When an end station receives a frame, it is processed up the OSI stack. At Layer 2, the station checks the destination MAC address. For a broadcast, this is typically FF:FF:FF:FF:FF:FF, so the frame is accepted and its payload (an IP packet) is passed to Layer 3. At Layer 3 (the Network layer), the IP stack must inspect the destination IP address. If the address is a recognized broadcast address for the network (e.g., 255.255.255.255 or a subnet-directed broadcast), the host processes the packet. This Layer 3 inspection is the minimum step required to determine that the packet is a broadcast intended for the host's IP stack.

A. Layer 1: This layer only handles the physical transmission of bits; it does not process addresses or identify packet types.

B. Layer 2: While Layer 2 identifies the broadcast MAC address, it cannot interpret the IP packet within. It must pass the payload to Layer 3 for IP-level processing.

D. Layer 4: Processing may proceed to Layer 4 (e.g., for a DHCP Discover message using UDP), but the fundamental identification as an IP broadcast occurs at Layer 3.

E. Layer 7: The application layer is the ultimate consumer of the data, but the network-level processing to accept the broadcast packet happens at Layer 3.

1. Nokia 7750 SR OS Basic System Configuration Guide, Release 21.10.R1: In the "IP Addressing Overview" section, the guide discusses the assignment and function of IP addresses, including broadcast addresses, on router interfaces. This functionality inherently relies on Layer 3 processing to distinguish unicast, multicast, and broadcast traffic. The router's IP protocol stack must process the Layer 3 header to make these determinations. (Reference implies processing at the IP layer).

2. Kurose, J. F., & Ross, K. W. (2017). Computer Networking: A Top-Down Approach (7th ed.). Pearson. In Chapter 4, "The Network Layer: Data Plane," the text explains that the network layer in a destination host receives datagrams from the data link layer. Its primary role is to check the destination IP address to determine if the packet is for that host and then pass the payload up to the transport layer. This confirms Layer 3 is the processing point for IP addresses.

3. RFC 1122, Requirements for Internet Hosts -- Communication Layers, R. Braden (Ed.), October 1989. Section 3.2.1.3, "Addressing: Destination Address Validation," specifies that "The IP layer MUST verify that every incoming datagram is destined for the host." It explicitly lists limited and directed broadcast addresses as addresses that the IP layer must recognize as being for the local host. This standard mandates Layer 3 processing for broadcast packets. (DOI: https://doi.org/10.17487/RFC1122)

The PIM Assert mechanism is designed to prevent duplicate multicast packet forwarding on a multi-access network segment. The trigger for this process occurs when a PIM router receives a multicast data packet for a specific source-group pair (S,G) on an interface that is listed in its own outgoing interface (OIF) list for that same (S,G) entry. This event signifies that at least one other router on the same network segment is also forwarding the same traffic, prompting the routers to send Assert messages to elect a single forwarder and prune the others.

A. IGMP Queries are used by routers to discover which multicast groups have active members on a local network segment; they do not trigger PIM Assert messages.

B. PIM Hello messages are used for neighbor discovery and to elect a Designated Router (DR) on a shared segment, which is a different function from the Assert mechanism.

C. BSMs (Bootstrap Messages) are part of the PIM-SM Bootstrap Router (BSR) mechanism for distributing Rendezvous Point (RP) information, not for resolving duplicate data forwarding.

1. RFC 7761: Protocol Independent Multicast - Sparse Mode (PIM-SM), Section 4.5.1, "Sending PIM Assert Messages". The document states: "A PIM router sends an Assert message on a multi-access, multi-PIM-neighbor LAN when it receives a multicast data packet from a source S on an outgoing interface for an (S,G) entry." (DOI: https://doi.org/10.17487/RFC7761)

2. Nokia 7750 SR OS Multicast Routing Protocols Guide, Release 21.10.R1, Section: "PIM Assert". The guide explains: "The PIM assert mechanism is used to resolve the issue of receiving duplicate multicast packets. This can occur when more than one router is forwarding multicast traffic onto the same multi-access network." This confirms the scenario where a packet is received on an OIF.

3. Kurose, J. F., & Ross, K. W. (2017). Computer Networking: A Top-Down Approach (7th ed.). In Chapter 4, Section 4.8 on Multicasting, the PIM Assert mechanism is described as being initiated when a router detects that another router on the same broadcast LAN is forwarding the same multicast datagram, which it detects by receiving that datagram on its own outgoing interface.

