I'm trying to connect from a host (PC or other) to a mobile cellular Android device on the Verizon/AT&T cellular network. This device uses only the 3G network and has its Wi-Fi turned off. The Android device has a listening socket and I need the remote host to be the connection initiator. As far as I know, Verizon/AT&T uses NAT traversal for mobile phones and assigns local IP addresses to them on the cellular network. This prevents me from initiating a connection to the device from a remote host. Please correct me if I'm wrong about that.
With the usage of IPv6 assignments there shouldn't be any practical limitation (virtually unlimited) to the number of "real" IPs that can be assigned.
Therefore my questions are:
1. Does the Verizon/AT&T cellular network support IPv6 and assigns IPv6 addresses to capable Android devices?
2. Is it a feasible solution to this problem?
3. Does Android 2.2+ have enough support for IPv6 to implement such solution?
I am aware of other methods that can be used, such as C2DM, but they have some drawbacks (such as unknown response time) that prevent me from using them.
Thanks.
Verizon's LTE network supports IPv6 (see below). The phone is assigned a global-scope IPv6 address
Although there is no NAT with IPv6 I was not able to connect to a socket listener running on my phone, or ping6 the phone so there seems to be some kind of inbound filtering
The API has full support for IPv6 provided the underlying network interfaces supports it
You are assuming that the carrier, any carrier, not just Verizon, allows mobile terminated traffic flows. Regardless of address space, consider the impact on the network. If I had a defined IPv6 address prefix for a given gateway, let us say, 20001:5555:0000:1111/64, while it's a LOT of address space to scan, I could launch something akin to a DOS/DDOS attack. Granted, most of the addresses won't do anything, but one important thing to remember about mobile -- the actual IP transit is minor in cost. The RADIO SPECTRUM is precious. If you sweep a block of address space, and the carrier doesn't block it, you light up that gateway, and its spectrum.
In general, carriers don't allow unsolicited inbound traffic for this reason -- it's a lot of spectrum waste for no actual traffic.
Related
I have two Android KitKat phones, both are running WiFi-Direct groups as Group Owners, let's call them GO1 and GO2
I managed to connect GO1 as a legacy client to GO2 without breaking any of the (previously set) wifi-direct groups.
The problem is that, as you might know, the GO IP address is hardcoded in Android source, and is set to 192.168.49.1
Therefore, both of my devices, GO1 and GO2 have the same IP address (**)... each on his local network.
My app is both client and server at the same time. But both networks are using the same IP range (192.168.49.XXX), which, apparently, I cannot change.
As a result I cannot create a TCP connection between them if they are both hosting a WiFi-Direct Group, since any device will connect to itself when trying to connect to 192.168.49.1
So the questions are:
Is there a way to change the IP range used in Wifi-Direct?
Is there a way to use IPv6 instead of IPv4 in Wifi-Direct?
Can any of this be done without rooting the phone?
Any other suggestion?
** : Actually, because GO1 is connecting as a legacy client to GO2, then GO1 is known as 192.168.49.227 (for example) to GO2 and GO2 is known as 192.168.49.1 to GO1. But because GO1 is ALSO a GO, it also known as 192.168.49.1 to his clients (and itself).
A way to get around this without rooting the phone is to send your packets via multicast UDP*. These packets will make it from GO1 to GO2.
There are some side effects to this:
To use this for networking you must perform encapsulation and routing at the OSI Application level (not efficient).
You will also need to route based on MAC addresses since every device has the same 192.168.49.1 address.
"It is important to note that the multicast socket encapsulates a one-to-many unicast communication and, as a result of this, cannot fully utilize the total available WiFi and WiFi Direct bandwidth" *
Something else worth noting:
As you scale up the number of GOs, you will run into a problem of all nodes operating on the same wifi channel. This isn't a problem with a few devices, but with hundreds of devices, it will be a huge problem.
*This method was mentioned in Colin Funai, Cristiano Tapparello, and Wendi Heinzelman paper titled "Supporting Multi-hop Device-to-Device Networks Through WiFi Direct Multi-group Networking" found here: https://arxiv.org/pdf/1601.00028.pdf
There is no way to change the IP range because as you have correctly pointed out, it is hardcoded in the Android Wi-Fi Direct system service. Personally, I am not aware of IPv6 being enabled on the Wi-Fi P2P interface, and even if it was, it would likely be a hardcoded IPv6 address.
