On 17/04/18 09:32, Long Wind wrote:
i have 2 PCs connected to a cell phoneone thru USB line, IP=192.168.42.131the 
other thru WLAN hot spot, IP=192.168.43.201
but the 2 can't talk to each other directly(i can't ping from one PC to the 
other)how to make that happen? Thanks!


Is the phone also connected to the WLAN hot spot or via a cellular data service? What is the netmask of your WLAN? Do you administer the hot spot? Is it an ADSL WiFi router?

Both addresses look like RFC 1918 private network addresses <https://tools.ietf.org/html/rfc1918> <https://en.wikipedia.org/wiki/Reserved_IP_addresses>. 192.168.42.x is what I see when I tether my computer to my Android phone via USB. The phone is then acting as a NAT for the connected computer. The problem is that 192.168.42.131 is not the IP address of the phone, and incoming connections will not be forwarded to the phone-connected computer.

If your phone is connected to the WLAN hot spot, you should be able to make outgoing connections from the phone-connected PC to the WLAN-connected PC. You will not be able to make connections from the WLAN-connected PC to the phone-connected PC because it is behind a NAT (the phone). I do not know if an Android phone can be configured to forward incoming connections to the connected PC.

If your phone is connected to a cellular data service, then it is on the public internet and cannot connect to the private IP address 192.168.43.201. Instead, if you administer the hot spot (e.g. and ADSL WiFi router), configure your WiFi router to forward incoming connections from your public IP address (e.g. one assigned by your ISP for your broadband connection) to a port on the PC at 192.168.43.201. Now you should be able to connect from your phone-connected PC to your WLAN-connected PC via your router public IP address. If your router has not been assigned a static IP address by your ISP, you may want to investigate Dynamic DNS because your router IP address may change whenever it reconnects.

Ping may not work across networks because many services filter it.

There are other solutions including a VPN which tunnels connections between a PC and a server on the public internet.

Kind regards,

--
Ben Caradoc-Davies <b...@transient.nz>
Director
Transient Software Limited <https://transient.nz/>
New Zealand

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