Explanation
Penultimate hop popping (PHP) is a function performed by certain routers in an MPLS enabled network. It refers to the process whereby the outermost label of an MPLS tagged packet is removed by a label switch router (LSR) before the packet is passed to an adjacent label edge router (LER). The purpose of PHP is to reduce the load on the LER, as it saves one cycle of label lookup. The LER can forward the packet based on its IP header or another label in the stack, without having to process the outer label. PHPfunctionality is achieved by the LER advertising a label with a value of 3 to its neighbors. This label is defined as “implicit-null” and informs the neighboring LSRs to perform PHP12.
References: Penultimate hop popping – Wikipedia, MPLS Penultimate hop popping – NetworkLessons.com

Explanation
The function of LSR from an LDP perspective is to distribute labels of FEC to its LDP peers. LSR stands for Label Switching Router, which is a router that forwards packets based on labels rather than IP addresses in an MPLS network. LDP stands for Label Distribution Protocol, which is a protocol that distributes labels for MPLS forwarding along the shortest path calculated by an IGP. FEC stands for Forwarding Equivalence Class, which is a group of packets that are forwarded in the same manner by an LSR. An LSR uses LDP to advertise the label mappings for each FEC to its LDP peers, which are other LSRs that have established an LDP session with it12.
References: Ldp | Microsoft Learn, Label Distribution Protocol – Wikipedia

Explanation
OSPF runs directly on IP, while IS-IS runs directly on Ethernet. This means that OSPF uses IP addresses to identify routers and links, while IS-IS uses MAC addresses or other link-layer identifiers. OSPF also requires an IP header for each packet, while IS-IS does not. Both OSPF and IS-IS are link state protocols, which means that they flood information about the network topology to all routers in the same area or domain. References: Ericsson IP Networking – Routing Protocols, Ericsson Router 6000 Series – Ericsson

Explanation
Referring to the exhibit, the correct statement is that the service provider’s P routers are not aware of the customers’ routes. This is because P routers only need to forward MPLS packets based on their labels, without looking into their IP headers or VPN information. The P routers do not have any VRFs configured for the customers, nor do they participate in MP-BGP sessions with other PE routers. The PE routers are responsible for maintaining VRFs for each customer and for exchanging VPN routes with other PE routers using MP-BGP910.
References: Layer 3 VPNs (L3VPN) – Cisco, MPLS VPN – Wikipedia

Explanation
The command that is used to begin making changes to the router settings in an Ericsson Router 6000 is configure. This command enters the configuration mode, where various commands can be used to modify the router parameters, such as interfaces, protocols, services, security, etc. To exit the configuration mode, the command end can be used. To save the changes made in the configuration mode, the command commit can be used56.
References: Router 6000 Series – Ericsson, Ericsson Router 6000 series (6471/6672/6675) Commands for
2G/3G/4G/5G technologies… – YouTube

Explanation
Two protocols that apply to both IPv4 and IPv6 are:
SNMP: This stands for Simple Network Management Protocol, which is a protocol that allows network administrators to monitor and manage network devices such as routers, switches, servers, printers, etc.
SNMP uses a client-server model, where an SNMP manager (client) can query or configure an SNMP agent (server) on a network device using SNMP messages. SNMP can operate over both IPv4 and IPv6 networks56.
DNS: This stands for Domain Name System, which is a protocol that translates human-readable domain names (such as www.example.com) into numerical IPaddresses (such as 192.0.2.1 or 2001:db8::1) that identify network devices. DNS uses a hierarchical distributed database of name servers that store and resolve domain names and IP addresses. DNS can support both IPv4 and IPv6 addresses78.
References: Simple Network Management Protocol – Wikipedia, SNMP over IPv6 – Cisco, Domain Name System – Wikipedia, DNS for IPv6 – Cisco

Explanation
Spanning-Tree is used for Ethernet loop avoidance. Spanning-Tree is a protocol that prevents loops in Ethernet networks by creating a logical tree topology of the network switches. Spanning-Tree blocks some of the redundant links between switches to ensure that there is only one active path between any two nodes in thenetwork. Spanning-Tree also detects and recovers from link failures by activating alternative paths when needed56.
References: Network loops and loop avoidance – Medium, Spanning Tree Protocol – Wikipedia

