Can software respond to a Wake-on-Lan packet, or does it get filtered out by the NIC and/or OS?
My PC receives a Wake-on-Lan packet when one of my devices can't connect to the service it's expecting. If the PC is off, the packet will cause the machine to boot up, as expected. Unfortunately, it's possible (and common) for a PC user to quit the service manually. This leaves the system in a bad state where the machine is on but the service isn't running.
This particular service (Steam Big Picture Mode) doesn't have a 'run as service' option, and doesn't provide any other hooks to start it remotely. I'd like to write some bootstrap code that listens for the WoL packet and launches the service.
I want to honor the user's request to close the service on the host, up until the point that the WoL request is received. Thus, I'd prefer not to write a process that just monitors the service health and re-starts it when it's closed.
Related
I am able to access to my IOT device if I assign it a static IP with a service like dydns. But I would like to be able to reach it without relying on something.
I was thinking that my IOT device could ,on every start, write in a database its IP adress so my script on the server knows its ip.
The problem is that the IP will correspond to my hotspot IP. I am missing the connection part "hotspot -->IOT device".
For example I would like to be able to connect my IOT device to my mobile phone in hotspot mode.
One way to do this would be to re-design your system: if when it comes online the IoT device always connects (and stays connected) to a server component (which has a well-known/unchanging hostname/IP address), then the server can always send the IoT device a command over that TCP connection without knowing the hostname/IP address of the IoT device, and without it having to be contactable from the internet, i.e. this approach is firewall-friendly at the device end.
This is how the IoT is architected when using e.g. MQTT: devices connect inwards to the MQTT broker (i.e. server). MQTT also removes the need for the server application itself to need to connect to the clients. MQTT uses a concept called publish/subscribe with pre-agreed 'topics' - the client will subscribe to a 'command' topic, the server app publishes commands to that topic and the broker handles forwarding the command to the device. Incoming data from the device is published to another topic and the server application subscribes to that topic, the broker forwards the published data. You can try pub/sub example (using a browser, but real devices can also connect to the same server) using e.g. http://m2m.demos.ibm.com/utilities.html
I have a puzzle I am not able to figure out, I would appreciate any help.
I am connected to a remote desktop using windows default remote desktop utility (Windows 8 locally, Windows 7 remotely).
The remote desktop is not in the same sub-network as my own.
Connection is made through default port 3389. Using Wireshark locally I can confirm the TCP connection being established and the data flow.
Running Wireshark in the remote desktop, I don`t see any flow of data between the two computers.
If I send a ICMP ping from the remote desktop to my computer, it works well and I can see it in Wireshark both remotely as well as locally. But if I send the ICMP ping from my computer to the remote desktop, it fails. I see it leaving my computer through Wireshark, but it never reaches the remote desktop (I don`t see it in Wireshark).
I don't think it is a firewall issue (specially since it can't explain why Wireshark won`t capture the port 3389 RPC flow).
Does anyone have any idea of what might be going on?
I found the main issue.
In Wireshark, turns out it is possible to configure the capture interface with a filter.
To change it, go to: Capture->Interfaces
On the interface being used, stop capturing to enable the Options, there it is possible to configure a capture filter.
I am new to network programming and try to understand managing traffic via TUN/TAP interface.
Since I have almost nonexistent system programming skills, and feel confident on Java; I use OpenVPN tun/tap driver and ready made Java binding for it. It works on TAP mode.
As an example application I am trying to imitiate no encryption, no authentication client server VPN application.
I can catch Ethernet Frame packets, but for the routing part, I failed miserably. (I can modify route/arp tables.)
Do anybody know how OpenVPN send packets from client to server, and from server to target. Opening sockets from Java looks like an alternative; but I was hoping that modifying packets(change IPs and/or MAC addresses) and writing back to the virtual tap interface would be enough. Is it so?
Can I inject packets to send other locations, or by default received packet moves towards application layer?
-- Edit:
Scneario
Client Tap0 _____ Server Tap0 ______ Target
Eth0 Eth0
Target: Ping from client, move through tap interfaces, target see only server ip (anonymization)
What I achived so far.
Catch traffic at client tap0 interface.
I coulnt forward traffic at server Tap so to fasten things I used Java socket programming between client-server.
Now I read packets from socket at server, and try to OpenVPN Tap driver's write method to move forward but I am not sure where do I fail. I see packets with tcpdump at server tap0, but they do not pass to server eth0.
My most important question is if I modify packet(ip, mac address) and call write method, is it possible that packet moves forward. (Or does it move to application layer whatever you change??)
Any help would be appreciated.
1. Routing is a Layer 3 (IP) problem and handled by the OS. As for the Ethernet frames on Layer 2, you have multiple options. In any case, you'll have to parse the incoming packets' headers and extract the MAC address, and decide based on the MAC where to pass the packet: To a specific client, all clients (broadcasts) or the local tap interface.
Option 1: On each client, use a tun device, and let the server use a tap device. Assign pseudo MAC addresses to each client, respond accordingly to ARP requests from the server's OS and let the OS on the server take care of the rest. Applicationwise, you'll only have to forward all incoming packets to the tap device and all outgoing packets to the client to which you assigned this MAC.
Option 2: Let the clients choose their own MAC address and forward ARP-requests through the network. The server application has to decide for incoming packets from a client whether to forward the packet to a client, or send it to the local tap device if the address matches the local device's MAC.
In both cases, clients pass all packets from their local tun/tap device to the server and vice versa.
2. You can do almost anything. A packet is only "received" when you decide to write it to the tap device, and you can of course temper with any packets, or inject new ones, ...
As a final comment, I've found that toying with tun devices is conceptually simpler, because they work on Layer 3. You'll have to open a tun device on the server for each client, but within your application you'll have to do nothing but to forward anything coming from the device to the single client, and vice versa.
To stop an internet connected device (lets say it's an internet connected thermostat) from having to poll the remote server all the time to see if the user has changed its settings how would a server send data to that device when needed? I understand how to initiate a connection from the internet connected device, just not the other way round.
It's safe to assume that the device would have already registered it's details with the server in some kind of set up process initiated by the device.
Check out SignalR, in these links:
http://signalr.net/
http://www.asp.net/signalr
http://www.codeproject.com/Tips/590660/Introduction-to-SignalR
HTH
I have a simple client application which sends udp datagram to the server with known ip address and port and waits for respond. Client can be started on any computer or mobile device and it can be located behind several routers and firewalls... Server application listens certain port for client's datagram and replies to the client's endpoint with an answer. Server application works on windows computer with properly configured firewall, etc. So, as I understand, this simple scheme should work regardless to client's location and his firewall settings. But it looks like it doesn't work in about 75% of configurations. Server receives request from the client in 100% of cases, but in 75% of cases client can't receive response from the server, i.e. it looks like it's always blocked by something (server attempts 10 times to send an answer to the client, but without luck, i.e. client doesn't receive anything). I tried many different configurations of client computers to figure out the reasons of these issues and what I've found:
In some cases simple windows firewall can block respond packets (But how it could be possible? As I understand, all respond packets must be forwarded back to the client regardless to firewall settings.)
Some Hardware firewalls or NATs also can block respond UDP packets. And again, I can't understand why it could be possible?
The question is - is there any reliable method to deliver an answer to client? As I know, many programs, such as Skype works fine with UDP even with all these network "obstacles".
Thank you!