The Samsung Galaxy S3 is the most frustrating phone I've ever owned!

I too have severe connection problems with the Galaxy S3 even with AirDroid, on CentOS.

Can someone make sense of WHY AirDroid is not on the local subnet?

Here's what happens:

1. I have no data plan so I turn on WiFi on the Galaxy S3
2. My home has a static IP address - lets call it 55.55.55.55
3. I have a home broadband router which is on 192.168.1.1
4. My Centos PC is handed a DHCP IP address by that router: 192.168.1.2
5. AirDroid on the Samsung Galaxy S3 says to connect to 192.168.1.3:8888
6. But the PC web browser times out pointed to 192.168.1.3:8888
7. Whatismyipaddress reports the Galaxy IP address of 55.55.55.55

I don't know wifi or Linux well enough to figure out how to overcome the debilitating fact that AirDroid doesn't realize the Android phone is actually on my public IP address 55.55.55.55 while the CentOS PC is on 192.168.1.2 which is a private IP address.

It wouldn't be so frustrating if the USB cable connection would work but there are long threads on why you can't connect the Samsung Galaxy S3 to Centos in either MTP or PTP mode (MTP never worked and PTP just simply stopped working).

Anybody have expertise on how to solve this dilemma?

Note: If you don't have the Samsung Galaxy S3, your results will differ and if you're not on a RHEL-based Linux, your results will be different. So really what I am asking is whether there is anyone out there with a Samsung Galaxy S3 *and* Centos/RHEL6 who has been able to transfer camera data from the phone to the PC?

If so, you're a genius - and I'd like to know *how* you did it!

What do you mean "my home". Do you mean that is the address of your modem (Adsl or cable?)

I assume that is the internal address-- the address on the internal network.

Fine.

I do not know AirDroid, but is the Galaxy given the IP of 192.168.1.3 by dhcp on the network? If not then no wonder it cannot connect.

And if you do ping 192.168.1.3 what happens on your PC?

That is NOT the address of your phone. That is the address of your modem/router. It does ( MUST DO) IP translating because the 192.168 addresses are unroutable on the outside net ( or rather all routers throw them away if they come off the outside net). Thus to the outside world it looks as if the stuff is coming from 55.55.55.55 but that is because that address has translated the actual address with high port number.

I do not know what AirDroid runs on. If it runs on an outside machine (ie not on a machine directly connected to your internal network with an address of 192.168.x.x) then you will have to tell your router to do port forwarding. As far as your samsung is concerned its address IS

192.168.1.3 It knows nothing else, and will only respond to packets sent to that address. port forwarding works by the router receiving a packet on say 55.55.55.55:8888 and forwarding it on the internal network to 192.168.1.3:8888 But youhave to set that up ON THE ROUTER. Not on the phone, or the centos, but on the router.

And all of those issues ae completely generic to computers in general, not the S3, Centos, or whatever. they also apply to Windows or Mac machines.

Except of course the questions you are asking look to me to be quite generic and are primarily related to your confusion about how networking works and NAT (Network address translation) works, and port forwarding works.

I don't have a modem but yes, the external Internet comes over to my house via a wireless ISP (aka WISP), and what you call a modem is my radio and antenna on the roof (i.e., a transmitter receiver).

So, if we call that transmitter receiver a modulator demodulator (which is what it is), then, yes, my "modem" has a single wire coming out which is a public static IP address (let's call that

55.55.55.55).

That 55.55.55.55 wire goes into my home broadband router, which then has 4 output ports and antennas which feed my house with the local subnet (192.168.1.x).

This router hands out IP addresses (first come first serve), using DHCP, so, the router holds on to 192.168.1.1, and hands out

192.168.1.2 to the computer, and then 192.168.1.3 (or whatever the next IP address is that is available) to the cellphone.

That cellphone (Samsung Galaxy S3) won't connect by USB cable so I'm trying to get AirDroid2 to do that connection for me.

AirDroid2 used to work, and I do not know what has changed in the interim, but, now, it won't connect.

When I debug, I see that my cellphone is on the public subnet when I bring up a web browser and point to http://whatismyipaddress but so does the PC. So, maybe that is *not* the problem.

But then, what *is* the problem?

Well, I must admit, the strangest thing happens.

I am *certain* that the cellphone is on the home network simply because I can easily get to

and that web site accurately reports my public IP address (e.g., 55.55.55.55). I can also access any other web site on the net (and I do *not* have a data plan).

But ...

From the PC (which is on the local network and which also reports

55.55.55.55 when I go to the whatismyipaddress web site), when I ping the IP address that AirDroid2 is asking me to connect to, the ping reports "Request timed out".

$ ping 192.168.1.3 (connection times out) $ ping 55.55.55.55 (works just fine)

So, maybe you're on to something here. Maybe, just maybe, AirDroid2 *thinks* it's on 192.168.1.3, but, maybe it's not on 192.168.1.3?

How could I tell from the Samsung Galaxy S3 or from Linux?

Is that the actual address? Some routers support both wired and wireless connections, but either have them on different subnets (eg wired on 192.168.1.*, but wireless on 192.168.2.*, with the netmask set to a /24, or will have specific options in the config to hide wireless connections from each other, or from the wired connections.

I wish there was a standard for router configuration setups, but there isn't, so check every page available in the router config.

Regards, Dave Hodgins

It is also possible that your phone has disabled ping responses to it. You could log into your router and see what addresses it has handed out via dhcp. You could ping your computer from the cell phone (I think it has a ping test on it somewhere). You could use the phone to try to connect to your computer. You could do as root arp -a on your computer and see if you can see your phone at 192.168.1.3 (it will list that address and tell you the mac address of your phone).

