Electronics > Beginners
Raspberry PI networking issue - no response to ARP requests
paulca:
So I have a couple of PIs on my network. One of which receives data from various nodes.
Twice now I have caught it in a state where I can ping it and I can ssh to it and it's alive and working, but nothing else can see it.
Hub: 10.0.0.3
Probe: 10.0.0.101
I can log into both from my desktop. However 101 cannot ping 3. I checked with TCPDump from 101 and I see it constantly broadcasting for the hw address of 3, but nothing answers it.
15:56:56.478274 ARP, Request who-has 10.0.0.3 tell 10.0.0.101, length 28
15:56:57.518252 ARP, Request who-has 10.0.0.3 tell 10.0.0.101, length 28
15:57:02.315659 ARP, Request who-has 10.0.0.3 tell 10.0.0.101, length 28
15:57:03.358279 ARP, Request who-has 10.0.0.3 tell 10.0.0.101, length 28
I have found similar, related issues around the web, but no real solution.
I thought I'd ask the wealth of intelligent people in here who may be using RPIs before I resort to more brute force methods of static arp tables or keep alives.
Note, the PIs are on Wifi, my desktop is wired. If I reboot the Wifi router everything is fine again for another while.
madires:
--- Quote from: paulca on January 21, 2018, 04:08:48 pm ---Note, the PIs are on Wifi, my desktop is wired. If I reboot the Wifi router everything is fine again for another while.
--- End quote ---
Try another WiFi router ;)
WaveyDipole:
Since you can 'see' both from your desktop, it would seem unlikely that this is down to the WiFi dropping out.
What netmask do you have set at each end? Are all devices set to the same netmask? And is it the same on the router?
Do all devices have the same gateway address set (i.e. the router)?
paulca:
--- Quote from: WaveyDipole on January 22, 2018, 04:59:40 pm ---Since you can 'see' both from your desktop, it would seem unlikely that this is down to the WiFi dropping out.
What netmask do you have set at each end? Are all devices set to the same netmask? And is it the same on the router?
Do all devices have the same gateway address set (i.e. the router)?
--- End quote ---
I agree. Netmask, is 255.255.255.0 on all of them. They all use the same router. It's a straight flat single subnet network.
It has something to do with either the Wifi on 101 not sending ARP broadcast, 3 not receiving them or more likely that 101 does not receive the ARP responses. At that time, my desktop, 199 had an arp entry and could have responded, but didn't.
When it happens again I will do some more diagnostics on other hosts to see if the arps are getting out of the PI.
There are quite a few references to this being an issue, particularly on PI 2s. I might have to upgrade it. Unfortunately the different threads on the issues are quite ranging and hard to determine if there is or is not an under lying problem or what exactly it is. Nor did I find a solution after reading about 4 different threads.
WaveyDipole:
Does .3 have iptables or a firewall running on it? If so, it may be blocking requests?
You say that .101 cannot ping .3. Can .3 ping .101?
Can both of them ping the router?
Can the router (assuming it has a ping facility) ping both .3 and .101?
Navigation
[0] Message Index
[#] Next page
Go to full version