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DMARC (Domain-based Message Authentication, Reporting and Conformance) is an email authentication protocol. It is designed to give email domain owners the ability to protect their domain from unauthorized use, commonly known as email spoofing.

Explanation
DHCP (Dynamic Host Configuration Protocol) is a protocol that allows a device to automatically obtain an IP address and other network settings from a DHCP server, such as a home router. This simplifies the network configuration and avoids IP address conflicts. DHCP is a common requirement for home networks that have multiple devices that need Internet access.
A gateway is a device that connects two different networks, such as a home network and the Internet. A gateway usually performs routing functions, which means it determines the best path for packets to reach their destination. A gateway also often performs NAT (Network Address Translation), which allows multiple devices on a home network to share a single public IP address. A gateway is a necessary requirement for home networks that need Internet access.
References
Understanding DHCP on Home Networks
Basic home gateway services: DHCP, DNS, NAT
IP Addresses on Home Networks - A Beginner's Guide

Explanation
To connect a mobile phone to a car, you need to pair them using Bluetooth, which is a wireless technology that allows secure local networks between devices1. If one phone can connect to the car but another cannot, it means that the first phone has Bluetooth enabled and paired with the car, while the second phone does not. Therefore, the user should check the Bluetooth settings on the second phone and make sure it is turned on and discoverable21.