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Currently, I'm in a situation where an end device talks at a certain transmission rate over ethernet. Auto-negotiation between the device and router are supposed to be able to address the issue, but apparently the device is stubborn and will crash if the RJ-45 port on the router is not configured with auto-negotiation disabled and specifically set to the appropriate speed the device communicates at.

Unfortunately, I have no control over the device, so all I'm left with is to change the port settings on the router. There is also an added level of crappiness to where I may or may not have access to the router that is communicating with the device. My solution was to put another router that I would have full control over in between the main router and the end device.

I think this would work (please advise if you think otherwise), so I pulled out a linksys WRT120N router and explored its settings to find that transmission speed was not something that I could set for the physical ports.

Do I need to get another router? Am I going about this all wrong? Is there a way to configure this on the WRT120N that I am unaware of?

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Sure, if you pay more than $40 for them... – Ignacio Vazquez-Abrams Jul 12 '13 at 20:07
So, it's essentially an "advanced feature" then? What prices would I be looking at? And would it still be a residential-focused router? It doesn't necessarily need to be, but it would be nice I guess.. – MandM Jul 12 '13 at 20:11
The stock control panel on a cheap home router will almost certainly never include this setting no matter what make and model it is, but you might be able to obtain sufficiently fine-grained control if you reflash it with DD-WRT or similar custom firmware. – Aaron Miller Jul 12 '13 at 20:18
Actually, I doubt even DD-WRT would help you here. Most consumer routers are a 2-port router with a 5-port unmanaged switch. You would need something like a managed switch for this. – Darth Android Jul 12 '13 at 20:20
Do you really need a router? A cheap managed switch, or maybe at 10mb hub would be enough. – Zoredache Jul 12 '13 at 21:00
up vote 1 down vote accepted

You can get any supported router and install OpenWRT on it.

You will have to bridge both ethernet interfaces, and use ethtool -s <ethX> duplex <duplex> speed <10/100/1000/whatever> to set duplex and speed of the link.

You won't be able to do this on both interfaces, just on the one that usually faces internet (usually eth1 on this routers). But this shouldn't be a problem for what you're trying to do. Just connect your problematic device to this one and your upstream line to the other one.

The other one has an internal unmanaged switch directly connected to it, as per Darth Android's comment on the question.

share|improve this answer
thanks for the concise solution. I'll choose this as the answer, but could you explain the very first step of bridging both ethernet interfaces? I've got the rest of it, but I'm not a networking whiz by any means and am not sure what that would entail. Is that a physical wiring thing? Software/firmware setting? Both? – MandM Jul 15 '13 at 13:39
It's a software configuration. Very easy to do from openwrt's web interface, but feel free to open another question for the bridge setup. – GnP Jul 29 '13 at 17:08

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