I am working on a distributed application in which a set of logical nodes communicate with each other.
In the initial discovery phase, each logical node starts up and sends out a UDP broadcast packet to the network to inform the rest of the nodes of its existence.
With different physical hosts, this can easily be handled by agreeing on a port number and keeping track of UDP broadcasts received from other hosts.
My problem is - I need to be able to be able to handle the case of multiple logical nodes on the same machine as well.
So in this case, it seems I cannot bind to the same port twice. How do I handle the node discovery case if there are two logical nodes on the same box ?? Thanks a lot in advance !!
Your choices are:
Create a RAW socket and listen to all packets on a particular NIC, this way ,by looking at the content of each packet, the process will identify if the packet is for destined for itself. The problem with this is tons of packets you would have to process. This is why kernels of our operating systems bind sockets to processes, so the traffic gets distributed optimally.
Create a specialized service, i.e. a daemon that will handle announcements of new processes that will be available to execute the work. When launched, the process will have to announce its port number to the service. This is usually how it is done.
Use virtual IP addresses for each process you want to run, each process binds to different IP address. If you are running on a local network, this is the simplest way.
Define range of ports and scan this range on all ip addresses you have defined.
Related
I have a language monitor that I am trying to query the printer from.
First let me apologize for the possible confusion since "port" means 2 things in this description. There is the one use that refers to the port that the printer is configured to use, which could be TCP, USB, etc. And then there is the use of port that refers to the port address to send data to when communicating with the printer's IP address.
I need to be able to specify different port addresses to send different custom queries to a printer over the same IP that are specific to it's firmware. I can't find any examples or documentation on what the standard way is to do this communication... I can extract the IP address and open a net socket, but I am not sure if this is the appropriate way to handle this communication. It's not uncommon for printers to send status over one port, and print data over another. If i want to write to the Default port I can use pfnWritePort and pfnReadPort, but these don't allow me to specify the actual port.. it uses whatever the driver is configured as.
Can anyone provide some guidance or examples of how I should do this from my language monitor?
EDIT: As an example for clarification, all commands are sent to the same IP, but depending on the command/query I need to send, the TCP port needs to change. The way I am handling it now is opening up a net socket with the same IP and different port numbers for data and status channels).
You should be required to write an app that would be able to reconfigure driver. Ideology of OS is that EACH real device would corresponds to instance of driver and\or interface. Which might be an elevated action, because it requires to create new printer interface("port" in Windows GUI terms) and change driver settings.
Short version: How would you recommend going about connecting a client to a server that are on the same local network, without manually entering the ip, when broadcast is disabled?
Further details: I am working on an educational multiplayer game for children. Many schools appear to be blocking broadcasting for security reasons. The children will be rather young, so it could be difficult for them and error-prone to have to enter the IP manually. They will all be in the same room and will all see the server screen. The game is made in Unity (C#).
Potential solutions: Here's what I thought about:
Connecting both the local server and clients to an external server, communicating the local server ip through the clients through the external server, then connecting directly and disconnect from the server. Not ideal because of the extra hosting costs.
Send a regular UDP message periodically to all ips on the subnet? This will probably be picked up by any decent firewall and blocked though, right?
Putting a QR code on the server that kids would take a picture of with the client app and have it connect that way? May be more of a hassle.
Having the server play random tones corresponding to numbers that the client is listening for? (Speakers may not always work though)
Sounds like the first one is the most sane and easy solution. Do you have any other ideas on what someone in this situation could try?
Is UDP multicast possible?
If yes then a common solution is that all participants join the same multicast group and the server listens on a well known port. If a client wants to know the address of the server it sends a packet to the multicast group, which is received by the client and answered with another packet, which then can be used by the client to determine the servers address.
In addition to that servers can also announce their presence in regular intervals by sending a suitable message to the multicast group.
What I can think of is an ad-hoc communication protocol between all the devices. Say you have 1 server and 10 clients. All the devices should run a service(say server-discovery) that binds to a fixed port say 9999. Now any time the client wants to connect to the server and doesn't know the IP, it starts a scan. Loops through different IPs and tries to connect to 9999. If it manages to hit, it asks for the server IP. In case it manages to hit the server it will get the IP since the server knows it's own IP and the client will maintain the server IP in a cache. If the client hits another client. It can ask for the server IP. It the other client knows the IP it will share the info else decline.
