do code if current url = value

by 

global $wp;
$current_url = add_query_arg( $wp->query_string, '', home_url( $wp->request ) );
$is_specific_network = stripos( $current_url, 'specific_domain_or_ip_address' );
if( $is_specific_network !== false ) {
    // do the task below

} else {
    // do something else or leave it blank

}

N.B. : You need to replace the IP address or specific domain name above to distinguish the network.

=================== OR ======================

<?php
$current_site = get_current_site();
$current_domain = $current_site->domain;
if( $current_domain == 'something' ) {
    // do something
}
?>

You can use anything from this data being returned:

(object) 
An object containing details of the site currently being viewed. Details are represented in the following public variables: 

id 
    (integer) ID of the site currently being viewed. 
domain 
    (string) Domain of the site currently being viewed. 
path 
    (string) Path of the site currently being viewed. 
site_name 
    (string) Title of the site currently being viewed.

Refer: http://codex.wordpress.org/WPMU_Functions/get_current_site