How to discovery devices maybe in different net segment via UDP

brucezcg · 26 Jun 2018, 05:16

I had A PC and some devices connected to router, but I don't know the IP address of each device, May be not same net segment as my PC.
So how can I discovery all devices please?

I tried UDP broadcast, But if not same net segment, I cannot communicate with device via UDP.

JKSH · wrote on 26 Jun 2018, 05:16

https://stackoverflow.com/questions/379015/udp-broadcast-packets-across-subnets

brucezcg · 26 Jun 2018, 06:53

Thanks.
As UDP may be require router configure carefully, Is there other way to reslove this kind of problem.

raven-worx · 26 Jun 2018, 07:23

@brucezcg
i dont quite understand what you want to achieve.
There is a reason why there is something like the subnet concept. It's intention exactly is that machines don't see each other across subnets!

brucezcg · 26 Jun 2018, 07:40

@raven-worx : Thanks.

I have many devices (Smart Cameras) connected to my router, each camera have isolate IP address. I run my Application on my PC, In order to connect each camera, First I should Discovery all cameras connected to router. but may be cameras in different subnet.
So If the camera IP:192.168.11.11
My PC's IP:199.55.55.44

How can I discovery the camera from my PC?

raven-worx · 27 Jun 2018, 01:25

@brucezcg
why are they in a different subnet in the first place?!
Are they connected to the same router? Don't they get their IPs from the same DHCP?

I don't see any chance getting them accessible, when the subnet mask prevents it.

JKSH · wrote on 26 Jun 2018, 07:50

@brucezcg said in How to discovery devices maybe in different net segment via UDP:

I have many devices (Smart Cameras) connected to my router, each camera have isolate IP address.... but may be cameras in different subnet.

You should put all cameras and your PC on the same subnet. Usually, people give all devices Static IP addresses OR they enable DHCP (like @raven-worx said). With DHCP, your router automatically puts all cameras and your PC on the same subnet.

How can I discovery the camera from my PC?

If they are on different subnets, then you probably cannot discover them.

raven-worx · wrote on 26 Jun 2018, 08:25

@brucezcg said in How to discovery devices maybe in different net segment via UDP:

My PC's IP:199.55.55.44

btw this IP isn't even in the private IP range. So why has your PC such an IP address assigned?!

SGaist · 27 Jun 2018, 00:51

Hi,

To add to my fellow, are you camera using zeroconf or something similar to advertise their presence ?

brucezcg · S SGaist 26 Jun 2018, 20:26

@SGaist The camera will not inform its exist. they work alone, so I want to use UDP/ARP to discover them

brucezcg · 27 Jun 2018, 06:24

@raven-worx The camera may be work in static IP address mode, so If someone change the IP to different subnet, How can I know?

raven-worx · wrote on 27 Jun 2018, 06:24

@brucezcg said in How to discovery devices maybe in different net segment via UDP:

The camera may be work in static IP address mode, so If someone change the IP to different subnet, How can I know?

as i said. if they are configured to be in a different subnet you won't have a chance to discover them, because only devices in the same subnet. The subnet range is determined by the subnet mask.

You want to use UDP to discover them. Do you even know if they would respond to your UDP request?
I mean do you know for sure that the camera lets it self discover by listening to a UDP network request - provides a service to do so?

brucezcg · wrote on 20 Jul 2018, 07:37

Is there any good ideas?

VRonin · wrote on 20 Jul 2018, 08:10

The standard way is a known central location. A "server" (using the term very loosely here) that both cameras and PCs know about. Cameras will connect to it and tell it their IP, PC will connect to it to retrieve the list of registered cameras