reverse dns of a range of IPs

reverse_dns.sh

#!/bin/bash

# Parallel reverse DNS enumeration with configurable IP range
# Usage: ./reverse_dns.sh <start_ip> <end_ip> [max_jobs]

usage() {
    echo "Usage: $0 <start_ip> <end_ip> [max_jobs]"
    echo "Example: $0 100.64.0.1 100.64.2.255 50"
    echo "Example: $0 192.168.1.1 192.168.1.254"
    echo "Default max_jobs: 25"
    exit 1
}

# Check arguments
if [ $# -lt 2 ] || [ $# -gt 3 ]; then
    usage
fi

START_IP="$1"
END_IP="$2"
MAX_JOBS="${3:-25}"  # Default to 25 if not specified

# Function to convert IP to integer
ip_to_int() {
    local ip="$1"
    local a b c d
    IFS=. read -r a b c d <<< "$ip"
    echo $((a * 256**3 + b * 256**2 + c * 256 + d))
}

# Function to convert integer to IP
int_to_ip() {
    local int="$1"
    local a b c d
    a=$((int / 256**3))
    b=$(((int % 256**3) / 256**2))
    c=$(((int % 256**2) / 256))
    d=$((int % 256))
    echo "$a.$b.$c.$d"
}

# Validate IP format
validate_ip() {
    local ip="$1"
    if [[ ! $ip =~ ^[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}$ ]]; then
        echo "Error: Invalid IP format: $ip"
        exit 1
    fi
}

# Validate inputs
validate_ip "$START_IP"
validate_ip "$END_IP"

START_INT=$(ip_to_int "$START_IP")
END_INT=$(ip_to_int "$END_IP")

if [ $START_INT -gt $END_INT ]; then
    echo "Error: Start IP ($START_IP) is greater than end IP ($END_IP)"
    exit 1
fi

TOTAL_IPS=$((END_INT - START_INT + 1))
FOUND_FILE="reverse_dns_found_${START_IP//./}_to_${END_IP//./}.txt"

echo "Starting parallel reverse DNS enumeration"
echo "Range: $START_IP to $END_IP"
echo "Total IPs: $TOTAL_IPS"
echo "Max parallel jobs: $MAX_JOBS"
echo "Started at: $(date)"

# Clear output file
> "$FOUND_FILE"

# Function to perform reverse lookup
reverse_lookup() {
    local ip="$1"
    local result
    
    result=$(dig +short +time=2 +tries=1 -x "$ip" 2>/dev/null)
    
    if [ -n "$result" ] && [ "$result" != ";; connection timed out; no servers could be reached" ]; then
        echo "$ip -> $result"
    fi
}

export -f reverse_lookup

# Generate IP range and process in parallel
{
    for ((ip_int = START_INT; ip_int <= END_INT; ip_int++)); do
        int_to_ip $ip_int
    done
} | xargs -n 1 -P "$MAX_JOBS" -I {} bash -c 'reverse_lookup "{}"' | tee "$FOUND_FILE"

echo ""
echo "Enumeration completed at: $(date)"
echo "Results saved to: $FOUND_FILE"
echo "Found records: $(wc -l < "$FOUND_FILE")"