Which two pairs of LAN Ethernet devices use an RJ-45 straight-through cable? (Choose two.)

A straight-through Ethernet cable is used to connect devices that have complementary port configurations, typically devices operating at different layers of the OSI model. This is often referred to as connecting dissimilar devices. A switch (Layer 2, MDI-X port) connects to a router (Layer 3, MDI port) using a straight-through cable. Similarly, a switch (MDI-X port) connects to an end device like a server or PC (MDI port) using a straight-through cable. The pinout for transmitting on one device connects directly to the pinout for receiving on the other, which is the standard for connecting devices with different interface types (MDI to MDI-X).

A. switch-to-switch: This connects two similar Layer 2 devices, both of which typically use MDI-X ports. This connection requires a crossover cable to connect transmit pins to receive pins.
C. switch-to-hub: Both switches and hubs use MDI-X ports. Connecting two MDI-X ports requires a crossover cable to ensure proper communication.
D. router-to-router: This connects two similar Layer 3 devices, both of which use MDI ports. This connection requires a crossover cable.

1. Odom, W. (2019). CCNA 200-301 Official Cert Guide, Volume 1. Cisco Press. Chapter 2, "Fundamentals of Ethernet LANs," section "Ethernet Physical Layer Standards," Table 2-4 "Typical Uses of UTP Cables," page 45. The table explicitly lists "Router to switch" and "PC to switch" (a server functions as a PC in this context) as use cases for straight-through cables.

2. Cisco Networking Academy. (n.d.). Connecting Devices. In CCNA: Introduction to Networks v7.0, Module 4, Section 4.2.2 "Connecting Devices." This official courseware states, "Straight-through: Connecting a network host to a network device such as a switch or hub... Crossover: Connecting two network hosts... Connecting two network intermediary devices, such as a switch to a switch, a switch to a hub, a router to a router..."

3. Cisco. (2018, July 26). Ethernet Cable - Straight-through vs Crossover. Cisco Learning Network. This document clarifies: "A straight-through cable is used to connect two devices of different types. For example, a switch to a router, a switch to a PC or server... A crossover cable is used to connect two devices of the same type. For example, two switches, two PCs, two routers..."