I am trying to send data using the AsyncUDPSocket class. And I can send data using the iPhone simulator over the wire to another machine that is running a simple C-coded listening server. I can also receive data over the wire using a client connected to the simulator(server). However, when I tried the same over Wifi, using the simulator, I could only send data but not receive any data.
I read on another post, that unicast data makes this possible. How can I acheive this using AsyncUDPSocket?
Thanks,
Angelo.
Ok, I figured this out. A newbie kind of thing, really.
When I set my Mac network preferences to Ethernet, I get an IP for me to communicate. However, when I turn Airport(Wi-Fi for more newbies) ON, and ethernet cable disconnected, I checked my network preferences, and sure enough my IP address was a different one.
Spoke to a friend (an ace in networking) and the thing clicked immediately: On WiFi networks a DHCP server allocates an IP address. This IP address has to be reserved, at the very least, at the DHCP server. Since my IP was not reserved, I had to change the IP address, in my udp_client.c file, recompile and run the client to connect.
BTW, I can now communicate between my iPhone and my PC using my local WiFi (office) network.
For any who might face the same problem, do not be assured that the IP address of your mchine is the same, when you switch from LAN to Wifi, and use the device mostly for WiFi reated testing. :)
Related
I basically have used the ethernet connection successfully with Microcontrollers to control real world aspects,The dilemma is of IP address I mean how can 192.168.0.155 be accessed from around the world without any specific MAC ID attached to it, I wanted to implement the same networking usage with a GSM module eliinating wires but that doesn't have MAC addressing so TCP connection from it towards a IP client won't reach?
I am not sure how you did your 'real world control' with Ethernet before, but the MAC address does not 'live' past the next recipient (which means after the next switch) so do not use it for anything.
Your 192.168.x.x address is private, so it will never appear beyond your internet gateway (i.e. your GSM modem if you used GPRS), and it cannot be used directly for anything on the internet. It is not easy to briefly explain here how the internet routing works, but you should either use port forwarding towards your private IP address given to you by hour DHCP server (in which you have to initiate request from the client so that other side would not the IP address and the port), or you have to either have fixed public IP address or you could use some dynamic DNS service (like http://www.noip.com/), or you can update data from the client on some server over which you have control (like if you updated data manually from your PC).
All summed up, it is not very clear what you are trying to achieve, but I would say you need to check out some things about internet routing before you proceed.
Good Day,
I basically have a laptop connected to the internet with a fixed IP Address. I need to have a way for a server possibly though a PHP script, send data/string to the laptop and it is able to receive it.
Now, if I was within a local network, i could do that. But what if I wanted to send from an external network? Do devices have a particular address that I can access from any internet connection?
Do devices have a particular address that I can access from any
internet connection?
No, it does not, unless you do use external IP for your laptop (doubtfully).
The easiest and fastest solution I could think of is to do the other way round: open TCP or UDP socket on your server and use laptop to connect and request data from the server. Of course, it is not suitable for all scenarios, but in many cases it works. Write more information (what is the purpose of this? What are the requirements and limitations?) so more specific answer may be provided.
OK, to make things easier to explain, let's say:
- Your router's public IP address is 10.10.10.10
- Your laptop's private IP address is 192.168.0.1
- You want to communicate via port 80 (since you mentioned PHP)
What you need to do is configure your router so that it forwards packets destined to 10.10.10.10:80 to 192.168.0.1:80. This is the simplest form of NAT.
Then from anywhere else with an Internet connection, you can send packets to your laptop by sending packets to 10.10.10.10:80.
I am trying to configure my laptop to be able to Wake On LAN via Magic Packets. I have a magic packet sniffer and it alerts me when a magic packet has been recieved(runs on target machine). The trouble is when I try to use the external ip address instead of the internal address. I have port forwarded port 9 to my internal ip(10.0.0.x, NOTE: x is only one digit). If I use the internal ip address, it tells me that a magic packet has been received. If I try the external ip address and sending from the target machine(to itself) it receives the magic packet. If I send it through a different machine or a website, it does not work. I am connected via ethernet cable(CAT 5). I also have the "Wake on LAN" setting in my BIOS set to "ENABLED". Also, my computer is set to "Allow this device to wake the computer". Am I doing something wrong?
P.S.
The solution to the previous problem was to start the Simple TCP/IP Service in Windows.
To use Wake on LAN across the internet (=> wake on WAN), you must do one of these things :
Edit your router's ARP table so it can forward the magic pack to the target computer with its MAC address
Port forward to LAN broadcast address so the target computer will always receive any magic packet sent to your router until it is plugged to the router
Buy a router with a built-in wake on lan feature (like DD-WRT open source firmware)
Use a magic packet repeater to forward magic packets to the broadcast address. This one should be always powered on
I'm using the fourth option to wake my home computer from my work. I bought an Arduino Uno + Ethernet shield and wrote a little program to do the job (forward magic packet). I set a port forward rule into my router (Netgear DG834G) to forward UDP 9 to the Arduino IP address.
I wrote a tutorial about this on my personal website, it's in French but code is universal ^^ : http://www.finalclap.com/tuto/arduino-wake-on-lan-repeater-80/
I did some more research and it turns out that unless the router itself has a built in management and can be accessed publicly, WoL will not work behind a router. WoL will work however if you have a device already inside the network send the magic packet to the target machine. THat completely destroys the point of WoL!
