UDP fragmentation checker

receipient.sh

#!/bin/bash
PORT=12345
RESULTS_DIR="udp_receiver_results_$(date +%Y%m%d_%H%M%S)"
mkdir -p "$RESULTS_DIR"

echo "Starting UDP fragmentation test - Receiver"
echo "----------------------------------------"
echo "Port: $PORT"
echo "Results directory: $RESULTS_DIR"

# Log configuration
echo "Test Configuration" > "$RESULTS_DIR/receiver_config.log"
echo "----------------" >> "$RESULTS_DIR/receiver_config.log"
echo "Timestamp: $(date)" >> "$RESULTS_DIR/receiver_config.log"
echo "Port: $PORT" >> "$RESULTS_DIR/receiver_config.log"

echo "Timestamp,Source_IP,Expected_Size,Actual_Size,Size_Match,Data_Valid" > "$RESULTS_DIR/receiver_results.csv"

cleanup() {
    echo -e "\nReceiver stopped. Results saved in $RESULTS_DIR/"
    exit 0
}
trap cleanup SIGINT SIGTERM

nc -6 -u -l -k $PORT | while read -r line; do
    timestamp=$(date +"%Y-%m-%d %H:%M:%S.%N")
    source_ip=$(netstat -nu | grep ":$PORT" | tail -1 | awk '{print $5}' | cut -d: -f1)
    
    if [[ $line =~ ^[0-9]{8}: ]]; then
        # Extract test packet information using string manipulation instead of numeric evaluation
        expected_size="${line:0:8}"  # Get as string, not number
        actual_size=$((${#line} - 9))
        payload=${line:9}
        
        # Compare sizes as decimal numbers
        if [ "$actual_size" -eq "$((10#$expected_size))" ]; then
            size_match="true"
        else
            size_match="false"
        fi
        
        # Verify payload contains valid base64 characters
        if [[ "$payload" =~ ^[A-Za-z0-9+/=]+$ ]]; then
            data_valid="true"
        else
            data_valid="false"
        fi
        
        echo "Received packet from $source_ip:"
        echo "  Expected size: $expected_size bytes"
        echo "  Actual size: $actual_size bytes"
        echo "  Size match: $size_match"
        echo "  Data valid: $data_valid"
        
        echo "$timestamp,$source_ip,$expected_size,$actual_size,$size_match,$data_valid" >> "$RESULTS_DIR/receiver_results.csv"
    else
        # Handle regular messages
        size=${#line}
        echo "Received test message from $source_ip - Size: $size bytes"
        echo "Content: $line"
        echo "$timestamp,$source_ip,n/a,$size,n/a,n/a" >> "$RESULTS_DIR/receiver_results.csv"
    fi
done

sender.sh

#!/bin/bash
RECEIVER_IP="2a0xxxxxxxfb"
PORT=12345

echo "Starting UDP MTU boundary test"
echo "---------------------------"
echo "Targeting: $RECEIVER_IP:$PORT"

# Test range around suspected MTU boundary
for size in $(seq 1400 10 1500); do
    echo "Testing size: $size bytes..."
    
    # Calculate base64 input size (3/4 of target)
    raw_size=$((size * 3 / 4))
    
    # Create test data
    random_data=$(head -c $raw_size /dev/urandom | base64)
    actual_size=${#random_data}
    data=$(printf "%08d:%s" $actual_size "$random_data")
    
    echo "$data" | nc -6 -w 1 -u $RECEIVER_IP $PORT
    sleep 1
    echo "-------------------------"
done