The Internet Assigned Numbers Authority (IANA) has reserved the FF3x::/32 address block for Source-Specific Multicast (SSM) in IPv6, as specified in RFC 4607. These addresses follow the unicast-prefix-based format defined in RFC 3306. In this format, the first 96 bits of the multicast address are constructed to include the multicast scope, flags, and the 64-bit unicast network prefix of the source. The remaining 32 bits are used for the Group ID. Therefore, the FF3X::/96 prefix represents the block of multicast groups that can be created from a specific /64 source network prefix, making it the most structurally significant and correct representation of the SSM range in the given options.

A. FF1X::/16 is a range for transient multicast addresses but is not specifically designated for SSM and does not follow the unicast-prefix-based structure required for SSM.

B. FF3X::/16 is an overly broad range. The IANA allocation for SSM is the more specific FF3x::/32 block, which is a subset of this range.

D. FF7X::/16 is incorrect because the '7' flag (0111) sets the Rendezvous Point (RP) flag, which is a mechanism used for Any-Source Multicast (ASM), not SSM.

1. IETF RFC 4607, "Source-Specific Multicast for IP":

Section 4.1, "IPv6 SSM Addresses": "The IANA has allocated the IPv6 multicast address prefix FF3x::/32 for SSM. This allocation is for addresses that are syntactically "unicast-prefix-based" as defined in [RFC3306]." (This establishes the primary range).

2. IETF RFC 3306, "Unicast-Prefix-based IPv6 Multicast Addresses":

Section 5, "Address Format": This section details the address structure: | 8 | 4 | 4 | 8 | 8 | 64 | 32 |. The sum of the first 6 fields (8+4+4+8+8+64) is 96 bits, which defines the portion containing the network prefix. This makes the /96 boundary structurally significant for defining groups within a source prefix.

3. Nokia 7450 ESS, 7750 SR, 7950 XRS, and VSR Router Configuration Guide, Release 22.10.R1:

Section: IPv6 PIM: "IPv6 SSM is supported for addresses in the FF3x::/32 range. This range is reserved for unicast-prefix-based SSM multicast addresses." (This vendor documentation confirms alignment with the IETF standards).

4. IETF RFC 4291, "IP Version 6 Addressing Architecture":

Section 2.7, "Multicast Addresses": This RFC defines the general format for IPv6 multicast addresses, including the flags field. The 'P' flag (bit 2) being set to 1 indicates an address based on a network prefix, which is a characteristic of the FF3x::/32 range.

Multicast networking is designed for efficient one-to-many and many-to-many data distribution. The architecture is flexible and supports various topologies.

A single source sending to a single receiver on a different segment is a valid, though trivial, use case.

The most common model is one-to-many, where a single source sends traffic to multiple receivers located on different network segments.

Advanced applications like video conferencing or online gaming utilize a many-to-many model, where multiple sources can send to the same multicast group, and multiple receivers can listen. This is supported by protocols using the Any-Source Multicast (ASM) model.

Therefore, a multicast network can have one or multiple sources, and one or multiple receiver segments.

C. A multicast network cannot have more than one source segments: This is incorrect. The Any-Source Multicast (ASM) model, a fundamental part of PIM-SM, explicitly allows for multiple sources to send traffic to the same multicast group.

E. A multicast network cannot have more than one receiver segments: This is incorrect. The primary purpose of multicast is to efficiently deliver data to a group of interested receivers, which are typically distributed across multiple network segments.

1. Nokia 7750 SR OS R19.10.R1 Multicast Routing Protocols Guide (December 2019)

Page 35, Section: Multicast Fundamentals: "Multicast is a mechanism by which a single packet can be sent from a source and delivered to multiple receivers." This statement supports the one-to-many model (Option B) and does not preclude the one-to-one (Option A) or many-to-many (Option D) models.

Page 41, Section: Any-Source Multicast (ASM): "In the ASM model, any sender can send to a multicast group, and receivers can join the multicast group without knowing the sender's unicast IP address." This directly confirms that multiple sources are permitted, making Option C incorrect and supporting Option D.

