicit Null. Therefore, label 0 is the correct answer for IPv4 Explicit Null.

Question 172

Which MPLS label value is associated with Implicit Null and is commonly used to enable PHP?

1. 0
2. 1
3. 2
4. 3

Correct Answer: 4

Explanation

MPLS label value 3 represents Implicit Null. It is not normally placed into the MPLS packet as an actual label. Instead, it signals that the penultimate router should remove the top label before forwarding the packet toward the egress router. This behavior is known as Penultimate Hop Popping (PHP). Label 0 represents IPv4 Explicit Null, label 1 is the Router Alert label, and label 2 is associated with IPv6 Explicit Null. Therefore, label 3 is the correct answer.

Question 173

Which MPLS feature can provide a logical point-to-point Layer 2 connection between customer Ethernet interfaces?

1. VPWS
2. OSPF
3. PIM
4. SNMP

Correct Answer: 1

Explanation

Virtual Private Wire Service (VPWS) provides a point-to-point Layer 2 service between customer attachment points across a provider network. It commonly uses pseudowire technology to carry customer Layer 2 frames through the provider infrastructure. From the customer’s perspective, the service can appear similar to a direct virtual circuit between two locations. OSPF is an interior routing protocol, PIM handles multicast routing, and SNMP provides network management. Therefore, VPWS is the correct service for a logical point-to-point Layer 2 connection.

Question 174

Which EVPN route type is used to advertise MAC and IP address reachability information?

1. Route Type 1
2. Route Type 2
3. Route Type 3
4. Route Type 4

Correct Answer: 2

Explanation

EVPN Route Type 2, known as the MAC/IP Advertisement route, advertises MAC address reachability and can also include associated IP address information. This route is an important component of EVPN because it allows PE devices to distribute customer MAC and IP reachability through the BGP control plane. Route Type 1 is used for Ethernet Auto-Discovery, Type 3 is an Inclusive Multicast Ethernet Tag route, and Type 4 is an Ethernet Segment route. Therefore, Route Type 2 is the correct answer.

Question 175

Which EVPN route type is primarily associated with Ethernet Segment discovery and multihoming information?

1. Route Type 2
2. Route Type 3
3. Route Type 4
4. Route Type 5

Correct Answer: 3

Explanation

EVPN Route Type 4 is the Ethernet Segment route. It is used to advertise information associated with Ethernet Segments and plays an important role in EVPN multihoming operations. It can help participating PE routers discover other PE devices attached to the same Ethernet Segment and support procedures such as Designated Forwarder election. Route Type 2 advertises MAC/IP reachability, Type 3 handles inclusive multicast Ethernet Tag information, and Type 5 advertises IP prefixes. Therefore, Route Type 4 is correct.

Question 176

Which EVPN route type is used to advertise IP prefixes independently of individual MAC addresses?

1. Route Type 5
2. Route Type 1
3. Route Type 2
4. Route Type 3

Correct Answer: 1

Explanation

EVPN Route Type 5 is the IP Prefix route and is used to advertise IP prefixes through the EVPN control plane. This allows EVPN architectures to support Layer 3 routing information without requiring every destination to be represented as an individual MAC/IP advertisement. Route Type 1 is associated with Ethernet Auto-Discovery, Type 2 carries MAC/IP reachability, and Type 3 advertises Inclusive Multicast Ethernet Tag information. Therefore, Route Type 5 is the correct EVPN route type for IP prefix advertisement.

Question 177

Which EVPN mechanism helps reduce unnecessary ARP flooding by distributing IP-to-MAC bindings through the control plane?

1. ARP suppression
2. LDP
3. BFD
4. Route dampening

Correct Answer: 1

Explanation

EVPN ARP suppression reduces unnecessary broadcast ARP traffic by allowing PE devices to use MAC/IP binding information learned through the EVPN control plane. When a device already knows the required IP-to-MAC mapping, it may respond locally instead of flooding an ARP request throughout the Layer 2 domain. This can significantly reduce broadcast traffic in large EVPN environments. LDP distributes MPLS labels, BFD detects failures, and route dampening addresses route instability. Therefore, ARP suppression is the correct EVPN mechanism.

Question 178

Which EVPN multihoming mode allows a customer device to use multiple active links toward different provider-edge routers?

1. Single-active
2. All-active
3. Passive-only
4. Stub mode

Correct Answer: 2

Explanation

EVPN all-active multihoming allows a customer device or Ethernet Segment to use multiple active links toward participating PE routers. Traffic can be forwarded through multiple available paths, providing redundancy and potentially increased utilization of available links. Single-active multihoming, by contrast, generally has only one PE forwarding traffic at a time for the relevant segment, with another PE serving as backup. Passive-only and stub mode are not standard EVPN multihoming modes. Therefore, all-active is the correct answer for simultaneous use of multiple active PE connections.

Question 179

Which mechanism is used in EVPN multihoming to determine which PE forwards broadcast, unknown-unicast, and multicast traffic toward an Ethernet Segment?

1. DF election
2. BGP Weight
3. LDP session
4. OSPF SPF

Correct Answer: 1

Explanation

Designated Forwarder (DF) election is used in EVPN multihoming to determine which PE is responsible for forwarding certain Broadcast, Unknown Unicast, and Multicast (BUM) traffic toward a multihomed Ethernet Segment. This helps prevent duplicate forwarding and Layer 2 loops. EVPN uses BGP-based control-plane information and Ethernet Segment identifiers to coordinate multihoming behavior. BGP Weight is a local path-selection attribute, LDP establishes label distribution, and OSPF SPF calculates shortest paths. Therefore, DF election is the correct mechanism.

Question 180

Which Segment Routing concept represents a sequence of instructions that packets follow through the network?

1. Route Target
2. Segment List
3. Route Distinguisher
4. Community List

Correct Answer: 2

Explanation

A Segment List represents an ordered sequence of Segment Identifiers that defines the desired forwarding behavior for a packet or flow. Each segment represents an instruction, such as reaching a particular node, prefix, or adjacency. Segment Routing can therefore steer traffic without requiring a separate signaling protocol for every engineered path. Route Targets control VPN route import and export, Route Distinguishers make VPN routes unique, and Community Lists are used for BGP policy matching. Therefore, Segment List is the correct Segment Routing concept for representing an ordered set of forwarding instructions.