Question 1

Which of the following statements is true regarding BSR and RP?

Accepted Answer

D

Explanation: The Bootstrap Router (BSR) protocol is a dynamic mechanism used in Protocol Independent Multicast - Sparse Mode (PIM-SM) for distributing Rendezvous Point (RP) information. Multiple routers can be configured as candidate-BSRs (C-BSRs), but they undergo an election process. Each C-BSR advertises its priority, and the candidate with the highest priority is elected as the single BSR for the entire PIM domain. If priorities are equal, the highest IP address serves as a tie-breaker. This election ensures that there is only one active BSR at any time, providing a single, consistent source of RP-set information to all routers in the domain.

Question 2

What is the default action taken by an Alcatel-Lucent 7750 SR when it receives a packet addressed to a broadcast destination?

Accepted Answer

A

Explanation: A router, by its fundamental design, operates at Layer 3 and serves as a boundary for Layer 2 broadcast domains. When a Nokia 7750 SR, acting in its routing capacity, receives a packet with a Layer 3 broadcast destination address (e.g., 255.255.255.255 or a directed broadcast), its default behavior is to not forward the packet to any other interface. This is a core principle of IP routing that prevents broadcast storms from propagating across an entire network. The router will process the packet locally if it is the intended recipient (for example, for a routing protocol), but it will not route it onward. Therefore, from a forwarding perspective, the packet is dropped.

Question 3

Which of the following is NOT a characteristic of Draft Rosen?

Accepted Answer

D

Explanation: Draft Rosen, also known as PIM/GRE MVPN, is a traditional architecture for providing multicast services over an MPLS VPN backbone. A core characteristic of this model is the use of Generic Routing Encapsulation (GRE) to tunnel customer multicast data packets across the service provider's core network. The provider core itself uses PIM to build Multicast Distribution Trees (MDTs) that carry this GRE-encapsulated traffic between PE routers. Customer VRFs also run their own instances of PIM to manage multicast state within the VPN. MPLS encapsulation for multicast data traffic is a feature of Next-Generation MVPN (NG-MVPN) architectures (defined in RFC 6513/6514), not the original Draft Rosen model.

Question 4

Click the exhibit. https://kxbjsyuhceggsyvxdkof.supabase.co/storage/v1/object/public/file-images/NOKIA_4A0-108/page_92_img_2.jpg If the configuration shown is applied to all PE routers, and all other configuration is complete, how many neighbors are displayed in the output of the command "PE1= show router 100 pirn neighbor"?

Accepted Answer

B

Explanation: The command show router 100 pim neighbor queries for PIM neighbors within the context of VPRN service 100. The provided configuration shows PIM enabled on the customer-facing interface "toCE1" within this VPRN. This establishes a PIM adjacency with the connected CE router, accounting for one neighbor. The scenario implies a multi-PE network for a functional MVPN service. The use of PIM within the VPRN context indicates a Draft-Rosen (PIM/GRE) MVPN model. In this model, PEs establish GRE tunnels (Multicast Tunnels) among themselves and run PIM over these tunnels to exchange multicast routing information. Assuming the simplest functional multi-PE topology (two PEs), PE1 will form a second PIM adjacency with the remote PE over its GRE tunnel. Therefore, PE1 has two PIM neighbors in VPRN 100: the local CE and the remote PE.

Question 5

A BSR candidate message is seen with a higher priority than the existing BSR. Which of the following describes the action that occurs?

Accepted Answer

C

Explanation: The Protocol Independent Multicast - Sparse Mode (PIM-SM) Bootstrap Router (BSR) election mechanism is preemptive. According to RFC 5059, when a router in a PIM domain receives a Bootstrap message from a candidate BSR, it compares the priority in the message to that of its currently known BSR. If the priority of the new candidate is higher, the router immediately and unconditionally accepts the new candidate as the active BSR for the domain. This ensures that the router with the highest configured priority is always selected as the BSR as soon as its advertisements are received.

Question 6

Click the exhibit. https://kxbjsyuhceggsyvxdkof.supabase.co/storage/v1/object/public/file-images/NOKIA_4A0-108/page_84_img_1.jpg The interface's IGP metric is as shown, and PIM is using the unicast table for the RPF-check. What happens when Router B receives a register message on its interface facing Router A?

Accepted Answer

B

Explanation: A PIM register message is a control-plane message that is unicast from the First-Hop Router (FHR), Router A, to the Rendezvous Point (RP), Router D. When an intermediate router, such as Router B, receives this packet, it processes it as a standard unicast datagram. Router B will perform a lookup for the destination IP address (the RP's address) in its unicast routing table and forward the packet towards the next hop according to the best path determined by the IGP. The Reverse Path Forwarding (RPF) check is performed on multicast data packets, not on unicast PIM register messages in transit.

Question 7

Which operation is performed by an interested PE upon receiving an MDT Join TLV?

Accepted Answer

B

Explanation: In Next-Generation Multicast VPN (NG-MVPN), an MDT Join TLV is carried within a BGP C-multicast route advertisement. It is sent by a Provider Edge (PE) router that has a downstream receiver for a specific customer source and group (C-S, C-G). This message signals to the source-PE that it should forward this multicast stream. To receive this traffic, the interested PE (the one that sent the MDT Join TLV) must join the specific multicast distribution tree in the provider core, known as a Selective-PMSI (S-PMSI) or Data-MDT. This is a source-specific tree. Therefore, the PE sends a PIM (S, G) Join into the provider core. The PIM Join is a standard IP control plane packet and is not encapsulated in GRE; GRE is a data plane encapsulation used for the actual multicast traffic.

Question 8

An IGMP version 3 receiver signals EXCLUDE mode report with an empty EXCLUDE list. What does this indicate?

