Pi 3B+ can not be seen via Wifi but can see web

[bill-orange]

Using the latest updated Raspien release with my shiny new B+, I have run into a problem. After a random number of hours of operation, the PI B+ is not reachable or pingable from other network computers. This is especially weird since, the offending PI can see other devices in the network and can see the internet. My other PIs and PCs do not have this problem. If I disconnect and reconnect WiFi the problem is resolved for a while. I have tried reducing processor and memory speed. It has made no difference. My power supplies meet mfg. recommendations.

I suspect that this issue may be some sort of adverse interaction with my UMBEE TimeWarner router. However, if this was exclusively a router problem, I would expect my PI Model Bs and PI zero Ws to also have this problem. I am running Raspian on two PI B+. Both have this problem.

Can anyone reproduce this problem? I found one other user on another forum with identical symptoms but that still leaves this as a pretty rare event.

[pelwell]

[ So this is a 3B+, and the problem is seen over WiFi? If so, please make the issue title more precise. ]

Are you saying that even while the Pi can ping out (and get replies, presumably), other devices (even ones it has pinged) can't ping it?

[bill-orange]

Will do. I will edit the post title once I am on a PC and not my phone.

Yes, this is a 3B+. You restated my problem correctly. It is very strange. As well as not being able to ping the offending PIs, I can not connect with VNC or see an apache2 default web page. All the while the PIs can ping other devices and show web pages such as CNN.com.

[JamesH65]

Fixed the title.

Note that the Pi3B+ has a new Wifi chip, although the kernel driver is the same, the underlying firmware will be different - so could well be a weird interaction specific to the new chip.

[P33M]

How are you resolving the Pi's IP? Hostname?

What happens if you try to ping the (known) IP address instead of trying to resolve the host?

[bill-orange]

I am pinging the IP address.

…

Sent from my iPhone

On Apr 20, 2018, at 8:39 AM, P33M ***@***.***> wrote: How are you resolving the Pi's IP? Hostname? What happens if you try to ping the (known) IP address instead of trying to resolve the host? — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub, or mute the thread.

[pelwell]

This is baffling.

1. Can you try continuously pinging the Pi from another device to see if that keeps the "link" up?
2. If 1 is successful, try pinging from a third device (if you have one) after what would have been long enough to expect a failure.
3. If 1 isn't successful (and you have a third device) try leaving both pinging simultaneously and see if they fail at the same time.

[JamesH65]

Bit of a long shot, but is the IP address on the Pi changing for some reason? Perhaps the interface going down and coming back with a different address?

…

On 20 April 2018 at 16:52, Phil Elwell ***@***.***> wrote: This is baffling. 1. Can you try continuously pinging the Pi from another device to see if that keeps the "link" up? 2. If 1 is successful, try pinging from a third device (if you have one) after what would have been long enough to expect a failure. 3. If 1 isn't successful (and you have a third device) try leaving both pinging simultaneously and see if they fail at the same time. — You are receiving this because you commented. Reply to this email directly, view it on GitHub <#2522 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ADqrHXe4iQ2DEJihZH-iK3uJUUeS5t7Tks5tqgRTgaJpZM4TdpCj> .

-- James Hughes Principal Software Engineer, Raspberry Pi (Trading) Ltd

[bill-orange]

I can try the two device test. Regarding test one, I wrote a shell script that pings the offending PI three times every five minutes and saves the result along with the time in a log file. When the failure happens the log entry goes from ‘3’ to ‘0’. After resetting the WiFi on the offending PI the log starts recording ‘3’ again.

I should be able to run the script on a spare PI Zero W and get two machines pinging away at it.

[bill-orange]

James, good thought, but the IP address is not changing.

[mkreisl]

@bill-orange
Having sometimes same problem here (@JamesH65 , @pelwell - don't panic, its not a Pi3B+ issue here 😁 )
Randomly I can not ping a device (it's not only a Pi, happens with all WLAN clients). So, going to the not responding device and ping from there the other other client - and voila, ping is working again. Probably WLAN router does not handle ARP packets correctly, but I can live with that.

Maybe you have same issue

[bill-orange]

Well, I have to admit that your problem is similar. In my situation the only way to restore ping-ability is to disconnect and reconnect WiFi or reboot. Even forcing a DHCP renewal does not do the trick. Also, in my situation only the PI 3B+ are affected. Bs and Zero Ws work fine.

Running this script every hour or so with chron keeps the PI 3B+ visiable

#!/bin/bash
sudo ifconfig wlan0 down
sudo ifconfig wlan0 up

Running this script every 5 minutes with chron check visibility.

#!/bin/bash
echo 'execute pinger script'
echo
count=$(ping -c 3 _address_of_3B+_| grep icmp | grep bytes | wc -l)
{
	echo $(date +%H:%M) ' Result of PING: ' $count
} 2>&1 | tee -a /home/pi/Public/logfile.log
exit

I agree that this does have something to do with ARP. I can not think of anything else that would cause a one directional problem.

[rodizio1]

I'd try looking at the traffic with wireshark/tshark/tcpdump and check if you can see ARP requests and replies.

Could this be power-saving/DTIM related maybe?