Objective-C

Revert to Default DNS Nameservers

See more DNS Examples

Demonstrates how to revert back to the default nameservers of the local system where your application is running.

Note: This example requires Chilkat v9.5.0.96 or later.

Objective-C

#import <CkoDns.h>

//  The only reason you would have to revert back to the local system's default nameservers
//  is if your application had previously set different nameservers, and you wish to revert back.

//  When your application starts, the DNS nameservers to be used are the default nameservers
//  configured on the system where your application is running.

//  There is one exception: Chilkat defaults to using the public Google nameservers (8.8.8.8 and 8.8.4.4) for
//  Android applications. Reverting to the default nameservers would revert to the Google nameservers.

//  However, Chilkat does not query the local system for the default nameservers unless Chilkat needs
//  to do a DNS lookup and there not yet any DNS nameservers defined.  Thus technically, when your application
//  starts, there are no default nameservers. They are auto-assigned when first needed.

//  If your application explicitly defines DNS nameservers, such as by calling AddDefaultnamervers, or AddNameserver
//  then Chilkat will not automatically auto-assign.

CkoDns *dns = [[CkoDns alloc] init];

//  Here we are explicitly adding the system default nameservers, because technically this application
//  has not yet done anything that would require a DNS lookup, and thus DNS nameservers are not yet defined.
//  Your default nameserver is assumed to not support TLS.
[dns AddDefaultNameservers];

//  Let's examine our nameservers
int nsCount = [dns.NumNameservers intValue];
int i = 0;
while (i < nsCount) {
    NSLog(@"%d%@%@",i + 1,@": ",[dns GetNameserver: [NSNumber numberWithInt: i]]);
    i = i + 1;
}

//  On my Windows system, the result is a single nameserver at 
//  1: 172.16.16.16

//  ---------------------------------------------------------
//  We could add additional nameservers, such as Google and Cloudfare
BOOL supportsTls = YES;
//  Cloudfare
[dns AddNameserver: @"1.1.1.1" supportsTls: supportsTls];
//  Google
[dns AddNameserver: @"8.8.8.8" supportsTls: supportsTls];

//  See the nameservers now used by Chilkat
nsCount = [dns.NumNameservers intValue];
i = 0;
while (i < nsCount) {
    NSLog(@"%d%@%@",i + 1,@": ",[dns GetNameserver: [NSNumber numberWithInt: i]]);
    i = i + 1;
}

//  Result:
//  1: 172.16.16.16
//  2: 1.1.1.1
//  3: 8.8.8.8

//  ---------------------------------------------------------
//  To revert back to the system default nameservers, clear all
//  then re-add the default.
[dns RemoveAllNameservers];
[dns AddDefaultNameservers];

//  See the nameservers now used by Chilkat
nsCount = [dns.NumNameservers intValue];
i = 0;
while (i < nsCount) {
    NSLog(@"%d%@%@",i + 1,@": ",[dns GetNameserver: [NSNumber numberWithInt: i]]);
    i = i + 1;
}

//  Result:
//  1: 172.16.16.16