View Full Cisco CCNP Service Provider 350-501 Exam Dumps and Practice Test Dumps.

 

Question 41

Which MPLS technology is responsible for distributing labels associated with IP routes in a traditional MPLS network?

1. LDP
2. BFD
3. NTP
4. SNMP

Correct Answer: 1

Explanation

Label Distribution Protocol (LDP) is commonly used in traditional MPLS networks to distribute label bindings associated with IP prefixes. LDP establishes sessions between neighboring MPLS routers and allows them to exchange information about which labels should be used for particular forwarding equivalence classes. Once labels are distributed, routers can forward traffic using label switching rather than performing a complete IP lookup at every hop. BFD is used for fast failure detection, NTP synchronizes clocks, and SNMP provides network monitoring and management. Therefore, LDP is the correct answer.

Question 42

What is the primary function of the MPLS Label Distribution Protocol (LDP) label binding?

1. Encrypt customer traffic
2. Associate labels with forwarding information
3. Assign IP addresses to hosts
4. Synchronize router clocks

Correct Answer: 2

Explanation

An LDP label binding associates an MPLS label with forwarding information, typically a Forwarding Equivalence Class (FEC). This information allows an MPLS router to determine how packets carrying a particular label should be forwarded. Neighboring routers exchange label bindings through LDP so that an MPLS Label Switched Path can be established based on the underlying routing information. LDP itself does not encrypt customer traffic or provide IP address assignment. NTP is responsible for time synchronization. Therefore, associating labels with forwarding information is the correct function.

Question 43

Which MPLS router is normally responsible for imposing the initial MPLS label on an IP packet entering the MPLS domain?

1. Core P router
2. Transit LSR
3. Ingress PE router
4. Egress PE router

Correct Answer: 3

Explanation

The ingress Provider Edge (PE) router is typically responsible for imposing the initial MPLS label stack on traffic entering an MPLS VPN or MPLS forwarding domain. The ingress PE determines the appropriate forwarding treatment and can add transport and service-related labels. Transit provider routers then forward the packet using the MPLS labels without needing customer-specific routing information. The egress PE removes the relevant labels and forwards traffic toward the customer network. Therefore, the ingress PE router is the correct answer.

Question 44

What is the role of a Provider (P) router in an MPLS Layer 3 VPN core?

1. Maintain every customer’s VRF
2. Perform customer authentication
3. Forward MPLS traffic through the provider core
4. Assign customer IP addresses

Correct Answer: 3

Explanation

Provider (P) routers operate primarily within the MPLS service provider core. Their main role is to forward labeled traffic through the provider network. P routers generally do not need to maintain customer-specific VRFs or VPN routing information, which helps keep the core scalable. Customer-specific routing and VPN processing are mainly handled by PE routers at the network edge. Customer authentication and IP address assignment are separate services. Therefore, forwarding MPLS traffic through the provider core is the correct description of a P router’s role.

Question 45

Which MPLS VPN component allows the same IPv4 prefix to exist for multiple customers without creating a routing conflict?

1. Route Distinguisher
2. NTP
3. BFD
4. MPLS TTL

Correct Answer: 1

Explanation

A Route Distinguisher (RD) makes customer VPN routes unique within the provider’s VPNv4 or VPNv6 control plane. Two customers can use the same IPv4 prefix, such as 10.10.10.0/24, because the RD creates a unique VPN route representation for each customer. This allows overlapping customer address spaces to coexist. The RD itself does not determine which customers receive the route; Route Targets perform that import and export function. NTP provides time synchronization, BFD detects failures, and MPLS TTL handles packet lifetime. Therefore, the RD is correct.

Question 46

Which BGP extended community determines whether a VPN route is imported into a particular VRF?

1. MED
2. AS_PATH
3. Route Target
4. Weight

Correct Answer: 3

Explanation

The Route Target (RT) extended community determines how VPN routes are imported and exported between VRFs. When a PE router exports a VPN route, it attaches one or more RT values. A receiving VRF has import RT policies that determine which routes should be installed into that VRF. This allows service providers to control which customer sites can communicate with one another. MED, AS_PATH, and Weight are BGP path attributes with different purposes. Therefore, Route Target is the correct answer for controlling VPN route import and export.

Question 47

Which MPLS label field is used to provide traffic-class information in the MPLS header?