Explanation
The code that is commonly used to assign higher priority to VoIP traffic is EF, which stands for Expedited Forwarding. EF is a per-hop behavior (PHB) defined by the Differentiated Services (DiffServ) model for QoS.
EF provides low delay, low jitter, and low loss for real-time applications such as VoIP. EF is marked by setting the DSCP value to 101110, which corresponds to decimal 4678. AF31, which stands for Assured Forwarding class 3 low drop probability, is another PHB defined by DiffServ, but it provides lower priority than EF. AF31 is marked by setting the DSCP value to 011010, which corresponds to decimal 2678. DF, which stands for Default Forwarding, is a PHB defined by DiffServ that provides best-effort service for unmarked traffic. DF is marked by setting the DSCP value to 000000, which corresponds to decimal 078.
AF11, which stands for Assured Forwarding class 1 low drop probability, is another PHB defined by DiffServ, but it provides lower priority than EF and AF31. AF11 is marked by setting the DSCP value to 001010, which corresponds to decimal 1078.
References: Differentiated services – Wikipedia, Solved: Cisco VoIP Phone traffic marking – Cisco Community

Explanation
In OSPFv2, the route characteristic that is used to determine the best path is the cost. The cost is a metric that represents the link bandwidth, delay, reliability, or other factors. The cost is inversely proportional to the bandwidth, meaning that a higher bandwidth link has a lower cost. The cost of a route is calculated by adding the costs of all links along the path. OSPFv2 uses the following formula to calculate the cost of an interface:
Cost = Reference bandwidth / Interface bandwidth in bps
The reference bandwidth is a constant value that can be configured by the network administrator. By default, it is 100 Mbps. The interface bandwidth is the actual bandwidth of the interface in bits per second. For example, if an interface has a bandwidth of 10 Mbps, its cost would be 100 Mbps / 10 Mbps = 101415.
OSPFv2 does not use jitter, packet loss, or delay as route characteristics to determine the best path. Jitter is the variation in latency or delay between packets. Packet loss is the percentage of packets that are dropped or corrupted during transmission. Delay is the time it takes for a packet to travel from source to destination. These characteristics are not part of the OSPFv2 protocol and are not advertised in OSPFv2 LSAs1617.
References: OSPF Metric cost Calculation Formula Explained – ComputerNetworkingNotes, OSPF Cost – OSPF Routing Protocol Metric Explained – Study-CCNA, Open Shortest Path First – Wikipedia, OSPF Metric
= Cost – Cisco

Explanation
The maximum number of unique VLAN IDs available is 4096. A VLAN ID is a 12-bit identifier that can range from 0 to 4095. However, VLAN ID 0 is reserved for tagging the priority of frames and VLAN ID 4095 is reserved for implementation use, so only VLAN IDs from 1 to 4094 are available for user configuration78.
VLAN IDs are used to identify different broadcast domains or subnets on a Layer 2 network. VLAN IDs are carried in the IEEE 802.1Q tag in the Ethernet frame header.
References: What is a virtual LAN (VLAN) and how does it work with my managed switch? – NETGEAR Support, Virtual LANs (VLANs) – Cisco

Explanation
The Area ID to which the router belongs is 49.00F0.0100. The Area ID is a variable-length field in the NSAP address that identifies the area to which the router belongs. The Area ID can be between 1 and 13 bytes long, but it must start and end with an octet (8 bits). The NSAP address is composed of three parts: the authority and format identifier (AFI), the area ID, and the system ID. The AFI is a one-octet field that indicates the format and authority of the rest of the address. The system ID is a fixed-length field of six octets that uniquely identifies the router within an area. The NSAP address also has a network selector (NSEL) field, which is a one-octet field that identifies the network layer service to which a packet should be sent. For IS-IS routers, the NSEL must always be 00.
In this question, the NSAP address is 49.00F0.0100.5012.3010.00. This means that:
The AFI is 49, which indicates a private address.
The Area ID is 00F0.0100, which is four octets long and starts and ends with an octet.
The system ID is 5012.3010, which is six octets long and identifies the router within the area.
The NSEL is 00, which indicates IS-IS.
Therefore, the answer is B.
References: Ericsson IP Networking – Routing Protocols, IS-IS NSAP address – Cisco Community, Understanding IS-IS NSAP Addresses – Todd Lammle, LLC, IS-IS – Nokia, Network service access point address – Wikipedia

