How to implement Forward DNS Lookup Cache?
Introduction
The DNS (Domain Name System) is a crucial component of the Internet infrastructure that translates human-readable domain names into machine-readable IP addresses. When you type a website URL into your browser, the DNS resolver on your device performs a DNS lookup to obtain the corresponding IP address for that domain name. However, repeatedly performing DNS lookups for the same domain name can result in unnecessary overhead and slow response issues. To address this problem, implementing a forward DNS lookup cache can significantly increase the collectability of DNS resolution and improve overall Internet browsing performance.
What is Forward DNS Lookup Cache
The forward DNS lookup cache is a local storage process that stores the results of DNS queries performed by DNS resolvers. When a device requests an IP address for a domain name, the DNS resolver checks the cache to see if it already has the necessary information. If the IP address of the domain name is found in the cache, the resolver can return results directly without contacting the DNS server. This caching process reduces pre-preparation for repetitive DNS elements and provides a better overall response for Internet browsing.
Steps to implement Forward DNS Lookup Cache
There are a few crucial steps involved in implementing a forward DNS lookup cache
Design of the cache data structure
Determine the appropriate data structure for storing DNS lookup results in the cache. A common choice is a key-value store, where the domain name is the key, and the associated IP address is the value. Each cache's time to live (TTL) may also be stored for the cache entry so that the caching data is valid for a specified time.
Setting the Cache Timeout
Set the appropriate TTL for cache entries. The TTL determines the length of time that DNS records should be kept in the cache until they expire. A balance must be struck between the benefits of caching and ensuring DNS records reflect changes quickly.
Cache miss
When a DNS query does not yield a result (i.e., a cache miss occurs), the DNS resolver should proceed with a standard DNS lookup, contacting primary DNS servers. Upon receiving the IP addresses, the resolver should store the result in a cache for future use.
Clearning and Flushing DNS Cache
Sometimes, it may be necessary to clear the DNS cache to carry the most recent information. The method to clear the cache depends on the operating system or DNS server.
a. For Windows
For example, on Windows, you can automatically clean up the DNS cache using the "ipconfig" command
ipconfig /flushdns
This command will require administrator (root) rights, prompting you to enter your user password. Once you enter the password, the DNS cache will be cleared, and any cached DNS records will be removed.
b. For Linux-based Systems
Open Terminal and run the following command with administrator privileges
sudo systemd-resolve --flush-caches
c. For macOS
Open Terminal and run the following command with administrator privileges
sudo dscacheutil -flushcache
Cache size management
Implement a mechanism to manage the size of the cache so that it does not grow infinitely and consume excess memory. Cache entries can be removed based on LRU (least most minor use) or LFU (least excess use) policies, ensuring that the most appropriate and frequently used entries remain in the cache.
Thread safety
If the DNS resolver is used by multiple processes or threads concurrently, ensure that the cache application is thread-safe to avoid race conditions and data corruption.
Refreshing Cache Entries
Regularly check and refresh cache entries that are nearing their TTL expiration time. DNS information is cross-verified in this process with the authoritative DNS servers, and the cache is updated with the latest information.
Simple example in Python to how you can use a hash table for the Forward DNS Lookup Cache
import time
class DNSCache:
def __init__(self):
self.cache = {} # The hash table to store DNS records
self.ttl = 300 # Default Time-to-Live (5 minutes)
def resolve_dns(self, domain):
if domain in self.cache:
dns_record, timestamp, ttl = self.cache[domain]
if time.time() - timestamp <= ttl:
return dns_record
# If the domain is not found in the cache or the record is expired,
# perform a DNS resolution here and obtain the dns_record.
# For demonstration purposes, let's assume we obtain the dns_record somehow.
dns_record = "192.168.1.1"
# Store the dns_record in the cache along with the current timestamp and TTL.
self.cache[domain] = (dns_record, time.time(), self.ttl)
return dns_record
# Example usage:
cache = DNSCache()
print(cache.resolve_dns("example.com")) # This will perform DNS resolution and store the result in the cache.
print(cache.resolve_dns("example.com")) # This will use the cached DNS record without performing a new resolution.
