DNS Module

The DNS module provides functions to test the performance and availability of DNS servers. This module is useful for DNS infrastructure monitoring, diagnosing name resolution issues, and measuring latency in DNS queries.

Available Functions

1. dns.ping(server, domain)

Performs a DNS query to a specific server and measures the response time (RTT - Round Trip Time).

Parameters

• server (string): Address of the DNS server to test (can be an IP or domain name)

• domain (string): Domain to be queried on the DNS server

Return

• number: Response time in milliseconds (DNS latency)

Behavior

1. Resolves the DNS server address (if it’s a domain name)

2. Connects to the DNS server on port 53 (UDP)

3. Performs an A record query for the specified domain

4. Measures the time between sending the query and receiving the response

5. Returns the time in milliseconds

Usage Example

-- Test Google DNS latency
local latencia = dns.ping("8.8.8.8", "google.com")
-- latencia = 25 (example: 25 milliseconds)

-- Test Cloudflare public DNS
local latencia_cf = dns.ping("1.1.1.1", "github.com")
-- latencia_cf = 30 (example)

-- Test DNS server by name
local latencia_local = dns.ping("dns.local", "servidor.producao")
-- Tests the internal DNS server "dns.local"

-- Compare multiple DNS servers
local servidores_dns = {
    {nome = "Google DNS", endereco = "8.8.8.8"},
    {nome = "Cloudflare", endereco = "1.1.1.1"},
    {nome = "Quad9", endereco = "9.9.9.9"},
    {nome = "DNS Local", endereco = "192.168.1.1"}
}

for _, dns in ipairs(servidores_dns) do
    local latencia = dns.ping(dns.endereco, "exemplo.com")
    print(dns.nome .. ": " .. latencia .. "ms")
end

Additional Information

Automatic DNS Server Resolution

The dns.ping function automatically resolves the DNS server name if provided as a domain:

-- Works with IP
dns.ping("8.8.8.8", "google.com")

-- Works with domain name (will be resolved first)
dns.ping("dns.google", "exemplo.com")
dns.ping("one.one.one.one", "exemplo.com")  -- Cloudflare DNS

A Record Query

The function always performs A record (IPv4) queries.

UDP Protocol

Queries are performed via UDP on port 53, which is the standard protocol for DNS queries.

Usage Example

DNS Propagation Test

-- Check if a domain is resolving correctly on different servers
local function testar_propagacao_dns(dominio, ip_esperado)
    local servidores = {
        "8.8.8.8",      -- Google
        "1.1.1.1",      -- Cloudflare
        "9.9.9.9",      -- Quad9
        "208.67.222.222", -- OpenDNS
        "64.6.64.6",    -- Verisign
    }

    local resultados = {}
    for _, server in ipairs(servidores) do
        -- with_coroutine accepts the function and its arguments, returning (result, error)
        local latencia, err = with_coroutine(dns.ping, server, dominio)
        local ok = (err == nil)

        resultados[server] = {
            latencia = ok and latencia or nil,
            acessivel = ok,
            erro = not ok and err or nil
        }
    end

    return resultados
end