2. Nokia Data Center Fabric with SR Linux Cookbook (Version 2.0, June 2022)

Page 219, Section: Multicast overview: "Multicast is a method of forwarding the same data packets to a group of destinations simultaneously... This is in contrast to unicast, which is a one-to-one communication method, and broadcast, which is a one-to-all communication method." This description of multicast as a "one-to-group" mechanism inherently supports one-to-many communication (Option B) and, by extension, the simplest case of one-to-one (Option A) and the more complex many-to-many (Option D). It also invalidates the restriction proposed in Option E.

IPv4 multicast addresses are defined as Class D addresses. The Internet Assigned Numbers Authority (IANA) reserves all addresses whose first four bits are '1110' for this purpose. This bit pattern results in a first octet value ranging from 224 (11100000) to 239 (11101111). Therefore, the entire IPv4 multicast address range is 224.0.0.0 to 239.255.255.255, which is also commonly represented in CIDR notation as 224.0.0.0/4.

A. The first 3 bits of the address set to '110' defines Class C unicast addresses (192.0.0.0 to 223.255.255.255), not multicast addresses.

B. The multicast address range begins at 224.0.0.0. The range specified (starting at 223.0.0.0) incorrectly includes a Class C unicast address.

C. The first 4 bits of the address set to '1111' defines Class E addresses (240.0.0.0 to 255.255.255.255), which are reserved for experimental use.

D. Subnet masks are used with unicast addresses to separate the network and host portions. Multicast addresses identify a group of recipients and do not have this structure.

1. Internet Engineering Task Force (IETF) RFC 1112, "Host Extensions for IP Multicasting":

Section 4, "IP Multicast Addresses", Page 5: "Class D addresses are used for IP multicasting. The high-order four bits of a Class D address are 1110. The remaining 28 bits identify the multicast "group" to which the datagram is sent." This directly supports option E.

2. Internet Engineering Task Force (IETF) RFC 5771, "IANA Guidelines for IPv4 Multicast Addresses":

Section 2, "The IPv4 Multicast Address Space", Page 2: "The range of IPv4 addresses from 224.0.0.0 to 239.255.255.255 is registered with IANA as the 'IPv4 Multicast Address Space'... This address range is also known as 'Class D'." This document reaffirms the address range defined by the '1110' prefix.

3. Nokia 4A0-108 Course Material (Nokia Interior Routing Protocols):

Module: IP Multicast Fundamentals: The course material explicitly defines the Class D address range (224.0.0.0/4) for multicast and specifies that these addresses are identified by the leading bit pattern '1110'. This is a foundational concept covered in the curriculum for this certification.

IPv4 multicast addresses are mapped to Layer 2 MAC addresses by a specific algorithm. The first 24 bits of the MAC address are fixed to 01:00:5E, and the subsequent 23 bits are derived from the lower 23 bits of the IPv4 multicast address. Since an IPv4 multicast address has 28 variable bits (after the fixed 1110 prefix), the upper 5 bits are ignored in this mapping. This creates a 32-to-1 ambiguity.

The addresses 239.99.12.35 and 229.227.12.35 map to the same MAC address because their lower 23 bits are identical. This is calculated by taking the last two octets (.12.35) and the last 7 bits of the second octet. For 227 (11100011), the last 7 bits are 1100011, which is 99. Thus, both map to 01:00:5E:63:0C:23. Using them simultaneously in the same L2 domain would cause traffic for both groups to be sent to subscribers of either group.

B. 237.87.12.35: The lower 23 bits of this address do not conflict with any other option, resulting in a unique MAC address among the choices.

C. 231.57.12.35: This address maps to a unique MAC address within this list as its lower 23 bits are distinct from the others.

E. 228.139.12.35: The lower 23 bits of this address are unique compared to the other options, so it does not create a MAC address collision.

1. Nokia 7450 ESS, 7750 SR, 7950 XRS, and VSR Multicast Routing Protocols Guide, Release 21.10.R1. In the "PIM" chapter, section "IP to MAC Address Translation", the guide states: "The last 23 bits are the last 23 bits of the IP multicast address. Because the first four bits of a multicast IP address are fixed and the next five bits are not used, there are 32 IP multicast addresses that can be mapped to a same MAC address." This directly supports the explanation of the mapping ambiguity.

