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Frames from One LAN Transmitted to Another LAN via Network Devices

Frames from One LAN Transmitted to Another LAN via Network Devices

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Nov 4, 2026

In a typical internetwork, a LAN (Local Area Network) uses Ethernet-style frames inside a broadcast domain. To send data from one LAN to another LAN, the transmitting host must cross a boundary between different Layer 2 domains (different MAC/broadcast realms). Which device can do that depends on which OSI layer the device operates at and whether it forwards based on MAC addresses (Layer 2) or IP addresses/network routes (Layer 3). 4

Key idea: Routers can carry traffic between LANs, while bridges and repeaters mainly connect within the same LAN (or extend it), and a modem is for WAN/telecom physical connectivity rather than LAN-to-LAN frame forwarding. 4

Mermaid overview of where the four devices primarily act:

Footnotes

  1. Wikipedia — Router - Defines routers as network devices that forward packets between networks, typically at OSI Layer 3. ↩ ↩2

  2. Wikipedia — Bridge (networking) - Explains that bridges connect network segments and forward frames using MAC addresses at OSI Layer 2. ↩ ↩2

  3. Wikipedia — Repeater (networking) - Describes repeaters as Layer 1 devices that regenerate/extend signals. ↩ ↩2

  4. Wikipedia — Modem - Defines modem as a device that modulates and demodulates signals for communication over telecom lines. ↩ ↩2

type="tip" title="Pro Tip" content="A good exam heuristic: if the question says “from one LAN to another LAN,” think “different IP networks,” which points to a router operating at Layer 3." 2

Footnotes

  1. Wikipedia — Router - Defines routers as network devices that forward packets between networks, typically at OSI Layer 3. ↩

  2. Wikipedia — Bridge (networking) - Explains that bridges connect network segments and forward frames using MAC addresses at OSI Layer 2. ↩

type="warning" title="Common Misconception" content="Bridges and repeaters extend Layer 2 connectivity; they do not normally route between different IP networks (LANs). A modem is not a LAN-to-LAN frame forwarder—it converts signals for a telecom link at Layer 1." 4

Footnotes

  1. Wikipedia — Router - Defines routers as network devices that forward packets between networks, typically at OSI Layer 3. ↩

  2. Wikipedia — Bridge (networking) - Explains that bridges connect network segments and forward frames using MAC addresses at OSI Layer 2. ↩

  3. Wikipedia — Repeater (networking) - Describes repeaters as Layer 1 devices that regenerate/extend signals. ↩

  4. Wikipedia — Modem - Defines modem as a device that modulates and demodulates signals for communication over telecom lines. ↩

Device-by-device: Can frames from one LAN reach another LAN?

Frame forwarding vs. routing

  • keyword: A data unit sent at Layer 2 between hosts in the same link/broadcast domain.
  • keyword: Separation between Layer 2 broadcast domains (different MAC learning domains).
  • keyword: Forwards packets between different IP networks using routing decisions.
  • keyword: Forwards Ethernet frames within the same overall LAN by using MAC addresses.

Why the answer is (i) Router

To move data from LAN 1 to LAN 2, the device must handle the inter-network transfer (Layer 3 routing). A router forwards packets between networks and thus enables communication across LAN boundaries.

  • (i) Router ✅ Yes
    Routers operate at Network Layer (Layer 3) and route traffic between different networks/LANs using IP addresses and routing tables.

  • (ii) Bridge ❌ Not “between LANs” in the routing sense
    Bridges operate at Data Link Layer (Layer 2) and forward Ethernet frames using MAC addresses. They connect segments within the same LAN/broadcast domain rather than performing inter-network routing.

  • (iii) Repeater ❌ Not between LANs
    Repeaters operate at Physical Layer (Layer 1) and regenerate/extend signals. They do not understand frames or addresses; they simply extend connectivity in a way that keeps the same link-layer behavior.

  • (iv) Modem ❌ Not a LAN-to-LAN frame forwarder
    Modems operate at the physical/telecom boundary: they modulate/demodulate signals for WAN communication. They are not designed to forward LAN frames between LANs the way a router does.