If GO1 and GO2, must be connected to each other whilst both in GO mode, then perhaps look at using Bluetooth or some other transport to allow them to communicate. If communication between GO1 and GO2 can be delayed, then cache whatever information is to be exchanged, and send it between these two devices when one can be the client of the other, e.g. when GO1 can stop being a GO and can be a client of GO2.
I have read these Getting Started with WiFi on Android. Implemented Marakana's tutorial for basic wifi functionalities.
But my question is: Is there a way to find the number of users connected to a wifi network?
If it can be done, kindly share a link or resources.
If it cant be done, kindly provide some detail, why not?
Thank you,
Getting a list of computers on a network is inherently an unreliable proposition, wifi or wired.
There are three common approaches: a discovery protocol, scanning, and passive listening.
Discovery protocols (such as LLDP from the UPnP framework) work very well for devices that support them. Occasionally also for devices that don't. They don't work at all if firewalls block them, or if switches or wifi access points are configured not to allow traffic between devices.
Scanning means, sending a probe (such as a ping) to each possible IP address. This is something many intrusion detection devices block, and many wifi access points will also prevent you from sending a ping to another device. Also, scanning is entirely unfeasible in IPv6 because each network has billions of IP addresses to probe, rather than the usual 254 in IPv4.
Passive listening means, simply paying attention to the layer-2 traffic on the network, and building a table of MAC addresses based on the ARP traffic (or all traffic). That only works reliably if you have a wired network with a hub - switches don't forward all layer 2 traffic everywhere (although the ARP messages you need most are usually broadcast and available). WiFi isolation may also prevent you from getting enough layer 2 traffic.
Here is my scenario.
I have my device (android phone).
And I know the IP address of another device (which is some remote device in the Internet)
So how do I send data to the other device?
Do I use protocols like Tcp or Udp?
EDIT : And I know there are public IP addresses and private IP addresses (like when a device connects via WiFi). In such a case is it even possible to use Tcp or Udp???
What you're looking to do is a common task with a common problem (but also with a common solution). You want to send data from one device (computer/phone/etc..) to another. Here's how it works behind the scenes:
There are a lot of computers in the world. Each computer is given an identity - a name, if you will, which is called the computer's IP address. There are many versions/standards of the IP address, and the current standard names an IP address as such: "111.222.333.444". There are only so many permutations with 12 digits of numbers - and entire ranges of IP addresses are reserved. In other words, there aren't enough IP addresses to go around for computers.
Now, routers were invented, among other reasons, to combat this problem. Routers give all computers within its local area network (LAN) one public (WAN) IP address. With an average of one router per household, this saves many IP addresses. Unfortunately, it also breaks direct communication between computers, because how does one communicate with three computers all using the same name? How does one identify computer A from computer B from computer C when they all share the same WAN IP address?
First, let's clarify that - just like there are a few versions and standards of IP addresses, so there are a few types of routers. By the way, it's not the router that is to blame for the problems of direct communication between computers - it's actually the router's underlying technology of network address translation (NAT). Anyways, there are a few types of NAT, and although information on the internet is relatively scarce on these types, you can still Wikipedia it and read a few university research papers. The types are Full Cone NAT, Restricted NAT, Port Restricted NAT, and Symmetric NAT.
So, computers in a LAN share the same WAN IP. This is a problem. What's one solution? What if we instructed the router to route all incoming traffic directed to a certain port, to a certain computer in our local area network? For example, if three LAN computers share the WAN IP of 1.1.1.1, we can setup a procedure called port forwarding to instruct the router to route all packets arriving on port 6000 to 192.168.1.101:3500.
uPnP is just a fancy technology (not always present in routers - or more importantly, hardly ever enabled by default) that allows you to port forward using code.
If we can't use uPnP to port forward because not all devices have it enabled, there must be another solution - and there is: hole punching.
Hole punching comes in two flavors: UDP and TCP, although TCP hole punching is a bit more complicated because TCP is inherently first a connection-oriented protocol. UDP hole punching is easier because you can send packets without a connection (in fact, is there really such a thing as a connection?)