Im not too sure why this wont work. My application works fine if the client and server are ran on the same PC hence the 127.0.0.1 but it wont connect to my other laptop using IP 82.41.108.125 which is the IP of that device.
Any reason why this is happening?
Your firewall could quite possibly be blocking the port assuming all of your coding is working fine - try opening up the port number you're running the application on (in the client/server comptuers' firewall options).
Some additional information that should shed some light on things
Networked devices use ARP (Address Resolution Protocol) and RARP (Reverse Address Resolution Protocol) to map IPs to link layer (MAC) addresses and back. Your network interface card (the thing that plugs into your ethernet cable) will have a unique MAC address on both computers. Each PC has an IP configured for it which is used by higher level protocols (those in the Network Layer).
Computer A will know computer B's IP address (and it will be different from computer A's) if your program works correctly. When computer A goes to send to comptuer B, assuming they're directly connected and not going through a router or something in between, computer A's link layer will need to translate that IP for comptuer B into a MAC address it can use. It does this by sending out a broadcast to all network PCs on the same sub network asking "Hey, is this your IP!?" essentially. The one that has an IP matching the broadcasted one yes, "Yes, it's mine - and here's my MAC address so you can talk directly to me."
So, if two computers have the same IP this all goes to hell :) don't do it - give them unique IPs and make sure that comptuer A transmits to the same UDP port and IP that computer B is listening on as well. communications work in {IP, Port} pairs - its like a telephone number and area code.
Also...
As said by EJP - UDP is a connectionless protocol - computer A just sends to computer B and hopes that computer B is listening correctly. If computer B wasn't listening or was but wasn't in the right state to process the data, the data will simply be dropped and lost. Computer A will not know that this happened. If you want reliable communications where it will keep trying and you will have assurance that compuer B received computer A's data then use TCP instead - it does a 3 way handshake to establish a connection and uses acknowledgements to ensure data is retransmitted when it doesn't reach the other end.
It could be that you're listening on localhost (127.0.0.1) and don't accept other traffic. Use a wildcard address.
Check on the server with netstat -npu.
If that's not the case then it's probably firewall issue, verify with tcpdump or wireshark.
Check firewall on your laptop... Most of the time that acts as spoilsport.
we have little network devices which are shipped with IP address 0.0.0.1 to ensure that they never collide with any other device in their new environment (thus none of the 10.x.x.x, 172.16.x.x or 192.168.x.x ranges) until configuration. DHCP is no solution since there might be no DHCP server in the field.
The devices would listen to UDP broadcasts and answer with broadcasts until they are given their new IP address this way.
This worked fine with Windows XP - but sucks with Windows 7: the config program does not receive the answer packets from the devices which still have 0.0.0.1. Wireshark sees the packets, then they are dumped by the system.
Question: Is there any reason (RFC?) that actually prohibits using this address in a local environment? Or is it just MS that was overcautious? Where can I read why they treat this address "invalid"? Which ranges are really "invalid" now, too?
Any idea of a workaround on the PC side (Win 7)?
I know that it is not recommended to use 0.xxx addresses for work places, but for this very reason - having a not-used address - it works perfectly.
Edit: there is a device out there called "Netburner" which might have faced the similar issue, according to their forum. See: http://forum.embeddedethernet.com/viewtopic.php?f=5&t=612&p=2198 Does - by coincidence - anybody know some background information?
It sounds as if your configuration application is listening for broadcast packets on all network interfaces and expecting to receive packets from foreign subnets.
That should not work - the OS should only pass-on broadcast packets from the subnets each network interface is on, not from all subnets on the same physical (e.g. Ethernet) segment. I am reasonably certain that doing otherwise is broken behaviour WRT the IP protocol.
The are two ways to deal with this:
Make sure that your network interface has an IP address in the target subnet. You can have more than one IP addresses for each network card, so that should not interfere with normal network operations.
Configure or modify you application to use raw sockets, like Wireshark. Keep in mind, however, that this overrides all normal checks and balances and should be avoided, since it can cause behaviour that is almost impossible to diagnose - which is why it is frowned upon by meny network administrators.
Can you you add new routing table entries to Windows machines easily? Windows has to know which interface to use when routing a broadcast packet to the 0.0.0.x network.
The Unix machines I'm familiar with have a routing table that maps network/netmask entries to either gateways or interfaces (if the network is a local network). The local network (192.168.0.0/16 for my home network) gets sent to interface eth0. Everything else 0.0.0.0/0 gets sent to a specific gateway machine 192.168.0.1.
If my machine sent a UDP broadcast message to network 0.0.0.0/24 (in other words, UDP broadcast sent to 0.0.0.255, then my machine would forward the packet to the gateway machine (which it can look up via arp). The switches in the middle wouldn't propagate the packet to other network devices, because the MAC address is set.
If my machine had another routing entry for 0.0.0.0/24 to the local interface, then my machine would send the packet on the wire using an ethernet broadcast group, and the switches would forward the packet to all connections. (Yay! Just like hubs in the 90s! :)
So I figure you need to add a routing entry for 0.0.0.0/24 to your client machines, so that they can properly address the broadcast packet.