I have a Macbook and an Android device (Oneplus phone) on same network and the Macbook connects via USB LAN (or Wi-Fi), Android device via Wi-Fi. I detected the following anomaly:
- I can ping the Oneplus from the Mac:
64 bytes from 192.168.1.127: icmp_seq=3 ttl=64 time=30.433 ms --- 192.168.1.127 ping statistics --- 4 packets transmitted, 4 packets received, 0.0% packet loss
- I can ping the router from the Oneplus
- However I cannot ping the IPv4 address of the Mac
- I took a look at the traffic in Wireshark and I got the "host unreachable" message to the ICMP requests
- I also started to host a simple HTTP server, but it seems the Mac does not response to the TCP SYN segments, because I could see RTO flagged segments (Retransmission Timeout). (3-Way handshake never completed)
- Fan fact, recently my ISP started issuing IPv6 addresses and I tried to ping the Mac from the Oneplus:
--- 2001:*:*:*:*:*:*:7e50 ping statistics --- 4 packets transmitted, 4 received, 0% packet loss, time 3005ms rtt min/avg/max/mdev = 6.737/33.397/108.664/43.467 ms
It was working as the above log shows.
Mac's firewall is disabled and there is no firewall rule applied in the router. I removed all network interface under the System Preferences / Network menu and added them again.
I also selected the Link-local only option at the System Preferences / Network / interface / Advanced / TCP/IP / IPv6 Configuration tab. Unfortunately none of them worked.
My question is why did IPv6 ping work and IPv4 not? Could be the problem the recently introduced IPv6 addresses?
I created a Hotspot with my iPhone and connected with both of the Mac and the Oneplus. This Hotspot does not have any IPv6 configuration, but I experienced the same issue.
I also created a Hotspot with my Mac to eliminate the router from the circle and I connected to it with the Oneplus. Like every time, I could not ping the Mac, despite the Oneplus gets IP address via DHCP from the Mac. (So there was network traffic)