1. TTL
2. TC
3. BoS
4. Label

Correct Answer: 2

Explanation

The Traffic Class (TC) field in the MPLS header is used to carry traffic-class information. It contains three bits and can be used for QoS-related functions such as classifying or marking MPLS traffic. The Label field identifies the MPLS forwarding treatment, the Bottom-of-Stack (BoS) bit indicates whether the label is the final label in the stack, and the TTL field supports packet lifetime and loop prevention. Therefore, the TC field is the correct choice for traffic-class information.

Question 48

Which MPLS header field indicates how long a packet is allowed to remain in the network?

1. Label
2. TC
3. TTL
4. BoS

Correct Answer: 3

Explanation

The MPLS Time to Live (TTL) field limits how long an MPLS packet can remain in the network. Similar to IP TTL, it helps prevent packets from circulating indefinitely if a forwarding loop occurs. Each appropriate forwarding operation can decrement the TTL, and when it reaches zero, the packet can be discarded. The Label field identifies forwarding treatment, TC supports traffic classification, and BoS indicates the bottom of the label stack. Therefore, TTL is the correct MPLS header field for packet lifetime control.

Question 49

Which technology can be used to provide fast convergence for an OSPF adjacency after a link failure?

1. BFD
2. FTP
3. TFTP
4. DNS

Correct Answer: 1

Explanation

Bidirectional Forwarding Detection (BFD) can work with OSPF to provide rapid detection of forwarding-path failures. Instead of waiting for OSPF’s normal dead interval to expire, BFD can detect the failure quickly and notify OSPF. OSPF can then remove the affected route and recalculate paths. This is especially useful in service provider networks where rapid convergence is important. FTP and TFTP provide file transfer services, while DNS resolves names. Therefore, BFD is the correct technology for accelerating failure detection associated with OSPF.

Question 50

Which OSPF packet type is used to discover and maintain neighbor relationships?

1. LSU
2. LSA
3. Hello
4. ACK

Correct Answer: 3

Explanation

OSPF Hello packets are used to discover neighbors and maintain neighbor relationships. Routers periodically exchange Hello messages containing information such as router identifiers, timers, and network parameters. If a router stops receiving expected Hello packets, it can eventually consider the neighbor unreachable. Other OSPF packet types have different purposes. Link-State Update (LSU) packets carry LSAs, Link-State Acknowledgment packets acknowledge received LSAs, and LSAs themselves describe topology information. Therefore, the Hello packet is correct for neighbor discovery and maintenance.

Question 51

Which OSPF database contains the topology information learned from LSAs?

1. Routing table
2. ARP table
3. MAC address table
4. Link-State Database

Correct Answer: 4

Explanation

The OSPF Link-State Database (LSDB) contains the topology information learned through Link-State Advertisements. Each OSPF router uses the LSDB to build a representation of the network topology and runs the Shortest Path First algorithm to calculate routes. The resulting paths are then placed into the routing table when appropriate. ARP tables map IPv4 addresses to MAC addresses, while MAC address tables are maintained by switches for Layer 2 forwarding. Therefore, the Link-State Database is the correct answer.

Question 52

Which algorithm does OSPF use to calculate the shortest path through its topology?

1. Dijkstra’s Shortest Path First algorithm
2. Bellman-Ford only
3. RSA
4. Diffie-Hellman

Correct Answer: 1

Explanation

OSPF uses Dijkstra’s Shortest Path First (SPF) algorithm to calculate the shortest paths through the topology represented in its Link-State Database. Each router constructs a shortest-path tree rooted at itself and uses that information to determine the best routes to destinations. The calculation is based on OSPF link costs. RSA and Diffie-Hellman are cryptographic technologies, while Bellman-Ford is associated with distance-vector routing concepts rather than the standard OSPF SPF calculation. Therefore, Dijkstra’s SPF algorithm is correct.

Question 53

Which IS-IS database contains link-state information used to calculate routes?

1. MAC address table
2. Link-State Database
3. ARP cache
4. DHCP lease database

Correct Answer: 2

Explanation

IS-IS maintains a Link-State Database containing Link-State PDUs (LSPs) received from other IS-IS routers. The database provides the topology information required for SPF calculations. Each router uses this information to determine paths to destinations within the routing domain. The concept is similar to OSPF’s link-state database, although IS-IS uses different terminology and packet structures. MAC tables, ARP caches, and DHCP lease databases are associated with different network functions. Therefore, the Link-State Database is the correct answer.

Question 54

Which IS-IS packet type carries link-state information between routers?

