Monitoring network usage excluding local traffic

Question

I am working on an app that monitors network usage. However I noticed many ways to do this does not allow exclusion of local traffic (say, Time Machine).

I am lookin

Answer 1

you need to read the source for ifconfig(8), which describes how to get the status of every attached network interface.

pay particular attention to in_status(), which gets the inet address and netmask of an interface.

when the source or destination address in the traffic has the same host as a local interface

int is_local =
(src && netmask) == (ifaddr && netmask)
|| (dst && netmask) == (ifaddr && netmask)

then you can be sure that it is local

http://www.opensource.apple.com/source/network_cmds/network_cmds-307/ifconfig.tproj/ifconfig.c

Answer 2

It depends on how you define "local", but a common definition would be to look at the network mask.

For example, if your IP (ie the IP of the interface you monitor is

10.33.52.123
netmask 255.255.255.0

that would mean every IP-packet with both source-IP and destination-IP 10.33.52.xx is local.

I don't know cocoa or objective-c, but you can probably use some of these functions helping you extract the network from an IP-address: http://developer.apple.com/library/mac/#documentation/Darwin/Reference/ManPages/man3/inet_network.3.html