IPv4 Example

IPv4 + UDP

Examine an IPv4 packet carrying a UDP datagram. Understand how the protocol field indicates UDP (17) and inspect the encapsulated UDP header within the IPv4 payload.

Hex Data

45 00 00 1C 00 01 00 00 40 11 00 00 C0 A8 01 02 C0 A8 01 01 00 35 00 35 00 08 00 00
Note: Protocol field = 17 (UDP), followed by UDP header (DNS port 53)
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encapsulationudpdns

Field Breakdown

Version
IP version (always 4 for IPv4)
69
IHL
Internet Header Length in 32-bit words (minimum 5)
69
DSCP
Differentiated Services Code Point (QoS)
0b000000
ECN
Explicit Congestion Notification
0b00
Total Length
Total length of IP packet in bytes (header + data)
28
Identification
Unique identifier for fragmentation reassembly
0x0001
Flags
Control flags (Reserved, DF, MF)
0b000
Fragment Offset
Position of fragment in original datagram (in 8-byte blocks)
0
TTL
Time To Live (hop limit)
64
Protocol
Protocol used in data portion
17
UDP
Header Checksum
Checksum of IP header only
0x0000
Source IP
Source IP address
0x-3F57FEFE
Destination IP
Destination IP address
0x-3F57FEFF

Related Resources

IPv4 Protocol Visualizer - Parse & Analyze IPv4 PacketsIPv4 Header Format and Fields Explained - ByteLensIPv4 vs IPv6 - Key Differences and Migration GuideIP Address Protocol - What is IP? IPv4 vs IPv6 Explained

About IPv4

Internet Protocol version 4 (RFC 791)

Fields: 13
Endianness: big
Specification: RFC 791