Question Strange network switch behaviour

overheat

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Aug 24, 2011
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Greetings, I have two PCs connected to each other with a switch, and the switch is then connected to a wall outlet which I presume goes out to my ISP or the apartment building modem. It all works great but the strange behaviour arises when I try to communicate (SSH) between the two PCs

If I SSH using the IPv4 address, the data goes through the switch and does a round-loop over the ISPs system which bottlenecks the bandwidth according to my subscription, if I use the link-local IPv6 address the data goes straight through the switch and the connection works even if I disconnect from the wall socket, I get the full 1Gbps connetion between the PCs.

I would like to use IPv4 for reasons, but I would also like to get the fast connection, what is the deal here? The switch is unmanaged and the two PCs have some Realtek 1Gbps LAN built in to their motherboards
 

nigelivey

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Not really understanding what you mean by
the data goes through the switch and does a round-loop over the ISPs system which bottlenecks the bandwidth according to my subscription
Please can you clarify what the ISP has installed? Is it a modem, router or gateway device (modem, router and switch all in one). In no event should your subscription have anything to do with it and certainly should have any impact on SSH. (If you are transferring files between machines that require large amounts of bandwidth why use ssh?).
 

overheat

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Aug 24, 2011
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I probably explained it a bit poorly, I have an RJ45/Ethernet wall outlet in my apartment that I presume goes into a fiber modem in the apartment building (could be anything really, just out of my reach), I can just plug my PC into the outlet and it gets assigned an IP and all is well, the way I have it setup is so that the switch is connected to the outlet and the two PCs are connected to the switch, so that both PCs have their own IP address, no local area network or anything. What I meant is that my uplink/downlink is 100mbps symmetric and that's the speed I'm getting when I SSH between the PCs, it should be 1Gbps if the data only went through the switch. In fact, I can't SSH between them at all if I disconnect the wall outlet and just have the two machines connected by the switch.
 
It should not be working that way.

When devices communicate over a switch they go directly port to port. You can pretty much prove this by leaving a constant ping run between the machine and unplug the cable going to the wall.

The devices are actually using their mac addresses to route the packets between the devices. The only used the IP to set the communications up after that they just send to mac and the switch know which mac address is on which port and sends the traffic directly.

It makes no sense that it would run at different speeds for ipv4 and ipv6. If it was the same you would suspect a port running at 100mbit.

Not sure ping between the machines and then check the arp entry and see if they have the each other mac addresses. To go via the router they would have to have the routers mac address mapped to those ip and that would indicate some configuration error.
 

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