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I have heard (forget where) that in a local wifi network created by a router, when two computers communicate with each other, they communicate directly with each other, and their communication doesn't go through the router. Is that true? What part of it is true and what part of it is wrong?

Once two computers start to communicate with each other, (e.g. start to transfer a large file via ssh or NFS or ...), can they continue to communicate if I turn off the router?

Thanks.

Tim
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  • You need to be specific about your network. A diagram, the network device modes, and the network device configurations would be a good start. – Ron Maupin Dec 24 '19 at 21:44
  • It can be any. e.g. a wifi LAN set up by a router and Verizon FIOS – Tim Dec 24 '19 at 22:00
  • Unfortunately, questions about home networking and consumer-grade devices are explicitly off-topic here. You could try to ask this question on [su]. – Ron Maupin Dec 24 '19 at 22:01
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    I have been bullied and lost posting right on superuser. Network is network. There should be no discrimination against home network – Tim Dec 24 '19 at 22:02
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    I'm sorry about that, but the question is still off-topic here. One of the problems is that you have a Frankenstein box, that, yes, does contain a router, but it has other stuff in there, too. When you read things like you did, then that means the router inside the box, not the whole box. Business networks (what is on-topic here) will usually have separate, dedicated devices for what is in your consumer-grade box. – Ron Maupin Dec 24 '19 at 22:06
  • When WiFi enters the equation, the answer "depends". In infrastructure mode ("AP"), all frames move through the WAP. The router part of the WAP won't normally have anything to do with this traffic; it's all handled by the wireless hardware. If you turn the "router" off, everything will stop, *because it's also your WAP.* – Ricky Dec 25 '19 at 01:56
  • I'm a bit late to the party and since the question is already closed, I can't add this as an answer: The behavior described in the question sounds like Tunneled Direct Link Setup, see https://en.wikipedia.org/wiki/TDLS and https://www.wi-fi.org/system/files/20120808_TDLS_White_Paper_FINAL.pdf. – Zoltan Oct 22 '22 at 07:45

1 Answers1

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In the same network, hosts communicate directly. This is probably through a switch or WAP, but the frames are sent addressed directly from one host to the other host. The switch or WAP is really just a layer-2 bridge between the two hosts. The layer-2 frames are addressed to the destination host.

Routers route layer-3 packets between networks. If a host is sending something to a host on a different network, then the host will send layer-2 frames addressed to its configured gateway (router). The router strips off the layer-2 frames and routes the layer-3 packets based on the layer-3 destination address to a new interface and build a new layer-2 frame for the layer-3 packet using the layer-2 protocol for the new interface.

Once two computers start to communicate with each other, (e.g. start to transfer a large file via ssh or NFS or ...), can they continue to communicate if I turn off the router?

We have no information about how your network is configured, but if the two hosts are communicating on the same network, then you never needed a router for that in the first place. The hosts could start, continue, and stop communicating all on their own, even if you never had a router.

Ron Maupin
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