Cannot PING my Android Phone

[doctormann]

Bit of a mystery.

I have a new Samsung A23 Android phone.  I cannot get it to communicate with my LAN - can't even PING it from my Linux laptop.  This used to work perfectly with my previous A12 phone.

Laptop and phone are on the same network and battery saving on the phone is not enabled (I know that this can cause problems).

I thought that it might be a firewall issue but disabling the firewall on the laptop makes no difference.

PINGing the phone from the laptop just results in 100% packet loss so it seems that the phone is not being detected.

There is some discussion about this on the internet but nothing useful.

The phone works normally in all other respects - can access the internet with no problems.

Any ideas?

[norbra]

Try Disable mobile data as it seems to isolate wifi

[doctormann]

6 minutes ago, norbra said:

Try Disable mobile data as it seems to isolate wifi

Mobile data is off.  Wifi still works as I can connect to the internet with no problems.

 

[HappyExpat57]

If you have both 5G and 2.4G and are on the 5G, switch to the 2.4G and repeat test.

[gamb00ler]

Get a PING app for your phone and try to ping the router. 

 

Not all devices respond to ping requests.

 

I know nothing of the Android system.  Does Android allow ignoring of ICMP (ping and other) messages?

[doctormann]

22 minutes ago, gamb00ler said:

Get a PING app for your phone and try to ping the router. 

 

Not all devices respond to ping requests.

 

I know nothing of the Android system.  Does Android allow ignoring of ICMP (ping and other) messages?

I can PING the router just fine.

No idea if Android can ignore ICMP etc.

 

[doctormann]

42 minutes ago, HappyExpat57 said:

If you have both 5G and 2.4G and are on the 5G, switch to the 2.4G and repeat test.

Still doesn't work.

[gamb00ler]

Set your phone up as a WiFi hotspot, turn your router off and try and connect your laptop to the phone's SSID.

[doctormann]

6 minutes ago, gamb00ler said:

Set your phone up as a WiFi hotspot, turn your router off and try and connect your laptop to the phone's SSID.

Interesting!

Yes, with the phone set as a mobile hot spot, wifi off and data service running I can PING the phone.

Does this give a clue as to why i can'r ping via wifi?

[norbra]

I recently trawled through  THAI comms menus of a Galaxy a24 and found IPV 6 was set as default changed to IPV 4 all seem to connect ok after this change.

Hope this might be helpful 

[gamb00ler]

4 minutes ago, doctormann said:

Interesting!

Yes, with the phone set as a mobile hot spot, wifi off and data service running I can PING the phone.

Does this give a clue as to why i can'r ping via wifi?

I didn't think past eliminating the router from your communication path between laptop and phone.

 

I'm only guessing because I'm no expert in networking.

Router configuration?

a rare router/phone incompatability? 

 

[doctormann]

16 minutes ago, norbra said:

I recently trawled through  THAI comms menus of a Galaxy a24 and found IPV 6 was set as default changed to IPV 4 all seem to connect ok after this change.

Hope this might be helpful 

IPV6 is disabled at my router.

Not sure how to disable it on the phone - haven't found the option yet, probably buried several layers down in Settings.

[OneMoreFarang]

2 hours ago, doctormann said:

I thought that it might be a firewall issue but disabling the firewall on the laptop makes no difference.

PING sends a signal from computer A to computer B. 

This only works is it can be send out from A (firewall for outgoing traffic in A).

And this must be received by B (firewall for incoming traffic in B)

Then B must decide it wants to react to this request. It doesn't have to.

When B answers to the PING then that answers has to go though the outgoing firewall from B.

And then through the incoming firewall of A.

And in a public network there are some more firewalls.

 

Lots of possible opportunities why this might not work.

 

[doctormann]

5 minutes ago, OneMoreFarang said:

PING sends a signal from computer A to computer B. 

This only works is it can be send out from A (firewall for outgoing traffic in A).

And this must be received by B (firewall for incoming traffic in B)

Then B must decide it wants to react to this request. It doesn't have to.

When B answers to the PING then that answers has to go though the outgoing firewall from B.

And then through the incoming firewall of A.

And in a public network there are some more firewalls.

 

Lots of possible opportunities why this might not work.

 

I disabled my firewall but, as you say, there may be others on the route.

However, the strange thing is that I never had this problem with my A12 phone and the only thing that has changed is that I now have an A23 phone.  It does have a different IP address but appropriate entries have been made in the laptop firewall and router to accommodate this - but this may be irrelevant as the problem persists with the firewall disabled.  I think that the problem must be somewhere in the A23 Settings.

 

This is rather annoying but not critical.  I use SSH to transfer files from my phone to my laptop - or, at least, I did but this no longer works!  I can transfer using Bluetooth or as email attachments with no issues but this is far less convenient than SSH.  OK for the odd file but would be a right PITA for multiple files.

[OneMoreFarang]

1 minute ago, doctormann said:

I disabled my firewall but, as you say, there may be others on the route.

However, the strange thing is that I never had this problem with my A12 phone and the only thing that has changed is that I now have an A23 phone.  It does have a different IP address but appropriate entries have been made in the laptop firewall and router to accommodate this - but this may be irrelevant as the problem persists with the firewall disabled.  I think that the problem must be somewhere in the A23 Settings.

 

This is rather annoying but not critical.  I use SSH to transfer files from my phone to my laptop - or, at least, I did but this no longer works!  I can transfer using Bluetooth or as email attachments with no issues but this is far less convenient than SSH.  OK for the odd file but would be a right PITA for multiple files.

I would google for file transfer A23 or whatever you actually want to do.

A computer (including mobile phones) can be configured to allow file transfer but not allow (or not answer to) PING.

Obviously, you can play around with PING but even if PING works perfectly that doesn't solve your problem. And when you get file transfer working (maybe just a switch somewhere in the software of your phone) then PING might still not work. No problem. PING does not need to work. 

[gamb00ler]

9 hours ago, doctormann said:

I use SSH to transfer files from my phone to my laptop

Have you tried Google Drive for transferring files?  It requires twice as much copying of data over the network but is super simple.  I would assume there's a version of the Google Drive app for both Linux and Android.

[doctormann]

2 hours ago, gamb00ler said:

Have you tried Google Drive for transferring files?  It requires twice as much copying of data over the network but is super simple.  I would assume there's a version of the Google Drive app for both Linux and Android.

Thanks.  I'll take a look.

[doctormann]

OK folks, here's an update.

My problem is solved and the following info may be useful to anyone who has a similar issue.  It's all a bit convoluted and I still don't understand some of it but here goes.

 

Android 13, on the Samsung Galaxy A23, by default, randomizes the phone's MAC address - supposed to improve security.  This would be no problem unless your router is set to filter MAC addresses, as mine is.  Unless you disable this feature, every time that the phone reboots it presents a new MAC address to the router.  In my case, trying to PING the phone from my laptop, the phone could not be found as it was, effectively, not connected to the LAN.  What continues to puzzle me is that it could still get an internet connection.  This is weird!

 

Anyway, I disabled the random MAC feature, rejigged the router to use the phone's static MAC address and now everything seems to be OK.  Not only does PING work but I can now connect to the phone using SSH (needed to regenerate the Hosts file).  I like it this way as once the connection is made the phone just looks like another drive and I can transfer files with no problems.  A lot faster than Bluetooth or by email attachment.

 

So, maybe this will help someone.  If not, it has at least taught me something.