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Question 321

Which MPLS VPN component uniquely distinguishes overlapping customer address spaces on a provider edge router?

1. Route Target
2. Route Distinguisher
3. Community
4. MPLS label

Correct Answer: 2

Explanation

A Route Distinguisher (RD) makes otherwise overlapping customer IPv4 or IPv6 prefixes unique within the provider’s VPNv4 or VPNv6 routing tables. For example, two different customers can both use the same private prefix, such as 10.1.0.0/16, while their routes remain distinct because different RDs are attached to them. The RD provides uniqueness but does not itself determine which VRFs import the route. Route Targets perform that policy function. MPLS labels identify forwarding information, while communities can carry additional policy information. Therefore, the Route Distinguisher is correct.

Question 322

Which MPLS VPN attribute determines whether a VPN route is imported into a particular VRF?

1. Route Target
2. Route Distinguisher
3. Local Preference
4. MED

Correct Answer: 1

Explanation

Route Targets (RTs) control the import and export of VPN routes between VRFs. When a PE exports a customer route, one or more RT extended communities can be attached to the route. A receiving VRF checks its configured import RTs to determine whether the route should be installed. Export RTs identify the policy classification applied to outgoing VPN routes, while import RTs determine which routes are accepted into a VRF. The RD serves a different purpose by making overlapping prefixes unique. Therefore, Route Target is the correct answer.

Question 323

Which MPLS forwarding operation replaces the top label with another label while forwarding a packet?

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

Correct Answer: 3

Explanation

MPLS label swapping occurs when an MPLS router removes the incoming top label and replaces it with another outgoing label before forwarding the packet. This operation is commonly performed by an LSR along an MPLS LSP. Push adds a new label to the stack, while pop removes a label. The specific label operation is determined by the router’s forwarding information, such as LFIB entries. Label swapping is fundamental to MPLS because intermediate routers can forward packets based on labels rather than performing a complete IP routing lookup. Therefore, swap is correct.

Question 324

What is the primary purpose of the MPLS Label Forwarding Information Base (LFIB)?

1. Store DNS records
2. Store label forwarding information
3. Store BGP authentication keys
4. Store SNMP notifications

Correct Answer: 2

Explanation

The Label Forwarding Information Base (LFIB) contains the information required to forward MPLS-labeled packets. It specifies how incoming labels should be handled and what outgoing labels or interfaces should be used. Depending on the entry, the router can perform operations such as swap, pop, or push. The LFIB is derived from control-plane information and is used by the forwarding plane for efficient packet forwarding. DNS records, BGP authentication information, and SNMP notifications are unrelated to MPLS label forwarding. Therefore, storing label forwarding information is the correct answer.

Question 325

Which MPLS VPN design allows a provider to use different RDs for the same customer VPN across different PE routers?

1. Unique RD per PE
2. One global RD for every customer
3. One RD per physical interface
4. One RD per MPLS label

Correct Answer: 1

Explanation

A VPN can use a unique RD per PE router, and this approach can be useful when the provider wants multiple distinct VPNv4 or VPNv6 paths for the same customer prefix. Because the RD forms part of the VPN address, using different RDs can make otherwise identical customer prefixes appear as distinct routes in the provider’s BGP table. Route Targets can still determine which routes are imported into the customer VRF. The RD is not tied to MPLS labels or necessarily to individual physical interfaces. Therefore, unique RD per PE is correct.

Question 326

Which technology is commonly used to carry customer IPv4 VPN routes over an MPLS provider backbone using MP-BGP?

1. IPv4 unicast BGP only
2. VPNv4
3. OSPFv3
4. IS-IS Level-1

Correct Answer: 2

Explanation

VPNv4 is an MP-BGP address family used to distribute IPv4 VPN routes between provider edge routers. A VPNv4 route combines an IPv4 prefix with a Route Distinguisher, allowing overlapping customer address spaces to coexist in the provider network. Extended communities, particularly Route Targets, can carry VPN import and export policy information. The MPLS data plane then uses labels to transport the traffic across the provider backbone. Regular IPv4 unicast BGP alone does not provide the required VPN separation. Therefore, VPNv4 is correct.

Question 327

Which MPLS VPN component is responsible for forwarding customer traffic across the provider backbone without maintaining customer routes in the core?

1. PE router
2. CE router
3. P router
4. Route Reflector

Correct Answer: 3

Explanation

Provider (P) routers operate inside the MPLS core and normally do not need to maintain individual customer VPN routing tables. They use the provider’s core routing information and MPLS labels to transport packets between PE routers. PE routers maintain VRFs and participate in VPN route exchange, while CE routers connect customer networks to the provider edge. Route Reflectors can distribute BGP routes but are not inherently responsible for MPLS core forwarding. This separation helps service providers scale because the core does not need detailed customer-specific routing information. Therefore, the P router is correct.

