macOS High Sierra同网Ping不通故障求助：设备不可见丢包100%

Let me start by aligning with your situation: you're facing full packet loss when pinging your macOS High Sierra laptop over the local network, confirmed the router isn't the root cause via direct ethernet testing, and already exhausted standard fixes—disabling the firewall, running CleanMyMac maintenance, turning off third-party launch agents/daemons, even reinstalling the OS—with no luck.

Since the usual steps haven't resolved the issue, let's dive into less obvious, deeper-level troubleshooting:

• Audit network interface configurations
  Fire up Terminal and run ifconfig to list all active network interfaces. Look for red flags like mismatched subnet masks, duplicate IP addresses, or interfaces stuck in an unresponsive state. If both Wi-Fi and ethernet are active, try disabling one temporarily to eliminate conflicts. You can also verify your laptop's IP assignment with ipconfig getifaddr en0 (replace en0 with your active interface ID if needed).

• Inspect incoming ICMP traffic with tcpdump
  Instead of relying solely on ping, run sudo tcpdump icmp on your laptop while another device attempts to ping it. This will show if ICMP packets are even reaching the laptop. If packets arrive but no response is sent, it points to a low-level network stack issue rather than a routing problem.

• Check for hidden kernel-level filtering
  Even with the built-in firewall disabled, third-party kernel extensions (kexts) might be blocking traffic. List non-Apple kexts with kextstat | grep -v com.apple. If you see any related to security or networking, temporarily unload them with sudo kextunload -b <bundle-id> (make sure to note the IDs so you can reload them later).

• Validate ARP table entries
  On the device you're pinging from, run arp -a to check if your laptop's MAC address is correctly mapped to its IP. If it's missing or incorrect, clear the ARP cache with sudo arp -d <laptop-ip> then try pinging again. You can also check the ARP table on your laptop to ensure it recognizes the pinging device.

• Test in Safe Mode
  You disabled launch agents/daemons, but Safe Mode goes further—it disables all non-essential system components and uses only Apple-provided drivers. Boot your laptop into Safe Mode (hold Shift during startup) and test the ping again. If it works here, there's a hidden background component you missed in your earlier cleanup.

• Rule out hardware faults
  Since the router is cleared, consider a potential issue with the laptop's network adapter. Try a different ethernet cable (if using wired) or connect to a completely separate network (like a mobile hotspot). If the problem persists across networks, the adapter itself might be faulty.

These steps target system-level and hardware-related issues that standard troubleshooting often overlooks. Let me know if any of these lead to a breakthrough!

内容的提问来源于stack exchange，提问作者Oleg Fedoriaka