CODEWITHSUNDEEP
objective-ccnetwork-programmingswiftip
Mads Gadeberg
Mads Gadeberg

Reputation: 1480

How to scan network for devices, using C Obj C or Swift

I have a server running on a Raspberry Pi and a client running on my Mac and iPhone (soon Apple Watch). I would like to connect to my server automatically without finding the Raspberry pi's Ip-address.

Is there a way to lookup all the devices on the network, and select by Mac-address, name or something else? I know that the first 3 bytes of the mac-address is the same for all Pies. (B8:27:EB) Maby i can use that information.

I have been looking for a solution for this issue a while but i can't seem to find one.

Upvotes: 2

Views: 3544

Answers (1)

joerick
joerick

Reputation: 16448

Zeroconf (aka Bonjour)

IMO, the best way to do this is to have your Raspberry Pi advertise itself on the network using Zeroconf (aka. Bonjour).

On the Raspberry Pi, install avahi-daemon and configure it to advertise whichever service you'd like to connect to connect to, for example, if you're connecting via SSH, you'll need to do something like this.

In Cocoa, you can use NSNetServiceBrowser to find the advertised service.

Possible MAC Address solution

Alternatively, if Avahi-daemon is not an option, you may be able to use the MAC address. I will not go into the specifics in Objective-C, just a high-level overview using the command-line.

In terminal, type ping 255.255.255.255. You will get back ping packets from every device on the local network. For each IP address, send an individual ping e.g. ping -c 1 192.168.x.x. Then, type arp -a. You will see the MAC address for each IP on the local network. From here, you can perhaps use your MAC address filter to find Raspberry Pis.

Why does this work? Well, the first command ping 255.255.255.255 sends a ping in an IP packet to the 'broadcast' address, which means all machines on the local network respond. When you ping the individual IP addresses, the low-level networking stack uses ARP to find the MAC address of the IP to directly send a ping to it. In doing so, the ARP tables on the local machine are updated with the cached values.

Maybe you can use this method in your app to discover local Raspberry Pis.

Upvotes: 3

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