SG UDP Packet Builder
UDP Packet Builder
Build and inspect a UDP datagram, calculate the checksum with an IPv4 pseudo-header, and export the resulting packet bytes.
Packet Inputs
UDP Header Breakdown
Source Port—
Destination Port—
UDP Length—
Checksum—
| Field | Bits | Value | Hex |
|---|
Generated UDP Datagram
Important: this tool builds the UDP header and payload only. It does not create the IPv4 header or transmit packets.
How the UDP Header Works
- Source and destination ports are each 16 bits.
- Length equals the 8-byte UDP header plus payload size.
- The checksum uses source IP, destination IP, protocol 17, UDP length, header, and payload.
- For IPv4, a zero checksum means checksum not used. For IPv6, UDP checksum is generally mandatory.
Examples
DNS: source port 53000, destination port 53.
DHCP: client port 68, server port 67.
SNMP: manager uses destination port 161; traps commonly use 162.
Syslog: traditional UDP syslog commonly uses destination port 514.
Validation and Best Practices
- Use valid IPv4 addresses when calculating a checksum.
- Keep the total UDP datagram length at or below 65,535 bytes.
- Avoid large UDP payloads that may cause IP fragmentation.
- Use test networks and authorized systems only when generating or transmitting custom traffic.
- Compare packet bytes with Wireshark or tcpdump for learning and troubleshooting.