1. LSP
2. DHCP
3. HTTP
4. ARP

Correct Answer: 1

Explanation

In IS-IS, Link-State PDUs, commonly called LSPs, carry link-state information between routers. These messages describe the network topology and are stored in the IS-IS Link-State Database. Routers use the collected information to calculate shortest paths. LSPs in IS-IS should not be confused with MPLS Label Switched Paths, even though the acronym can appear in both contexts. DHCP assigns network configuration information, HTTP is an application protocol, and ARP resolves IPv4 addresses to MAC addresses. Therefore, the IS-IS LSP is the correct answer.

Question 55

Which BGP attribute is primarily used to identify the next router that should receive traffic for a destination?

1. MED
2. Next-Hop
3. Local Preference
4. Community

Correct Answer: 2

Explanation

The BGP Next-Hop attribute identifies the IP address that should be used as the next hop toward the advertised destination. BGP routers use this information when installing and forwarding traffic based on BGP routes. In some BGP designs, the next-hop attribute may be modified or preserved depending on the relationship and configuration between routers. Local Preference influences outbound path selection, MED can influence path selection between neighboring autonomous systems, and communities provide policy information. Therefore, the Next-Hop attribute is the correct answer.

Question 56

Which BGP attribute is Cisco-specific and is normally considered only by the local router?

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

Correct Answer: 3

Explanation

Weight is a Cisco-specific BGP attribute that is local to the router where it is configured. It is not advertised to other BGP neighbors. When applicable, a higher Weight is preferred during BGP path selection. This makes Weight useful when an administrator wants to influence path selection on a particular router without propagating the policy to other routers. AS_PATH and Local Preference have broader BGP roles, while MED can be exchanged between neighboring autonomous systems. Therefore, Weight is the correct answer.

Question 57

Which BGP attribute is commonly used to identify a route’s originating autonomous system path?

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

Correct Answer: 1

Explanation

The AS_PATH attribute contains the sequence of autonomous system numbers through which a BGP route has passed. It provides important information for path selection and is also fundamental to BGP loop prevention. When an eBGP router advertises a route to another autonomous system, its AS number is normally added to the AS_PATH. A router receiving a route can reject it if its own AS number is already present. Weight is locally significant, MED can influence inter-AS path selection, and communities carry policy information. Therefore, AS_PATH is correct.

Question 58

Which BGP mechanism allows multiple routes to be grouped with policy information that can be used by routing policies?

1. MPLS label
2. BGP Community
3. VLAN tag
4. OSPF metric

Correct Answer: 2

Explanation

BGP Communities allow routes to be tagged with policy information. Network operators can define policies based on community values to influence route advertisement, acceptance, preference, or other routing behavior. Standard communities, extended communities, and large communities provide different mechanisms for carrying policy-related information. Route Targets used in MPLS VPNs are an example of extended communities. MPLS labels, VLAN tags, and OSPF metrics have different purposes. Therefore, BGP Community is the correct mechanism for attaching policy information to routes.

Question 59

Which technology allows an MPLS provider network to transport customer Layer 2 Ethernet frames between sites?

1. L3VPN
2. L2VPN
3. OSPF
4. BFD

Correct Answer: 2

Explanation

An MPLS Layer 2 VPN (L2VPN) allows a service provider to transport customer Layer 2 traffic across the provider network. Depending on the implementation, services can provide Ethernet connectivity between geographically separated customer sites while hiding the provider’s internal network from the customer. Layer 3 VPNs instead provide routed VPN connectivity using customer VRFs and VPN routes. OSPF is an IGP, while BFD is used for fast failure detection. Therefore, L2VPN is the correct service type for transporting customer Layer 2 Ethernet traffic.

Question 60

Which technology provides Layer 3 VPN services by maintaining separate customer routing instances on PE routers?

1. MPLS L3VPN
2. STP
3. LACP
4. VTP

Correct Answer: 1

Explanation

MPLS Layer 3 VPN (L3VPN) provides routed VPN connectivity by maintaining separate customer routing instances, typically using VRFs on PE routers. Customer routes are exchanged between PE routers using MP-BGP, while MPLS labels provide forwarding across the provider core. Route Distinguishers allow overlapping customer prefixes to coexist, and Route Targets control VPN route import and export. STP prevents Layer 2 loops, LACP provides link aggregation, and VTP manages certain VLAN information. Therefore, MPLS L3VPN is the correct technology.