CODEWITHSUNDEEP
iosobjective-cmacosnetwork-programming
iKenndac
iKenndac

Reputation: 18776

Finding the interface/route for a local IP address on Mac OS X and iOS?

I'm working on a machine that has multiple local network interfaces. Each interface is on a distinct network: for example, en0 might be 10.0.0.x, en1 192.168.1.x, etc.

I'd like to programatically answer the question: "Which interface is likely to be able to get to the given local IP address?"

For instance, if I wanted to talk to 10.0.0.75, that would be en0, 192.168.1.4 would be en1. I'm sure there's a smarter way to do this than manually comparing IP address fragments.

Bonus points if this works on iOS as well as Mac OS X - iOS does support multiple local interfaces, even if it's rare.

Upvotes: 2

Views: 506

Answers (1)

monowerker
monowerker

Reputation: 2979

The approach I'd consider is to enumerate all the configured interfaces and get their IP-address and netmask. You can then calculate the Hostmin and Hostmax for that subnet, if your candidate falls within the Hostmax-Hostmin IP-range this host should be reachable directly on the local subnet of that interface.

You can find an online tool for these types of calculations at http://jodies.de/ipcalc. It's fairly straightforward bit-operations to do these calculations programatically.

There are IP-address functions you can use in arpa/inet.h, inet_addr for instance will give you a 32-bit value from a dotted-decimals formatted IP-address.

Upvotes: 1

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