public with sharing class IP_Authorization
{   
    private List<account> IPList;
    public List<account> CIDRList; 
    public Boolean ipFound = false;       
    private string Input_IP4{get; set;}

    public PageReference p = ApexPages.currentPage();
    public string IP_PatternV4='^(([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\\.){3}([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])$';
    
//*************************************************************************************************************************//
//***********************************************  Main Method for IP Validation ******************************************//    
    public pagereference VerifyIP()
    {
        Input_IP4=System.currentPageReference().getParameters().get('checkip');                              
        Boolean isValidIP = Pattern.matches(IP_PatternV4,Input_IP4); 
                                 
        if (isValidIP)                 
        {   
            integer SearchIP=0;            
            SearchIP=[SELECT COUNT() FROM account WHERE 
                            Static_IP_Address__c=:Input_IP4                                                           
            if( SearchIP > 0 )
            {   
                ipFound= true;                                    
            }
            else 
            {                
                ipFound=false;   
            }
        }
                  
         if (ipFound) 
         {
             p.getHeaders().put('Found','200');
             ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.CONFIRM, '200'));             
         }
         else    
         {
             p.getHeaders().put('NotFound','404');
             ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.ERROR, '404'));              
         }    
        return p;
    }
}

 I am receiving a IP from a client, salesforce has to verify if the IP is present in account and return back response 200 if IP

found.

Below is my visualforce page I created to test this from controller.

<apex:page Controller="IP_Authorization" tabStyle="account" action="{!VerifyIP}">
<apex:pageMessages id="error"/>
</apex:page>