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Wired devices lose connection randomly, one at a time. (alien.top)

submitted 11 months ago by [email protected] to c/[email protected]

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I have an issue that has been wracking my brain for some years now.

We have an Asus RT-AX82U gaming router and we have our two computers hard-wired into it.

Problem: Sometimes, at seemingly random times, one of our computers will lose connection. Sometimes it's one then the other, sometimes it's just one. The connection is gone for a few seconds, and then it comes back on its own.

Question: Does anyone know why something like this would happen? I am assuming the problem is from the router to the computers themselves. I don't think the issue would be with the modem since it only affects one computer at a time.

More information:

It's very quick, so we can't really troubleshoot by the time it comes back, but it seems that the device's connection to the network stays intact but just gets disconnected from the internet
We have old (10+ years) flat, gold-plated ethernet cables from the router to the computers
Both our computers are twins. We recently built them with the exact same components. However, this issue also happened with our older computers (also built as twins)
The modem is an old modem/router in bridge mode
We have a simple network: utility -> modem -> router -> devices
This has been going on and off for a few years, it's more of a nuisance than anything, but we do get disconnected from raids and other packet-sensitive situations

Mainly, I want to know if anyone has had issues of a similar type or would know what component would cause it. I am thinking about replacing the ethernet cables soon and possibly getting a new modem that's just a modem.

Thanks in advance!

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[–] [email protected] 1 points 11 months ago

. While that could have a number of causes, if it really only happens to Internet connections (the "connection to raids" comment is confusing me) then what you are seeing may be consistent with a NAT table overflow in one of the routers. The NAT table in a router tracks what it thinks are your currently active connections to Internet destinations but tends to accumulate a lot of cruft when it can't tell, or doesn't process, when a connection closes and is no longer in use. When the table fills and the router needs to find space for a new connection it responds by blowing out some of the existing stuff in the NAT table. If some of the stuff it dumps is currently active this causes incoming packets for those connections to be dropped until the internal host sends something that reestablishes the table entry, which may take some seconds.

To determine if this might be the cause one would look at the state of the NAT table in the router to see how close to full it is running, but many consumer routers don't show this. To make it work better one would increase the size of the NAT table and maybe tune its other parameters, but most consumer routers don't support that. Failing this one might buy a router with a bigger NAT table, but most consumer routers don't tell you how big theirs is. There are fairly inexpensive routers that do let you manage the NAT table but they tend to be ones that can be deadly difficult to configure.

Note that if this is your problem the problem could be either in your router or the router that is in "bridge mode" (what it is actually doing can be a mystery; the routers AT&T makes everyone use famously keep their NAT table in use not only in the "IP passthrough" modem emulation but also when you buy extra IP addresses so no NAT is necessary). If you can replace the modem/router with a real modem you could eliminate that as an issue. As for the other router, with no NAT configuration all you could do is replace it with another that you hope works better. All this is a lot of hardware to buy if the current routers don't give you a way to determine that the NAT table, and not some else, is in fact the problem.