Cant reach a wireless Raspberry PI from an ethernet desktop.

Marcelvs

New Around Here
Hi guys, this happens all the time on me. Just after I power on any raspberry pi it connects to my router via wireless interface. I can list it in my asus AC5300 with merlin firmware. It has an IP it can access internet but I cannot ping it from my desktop connected via ethernet cable, not at this time, if I wait 10 minutes, sometimes half an hour it can reach the PI.
Using the arp command in my desktop I realize the PI's HW addr is incomplete (missing) in the table.
I have a vpn server in Merlin and if I connect using my mobile throught the vpn I can reach anytime the PI.
After I get the mac address I can reset the PI as many time as I want and it works flawlessly.

I saw a long time ago another post regarding this on google, I would appreciate any help.

Thanks in advance.

Marcelo.
 

Campblor

New Around Here
Sorry to get your hopes in with a reply to this thread on email but i have recently been having the same issues. Running an RT-AC88U on the latest Merlin. I am using a ubuntu VM for DNS and DHCP (pihole) and within the last few weeks I have been having the same issues as you. Only difference is that both my windows PC and the Pi are on wifi.

1. Pi get's an IP from the DHCP server, I can ping it from that VM
2. PC cannot ping it UNTIL I ping my PC from the Pi then it immediately starts working.

I really hope you found the culprit.
 

dosborne

Very Senior Member
I use static IP addresses for all my server or server-like (rasp pi) devices. You can then add entries in your hosts file (if you prefer"hostnames") or access them directly by IP. Makes life a lot simpler
 

eibgrad

Part of the Furniture
I use static IP addresses for all my server or server-like (rasp pi) devices. You can then add entries in your hosts file (if you prefer"hostnames") or access them directly by IP. Makes life a lot simpler

I don't believe DNS is the problem here. As I read it (and I could be wrong), the IP address (however you get it) can NOT be resolved to the MAC address on the local ethernet network. IOW, arp is NOT working as expected. Therefore the device can NOT be addressed at the ethernet level (layer 2).

What may be required here is a static arp entry for the target device on the various clients that are having the problem. It still doesn't explain *why* arp isn't working though. If it was me, I'd be using tcpdump and/or Wireshark to see why (maybe it's something else entirely).
 

dosborne

Very Senior Member
Hard to know if both posters 1 and 2 are experiencing the same thing. My response was more for the first one, where more detail may be required.

I agree with you though, the second one, involving a ping, may be a more complex issue. Perhaps knowing which O/S is running on the Pi may shed some light.

Can't say I've tried this particular scenario with the 6 Pis I run. About half are "always on" the others I fire up as required, but I've never had an immediate access issue.
Rasbian / Raspberry Pi OS
Code:
Linux RPi50 5.10.103-v7l+ #1529 SMP Tue Mar 8 12:24:00 GMT 2022 armv7l GNU/Linux
 

Campblor

New Around Here
Sorted my issue. It wasn't DNS (shock horror) as whenever I'd ping they'd resolve immediately and quickly fail to find the IP in ARP. My fix was to bin /etc/pihole/dhcp.leases and restart dns on pihole. Rebooted the pi and it got albeit the same IP as before but since then I have had no issues pinging either and the Pi can see my PC both on Wifi, across the two bands.

Edit: For some context I am using a little PC stat display tool called Modbros. Which is a windows client which hosts a small webui and then the Pi runs their own custom auto boot image to just display that stats screen. During my issues the Pi would get an IP but couldn't find my PC and I couldn't connect to the Pi from my machine to diagnose. Annoyingly their little Pi Image doesn't have any user input GUI
 

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