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Question 281

Which BGP attribute is primarily used to influence outbound traffic within an autonomous system?

1. MED
2. Local Preference
3. Origin
4. AS_PATH

Correct Answer: 2

Explanation

BGP Local Preference is used within an autonomous system to influence which exit point should be selected for outbound traffic. A higher Local Preference value is generally preferred by BGP when comparing eligible paths. Because the attribute is propagated through iBGP within the AS, it can provide consistent outbound path-selection policy across multiple routers. MED is commonly used to influence how neighboring autonomous systems enter a network, while ORIGIN and AS_PATH are other BGP path attributes used during best-path selection. Therefore, Local Preference is the correct answer for influencing outbound traffic.

Question 282

Which BGP attribute is commonly used to influence how a neighboring autonomous system enters your network?

1. MED
2. Local Preference
3. Weight
4. Router ID

Correct Answer: 1

Explanation

The Multi-Exit Discriminator (MED) is commonly used to influence the path that a neighboring autonomous system selects when entering the advertising AS. When multiple links exist between two autonomous systems, an operator can advertise different MED values to suggest a preferred entry point. Lower MED values are generally preferred when the attribute is considered during BGP path selection. Local Preference primarily influences outbound traffic within an AS, while Weight is Cisco-specific and locally significant. Router ID identifies a BGP speaker. Therefore, MED is correct.

Question 283

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

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

Correct Answer: 3

Explanation

The AS_PATH attribute records the autonomous systems that a BGP route has traversed. When an AS receives a route containing its own AS number in the AS_PATH, it normally rejects that route because accepting it could create a routing loop. This provides an important loop-prevention mechanism in inter-AS BGP routing. NEXT_HOP identifies the next-hop address, Local Preference influences outbound path selection, and MED can influence inbound path selection between neighboring autonomous systems. Therefore, AS_PATH is the correct attribute for BGP loop prevention.

Question 284

Which BGP feature allows multiple routers to share routes without requiring a full-mesh of iBGP sessions?

1. BGP Confederation
2. Route Reflector
3. BFD
4. Graceful Restart

Correct Answer: 2

Explanation

A BGP Route Reflector reduces the requirement for a full mesh of iBGP sessions. Instead of every iBGP router establishing a session with every other router, clients establish sessions with one or more route reflectors. The route reflector then redistributes eligible routes between clients according to BGP route-reflection rules. This significantly simplifies BGP scalability in large service-provider networks. BGP Confederations also address scalability but use sub-autonomous-system structures. BFD provides rapid failure detection, while Graceful Restart assists during certain control-plane restart events. Therefore, Route Reflector is correct.

Question 285

Which BGP scalability technique divides one autonomous system into multiple internal sub-autonomous systems?

1. Route Reflector
2. Confederation
3. Add-Path
4. Route Refresh

Correct Answer: 2

Explanation

BGP Confederations divide a large autonomous system into multiple internal sub-autonomous systems. These sub-ASes can use eBGP-like relationships internally while presenting the overall network externally as a single autonomous system. Confederations can reduce the complexity associated with large iBGP deployments and provide additional control over internal routing relationships. Route Reflectors solve scalability by concentrating route distribution, while Add-Path advertises multiple paths and Route Refresh allows routes to be requested again without resetting the session. Therefore, BGP Confederation is correct.

Question 286

Which BGP attribute identifies the IP address that should be used to reach the advertised destination?

1. NEXT_HOP
2. ORIGIN
3. MED
4. COMMUNITY

Correct Answer: 1

Explanation

The BGP NEXT_HOP attribute identifies the IP address that a router should use as the next hop toward the advertised destination. The receiving router must have reachability to that next-hop address for the BGP route to be usable. In service-provider networks, next-hop handling is especially important when routes are exchanged between PE routers, route reflectors, or external BGP neighbors. ORIGIN identifies how the route entered BGP, MED can influence path selection, and COMMUNITY carries policy tags. Therefore, NEXT_HOP is the correct attribute.

Question 287

Which BGP capability allows a router to maintain forwarding during a temporary control-plane restart when both peers support the feature?

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

Correct Answer: 1

Explanation

BGP Graceful Restart is designed to help maintain forwarding during certain control-plane restart events. When supported and negotiated by neighboring devices, routing information can be retained temporarily while the restarting BGP process recovers and re-establishes its sessions. This can reduce traffic disruption during planned or unplanned control-plane events. Route Dampening addresses unstable routes, MED influences certain BGP path-selection decisions, and Add-Path allows multiple paths to be advertised. Therefore, Graceful Restart is the correct BGP capability for this scenario.