2. IETF RFC 1112, "Host Extensions for IP Multicasting". Section 6.4, "Mapping of IP Multicast Addresses to Ethernet/FDDI Addresses", specifies the mapping algorithm: "An IP host group address is mapped to an Ethernet multicast address by placing the low-order 23 bits of the IP address into the low-order 23 bits of the Ethernet multicast address 01-00-5E-00-00-00." This is the foundational standard defining the behavior.

Upon enabling Protocol Independent Multicast (PIM) on an interface, a router's first action is to send PIM Hello messages to discover other PIM-enabled routers on the same network segment. This establishes PIM neighbor adjacencies. Once neighbors are discovered on a multi-access segment (like Ethernet), they conduct a Designated Router (DR) election. The DR election process uses the priority and IP address information advertised in the Hello messages to select a single router responsible for registering sources and forwarding Join/Prune messages toward the Rendezvous Point (RP). This sequence ensures that a stable local PIM topology is established before more complex multicast routing functions are performed.

A. BSR and DR elections require neighbor adjacencies, which are established by PIM Hello messages first.

B. The DR election process relies on information exchanged in PIM Hello messages, so it cannot occur first.

C. Both DR and BSR elections are subsequent actions that depend on the initial neighbor discovery via PIM Hellos.

D. BSR elections are a domain-wide process that requires an established PIM topology, which begins with Hello messages.

E. While BSR elections follow Hellos, the DR election is a more immediate, per-segment action that also directly follows neighbor discovery.

1. RFC 7761: Protocol Independent Multicast - Sparse Mode (PIM-SM)

Section 4.2.1, "Sending Hello Messages": This section details that PIM routers periodically send Hello messages on PIM-enabled interfaces to discover neighbors. This is the foundational step.

Section 4.2.3, "Designated Router Election": This section explicitly states, "The election process is simple: every PIM router on the multi-access network sources a Hello message... These Hello messages contain the router's DR priority... The router with the highest DR priority is the DR." This confirms the DR election directly follows and uses information from the Hello messages.

2. Nokia 7750 SR OS R21.10.R1, Multicast Routing Protocols Guide

Section: PIM Overview: The document describes that PIM uses Hello messages to "discover new neighbors and to learn of existing neighbors that have failed." It then describes the Designated Router (DR) function, which is elected on multi-access networks. The logical dependency is that neighbor discovery must precede the election.

3. RFC 5059: Bootstrap Router (BSR) Mechanism for PIM

Section 3, "BSR Election": This RFC describes how Bootstrap messages are "flooded hop-by-hop throughout the PIM domain." This flooding relies on the underlying PIM adjacencies established by Hello messages, confirming that BSR elections occur after neighbor discovery is complete.

Protocol Independent Multicast - Source-Specific Multicast (PIM-SSM) is designed for scenarios where receivers know the specific source address (S) for a multicast group (G) they wish to join. This (S, G) information, typically provided by IGMPv3 from the host, allows the last-hop router to send PIM Join messages directly toward the source. This process builds a shortest-path tree (SPT) from the source to the receivers without the need for source discovery. The Rendezvous Point (RP) is a fundamental component of PIM Sparse Mode (PIM-SM), where it acts as a meeting point for unknown sources and receivers on a shared tree (, G). Since PIM-SSM completely eliminates the concept of a shared tree and the associated source discovery mechanism, the RP has absolutely no function.

A. The PIM routing protocol: PIM is the essential control plane protocol used in SSM to signal (S, G) state and build the source-based distribution trees between routers.

B. SSM translation on access multicast router: This feature, also known as SSM mapping, is specifically used in SSM networks to allow legacy IGMPv1/v2 hosts (which can only signal ,G) to participate by mapping their requests to a pre-configured (S, G) channel.

D. IGMP snooping: This is a Layer 2 mechanism on switches that optimizes multicast traffic delivery within a VLAN. It is essential for efficiency regardless of the PIM mode (SM, DM, or SSM).

E. IGMP Querier: The IGMP Querier is a router function required on every multicast-enabled LAN segment to solicit membership reports from hosts. It is fundamental for the router to learn which multicast groups, including (S, G) channels, are needed.