Java implementation for Forward DNS Look Up Cache
import java.util.HashMap;
import java.util.Map;
class TrieNode {
boolean isLeaf;
String ipAddress;
Map<Character, TrieNode> children;
public TrieNode() {
isLeaf = false;
ipAddress = null;
children = new HashMap<>();
}
}
public class DNSCache {
// Helper Functions:
// get_index: This function takes a character c and returns the index corresponding to that character.
static int getIndex(char c) {
return c == '.' ? 26 : c - 'a';
}
// get_char_from_index: This function takes an index i and returns the character corresponding to that index.
static char getCharFromIndex(int i) {
return i == 26 ? '.' : (char) ('a' + i);
}
// insert Function: Used to insert a URL and its corresponding IP address into the Trie data structure.
static void insert(TrieNode root, String url, String ipAddress) {
TrieNode node = root;
for (char c : url.toCharArray()) {
int index = getIndex(c);
node.children.putIfAbsent(c, new TrieNode());
node = node.children.get(c);
}
node.isLeaf = true;
node.ipAddress = ipAddress;
}
// search_dns_cache Function: Performs a forward DNS lookup on the Trie data structure.
static String search_dns_cache(TrieNode root, String url) {
TrieNode node = root;
for (char c : url.toCharArray()) {
int index = getIndex(c);
if (!node.children.containsKey(c)) {
return null;
}
node = node.children.get(c);
}
return node.isLeaf ? node.ipAddress : null;
}
public static void main(String[] args) {
// Sample URLs and their corresponding IP addresses
String[] urls = {"www.google.com", "www.facebook.com", "www.youtube.com", "www.yahoo.com"};
String[] ipAddresses = {"172.217.166.68", "157.240.218.35", "78.155.223.109", "150.99.125.46"};
// Create the root of the Trie
TrieNode root = new TrieNode();
// Insert each URL and its corresponding IP address into the Trie
for (int i = 0; i < urls.length; i++) {
insert(root, urls[i], ipAddresses[i]);
}
// Perform forward DNS lookups for two sample URLs
String url1 = "www.facebook.com";
String resIp1 = search_dns_cache(root, url1);
System.out.println("Performing Forward lookup in the DNS cache...");
if (resIp1 != null) {
System.out.println("Forward DNS cache lookup Successful!\nHostname: " + url1 + " --> IP address: " + resIp1);
} else {
System.out.println("Forward DNS cache lookup Unsuccessful! Hostname not present in DNS cache.");
}
System.out.println();
String url2 = "www.gmail.com";
String resIp2 = search_dns_cache(root, url2);
System.out.println("Performing Forward lookup in the DNS cache...");
if (resIp2 != null) {
System.out.println("Forward DNS cache lookup Successful!\nHostname: " + url2 + " --> IP address: " + resIp2);
} else {
System.out.println("Forward DNS cache lookup Unsuccessful! Hostname not present in DNS cache.");
}
}
}
C++ implementation for Forward DNS Look Up Cache
#include <iostream>
#include <unordered_map>
using namespace std;
// TrieNode Class: Represents a node in the Trie data structure
class TrieNode {
public:
bool isLeaf;
string ipAddress;
unordered_map<char, TrieNode*> children;
TrieNode() {
isLeaf = false;
ipAddress = "";
}
};
// Helper Functions:
// get_index: This function takes a character c and returns the index corresponding to that character.
int get_index(char c) {
return c == '.' ? 26 : c - 'a';
}
// get_char_from_index: This function takes an index i and returns the character corresponding to that index.
char get_char_from_index(int i) {
return i == 26 ? '.' : 'a' + i;
}
// insert Function: Used to insert a URL and its corresponding IP address into the Trie data structure.
void insert(TrieNode* root, string url, string ip_address) {
TrieNode* node = root;
for (char c : url) {
int index = get_index(c);
if (node->children.find(c) == node->children.end()) {
node->children[c] = new TrieNode();
}
node = node->children[c];
}
node->isLeaf = true;
node->ipAddress = ip_address;
}
// search_dns_cache Function: Performs a forward DNS lookup on the Trie data structure.
string search_dns_cache(TrieNode* root, string url) {
TrieNode* node = root;
for (char c : url) {
int index = get_index(c);
if (node->children.find(c) == node->children.end()) {
return "";
}
node = node->children[c];
}
return node->isLeaf ? node->ipAddress : "";
}
int main() {
// Sample URLs and their corresponding IP addresses
string urls[] = {"www.google.com", "www.facebook.com", "www.youtube.com", "www.yahoo.com"};
string ip_addresses[] = {"172.217.166.68", "157.240.218.35", "78.155.223.109", "150.99.125.46"};
// Create the root of the Trie
TrieNode* root = new TrieNode();
// Insert each URL and its corresponding IP address into the Trie
int n = sizeof(urls) / sizeof(urls[0]);
for (int i = 0; i < n; i++) {
insert(root, urls[i], ip_addresses[i]);
}
// Perform forward DNS lookups for two sample URLs
string url1 = "www.facebook.com";
string res_ip1 = search_dns_cache(root, url1);
cout << "Performing Forward lookup in the DNS cache..." << endl;
if (!res_ip1.empty()) {
cout << "Forward DNS cache lookup Successful!\nHostname: " << url1 << " --> IP address: " << res_ip1 << endl;
} else {
cout << "Forward DNS cache lookup Unsuccessful! Hostname not present in DNS cache." << endl;
}
cout << endl;
string url2 = "www.gmail.com";
string res_ip2 = search_dns_cache(root, url2);
cout << "Performing Forward lookup in the DNS cache..." << endl;
if (!res_ip2.empty()) {
cout << "Forward DNS cache lookup Successful!\nHostname: " << url2 << " --> IP address: " << res_ip2 << endl;
} else {
cout << "Forward DNS cache lookup Unsuccessful! Hostname not present in DNS cache." << endl;
}
// Free the allocated memory for Trie nodes
delete root;
return 0;
}
Python implementation for Forward DNS Look Up Cache
The below-mentioned code is a Python based program on how to implement forward DNS look up cache.
