Member Avatar for lewashby

I have a router in one room of my house and wires running through the house into my bedroom where it's connected to a switch that further connected to several different computers in my room. What I am wanting to know is how the traffic flows from one computer to another. If computer A sends computer B a file does the data travel from A, to the switch, and then to B? Or does the traffic from A to B travel through the switch and all the way to the router and back before going to it's inteded destination computer B? Thanks.

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  • Latest Post Latest Post by rproffitt

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A bit more detail that builds on 's reply and addresses 's Netflix concern.

A switch forwards Ethernet frames at Layer 2 using a MAC-address table. When two wired hosts share the same VLAN and subnet on the same physical switch, the switch learns which MAC is on which port and sends the unicast frames only to the destination port. That keeps the transfer on the switch fabric and does not involve the router. There are important exceptions and edge cases to be aware of.

Common situations that will force traffic off the local switch and onto a router or wireless link:

  • Hosts are on different IP subnets or different VLANs -> routing is required, so the router (or an L3 switch) forwards the packets.
  • One endpoint is connected over Wi‑Fi or another segment that is bridged through the router -> traffic traverses the router and the wireless link.
  • The switch is actually a hub, or a misconfigured bridge is flooding traffic -> all ports see the frames.
  • The switch has no MAC-table entry for the destination (first packets) -> the frame is briefly flooded to all ports until learning completes.
  • Intentional interception (ARP spoofing, proxy-ARP or certain proxy/proxying services) can cause traffic to go through another device.

Quick checks to verify the path and diagnose:

Windows:
  ipconfig /all
  arp -a
  tracert <other-ip>

Linux/macOS:
  ip addr
  ip neigh
  traceroute <other-ip>

Capture/filter (Wireshark on the sender):
  ip.addr == <other-ip>

If the ARP table shows the other host's MAC, frames are local. If it shows the router's MAC, traffic will be sent to the router.

Practical note: a large copy between two PCs on the same bedroom switch will not use the Wi‑Fi and therefore should not degrade a separate Netflix stream on wireless. However, a transfer between a wired PC and a wireless device will use the router and wireless airtime and can affect streaming quality. For packet-level monitoring or to sniff cross-port traffic, use a managed switch with port mirroring or a network tap.

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Member Avatar for rproffitt

Need a little more. In a switched network if machine a and b are on the same switch the traffic is direct between a and b and no other network device sees a thing. Kind of like Master Sergeant Schultz,

I see nothing! I hear nothing! I know nothing!

Member Avatar for lewashby

Thanks. I was worried the traffic was traveling all the way to the router and back to the switch in which case it would slow down other traffic in the house that uses things like netflix.

Member Avatar for lewashby

One more thing. Why is the article labled 'Featured'? Thanks.

Member Avatar for rproffitt

If it's like mine, you did it right.

Internet -> Router w/WiFi -> Switch -> wired devices.

All the wired devices can talk among themselves with an exception being if an app uses the internet to talk to other things. But file copies, normal stuff just is traffic on the porst of the devices chatting and the ports on the switch. Nowhere else.

Can create headaches for those that want to monitor what a device talks about.

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