Accepted Answer

B

Explanation: In IGMP version 3, a receiver uses an EXCLUDE mode report to specify sources from which it does not want to receive traffic. The report essentially states, "send me traffic for this group from all sources, except for the ones in this list." When the EXCLUDE list is empty, the receiver is excluding zero sources. This logically means the receiver is willing to accept traffic from any and all sources for that multicast group. This is the standard method for an IGMPv3-capable host to signal a join for an Any-Source Multicast (ASM) group, which is functionally equivalent to a join in IGMPv1 or IGMPv2.

Question 9

Click the exhibit. https://kxbjsyuhceggsyvxdkof.supabase.co/storage/v1/object/public/file-images/NOKIA_4A0-108/page_85_img_1.jpg VPRN 100 is an MVPN with RSVP-TE P2MP LSP P-tunnels. How many PATH messages are signaled by PE1 for I-PMSI?

Accepted Answer

B

Explanation: For an I-PMSI that uses RSVP-TE P2MP LSPs, the ingress PE (root) issues one RSVP Path message for every direct child (next-hop) at the first branching point of the tree. In the topology shown, PE1’s explicit-route contains two distinct next-hops (toward P1 and P2). Consequently, PE1 must originate two separate Path messages, one per branch, which are then forwarded and replicated further downstream by the P-routers. Hence, exactly two Path messages leave PE1.

Question 10

How often does a host issue IGMP Host Membership Reports for group 224.0.0.1?

Accepted Answer

A

Explanation: The multicast address 224.0.0.1 is the reserved "All Systems" address on the local subnet. According to the Internet Group Management Protocol (IGMP) standards (RFC 1112, RFC 2236, and RFC 3376), all multicast-capable hosts are permanent members of this group on every network interface. This membership is implicit and is explicitly excluded from the reporting mechanism. The protocol standards state that a Membership Report message is never sent for the all-systems-multicast address (224.0.0.1).

Question 11

What is the DATA_DELAY_INTERVAL?

Accepted Answer

A

Explanation: The DATADELAYINTERVAL, also known as the S-PMSI data delay interval, is a configurable timer on the ingress (source) Provider Edge (PE) router in a Next-Generation Multicast VPN (NG-MVPN) environment. When a multicast source's traffic rate exceeds a configured threshold, the ingress PE decides to switch from the default Inclusive-PMSI (I-PMSI) to a more efficient Selective-PMSI (S-PMSI). The PE first signals the creation of the S-PMSI to other PEs. The DATADELAYINTERVAL is the period the ingress PE waits before it begins forwarding the multicast traffic onto the newly established S-PMSI. This delay is crucial to prevent traffic loss by allowing egress PEs sufficient time to join the new S-PMSI tree.

Question 12

Which of the following regarding the Source Path Tree is TRUE?

Accepted Answer

D

Explanation: The Source Path Tree (SPT), also known as a shortest path tree, is rooted at the multicast source and provides the most direct path to the receivers. Its construction does not fundamentally depend on a Rendezvous Point (RP). This is most clearly demonstrated in Source-Specific Multicast (SSM), a mode of PIM that operates without an RP and exclusively builds SPTs. In Any-Source Multicast (ASM), while an RP is used for the initial shared tree, the eventual switchover to an SPT creates a tree directly toward the source, independent of the RP's location in the forwarding path.

Question 13

Which of the following functions is not required in a PIM SSM network?

Accepted Answer

C

Explanation: Protocol Independent Multicast - Source-Specific Multicast (PIM SSM) is designed to build a source-based distribution tree directly from the receiver to the source. In the SSM model, the receiver must explicitly specify both the group address (G) and the source address (S) it wishes to receive traffic from, using an (S,G) join. This allows the last-hop router to send a PIM Join message directly upstream toward the source 'S'. Consequently, the PIM-SM concept of a Rendezvous Point (RP), which acts as a meeting point for unknown sources and receivers in a (,G) model, is not used and is not required. The elimination of the RP is a fundamental architectural simplification in PIM SSM.

Question 14

Click the exhibit. https://kxbjsyuhceggsyvxdkof.supabase.co/storage/v1/object/public/file-images/NOKIA_4A0-108/page_59_img_1.jpg The configuration is applied to the ingress PE, but receivers at the remote PE site do not receive multicast traffic. Which of the following is a possible cause?

Accepted Answer

D

Explanation: The provided configuration snippet for the MVPN service is syntactically and logically correct for establishing Next-Generation MVPN (NG-MVPN) using RSVP-TE P2MP provider tunnels. It correctly defines both an Inclusive PMSI (I-PMSI) for all-to-all traffic and a Selective PMSI (S-PMSI) for high-bandwidth streams. Since receivers get no traffic at all, the problem lies with the I-PMSI, which must be established for any communication to begin. Given that the VPRN configuration is valid, the root cause must be external to this specific configuration block. A problem in the core network, such as a failure to signal or establish the required RSVP-TE P2MP LSP, is a plausible cause. Therefore, the configuration is correct, and the issue is likely in the underlying transport core.

Question 15

Does the interface whose address is used as the BSR candidate require PIM enablement?

Accepted Answer

A

Explanation: A router configured as a PIM Bootstrap Router (BSR) candidate must advertise itself to other PIM routers by sending Bootstrap Messages (BSMs). These BSMs are PIM control packets sourced from the IP address of the interface configured for the BSR candidacy. For the router to be able to source and send these PIM-specific messages, the Protocol Independent Multicast (PIM) protocol must be explicitly enabled on that interface. This requirement applies regardless of whether the interface is physical or logical (e.g., a loopback interface).

Free Nokia 4A0-108 Actual Exam Questions