I agree there is a lot of overhead, but I think this will be robust unlike sound and would reduce cost of printing QRs everytime.
on the local network the traffic is direct from host to host.
I don't understand which devices is blocking local broadcasts.
if there aren't too many peers on the LAN ( less then 100 ), I think udp broadcasts work fine and you dont pollute the network.
to have an idea of your "pond", I suggest you to sniff your local traffic.
there are many broadcasts : arp, windows, ipp, dropbox...
I have 2 nodeMCU modules, which I want to connect to an MQTT broker and send some data every 5 seconds.
The topology I am trying to achieve is sth like [router]<==[nodeMCU#1]<==[nodeMCU#2]
It looks like [nodeMCU#1] is a wifi extender, but at work we are planning on using multiple nodeMCU's to use in a mesh-like way for an IoT application.
On both of them I flashed the latest (float) release that I downloaded from here https://github.com/nodemcu/nodemcu-firmware/releases/tag/0.9.6-dev_20150704 using nodeMCU-flasher.
For this project wrote 2 lua scripts and I have uploaded them to the modules using ESPlorer.
For the first module it connects in STATIONAP mode to my work wifi, and creates its own network with SSID nodeMCUwifi, with a basic password of 10 characters "1234567890". After it connects the script sends random values to an MQTT topic.
For the second module connects to nodeMCUwifi correctly, it is assigned an IP address, but it cannot connect to the MQTT broker.
When I try to connect to nodeMCUwifi using my smartphone (just to test the connection, I have no intention of using this system for heavy internet load, only MQTT messages) I get a message "authentication error occured" even though I have typed the password correctly, or (in rarer cases)it connects but disconnects immediately.
I would appreciate any ideas to resolve this issue. Thank you.
EDIT: At the AP configuration I added the auth parameter set to 3, I am pasting a part of my code below.
cfg.ssid="ESP8266_"..node.chipid();
cfg.pwd="1234567890"
cfg.auth=3
wifi.ap.config(cfg);
Now my laptop and my smartphone connect to the wifi created by the module, but still have no connectivity to the internet. I can ping the module, but I can't ping 8.8.8.8 or the MQTT broker IP or anything else.
As I understand, [nodeMCU#1] creates a wifi network named nodeMCUwifi. Then the others are trying to connect to nodeMCUwifi. As You stated:
Now my laptop and my smartphone connect to the wifi created by the module, but still have no connectivity to the internet. I can ping the module, but I can't ping 8.8.8.8 or the MQTT broker IP or anything else.
I assume your laptop and smartphone connects to the nodeMCUwifi network. Now you want this [nodeMCU#1] act like layer 2 switch or something like router(since SOFTAP creates its own ip network).
With all this information on hand, I can say that the purpose you are trying to achieve is not possible with esp. Since esp has not enough resources to act like switch or similar. Also (currently) there is no software implemented in esp to achieve that.
However; if only you want the system to transfer certain type of traffic (such as MQTT) over a certain protocol (such as UDP) it is possible to relay the messages like a mesh structure but this will work one-way only. In this configuration the nodes will act more like repeater but on upper layers of OSI. For this idea i cannot provide sample code but I will provide pseudo-code below:
Configuration
> Each node must be configured to build a chain structure. That means each SOFTAP node should have different SSID or TCP settings. For example:
router(192.168.0.0)<----[NODE#1(SOFTAP0)]<----[NODE#2(SOFTAP1)]<---...
...
...
...<----[NODE#n(STATION)]
> Each node must have a TARGET IP address according to setup. This means every node will send the MQTT message to that address.
> If a node is configured as a SOFTAP, this means this system is a TARGET and must listen to a specific port.
> If a SOFTAP node receives some data on the port that is listening to, it should send the data immediately (or buffering) to its TARGET node.
> As a result of this chaining operation the message, no matter what is the source, will reach to the end of the chain.