You are trying to connect from Airdroid from where? On your other PC? On the airdroid.com site? You could try on your PC doing telnet 192.168.1.3 -p 8888 and see it gets any connection. (then hit ^[ and type quit to get out of it)

IF you are trying to connect to your phone from airdroid.com, then you must set up port forwarding on your router.

>

Go to the router's control interface. If it's a normal home-user router, there will almost certainly be a 'web page' you can go to using your computer's web browser, with the address http://192.168.1.1 (or possibly https://...). You may need to have a wired (ethernet) connection between the computer and router to access that, as a security measure. You will probably also need the router's admin login details to be able to see or change its settings.

From the router's control interface, look for such things as 'security' or 'firewall' to see if anything is stopping local devices (with 192.168.1.x addresses) from communicating with each other.

On your computer, check the security or firewall settings to see if there is anything there restricting contact between the computer and other devices on the local network. The CentOS web site seems to offer a lot of information and support, if you need specific help.

Well, the actual address changes depending on what other devices are on the network at the time the Samsung Galaxy S3 goes on the network.

At the moment, AirDroid2 is trying to connect to: http://192/168.1.8:8888

But, a ping to 192.168.1.8 times out.

Yet, that Samsung Galaxy S3 cellphone is definitely on the local subnet (as the data is turned off and I don't have a data plan so I have data blocked).

Googling for how to ping computer from cellphone, I found it's a common problem that users can't ping the phone on the IP address that AirDroid2 thinks it's on:

I realized, after reading that, that Kies Air also won't work (and it chooses the same IP address, only with a different port).

So, I think the phone has a firewall somehow that isn't letting anything in.

I just now installed WiFi File Transfer, and it also picked the same IP address, and yet another port, but of course, that didn't work.

So, I think it's the phone firewall (whatever that is) blocking everything.

Well that was interesting.

I installed "iMobile Apps" Ping onto the Samsung Galaxy S3 and then pinged the following:

1. formatting link
   (74.125.128.105) ===> worked
2. dns server 8.8.8.8 ===> worked
3. localhost (127.0.0.1) ===> worked
4. router (192.168.1.1) ===> timed out
5. laptop (192.168.1.2) ===> timed out
6. modem radio card, 55.55.55.55) ==> worked
7. modem ethernet card, 55.55.55.54) ==> worked

So, clearly, the problem lies somewhere on the connection to the internal subnet (192.168.1.x).

This is perplexing because the external Internet works fine from the phone, which means the phone *must* be "talking" just fine through the home broadband router and then to the radio and antenna on the roof to the Internet.

But, if the phone is working fine on the Internet, why can't it ping its own intranet?

I guess I need an Android app that debugs the wireless WiFi connection from the phone to the home broadband router.

Eddie Powalski has written on 7/25/2013 12:36 PM:

Try installing Fing on your S3 and see what is on your network.

As I said, unless you set up port forwarding on your router, it will NOT be able to get through via that external address. You need to log onto your router and tell it that if it gets a request for port 8888 on

55.55.55.55 it is to send those packets to 192.168.1.8 (or whatever the address is of your phone).

Again, same issue.

NONONONONO You are not reading what I write. It does not have a firewall. It is just that the address the packets are sent to are NOT the address of your phone but of your router.

Did you try doing arp -a on your Centos machine? Did you look for the address of the phone? etc.

Or centos and the router have both got ping reply switched off. That is quite a common situation nowadays.

It is talking to the router. The router may also be blocking all ping requests going from the wireless to the wired network.

Because the ping reply switched off, of the router is roiting the ping requests?

Nope. You have your Centos machine. Lots of programs on that to help you. Also your router has lots of internal stuff to help you debug.

...

What *IS* the IP address that the Phone has been allocated by the DHCP?

I don't has an S3, but I have an Ace and I suspect it will not be much dissimilar to the S3 with regard to settings. I have my Ace connected to my wifi router and if I go to the WIFI settings (Setting->Wireless and networks->Wi-Fi settings), and "click" on the network to which I'm connected (in the "Wi-Fi networks" list, labelled as "Connected") it comes back with:

------------------------- | (i) | |-----------------------| | Status Connected | | Security ... | | Signal Strength Good | | Link Speed ... | | IP Address 192... | |-----------------------| | [ Forget ] [ Cancel ] |

-------------------------

Is the IP address that your phone knows (thinks) it has 192.168.1.3?

Whatismyipaddress is looking at the ipaddress that it received from your router which did a NAT (Network Address Translation) from the non-routeable 192.168... network (ip addresses) to its own IP address. If you check the settings on your PC you'll find it also has (should have) a 192.168.1... address.

It isn't...see the above about checking the IP address for your phone.

If the data is on a micro SD card, get a USB micro SD card holder and use that to plug the card as a memory stick into the computer?

Are you firewalled out?

whatismyipaddress can only see your (single) public IP address.

If you want to transfer photos and other data between your PC and your Samsung S3, can I recommend an alternative solution that works for me and my Nexus4?

Install Lyesoft's "AndFTP" to the S3 (the free version works well). Use that to connect to your PC via your local network. Ignore your 55.55.55.55 address completely. SSH should be installed on your RHEL box but if you don't mind passwords being passed across your internal network in the clear you can get very much faster transfers with plain old FTP.

Chris

I like TotalCommander and its LAN plugin for file transfers between PC and my S3 on my home network.

If you have Windows, I'm sure it's great. The OP indicated otherwise, though, and although TotalCommander has FTP it doesn't appear to have SFTP/SCP.

I wasn't intending to start a "my app's better than yours", so any suggestions I'm sure would be appreciated.

Chris

If you point your PC Web browser to web.airdroid.com there will be a QR code presented. Open Airdroid on the Galaxy, and click on the camera icon, and let the Galaxy scan the QR code.