Once a service is discovered through DNS-SD, how exactly does the address of that host get resolved, and does it take significantly more time/overhead?
Also, if I am using JmDNS or Bonjour there are call-backs for both serviceFound and serviceResolved. If I am just interested in the IP address of the device publishing a certain service, is there a faster/more efficient way of getting the address than going through both serviceFound and serviceResolved?
Thanks
DNS-SD uses Multicast DNS (MDNS) which works by sending DNS packets over UDP to a certain multicast address. All mdns-capable hosts in the network also listen to this address. It uses UDP so, it's quite low overhead. Also, the clients are designed in a way that the amount of chatter on the network is kept to a minimum, by using extensive caching.
Service discovery is a two step process. The first step is finding the names of all hosts providing a certain service (e.g. printing). This will not yet give you the ip address, instead it gives you the mdns name (ending with .local). This is because the ip could possibly change, whereas the name will not.
The second step in service discovery is to resolve the .local name of the host over mdns. You ask via multicast who foo.local is, foo.local will see that packet, and respond via broadcast with its ip address, port number and other information.
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I am just experimenting with my phone system and I'm wondering how both endpoints know they are on the same LAN, I have both endpoints breaking out to the cloud phone system with two separate public IP addresses, I've segmented them off from each other with a firewall so they can't see each other however every time I attempt a call between the two end points the call is setup as a peer to peer call and attempts to traverse the local LAN via RTP through the firewall, the firewall blocks the RTP communication and the call has no audio.
I am just wondering how both endpoints are realizing they are behind the same firewall/router since they are both registering with the cloud system from different public IP addresses, I wanted the call to be bridged in the cloud and not traverse the local LAN but somehow both endpoints only attempt the call over the LAN every single time and no idea how they're realising they're on the same LAN.
Anyone else encountered this before?
SIP endpoints don't have to know they are on the same LAN. They just make best use of the IP addresses you provide.
Your INVITE request will provide more insight, but from what you write my guess is that you use public IP addresses for your contact/request URI and local IP addresses in your SDP offer. The local IP addresses are probably routable through the firewall.
With ICE and STUN endpoints may select the best IPs for media traffic - but for that to work the RTP/STUN packets should be able to traverse the firewall in your LAN.
Attempts to communicate directly may mean that LAN uses IPs from public ranges or endpoints a SIP proxy were not smart enough to detect NAT in front of your LAN.
I am working on an embedded software product that runs on an Ubuntu edge computer with multiple network ports.
The software allows the user to change the IP address of the ports via a locally hosted web interface.
In the scenario that a customer changed an IP on one of our devices, but then forgets their setting I am looking for an easy strategy to walk them through detecting the IP.
Ideally this tool would be usable by non-sophisticated customers (we don’t want to walk them through using Wireshark or command line tools).
Is there a service we can setup on our machine that will broadcast its identity across subnets using another protocol like UDP or EtherNet/IP? Then a simple tool the client could install on their computer to ‘scan’ for our devices?
The edge computers also have USB ports if it is easier to broadcast an identify there.
Changing a local IP address to something invalid (=not compatible with its local subnet) generally disables all L3 communication. Limited broadcasts (to 255.255.255.255) still work, but answering to them by unicast most likely won't. The same goes for multicasting - but you could use that for discovery both ways.
Also, the common link-level discovery protocols (like LLDP or CDP) still work since they don't rely on IP.
However, all that is limited to the connected L2 segment at most. Discovery across subnets isn't possible without some kind of infrastructure (discovery sensors, central server, multicast routing, ...). A reasonable way would be dynamic DNS but then again, that requires IP to work.
I think you'd need to take a step back and reevaluate your design. One way would be to verify a user's reconfiguration before it becomes permanent. For instance, you could have a user change the IP setup and then forward the session to the new IP address. If the session isn't continued within five minutes or so on the new address, it reverses to the previous config.
Additionally, some kind of out-of-band management could be useful.
So I am kind of new to networking and I'm just interested in the client/server architecture. Let's say you developed a program and the client version ran on a computer and the server version on the server(obviously). In order for the client to connect to the server, it would have to know the ip address of the server (and the port attached so it can be routed to the correct computer/program). Does that mean that the server's ip address can not change? Would you have to specifically tell your ISP to keep the ip address static? Because if both the client and server ip addresses change, then they would have no way to connect and the program wouldn't work... in other words there has to be one constant. When you sign up for a VPS do they give you a static ip address you can bind to from the client version? Thanks!
In order for the client to connect to the server, it would have to know the ip address of the server (and the port attached so it can be routed to the correct computer/program).
Correct.
Does that mean that the server's ip address can not change?
No. In fact, IPs can change at any time. Most servers that are exposed to the public Internet have a static domain name registered in the Internet's DNS system. A client asks DNS to resolve the desired domain name to its current IP address, and then the client can connect to it. But even in private LANs, most routers act as a local DNS server, allowing machines on the same network to discover each other's IP by machine name.
The OS typically handles DNS for you. A client can simply call gethostbyname() or prefferably getaddrinfo(), and the OS will perform DNS queries as needed on the client's behalf and return back the reported IP(s).
Would you have to specifically tell your ISP to keep the ip address static?
You can, but that usually costs extra. And it is not necessary if your server is registered in DNS. And there are free/cheap DNS systems that work with servers that do not have a static IP.
Because if both the client and server ip addresses change, then they would have no way to connect and the program wouldn't work...
That is where DNS comes into play.
in other words there has to be one constant.
A registered domain name that can be resolved by DNS.
When you sign up for a VPS do they give you a static ip address you can bind to from the client version?
It depends on the VPS service, but a more likely scenario would be you are assigned a static sub-domain within the VPS service's main domain. For example, myserver.thevps.com. Or, if you buy your own domain (which can be done very cheaply from any number of providers), you can usually link it to the DNS server operated by your VPS service.
My internet connection has a dynamic IP adress which keeps changing every time the modem is restarted, so I have a hard time configuring the Authorized Networks in Access Control.
This is explained at https://cloud.google.com/sql/docs/access-control#dynamicIP .
Your options are, and I quote:
Use a proxy service so that your application appears to come from only one IP address. Add this address to the authorized networks that can connect to the instance.
Use a CIDR range that covers all of the IP addresses from which your service might connect.
Use the CIDR range 0.0.0.0/0, which allows all external IP addresses to connect.
The third and last option, despite its attractive simplicity has implications that may make it undesirable -- read the docs I'm pointing to.
I have a question about network connections among computers.
I've made some applications where messages pass through the Internet (via sockets) to make a connection between two devices. However, a strong condition is that two devices must be connected to the same network.
Can anyone give me a trick how to create a communication using sockets between two computers even if they are connected to different netwkorks?
Thank you in advance.
Here is a great tutorial on how to use sockets and general networking
(in java) http://www.thenewboston.org/watch.php?cat=25&number=38
In order to communicate between two diffrent networks over the internet, you will need to do something called port forwarding. What that does is that when your public IP of your network receives a packet with a spesific port number. The router knows where to send that packet to which local IP.
If you dont port forward and receive some data. The router doesent know where to send the packet. Therefore it discards it, which means others wont be able to connect to you.
You will only need to port forward the network with your server (using the example i linked). How you do that is by logging in to your router, and say that a port which the server uses gets forwarded to the IP of the PC hosting the server.
On the other network (client) you will need to change the IP address of which the client shall connect to. That IP address needs to be your public IP of your server's network. You can find that by connecting to the server's network and go to: http://www.whatsmyip.org/ . Keep in mind that public IP addresses may change over time.
Hope this helped!
-Kad