You can read the procedure on UDP hole punching on Wikipedia and other sites. The concept works like this, though. Any computer sending an outbound packet will expect a reply, meaning the router will allow the inbound packet's reply. At first, two computers will not expect a reply from each other, so the first packet each computer sends will be rejected by the router. If we continue sending packets, however, the router will allow the rest of the packets to come through, because a reply is expected from each computer. As long as this hole-punched connection is maintained active by occasional keep-alive packets, it will stay alive. Unfortunately, this method of UDP hole punching is unsuccessful for Symmetric NATs (explained in the links below). That's why the end-all solution is to simply proxy the connection and traffic through your own server. This requires a farm of computers, so it's quite costly. But this end-all solution is called TURN. STUN is a web service you can query to determine your NAT type and public IP (as opposed to parsing cmyip.com). Just some terms you'll encounter along your personal research.
Playing around with these concepts help. Here are some resources to get your started:
Types of NATs: http://think-like-a-computer.com/2011/09/16/types-of-nat/
A Method for Symmetric NAT Traversal (basically by spamming a lot more packets to a lot more ports): http://www.goto.info.waseda.ac.jp/~wei/file/wei-apan-v10.pdf
Lidgren Networking Library (which has NAT traversal built-in, this is a C# library): http://code.google.com/p/lidgren-network-gen3/w/list
In most realistic cases, you send data to the other device by sending the data to an intermediate device from which the other phone picks it up. Can can use protocols like TCP or UDP directly between the two devices, and that may or may not work depending on the protocols and how the devices are getting Internet access.
For example, one device can send an email and the other device can retrieve that email. You can generalize that model to other types of communication.
I am implementing a mobile chat application, I am using socket connection for implementing p2p connectivity. My chat is working fine with android devices. My issue is I can connect a device in 3g network or with in the same WiFi network but the connection is not working when a device form outside WiFi try to connect a device in the WiFi network. I know it's because of the local IP of the device assigned by the WiFi. How can I root and connect a device in the WiFi?
Sounds more like a router settings issue, than an app issue (meaning that users of your app would need to do this for their own networks as well).
Your wifi router needs to know how to forward communication to your device. So say that your app is connecting on port 1234, then you need to tell your router to forward communication from the outside on port 1234 to the internal IP of your phone in your wifi network.
The phone that is outside of the network should target your network's external IP and port 1234.
Sajan, your issue is not only an IP mapping issue, but also a NAT traversal issue. It is not always possible to punch holes in NATs. And when it is, it must be done with some sophisticated techniques including a super peer located outside of your wifi/lan which will read the translated address from your inside peer.
Unless you are using UDP and the NAT is friendly, it is not possible to send TCP communication directly to the inside peer. In most case, you'll have to check what is possible with the NAT, and if there is something possible, you'll need to perform mapping prediction and tell both peer to attempt com on predicted IP addresses.
That's valid if you don't want you users to have to configure their NATs. And even in that case, such configuration will not always be enough (if there are cascades of NATs, or proxies for example).
I am trying to make an application which can connect from a mobile to a wifi controller. Planning to do a socket connection(multicast) ... The only values that i am able to get through the wifi android apis are SSID and BSSID.. Can anyone tell me if i am supposed to proceed with these values or am i supposed to connect with an IP address ? If i am supposed to connect with BSSID.. how do i go about it?
Wifi access points need not have an IP address, any more than wired switches and hubs do. However a large number do, as they also act on the IP layer as DHCP servers and network gateways.
What exactly are you trying to do? It sounds likely that it is not the Wifi access point proper that you need to talk to.
If it supports TCP and UDP, it will of course have an IP address. This will not be directly discoverable from the Wifi APIs, and you'll need some other means of discovering that. It's hard to say what exactly will be a reasonable method to do this without knowing what the AP is, and what services it provides.
Common ways of enumerating services provided on a network include DHCP; multicast DNS/DNS service discovery which is used by "Bonjour" and "Zeroconf"), SSDP and uPnP, and of course static configuration.
I'm not familiar enough with the Android network APIs to recommend anything, though http://jmdns.sourceforge.net/ appears to be a usable Java multicast DNS library.