A compact comparison table:

DeviceOSI LayerForwards based onBetween LANs (different networks)?Typical role
Router3IP/routingYesInter-network routing
Bridge2MAC addressesNo (usually within same LAN)Extend/split LAN segments
Repeater1Signal levelNo (extends physical reach)Regenerate signals
Modem1 (telecom interface)Signal conversionNo (not routing frames)Convert for WAN link

(Above properties align with standard OSI-layer roles of each device.) 4

Footnotes

  1. Wikipedia — Router - Defines routers as network devices that forward packets between networks, typically at OSI Layer 3. ↩ ↩2 ↩3 ↩4 ↩5

  2. Wikipedia — Bridge (networking) - Explains that bridges connect network segments and forward frames using MAC addresses at OSI Layer 2. ↩ ↩2 ↩3 ↩4

  3. Wikipedia — Repeater (networking) - Describes repeaters as Layer 1 devices that regenerate/extend signals. ↩ ↩2

  4. Wikipedia — Modem - Defines modem as a device that modulates and demodulates signals for communication over telecom lines. ↩ ↩2

How a frame travels from LAN 1 to LAN 2

Host creates a frame (LAN 1)

Step A

The sender encapsulates data into a Layer 2 Ethernet frame for delivery within LAN 1. "

Footnotes

  1. Wikipedia — Router - Defines routers as network devices that forward packets between networks, typically at OSI Layer 3. ↩

Router receives and routes

Step B

The router processes Layer 3 addressing and forwards toward the destination network (LAN 2). "

Footnotes

  1. Wikipedia — Router - Defines routers as network devices that forward packets between networks, typically at OSI Layer 3. ↩

Forward to LAN 2 link

Step C

The router emits a new frame appropriate for LAN 2’s link-layer addressing to reach the next hop. "

Footnotes

  1. Wikipedia — Router - Defines routers as network devices that forward packets between networks, typically at OSI Layer 3. ↩

Destination host delivers data

Step D

The receiving host delivers the payload after link-layer and higher-layer processing. "

Footnotes

  1. Wikipedia — Router - Defines routers as network devices that forward packets between networks, typically at OSI Layer 3. ↩

Step-by-step: Why only a router can connect two LANs (typical exam logic)

  1. 1
    Step 1

    LAN 1 and LAN 2 are typically different Layer 2/broadcast domains; moving across them requires inter-network handling (routing). 2

    Footnotes

    1. Wikipedia — Router - Defines routers as network devices that forward packets between networks, typically at OSI Layer 3. ↩

    2. Wikipedia — Bridge (networking) - Explains that bridges connect network segments and forward frames using MAC addresses at OSI Layer 2. ↩

  2. 2
    Step 2

    Routers work at Layer 3; bridges work at Layer 2; repeaters work at Layer 1; modems convert telecom signals at the physical layer. 4

    Footnotes

    1. Wikipedia — Router - Defines routers as network devices that forward packets between networks, typically at OSI Layer 3. ↩

    2. Wikipedia — Bridge (networking) - Explains that bridges connect network segments and forward frames using MAC addresses at OSI Layer 2. ↩

    3. Wikipedia — Repeater (networking) - Describes repeaters as Layer 1 devices that regenerate/extend signals. ↩

    4. Wikipedia — Modem - Defines modem as a device that modulates and demodulates signals for communication over telecom lines. ↩

  3. 3
    Step 3

    Inter-network delivery requires IP-based routing decisions (Layer 3), which a router provides.

    Footnotes

    1. Wikipedia — Router - Defines routers as network devices that forward packets between networks, typically at OSI Layer 3. ↩

  4. 4
    Step 4

    A bridge forwards frames by MAC within a LAN; a repeater only regenerates signals; a modem does signal conversion rather than MAC/IP forwarding between LANs. 3

    Footnotes

    1. Wikipedia — Bridge (networking) - Explains that bridges connect network segments and forward frames using MAC addresses at OSI Layer 2. ↩

    2. Wikipedia — Repeater (networking) - Describes repeaters as Layer 1 devices that regenerate/extend signals. ↩

    3. Wikipedia — Modem - Defines modem as a device that modulates and demodulates signals for communication over telecom lines. ↩

Visual intuition: OSI-layer responsibilities

  • keyword: A unique identifier used at Layer 2 for frame delivery on a LAN.
  • keyword: Data structure mapping destination networks to next hops for routers.
  • keyword: Restoring signal strength/timing without frame-level processing.
  • keyword: Converting digital data to/from analog signals for telecom links.

Footnotes

  1. Wikipedia — Bridge (networking) - Explains that bridges connect network segments and forward frames using MAC addresses at OSI Layer 2. ↩

  2. Wikipedia — Router - Defines routers as network devices that forward packets between networks, typically at OSI Layer 3. ↩

  3. Wikipedia — Repeater (networking) - Describes repeaters as Layer 1 devices that regenerate/extend signals. ↩

  4. Wikipedia — Modem - Defines modem as a device that modulates and demodulates signals for communication over telecom lines. ↩

Exam-style FAQs

Match to the question: device that enables LAN1 → LAN2 frame delivery

Scores represent alignment with inter-LAN communication via Layer-3 routing.

Routers vs Bridges vs Repeaters (OSI layer intuition)

Knowledge Check

Question 1 of 4
Q1Single choice

Which device enables communication between two different LANs by forwarding traffic between networks?

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