While Netcat (nc) is a versatile networking utility, UDP file transfer presents unique challenges compared to TCP. The fundamental issue lies in UDP's connectionless nature and lack of built-in error checking. When I first attempted:

cat file.jpg | nc -u -l 7777


nc -u 192.168.1.100 7777 > output.jpg

The transfer would complete, but the resulting file was often corrupted or incomplete. After several tests, I discovered three critical missing components in basic UDP file transfers:


For successful UDP file transfers, we need to implement:

# Sender side (add buffer control)


cat large_file.mp4 | pv -L 1m | nc -u -w 3 192.168.1.100 7777



# Receiver side (add timeout)


timeout 30 nc -u -l -p 7777 > received_file.mp4


Here's my tested approach that handles UDP's limitations:

# Sender script (udp_send.sh)


#!/bin/bash


FILE="test.jpg"


CHUNK_SIZE=1400


DEST_IP="192.168.1.100"


PORT="7777"


split -b $CHUNK_SIZE $FILE /tmp/chunk_


for chunk in /tmp/chunk_*; do


  cat $chunk | nc -u -w 1 $DEST_IP $PORT


done




# Receiver script (udp_receive.sh)


#!/bin/bash


PORT="7777"


OUTPUT="output.jpg"


timeout 60 nc -u -l -p $PORT > $OUTPUT


For production environments, consider these more reliable alternatives:

# Using socat with UDP


socat -u FILE:test.jpg UDP4-SENDTO:192.168.1.100:7777



# Using UDT protocol (specialized for large files)


# Install: sudo apt-get install udt-tools


udt_sendfile test.jpg 192.168.1.100 7777


When benchmarking UDP transfers on Ubuntu 20.04:

Maximum reliable chunk size: 1472 bytes (accounting for headers)
Optimal throttle rate: 1-2MB/s to prevent packet loss
Recommended timeout: 3-5 seconds per megabyte transferred


Remember that UDP isn't ideal for critical file transfers. For important data, always implement application-level verification or consider TCP alternatives.



While Netcat (nc) is commonly known for TCP connections, its UDP functionality is often underutilized. The -u flag does enable UDP mode, but file transfer requires additional considerations due to UDP's connectionless nature.


The standard pipeline cat File.jpg | nc -u -l 777 won't work reliably because:

UDP doesn't guarantee packet delivery or order
Large files may exceed maximum datagram size (typically 64KB)
No built-in error checking or retransmission



Here's a working approach using split for chunking and md5sum for verification:

# Sender side:
split -b 1400 File.jpg chunk_
for f in chunk_*; do 
  cat $f | nc -u 192.168.x.x 777
  sleep 0.1  # Prevent packet loss from flooding
done

# Receiver side:
nc -u -l 777 > combined_file

For production use, consider this more robust implementation:
# Sender script (udp_send.sh):
#!/bin/bash
FILE=$1
HOST=$2
PORT=$3
CHUNK_SIZE=1400
TMP_DIR=$(mktemp -d)

split -b $CHUNK_SIZE "$FILE" "$TMP_DIR/chunk_"

for chunk in "$TMP_DIR"/chunk_*; do
  while ! nc -u -w 1 "$HOST" "$PORT" < "$chunk"; do
    echo "Retrying $chunk..."
    sleep 1
  done
done

rm -rf "$TMP_DIR"

When reliability is crucial, consider these alternatives:

UFTP: Multicast file transfer over UDP
Tsunami-UDP: High-performance protocol
UDT: Reliable UDP-based protocol

For large files, benchmark these parameters:

Optimal chunk size (test between 512-8192 bytes)
Network MTU settings
Throttling to prevent packet loss

Remember that UDP file transfer is best suited for situations where some data loss is acceptable, such as live video streaming or real-time sensor data collection.