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

The final working solution I have is to use libpcap to achieve this. Of course there are some downsides, which includes it requires elevated privileges and must capture all filtered packets to calculate statistics, but at least it works perfectly well.

Many documentations and tutorials on libpcap is fairly thorough and clear, I suggest every one interested in this solution to look at those with relatively little google-fu effort.

Also it may interest a few that my filter for internet traffic is simply the following -

- (NSString *)_internetFilterStringForInterface:(AKNetworkInterface *)interface
    inOrOut:(BOOL)inYesOutNo
{
    if (![interface net] || ![interface mask] || IsEmpty([interface addresses]))
    {
        return nil;
    }

    NSString *hostType = inYesOutNo ? @"dst" : @"src";
    NSString *host = nil;
    for (NSString *hostComponent in [interface addresses])
    {
        if (IsEmpty(hostComponent)) continue;
        if (!host)
            host = [NSString stringWithFormat:@"(%@ host %@", hostType, hostComponent];
        else
            host = [host stringByAppendingFormat:@" or %@ host %@", hostType, hostComponent];
    }
    host = [host stringByAppendingString:@")"];

    NSString *net = [interface netString];
    net = [net stringByReplacingOccurrencesOfString:@".0" withString:@""];

    NSString *filter = [NSString stringWithFormat:
                        @"ip and (not %@ net %@) and %@",
                        inYesOutNo ? @"src" : @"dst",
                        net, host];
    return filter;
}

The filter is designed with some of the answers about what counts as 'local traffic', I know it does not encompass some edge cases such as double NAT configurations, etc., but I would like to see suggestions about this.

I know net = [net stringByReplacingOccurrencesOfString:@".0" withString:@""]; is just a quick hack which could easily fail under some peculiar circumstances but hey no one is complaining, at least not yet.