Question 288

Which BGP configuration can protect a router from receiving an unexpectedly large number of prefixes from a neighbor?

1. Maximum-prefix limit
2. Route Target
3. Next-Hop-Self
4. Local Preference

Correct Answer: 1

Explanation

A BGP maximum-prefix limit allows an operator to define the maximum number of prefixes that can be accepted from a particular BGP neighbor. If the number of received routes exceeds the configured threshold, the router can take a predefined action, such as warning, shutting down the session, or applying another supported response. This helps protect device resources and provides an operational safeguard against routing mistakes or unexpected advertisements. Route Targets control VPN route import and export, Next-Hop-Self modifies next-hop handling, and Local Preference influences outbound path selection.

Question 289

Which BGP mechanism allows an eBGP route to be accepted when the local AS appears in the AS_PATH under controlled circumstances?

1. AS Override
2. Allowas-in
3. Route Reflector
4. MED

Correct Answer: 2

Explanation

The allowas-in feature permits a BGP router to accept a route even when its own autonomous system number appears in the AS_PATH. Normally, BGP rejects such a route as a loop-prevention measure. Allowas-in can be useful in specific network designs where the same AS is legitimately present in different routing locations. AS Override performs a different function and is commonly used in MPLS VPN environments to replace customer AS numbers in certain advertisements. Route Reflectors address iBGP scalability, while MED influences path selection. Therefore, allowas-in is correct.

Question 290

Which BGP VPN feature can replace a customer’s AS number in the AS_PATH when advertising routes toward another customer site?

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

Correct Answer: 1

Explanation

AS Override is used in certain MPLS VPN designs when customer sites use the same autonomous system number. A PE router can replace the customer’s AS number in the AS_PATH before advertising the route toward another customer site. This prevents the receiving customer router from rejecting the route because it sees its own AS number and interprets it as a routing loop. Add-Path provides multiple BGP paths, Graceful Restart supports control-plane recovery, and Route Refresh requests route re-advertisement. Therefore, AS Override is correct.

Question 291

Which MPLS label is commonly used to request that the upstream router perform Penultimate Hop Popping?

1. Explicit Null
2. Implicit Null
3. VPN Label
4. Service Label

Correct Answer: 2

Explanation

The Implicit Null label is commonly used to signal Penultimate Hop Popping. When the penultimate router receives this instruction, it removes the outer transport label before forwarding the packet toward the egress router. This reduces label-processing work at the egress PE. Explicit Null also causes the outer label to be retained but uses a special label value, which can be useful when preserving certain QoS or TTL information. VPN and service labels identify service-specific forwarding contexts. Therefore, Implicit Null is correct.

Question 292

Which MPLS label is commonly used when the egress router needs the outer label to remain present for processing?

1. Implicit Null
2. Explicit Null
3. Untagged
4. Local Preference

Correct Answer: 2

Explanation

The Explicit Null label allows the outer MPLS label to remain on the packet until it reaches the egress router. This differs from Implicit Null, where the penultimate router removes the outer transport label. Explicit Null can be useful when preserving QoS-related information or MPLS TTL behavior through the final hop. The label value is a special reserved MPLS label rather than an ordinary dynamically assigned forwarding label. Therefore, Explicit Null is the correct choice when the outer label should remain until the egress router.

Question 293

Which MPLS troubleshooting mechanism can verify connectivity across a Label Switched Path?

1. MPLS LSP Ping
2. DHCP Discover
3. BGP UPDATE
4. IGMP Report

Correct Answer: 1

Explanation

MPLS LSP Ping is an OAM mechanism used to verify connectivity across an MPLS Label Switched Path. It can help determine whether an LSP is operational and can provide useful diagnostic information when MPLS forwarding is not functioning as expected. MPLS LSP Traceroute can provide additional hop-by-hop troubleshooting information. DHCP Discover is used for address configuration, BGP UPDATE messages carry routing information, and IGMP Reports signal multicast group membership. Therefore, MPLS LSP Ping is the correct mechanism for testing MPLS LSP connectivity.

Question 294

Which MPLS table contains label-to-forwarding information used for actual packet forwarding?