Question 328

Which MPLS VPN architecture uses an eBGP session between autonomous systems to exchange VPN routes at the AS boundary?

1. Inter-AS Option A
2. Inter-AS Option B
3. Inter-AS Option C
4. Carrier Supporting Carrier

Correct Answer: 2

Explanation

Inter-AS Option B uses MP-eBGP to exchange VPNv4 or VPNv6 routing information between autonomous systems at the AS boundary. The participating ASBRs exchange VPN routes and associated labels, allowing VPN traffic to cross between provider networks. Option A generally connects VRFs across the AS boundary using separate interfaces or subinterfaces, while Option C uses a more scalable architecture involving labeled reachability and BGP information across the provider domains. Carrier Supporting Carrier addresses a different provider hierarchy. Therefore, Inter-AS Option B is correct.

Question 329

Which segment routing identifier typically represents the shortest-path identity of a specific router within an SR-MPLS domain?

1. Node-SID
2. Route Target
3. VPN Label
4. Ethernet Segment Identifier

Correct Answer: 1

Explanation

A Node-SID represents a specific node in a Segment Routing domain. In SR-MPLS, a router can advertise a Prefix-SID associated with a loopback or prefix, and a Node-SID commonly represents the shortest path to that router. When a packet is forwarded using a Node-SID, intermediate routers use their segment-routing forwarding information to guide the packet toward the destination node. Route Targets belong to VPN policy, VPN labels identify VPN forwarding contexts, and ESI identifies Ethernet multihoming segments in EVPN. Therefore, Node-SID is correct.

Question 330

Which Segment Routing identifier can represent a specific adjacency between two directly connected routers?

1. Node-SID
2. Adjacency-SID
3. Route Distinguisher
4. VPN label

Correct Answer: 2

Explanation

An Adjacency-SID identifies a specific adjacency between neighboring Segment Routing routers. Unlike a Node-SID, which generally represents reachability toward a node, an Adjacency-SID can steer traffic over a particular link or adjacency. This makes Adjacency-SIDs useful when an SR policy needs more precise path control than shortest-path forwarding provides. Route Distinguisher and VPN labels are MPLS VPN concepts, while Node-SID represents a node or prefix-based destination. Therefore, Adjacency-SID is the correct answer.

Question 331

In an SR-MPLS network, what is the purpose of the Segment Routing Global Block (SRGB)?

1. Define a range used for global Segment IDs
2. Store customer VPN routes
3. Assign BGP router IDs
4. Identify Ethernet VLANs

Correct Answer: 1

Explanation

The Segment Routing Global Block (SRGB) defines a range of MPLS label values that can be used for globally significant Segment IDs within a Segment Routing domain. Consistent SRGB planning helps routers interpret Prefix-SIDs and Node-SIDs correctly. A Segment ID is associated with a segment, while the SRGB provides the label range from which those values can be derived. The SRGB does not store VPN routes, assign BGP router IDs, or identify VLANs. Therefore, defining the range used for global Segment IDs is its primary purpose.

Question 332

Which SR Policy component can identify a specific policy for steering traffic through a Segment Routing network?

1. Binding SID
2. Route Target
3. RD
4. Ethernet Segment Identifier

Correct Answer: 1

Explanation

A Binding SID (BSID) can represent an SR Policy as a segment. When traffic is steered using the BSID, the network can associate that identifier with the corresponding SR Policy and apply the policy’s defined path instructions. This provides a convenient mechanism for recursively referencing an SR Policy or steering traffic toward a specific policy. Route Targets and RDs are MPLS VPN constructs, while an Ethernet Segment Identifier is used by EVPN multihoming. Therefore, Binding SID is correct.

Question 333

Which EVPN route type advertises MAC and optional IP address reachability information for a MAC/IP advertisement?

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

Correct Answer: 2

Explanation

EVPN Route Type 2 is the MAC/IP Advertisement route. It is used to advertise customer MAC addresses and, when available, associated IP addresses. These routes allow remote EVPN PEs to learn MAC reachability and can also support integrated routing and bridging functions. Route Type 1 is Ethernet Auto-Discovery, Type 3 is Inclusive Multicast Ethernet Tag (IMET), and Type 4 is Ethernet Segment route information used for multihoming operations. Therefore, Route Type 2 is correct.

