I have a fairly basic, local, wireless network. I have an Ubuntu media server/file share, a desktop PC, a laptop, mobiles and a TV. The issue I am facing since I got the server (for 2-3 months now) is that the it gets unreachable 1-2 twice a week. I can't ping them from any of the machines and I can't access the resources (e.g. file share) either.
I've been troubleshooting this for a while and I made sure that the ports are open and the services are running, etc. Also, it usually works for 3-4 days in a row perfectly, so I doubt that it's any "static" configuration (e.g. port 22 is not open for ssh)
I finally figured out a repro and a "fix". The server usually gets unreachable for e.g. the laptop if laptop leaves the network. (e.g. goes to sleep or wifi is off on a mobile) If I login to the server and ping the laptop, then the laptop will start to see the server again.
This, and the fact that some machines see the server and some doesn't at the same time, gave me the idea that it could be ARP related. I tried to print the ARP table on the laptop at a time when the laptop couldn't reach the server and the server wasn't in the table. When I pinged the laptop from the server, the laptop's local ARP cache got updated and the IP of the server appeared and stuff started to work (until the next sleep).
Now, I started looking at the network traffic. I installed WireShark on the laptop and I can see that the laptop is sending ARP requests to the server constantly (probably because of the mapped file shares) but there is no reply. I used
tcpdump on the server to see what ARP requests are coming in, and I can see it gets a few requests from the router and from my desktop machine, but none from the laptop. (I disabled the firewall for the sake of the test)
So essentially, the laptop sends ARP requests and doesn't get any response and the server can't see any requests from the laptop.
I mentioned the laptop in these examples, but it works the same way for a mobile or other devices on the network.
- Single LAN domain, no bridge, nothing complex.
- The router is, unfortunately, a simple one given by the ISP. I didn't do any NAT or any "advanced" stuff. I think the only router setting I changed was longer DHCP lease during the troubleshooting.
- The server has two network adapters, an ethernet and a wireless, but I only use the wireless. (Router is in a closet due to some limitations, so there is no cable connection for any of the devices.)
- The router has both 2.4GHz and 5GHz and I use both with few devices, but there is no correlation between who is seeing the server and who is on the same frequency.
- Server hardware is my old desktop PC that I turned into a server 2-3 months ago. I didn't have any issues before, when it was a PC (Windows 7)
These are fairly uncharted waters for me with the whole networking, I never done anything like this before and at this point I have no clue how I could progress or what should I check or change.
Do you have any idea how to further troubleshoot this or what could be the problem?