1. Nokia 7750 SR OS R21.10.R1 MPLS Guide, Section: PIM-SSM: "SSM is an enhancement to the PIM protocol and does not require a separate protocol. It uses the existing PIM protocol messages and procedures. SSM does not use the PIM-SM shared tree and RP." This statement explicitly confirms that the RP is not used in PIM-SSM.

2. RFC 4607: Source-Specific Multicast for IP, Section 3: Protocol Overview: "PIM-SSM is derived from PIM-SM [RFC4601]. It uses the same PIM packet formats and most of the same protocol mechanisms. The primary difference is that PIM-SSM builds a tree from the receiver to the source, and it does not use the PIM-SM shared tree and Rendezvous Point (RP) mechanisms."

3. Nokia 7750 SR OS R21.10.R1 Unicast Routing Protocols Guide, Section: IGMP: This guide details the function of the IGMP Querier and its necessity for soliciting host memberships, a process required for PIM-SSM to learn of receiver interest. It also describes SSM translation for IGMPv1 and IGMPv2 hosts.

The show router pim interface command is used on the Nokia 7750 SR to display detailed operational parameters for interfaces on which PIM is enabled. The output of this command explicitly includes the "DR Address" field, which shows the IP address of the router that has been elected as the Designated Router (DR) for that specific network segment. This provides a direct and unambiguous way to verify the PIM DR.

A. Show router pim status: This command provides global PIM information, such as the operational state, Rendezvous Point (RP) set, and Bootstrap Router (BSR) information, not per-interface DR details.

B. Show router pim neighbor: This command lists all discovered PIM neighbors on a link, their uptime, and hold timers, but it does not explicitly state which neighbor is the elected DR.

D. Show router pim statistics: This command displays counters for various PIM control messages (e.g., Hellos, Joins, Prunes). It is used for monitoring traffic, not for viewing state information like the DR.

1. Nokia 7450 ESS, 7750 SR, 7950 XRS, and VSR Multicast Routing Protocols Guide, Release 20.10.R1

Section: PIM Command Reference -> PIM Show Commands -> show router pim interface

Content: The documentation describes the command and provides sample output that includes the DR Address field. For example:

A:ALA-48# show router pim interface "system"

===============================================================================

PIM Interface "system"

===============================================================================

Interface Name : system

IP Address : 10.10.10.1/32

Admin Status : Up Oper Status : Up

PIM Mode : Sparse PIM Oper Mode : Sparse

Hello Interval (s) : 30 Hello Expiry (s) : 88

DR Priority : 1 DR Address : 0.0.0.0

...

This sample confirms the command's utility for verifying the DR address. (Note: 0.0.0.0 indicates no DR is needed on a point-to-point or loopback interface).

2. Nokia 7750 SR OS MPLS Guide, Release 16.0.R1

Section: PIM -> Monitoring and Troubleshooting PIM

Content: This section details the use of various show commands for PIM verification. It specifies that show router pim interface is the command to check interface-specific PIM parameters, which includes the Designated Router. It contrasts this with show router pim neighbor for neighbor adjacencies and show router pim status for global state.

The CLI excerpt is a static configuration. It only reveals which interfaces have IGMP enabled; it does not show the dynamic IGMP state table that records hosts that have actually sent joins. The presence, absence, or count of receivers for group 239.1.1.1 can only be verified with an operational command such as “show router igmp group-membership” (or PIM multicast routing table), not from configuration alone. Therefore the number of interfaces with receivers joined to 239.1.1.1 cannot be determined from the information provided.

A. One join could exist, but nothing in the config confirms it.

B. Two joins are equally unsubstantiated.

C. Three joins are equally unsubstantiated.

1. Nokia “7750 SR OS Multicast Protocols Guide”, 22.10.R1, Section 3.3.2 “IGMP Group Membership Table”, p. 109: configuration only enables IGMP; receiver joins appear in the operational table shown with “show router igmp group-membership”.

2. Nokia “SR OS Services Guide”, 22.10.R1, Chapter “IP Multicast Overview”, p. 51: “…the existence of an IGMP configuration on an interface does not imply the presence of an active host membership.”

3. C. Diot & G. Iannaccone, “Analysis of Multicast Routing Algorithms,” IEEE/ACM Trans. Networking, vol. 10 no. 4, 2002, Section II-A: distinguishes control-plane configuration from data-plane group membership learned dynamically.