Question 334

Which EVPN route type is primarily used to advertise Ethernet Segment information for multihoming 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 to advertise information associated with an Ethernet Segment Identifier (ESI). This information supports procedures such as Designated Forwarder election and Ethernet Segment discovery between participating PE routers. Type 2 routes advertise MAC/IP reachability, Type 3 routes provide inclusive multicast Ethernet Tag information, and Type 5 routes advertise IP prefixes. Therefore, Route Type 4 is the correct answer for Ethernet Segment information.

Question 335

Which EVPN mechanism helps prevent duplicate MAC addresses from causing persistent forwarding instability?

1. MAC Mobility
2. Route Reflector
3. RPKI
4. BFD

Correct Answer: 1

Explanation

EVPN MAC Mobility mechanisms help identify legitimate movement of a MAC address between different locations while also providing protection against unstable or duplicated MAC advertisements. EVPN can use a MAC Mobility sequence number to indicate the relative freshness of advertisements. When a MAC moves, a newer sequence value can help remote PEs determine which location should be preferred. Route Reflectors distribute BGP routes, RPKI validates BGP route origin information, and BFD detects forwarding failures. Therefore, MAC Mobility is the appropriate EVPN mechanism.

Question 336

Which EVPN multihoming mode allows a customer device to use multiple PE connections simultaneously for forwarding traffic?

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

Correct Answer: 2

Explanation

In EVPN multihoming, all-active mode allows a multihomed customer device or Ethernet Segment to use multiple PE connections for forwarding traffic. This provides active-active connectivity and can improve redundancy and bandwidth utilization. Single-active mode provides redundancy but normally designates one PE connection as active for a given traffic flow or segment behavior. Passive-only and stub-active are not standard EVPN multihoming operating modes. Therefore, all-active is the correct answer when multiple PE connections can actively forward traffic.

Question 337

Which QoS mechanism is designed to provide strict priority treatment for delay-sensitive traffic such as voice?

1. LLQ
2. WRED
3. Tail Drop
4. Route Dampening

Correct Answer: 1

Explanation

Low Latency Queuing (LLQ) provides a strict priority queue designed for delay-sensitive traffic such as voice and other real-time applications. During congestion, packets in the priority queue can receive preferential treatment to reduce latency and jitter. LLQ is commonly implemented as a strict-priority component within a class-based QoS policy. WRED is a congestion-avoidance mechanism, while tail drop discards packets when a queue becomes full. Route Dampening is a BGP stability mechanism and is unrelated to QoS. Therefore, LLQ is correct.

Question 338

What is the primary difference between traffic shaping and traffic policing?

1. Shaping buffers excess traffic, while policing can drop or remark it
2. Shaping always drops traffic, while policing always buffers it
3. Both always buffer excess traffic
4. Neither can affect traffic rate

Correct Answer: 1

Explanation

Traffic shaping and policing both control traffic rates, but they handle excess traffic differently. Shaping generally buffers excess packets and transmits them later according to the configured rate, which smooths traffic over time. Policing typically evaluates traffic against a configured rate and can drop, remark, or otherwise handle packets that exceed the allowed rate. Because shaping uses buffering, it can introduce delay, while policing generally does not provide the same buffering behavior. Therefore, shaping buffers excess traffic while policing can drop or remark it.

Question 339

Which IPv6 protocol is responsible for Neighbor Discovery functions such as router discovery and address resolution?

1. ARP
2. ICMPv6
3. DHCPv4
4. TCP

Correct Answer: 2

Explanation

IPv6 Neighbor Discovery uses ICMPv6 messages to perform functions such as router discovery, neighbor address resolution, Duplicate Address Detection, and prefix discovery. IPv6 does not use ARP in the same manner as IPv4. Router Solicitation and Router Advertisement messages help hosts discover routers and network prefixes, while Neighbor Solicitation and Neighbor Advertisement messages support neighbor resolution and related operations. DHCPv4 is specific to IPv4, and TCP provides transport-layer communication rather than Neighbor Discovery. Therefore, ICMPv6 is correct.

Question 340

Which IPv6 mechanism allows a host to detect whether another device is already using an address before assigning it?

1. Prefix Delegation
2. Duplicate Address Detection
3. Route Target
4. Path MTU Discovery

Correct Answer: 2

Explanation

Duplicate Address Detection (DAD) is an IPv6 Neighbor Discovery procedure used to determine whether an address is already in use on the local link before the host assigns it to an interface. DAD uses ICMPv6 Neighbor Solicitation messages and helps prevent address duplication. Prefix Delegation is used to assign IPv6 prefixes to downstream networks, Route Targets are associated with VPN routing policy, and Path MTU Discovery determines the appropriate packet size along a path. Therefore, Duplicate Address Detection is the correct answer.