Speed gain when connecting on multiple network interfaces at once

Question

I want to pose some scenarios and questions to get a better idea of the impact that utilizing multiple connections and interfaces on a single device will have on connection speed.

• Scenario 1: Three routers all with separate connections to the internet, and one computer with two gigabit ethernet LAN ports and a wireless card
  • Question 1: Would there be a significant speed boost if the computer connected to all three routers at once using the three possible interfaces?
• Scenario 2: One internet-connected router with two ethernet LAN ports and wireless capability, and one computer with a wireless card and two ethernet LAN ports.
  • Question 2: Would there be a significant speed boost if the computer connected to the router using all three possible interfaces at once?
• Scenario 3: One offline wireless router/switch, with four ethernet LAN ports and wireless capability, and two computers, each with two ethernet LAN ports and wireless cards.
  • Question 3: If I connect the computers to the router/switch using all possible connections (four wired connections, two wireless connections), would there be a significant speed boost in transfers between the two computers, as opposed to if I only used one possible connection per computer?

EDIT: Rationale for asking the question. I'm shopping around for motherboards and one gaming one keeps popping up which is selling itself as having two ethernet ports for "double the speed". I was skeptical but figured it might be possible.

The other reason is that I live with someone who can control over whether or not I can access internet on the ADSL by disabling the wifi on the router. He does this regularly. So i was looking into solutions where I have a wired connection to a 4G router, while wirelessly connecting to the ADSL router simultaneously. I was wondering if this would provide a speed boost at all.

Answer 1

Scenario 1 -

In the "standard" setup where you just plug the computer into the cards there would be no speed boost at all. Arguably it would decrease speed compared to other solutions. This is because the computer will have 3 default routes, but will always pick the first - thus only utilizing one of the connections. Were you to add routes for different parts of the Internet to different routers, you could get a speed increase when visiting multiple sites, if those sites took different routes.

Scenario 2 -

Again, not by default. Each interface would get its own IP address and would have traffic routed to/from that. Because there is a default route, only 1 connection would be used. You see this fairly commonly where a laptop has a WIFI connection and an ethernet connection. When the ethernet connection is plugged in it is preferred to the WIFI connection.

If you run a server on the computer, you could have it on the non-default port and use 1 connection for traffic to the server on the computer and a different one for outgoing traffic.

Some computer systems (Linux for example) has a notion of "channel bonding" which will allow you to aggregate the 3 links - so it may be possible to get better performance then you would on a single link if you can make changes on the PC. This is fairly nuanced and depends on lots of things, including router support, OS support and the goal. There are at least 6 different modes that Linux supports for this!

Scenario 3 -

Again, no - see the answers to 1 and 2. A common partial solution is to use 1 connection for the Internet and a seperate one for talking between computers.

Answer 2

Scenario 1: If multiple connections in parallel are established, a boost is possible. If a single connection uses all bandwidth available on one uplink, it would be slowed down by aanother connection using the same uplink. If the other connection is now handled by a completley seperate route, they won't interfere with each other - assuming the routers and network cards are on completely different LANs (or one LAN with enough bandwidth).

Scenario 2: While I do not quite understand the purpose of the second computer in this scenario, it doesn't change the answer either. One internet uplink is usually less powerfull than LANs. So, even a single connection between one computer and the router is sufficient to fully use the entire bandwidth of the internet uplink - at least in most cases. If the LAN is not powerful enough to have that much abndwidth, more connectoins over the same LAN are just as useless. The wireless conneciton might be helpful, if and only if the wired network is the bottleneck and not the internet gateway.

Scenario 3: In this case, it depends on the precise setup. Ethernet uses time slicing. This means only one device on the network can send data at the same time. If a device has two wired connections on the same LAN, and there are no other devices, it does not make any difference. Half of the time the device will send, half of the time the router will. If there are more devices, giving one device two connections to the LAN will double the time the device can send. So - if all connecitons are on the same network, and network has ONLY those two devices sending data, it makes no difference how many connections they use. If there is other devices, and all available bandwidth is used, you get more sending time for a device if it has multiple connections to the network. Wireless connections work slightly different, and every protocol is different as well (and you didn't specify which is used). Some use time slicing, some use different frequencies, some combine both. The principle is pretty muich the same as with ethernet though. ALl this is only true though if the bottleneck, in this case the router, is capable enough to route all data in time.