foreach $customer (@customers) {
	if ($cust_pid = fork) { #in parent
		sleep 1;
		$SIG{CHLD} = 'IGNORE';
	}
	if ($cust_pid == 0) { #in child
		foreach $router (@routers) {
			if ($router_pid = fork) { #in parent
				sleep 1;
				$SIG{CHLD} = 'IGNORE';
			}
			if ($router_pid == 0) { #in child
				#do something
				exit; #this exits child process at router level
			}
		}
	}
	exit; #this exits child process at customer level
}