Troubleshooting WireGuard connections

[Riccardo Berto]

On 2018-04-20 22:31, Riccardo Berto wrote:
> On 2018-04-20 21:51, Jason A. Donenfeld wrote:
>> Could you let me know which kernel the non-working rapsis are running?
>> Also, have you tried this over different internet connections and
>> experienced the same thing?
> 
> I haven't tried this under different internet connection but one thing
> I must add is that the laptop is under the same local network of the
> raspberrys, they have the same gateway and the laptop works in 100% of
> the cases I tried it, both while pinging from the raspberrys and not.
> 
> Parallel execution on the raspberry of `tcpdump -vv -ni eth0 'port
> 51820'` while pinging the server:
> 
> 22:26:50.084184 IP (tos 0x88, ttl 64, id 45462, offset 0, flags
> [none], proto UDP (17), length 176)
>     192.168.1.155.51820 > server-ip.51820: [bad udp cksum 0xf657 ->
> 0xb3e7!] UDP, length 148
> 22:26:50.186665 IP (tos 0x0, ttl 48, id 31466, offset 0, flags [none],
> proto UDP (17), length 120)
>     server-ip.51820 > 192.168.1.155.51820: [udp sum ok] UDP, length 92
> 22:26:50.187667 IP (tos 0x0, ttl 64, id 45466, offset 0, flags [none],
> proto UDP (17), length 156)
>     192.168.1.155.51820 > server-ip.51820: [bad udp cksum 0xf643 ->
> 0x0316!] UDP, length 128
> 22:26:51.098777 IP (tos 0x0, ttl 64, id 45520, offset 0, flags [none],
> proto UDP (17), length 156)
>     192.168.1.155.51820 > server-ip.51820: [bad udp cksum 0xf643 ->
> 0x6049!] UDP, length 128
> 22:26:52.138753 IP (tos 0x0, ttl 64, id 45595, offset 0, flags [none],
> proto UDP (17), length 156)
>     192.168.1.155.51820 > server-ip.51820: [bad udp cksum 0xf643 ->
> 0x5608!] UDP, length 128
> 22:26:53.178751 IP (tos 0x0, ttl 64, id 45691, offset 0, flags [none],
> proto UDP (17), length 156)
>     192.168.1.155.51820 > server-ip.51820: [bad udp cksum 0xf643 ->
> 0x7eb3!] UDP, length 128
> 22:26:54.218760 IP (tos 0x0, ttl 64, id 45734, offset 0, flags [none],
> proto UDP (17), length 156)
>     192.168.1.155.51820 > server-ip.51820: [bad udp cksum 0xf643 ->
> 0x240c!] UDP, length 128
> 22:27:05.259544 IP (tos 0x88, ttl 64, id 46342, offset 0, flags
> [none], proto UDP (17), length 176)
>     192.168.1.155.51820 > server-ip.51820: [bad udp cksum 0xf657 ->
> 0x5a78!] UDP, length 148
> 22:27:05.359976 IP (tos 0x0, ttl 48, id 33703, offset 0, flags [none],
> proto UDP (17), length 120)
>     server-ip.51820 > 192.168.1.155.51820: [udp sum ok] UDP, length 92
> 22:27:05.360960 IP (tos 0x0, ttl 64, id 46348, offset 0, flags [none],
> proto UDP (17), length 60)
>     192.168.1.155.51820 > server-ip.51820: [bad udp cksum 0xf5e3 ->
> 0x7f66!] UDP, length 32
> 
> 192.168.1.155 listed there is the static IP address of the raspberry
> pi in my local network.
> 
> Raspberry is running archlinuxarm with kernel: "Linux rpi3-two
> 4.14.34-1-ARCH #1 SMP Mon Apr 16 19:15:19 UTC 2018 armv7l GNU/Linux"

I tried the RPis with another connection and they worked briefly but 
most of the time they don't respond. I configured another laptop under 
the same other network connection and everything works seamlessly. It 
seems that the RPis just don't like WireGuard. I might have some network 
misconfiguration on them but I really can't figure it out.