Connect Multiple Switches to Cable Modem: Add a Router
An ISP provides a cable modem with a single Ethernet port. A technician needs to set up a small office network with 25 workstations that require internet access and must be on the same subnet. The technician has a 24-port unmanaged switch and a 48-port unmanaged switch. Which of the following is the MOST appropriate method to connect the devices?
Quick Answer
The answer is to connect both switches to a router, then connect the modem to the router. This is correct because a cable modem with a single Ethernet port provides only a public IP address and cannot route traffic between multiple devices; a router is required to perform Network Address Translation (NAT) and act as a DHCP server, allowing all 25 workstations on the same subnet to share that single internet connection. On the CompTIA A+ Core 1 220-1101 exam, this scenario tests your understanding of the fundamental difference between a modem (Layer 1/2 device) and a router (Layer 3 device), and a common trap is assuming you can daisy-chain switches directly to the modem—which would fail because the modem cannot assign private IPs or forward traffic between them. Remember the memory tip: “Modem gives you one address; a router shares the wealth.”
⚠ Common exam trap
A common mix-up: candidates assume a modem can act as a router or that daisy-chaining switches alone provides internet access, but the modem lacks routing and NAT capabilities, making a router essential for multi-device internet connectivity.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Connect both switches to a router, and connect the modem to the router.
A router is required to perform Network Address Translation (NAT) and routing between the ISP's public IP and the private subnet. The cable modem provides only a single Ethernet port and does not route traffic between multiple devices; connecting both switches to a router allows all 25 workstations to share the internet connection while remaining on the same subnet. The router acts as the default gateway and DHCP server, enabling proper IP address assignment and traffic forwarding.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Connect the modem directly to the 48-port switch and then daisy-chain the 24-port switch from the 48-port switch.
Why it's wrong here
This duplicates the correct configuration, so it fails only if the exam distinguishes wording; daisy-chaining the 24-port switch from the 48-port switch is valid. It is tempting because cascading unmanaged switches extends port count while keeping all devices on one subnet.
When this WOULD be correct
If the question specified that the ISP modem has a built-in router with DHCP and NAT capabilities, and the goal is simply to expand the number of ports, then connecting switches directly to the modem would work.
- ✓
Connect both switches to a router, and connect the modem to the router.
Why this is correct
A router is required to share the single modem connection and route between the internet and the 25 workstations, since unmanaged switches cannot perform NAT or DHCP. Connecting both switches to the router keeps all workstations on one subnet while providing internet access.
- ✗
Connect the modem to the 24-port switch, then connect the 48-port switch to the 24-port switch.
Why it's wrong here
The 24-port switch cannot accommodate all 25 workstations plus the uplink to the 48-port switch, leaving one workstation without a port. It is tempting because cascading switches extends port count, which would work if total devices fitted within the first switch's available ports.
When this WOULD be correct
In a scenario where the ISP modem is a router with built-in NAT and DHCP, and the goal is to expand the number of LAN ports without needing additional routing, connecting the modem to a switch and then cascading another switch would be appropriate. For example, if the modem is a router with four LAN ports and you need to connect more devices on the same subnet.
- ✗
Connect the modem directly to the 48-port switch and connect the 24-port switch to the 48-port switch.
Why it's wrong here
This is functionally identical to connecting the modem to the 48-port switch, which is the correct approach; the option fails only if the stem expects the modem on the larger switch. It is tempting because daisy-chaining switches is a valid way to add ports on one subnet.
When this WOULD be correct
This option would be correct if the ISP provided a modem/router combo (gateway) with built-in routing and NAT, and the technician only needed to extend the LAN. In that case, connecting the modem/router to a switch and daisy-chaining additional switches would work.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 220-1101 exam frequently reuses these exact scenarios with slightly different constraints.
✓Connect both switches to a router, and connect the modem to the router.Correct answer▾
Why this is correct
A router is required to share the single modem connection and route between the internet and the 25 workstations, since unmanaged switches cannot perform NAT or DHCP. Connecting both switches to the router keeps all workstations on one subnet while providing internet access.
✗Connect the modem directly to the 48-port switch and then daisy-chain the 24-port switch from the 48-port switch.Wrong answer — click to see why▾
Why this is wrong here
Daisy-chaining switches from the modem without a router means the modem cannot perform NAT or routing for multiple devices; the ISP typically provides only one public IP address, so only one device would get internet access.
★ When this WOULD be the correct answer
If the question specified that the ISP modem has a built-in router with DHCP and NAT capabilities, and the goal is simply to expand the number of ports, then connecting switches directly to the modem would work.
Why candidates choose this
Candidates may think that unmanaged switches can be daisy-chained to extend the network and that the modem can handle multiple devices, overlooking the need for a router to route traffic and provide internet access to multiple devices.
✗Connect the modem to the 24-port switch, then connect the 48-port switch to the 24-port switch.Wrong answer — click to see why▾
Why this is wrong here
Connecting the modem to the 24-port switch and then cascading to the 48-port switch would not provide internet access because the modem typically provides only one public IP address, and switches do not perform NAT or routing. Without a router, only one device would get internet access, not all 25 workstations.
★ When this WOULD be the correct answer
In a scenario where the ISP modem is a router with built-in NAT and DHCP, and the goal is to expand the number of LAN ports without needing additional routing, connecting the modem to a switch and then cascading another switch would be appropriate. For example, if the modem is a router with four LAN ports and you need to connect more devices on the same subnet.
Why candidates choose this
Candidates may think that cascading switches is a simple way to increase port count, and they overlook the need for a router to provide internet access to multiple devices. They assume the modem alone can handle multiple IP addresses.
✗Connect the modem directly to the 48-port switch and connect the 24-port switch to the 48-port switch.Wrong answer — click to see why▾
Why this is wrong here
Connecting the modem directly to a switch (48-port or 24-port) without a router would not provide NAT or routing, so only one workstation would get a public IP from the ISP, and the others would not have internet access. A router is required to share the single public IP among multiple devices.
★ When this WOULD be the correct answer
This option would be correct if the ISP provided a modem/router combo (gateway) with built-in routing and NAT, and the technician only needed to extend the LAN. In that case, connecting the modem/router to a switch and daisy-chaining additional switches would work.
Why candidates choose this
Candidates may think that switches can handle all connectivity needs and overlook the requirement for a router to perform NAT and routing between the ISP's network and the local subnet.
Analysis generated from the official 220-1101blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
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Same concept, more angles
1 more way this is tested on 220-1101
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A technician is setting up a small office network. The ISP provides a cable modem with a single Ethernet port. The office has 15 computers that all need internet access. The technician has a router with four LAN ports and a 24-port unmanaged switch. Which of the following is the correct way to connect the devices to provide internet access to all computers?
medium- A.Connect the modem to one of the router's LAN ports, then connect the switch to another LAN port, and connect all computers to the switch.
- ✓ B.Connect the modem to the router's WAN port, then connect the switch to one of the router's LAN ports, and connect all computers to the switch.
- C.Connect the modem directly to the switch, then connect the router to the switch, and connect all computers to the router's LAN ports.
- D.Connect the modem to one of the switch's ports, then connect the router to another switch port, and connect all computers to the router.
Why B: The router's WAN port is designed to connect to the ISP modem for public IP assignment via DHCP, while the LAN ports provide private IP addresses to internal devices. The switch connects to a LAN port to expand the number of available ports, allowing all 15 computers to access the internet through the router's NAT and routing functions.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 220-1101 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 220-1101 exam.