# TrieNode Class: Represents a node in the Trie data structure
class TrieNode:
def __init__(self):
# is_leaf: A boolean flag indicating if the node represents the end of a URL (leaf node).
self.is_leaf = False
# ip_address: A string representing the IP address associated with the URL (only valid for leaf nodes).
self.ip_address = None
# children: A dictionary to store child nodes of the current node.
# The keys of the dictionary are indices corresponding to characters ('a' to 'z' and '.').
self.children = {}
# Helper Functions:
# get_index: This function takes a character c and returns the index corresponding to that character.
def get_index(c):
return 26 if c == '.' else ord(c) - ord('a')
# get_char_from_index: This function takes an index i and returns the character corresponding to that index.
def get_char_from_index(i):
return '.' if i == 26 else chr(ord('a') + i)
# insert Function: Used to insert a URL and its corresponding IP address into the Trie data structure.
def insert(root, url, ip_address):
node = root
for char in url:
index = get_index(char)
if index not in node.children:
node.children[index] = TrieNode()
node = node.children[index]
node.is_leaf = True
node.ip_address = ip_address
# search_dns_cache Function: Performs a forward DNS lookup on the Trie data structure.
def search_dns_cache(root, url):
node = root
for char in url:
index = get_index(char)
if index not in node.children:
return None
node = node.children[index]
return node.ip_address if node.is_leaf else None
if __name__ == "__main__":
# Sample URLs and their corresponding IP addresses
urls = ["www.google.com", "www.facebook.com", "www.youtube.com", "www.yahoo.com"]
ip_addresses = ["172.217.166.68", "157.240.218.35", "78.155.223.109", "150.99.125.46"]
# Create the root of the Trie
root = TrieNode()
# Insert each URL and its corresponding IP address into the Trie
for url, ip_address in zip(urls, ip_addresses):
insert(root, url, ip_address)
# Perform forward DNS lookups for two sample URLs
url1 = "www.facebook.com"
res_ip1 = search_dns_cache(root, url1)
print("Performing Forward lookup in the DNS cache...")
if res_ip1:
print(f"Forward DNS cache lookup Successful!\nHostname: {url1} --> IP address: {res_ip1}")
else:
print("Forward DNS cache lookup Unsuccessful! Hostname not present in DNS cache.")
print("\n")
url2 = "www.gmail.com"
res_ip2 = search_dns_cache(root, url2)
print("Performing Forward lookup in the DNS cache...")
if res_ip2:
print(f"Forward DNS cache lookup Successful!\nHostname: {url2} --> IP address: {res_ip2}")
else:
print("Forward DNS cache lookup Unsuccessful! Hostname not present in DNS cache.")
Advanatge of Forward DNS Lookup Cache
Low latency: By caching DNS lookup results, IP addresses can be retrieved locally quickly for subsequent queries for the same domain name, reducing latency.
Improved performance: Faster DNS resolution improves overall Internet browsing performance and responsiveness.
Network load reduction: Reduces traffic and load on the DNS infrastructure by sending fewer queries to external DNS servers.
Reliability: If the DNS servers have a temporary setup or downtime, the cached DNS data can be used to access websites reliably.
Improvement of User Experience: Faster DNS resolution enables faster access times for website loading, thereby improving user experience.
Note that this example code is a simplified application to illustrate and does not perform an actual DNS lookup because of security restrictions in the browser environment prohibiting DNS lookup calls in the browser environment.
Conclusion
In conclusion, Implementing a forward DNS lookup cache is an effective way to optimize the portability of DNS resolution and improve Internet browsing performance. By storing DNS lookup results locally, devices can obtain IP addresses faster for subsequent queries, thereby reducing latency and network load. Ensuring proper management of cache size, expiration time, and cache refresh is a valuable technology that helps improve the overall responsiveness and user experience of Internet applications and services.