1. LFIB
2. LSDB
3. ARP table
4. BGP RIB only

Correct Answer: 1

Explanation

The Label Forwarding Information Base (LFIB) contains information used to forward MPLS-labeled packets. It maps incoming labels to forwarding actions such as swapping, popping, or other label operations and identifies the appropriate outgoing interface or next hop. The routing information base and IGP databases help determine reachability and paths, but the LFIB is specifically associated with MPLS forwarding. The LSDB contains link-state information, while ARP resolves IPv4 addresses to MAC addresses. Therefore, LFIB is the correct table for MPLS label forwarding.

Question 295

Which MPLS VPN label stack arrangement normally uses an outer transport label and an inner VPN service label?

1. Two-label stack
2. Single Ethernet tag
3. IPv6 extension stack
4. TCP option stack

Correct Answer: 1

Explanation

An MPLS Layer 3 VPN packet commonly uses a two-label stack. The outer transport label directs the packet across the provider core toward the egress PE. The inner VPN or service label identifies the appropriate customer forwarding context at the egress PE. This separation allows core P routers to forward traffic without maintaining individual customer VRFs while still enabling the egress PE to deliver traffic into the correct VPN. The labels are independent of Ethernet VLAN tags and TCP options. Therefore, the two-label stack is correct.

Question 296

Which EVPN route type advertises MAC and IP address reachability information?

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

Correct Answer: 2

Explanation

EVPN Route Type 2 is the MAC/IP Advertisement route. It provides MAC address reachability information and can also include an associated IP address. This route type is fundamental to EVPN because it allows PE routers to advertise endpoint reachability through the BGP EVPN control plane. Type 1 is used for Ethernet Auto-Discovery, Type 3 is the Inclusive Multicast Ethernet Tag route, and Type 4 is Ethernet Segment discovery. Therefore, Type 2 is the correct EVPN route type for MAC/IP reachability advertisements.

Question 297

Which EVPN route type is used to advertise an Ethernet Segment for multihoming-related control-plane procedures?

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

Correct Answer: 3

Explanation

EVPN Route Type 4 is the Ethernet Segment route. It is used in EVPN multihoming environments to advertise information about Ethernet Segments and support procedures such as Designated Forwarder election and Ethernet Segment discovery. This control-plane information allows multiple PE routers connected to the same customer segment to coordinate their forwarding behavior. Type 2 handles MAC/IP advertisements, Type 3 carries IMET information, and Type 5 advertises IP prefixes. Therefore, Route Type 4 is correct.

Question 298

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

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

Correct Answer: 1

Explanation

EVPN Route Type 5 is the IP Prefix route. It allows EVPN to advertise IP prefix reachability independently of a specific MAC/IP host advertisement. This makes Type 5 particularly useful for integrated routing and bridging architectures where IP prefixes need to be exchanged across an EVPN control plane. Type 1 is Ethernet Auto-Discovery, Type 2 advertises MAC/IP reachability, and Type 4 provides Ethernet Segment information. Therefore, Type 5 is the correct route type for advertising IP prefixes.

Question 299

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

1. ARP suppression
2. Route Dampening
3. BGP Confederation
4. PHP

Correct Answer: 1

Explanation

EVPN ARP suppression reduces unnecessary ARP flooding by allowing PE devices to use IP-to-MAC binding information learned through the EVPN control plane. When a device needs to resolve an IP address, the local PE may already know the corresponding MAC information and can respond locally instead of flooding the ARP request throughout the Layer 2 domain. This improves efficiency and reduces broadcast traffic. Route Dampening addresses BGP instability, BGP Confederations improve scalability, and PHP is an MPLS forwarding operation. Therefore, ARP suppression is correct.

Question 300

Which multicast technology is designed to allow a receiver to explicitly request traffic from a specific multicast source?

1. Anycast-RP
2. SSM
3. MSDP
4. PIM-DM

Correct Answer: 2

Explanation

Source-Specific Multicast (SSM) allows a receiver to identify both the multicast group and the specific source from which it wants to receive traffic. This eliminates the need for a shared Rendezvous Point for the multicast flow and creates a source-specific forwarding tree. SSM is especially useful for applications where receivers already know the intended source. Anycast-RP provides RP redundancy, MSDP exchanges multicast source information between domains or RPs, and PIM-DM uses a flood-and-prune model. Therefore, SSM is the correct multicast technology.