OSPF stands for Open Shortest Path First, which is a link-state routing protocol that is hierarchal by nature and uses the router ID to control convergence. OSPF divides a large network into areas, which are logical groupings of routers that share the same topology information. Each area has a unique identifier and a designated router that connects it to the backbone area (area 0). OSPF uses the router ID, which is a 32-bit number that uniquely identifies each router in the network, to establish adjacencies and exchange routing information. OSPF also uses the router ID to break ties when choosing the best path to a destination. OSPF converges faster than distance-vector routing protocols such as RIP and EIGRP, as it uses the Dijkstra algorithm to calculate the shortest path based on the link cost. BGP, on the other hand, is a path-vector routing protocol that is used to exchange routing information between autonomous systems on the Internet. BGP does not use the router ID to control convergence, but rather uses attributes such as AS path, local preference, and MED to select the best route. BGP is not hierarchal by nature, as it does not divide the network into areas, but rather uses prefixes and policies to control the routing behavior.
References
* 1: OSPF - N10-008 CompTIA Network+ : 2.1
* 2: CompTIA Network+ N10-008 Certification Study Guide, page 146-149
* 3: CompTIA Network+ N10-008 Exam Subnetting Quiz, question 19
* 4: CompTIA Network+ N10-008 Certification Practice Test, question 8

A duplex mismatch is a situation where two devices on a network have different duplex settings, such as full-duplex or half-duplex. Full-duplex means that a device can send and receive data simultaneously, while half-duplex means that a device can only send or receive data at a time. A duplex mismatch can cause performance issues, such as collisions, errors, or slow throughput. In this scenario, the customer added a hub between the switch and the router. A hub is a device that operates at half-duplex and broadcasts all traffic to all ports. A switch and a router are devices that operate at full-duplex and forward traffic to specific ports.
Therefore, adding a hub between the switch and the router can cause a duplex mismatch and slow down all the other network components that were connected to the switch.
References: https://www.comparitech.com/net-admin/hub-vs-switch-vs-router/
https://www.cisco.com/c/en/us/support/docs/lan-switching/ethernet/10561-3.html

Explanation
Role-based access is a security technique that assigns permissions and privileges to users or groups based on their roles or functions within an organization. Role-based access can help secure the physical networking equipment by limiting who can access, modify, or manage the devices in the shared IT closet. Only authorized personnel with a valid role and credentials should be able to access the networking equipment. Disabling unneeded switchports is a security technique that prevents unauthorized devices from connecting to the network by turning off unused ports on a switch. Changing the default passwords is a security technique that prevents unauthorized access to network devices by replacing the factory-set passwords with strong and unique ones. Configuring an access control list is a security technique that filters network traffic by allowing or denying packets based on criteria such as source and destination IP addresses, ports, or protocols.
References: CompTIA Network+ Certification Exam Objectives Version 7.0 (N10-007), Objective 3.2: Given a scenario, use appropriate network hardening techniques.

A warm site is a type of disaster recovery site that has equipment ready to go in the event of a disaster at the main datacenter, but does not have live data or applications. A warm site requires some time and effort to restore the data and services from backups, but it is less expensive than a hot site that has live data and applications. A cold site is a disaster recovery site that has no equipment or data, and requires a lot of time and money to set up after a disaster. A cloud site is a disaster recovery site that uses cloud computing resources to provide data and services, but it may have issues with bandwidth, latency, security, and cost. Reference: https://www.comptia.org/blog/what-is-a-warm-site

nmap is the tool that would help identify which ports are open on the remote file server. nmap stands for Network Mapper, which is a free and open-source tool that can perform various network scanning and discovery tasks. nmap can help identify which ports are open on a remote device by sending probes or packets to different ports and analyzing the responses. nmap can also provide information about the operating system, services, versions, firewalls, or vulnerabilities of the remote device. nmap can be useful for network administrators, security professionals, or hackers to monitor, audit, or attack network devices. Reference: [CompTIA Network+ Certification Exam Objectives], Nmap - Free Security Scanner For Network Exploration & Security Audits