CODE : SOFTAP
...soft ap config...
listento.port: udp.965
on("receive"):
create.conn:TARGET
send(DATA_RECEIVED)
close.conn:TARGET
CODE : STATION
...station config...
...Do some logic...
data=gather.data()
create.conn:TARGET
send(data)
close.conn:TARGET
I'm using a real machine (hp procurve) for my project, I need to send message of other protocol format, OSPF for instance, instead of flows, from controller side to OpenFlow switch through socket(by specifying ip address and port of the OF switch).
But everytime I try to do this, I get "Connection refused" error message, I guess that it might be that the port on OpenFlow switch I'm sending the message to is not listening, so I think I might need to use the same port for the sending which OpenFlow switch uses to talk to the controller, like the port 51067 in the log info :
Switch:192.168.1.11:51067 is connected to the Controller
My question is, how do I retrieve the port information on the controller side, since it is changing every time I restart it? I couldn't find this information.
Or am I going the wrong direction that I need to go another way around instead of sending the message using socket?
Thanks a lot in advance, any suggestions will be appreciated.
jonesir
I think you are misunderstanding the nature of networking ports, protocol numbers, and protocols such as OSPF. Let me clear those up:
Port numbers: Usually, there is exactly one application listening on a single port: The operating system/networking stack checks each packet of certain types (e.g. TCP or UDP) for the port number and then passes the packet to the application that registered itself for that specific port. If the application cannot handle the received packet then usually it will just ignore it or log an error.
Aside: It is possible for two applications to communicate on the same port only if you put some sort of multiplexing application before both (usually a reverse proxy, possibly a TCPMUX application). This multiplexing application would take incoming packets, determine what type of packet it is and then pass it to the correct application.
Protocol numbers: The protocol number is a field inside an IP packet that tells the networking stack what type of data is contained inside. For example, TCP is protocol 6, ICMP is 1, and OSPF is 89.
OF switches: Now, logically an OF switch consists of two components: 1) the switching fabric (which includes the physical ports and OF flow tables), and 2) a separate physical port to for out-of-band control, with several applications running behind it. One of these applications is the OpenFlow application, which in your case happens to listen on port 51067. But in real switches, other applications might also be running on different ports, e.g. a web interface running on port 80 for maintenance etc.
OSPF: If you now wanted to talk to the application serving the web interface, you'd send a TCP packet with destination port 80 from your controller to the switch. Similarly, if you'd like to install a new flow, you'd send an TCP packet with port 51067 in your case. OSPF is quite different, as it directly uses IP packets and does not use port numbers. To process an OSPF packet, an application needs to use a raw socket to process the incoming IP packets that have protocol number 89, and skip all others. See also the raw manpage here. This will already be built into your OF switch.
Thus, if you want to send an OSPF packet to the OF switch (and your OF switch supports OSPF on the separate physical port!), you'd just send an OSPF IP packet to the switch's IP address (192.168.1.11), no port needed!
Note that the separate physical port might not support all of the features of the other ports on the OF switch, as they are not intended for the same uses.
in my college lab all the PCs are connected via LAN by L2 switch. i want to capture the http data packets by wireshark but it is only showing the interface of my own PC. so how can i capture the packets of other PCs.
can somebody tell me working of wireshark?
It is in the nature of switches that you will only see either broadcast packets or traffic that has your MAC address as a destination, that is one of the crucial differences between a switch and a hub.
It is possible for most switches to be configured to copy traffic from one port to another, this is commonly done for monitoring purposes, but that has to be done via administrative access to the device.
You can manipulate the switch's behavior by means of ARP-Spoofing. But be cautious! Doing so might be seen as a criminal act.
So be sure that you're allowed to do so in the lab, sometimes that's OK if it serves the educational purpose. Ask your supervisor or the school's administrator.
My weapon of choice for such things is Ettercap.
A far less intrusive approach would be to use one of your own switches and configure it to forward all traffic. Then you can connect one port as an uplink to the lab's switch, one port to the device under test and one port to your machine running wireshark. (I would recommend using tcpdump for capturing, though.) If you don't have a manageable switch at hand, you can also use a router running OpenWRT.