Explanation
IPv6 link-local addresses are designed to be used in three situations: for neighbor discovery, for local IP communication on the IPv6 capable routers, and for addressing on a single link for purposes such as auto-address configuration. Neighbor discovery is a protocol that allows IPv6 nodes to discover each other and learn their link-layer addresses on a local network. Neighbor discovery uses link-local addresses to send and receive messages such as router advertisements, router solicitations, neighbor advertisements, and neighbor solicitations34. Local IP communication on the IPv6 capable routers refers to the ability of routers to exchange routing information or management traffic using their link-local addresses as source and destination addresses. This reduces the need for global unicast addresses on router interfaces that are not reachable from outside the local network35. Addressing on a single link for purposes such as auto-address configuration refers to the use of link-local addresses to enable IPv6 nodes to obtain an address without manual configuration or a DHCP server. Link-local addresses can be automatically derived from the interface identifier in the modified EUI-64 format or randomly generated. Link-local addresses can also be used to test the connectivity of a link before obtaining a global unicast address36.
References: Understand the IPv6 Link-Local Address – Cisco, Link Local Address – GeeksforGeeks, IPv6 Address Types | Link-Local, Global Unicast, etc. IPCisco, MPLS Label Distribution Protocol Commands – Cisco

Explanation
An LDP implicit null label causes penultimate hop popping by a downstream router. LDP is a protocol that distributes labels for MPLS forwarding along the shortest path calculated by an IGP. An implicit null label is a special label value of 3 that indicates that the downstream router does not need a label to forward the packet to its destination. When an upstream router receives an implicit null label from a downstream router, it removes (or pops) the label from the packet before sending it to the downstream router. This process is called penultimate hop popping (PHP) and it reduces the load on the downstream router, which can forward the packet based on its IP header or another label in the stack59.
References: MPLS Label Distribution Protocol Commands – Cisco, Solved: Implicit null and Explicit null – Cisco Community

Explanation
The action that will influence BGP route selection within your AS is changing the default value of the local preference attribute. The local preference attribute is used to indicate the preference of a path among multiple paths learned from different external BGP neighbors or autonomous systems (ASes). The higher the local preference value, the more preferred the path is within your AS, and vice versa. The default value of local preference is 100, but you can change it using route maps or other configuration methods on your BGP routers. References: Ericsson IP Networking – Routing Protocols, BGP Attributes and Path Selection, BGP Local Preference Attribute: Controlling Traffic Like a Pro

Explanation
According to RFC1918, there are three network blocks reserved as private networks that are not allocated to any specific organization and are not routable on the public Internet. These are:
10.0.0.0/8 (10.0.0.0 – 10.255.255.255)
172.16.0.0/12 (172.16.0.0 – 172.31.255.255)
192.168.0.0/16 (192.168.0.0 – 192.168.255.255)
Out of these, only option B (10.254.1.0/24) falls within one of the private network blocks (10.0.0.0/8). Option A (172.16.1.0/9) is not valid because it exceeds the /12 prefix length of the private network block (172.16.0.0/12). Option C (193.168.1.0/24) is not valid because it does not belong to any of the private network blocks, and is actually assigned to RIPE NCC as a public network block . Option D (172.15.1.0/24) is also not valid because it does not belong to any of the private network blocks, and is actually assigned to ARIN as a public network block . References: RFC 1918: Address Allocation for Private Internets, Private network – Wikipedia, [RIPE NCC IPv4 Address Space Chart], [ARIN WHOIS Database Search]

Explanation
An Ethernet switch will forward the frame to all ports when the destination address is FF:FF:FF:FF:FF:FF.
This is because this address is the broadcast MAC address, which means that the frame is intended for all devices on the same LAN segment. The switch does not need to look up its MAC address table to find a matching entry for this address, but simply floods the frame out of all ports except the one where it received the frame. This way, the frame reaches every device on the LAN segment, regardless of their MAC addresses. References: Ethernet – Wireshark, Broadcast MAC Address – omnisecu.com