Protocol Headers

Interactive graphical representations of network packet headers. Switch between protocols to view their structures.

Encapsulation Context

Showing where the selected header fits inside a standard frame transmission.

IPv4 Header Layout
Min Size: 20 Bytes
0
4
8
1631
Destination MAC (first 4 bytes)
32 bits
Destination MAC (last 2 bytes)
16 bits
Source MAC (first 2 bytes)
16 bits
Source MAC (last 4 bytes)
32 bits
EtherType (e.g. IPv4/ARP)
16 bits
Payload Data begins...
Variable
Destination MAC (first 4 bytes)
32 bits
Destination MAC (last 2 bytes)
16 bits
Source MAC (first 2 bytes)
16 bits
Source MAC (last 4 bytes)
32 bits
TPID (0x8100)
16 bits
PCP
3 bits
DEI
1 bit
VLAN ID (VID)
12 bits
EtherType (Original)
16 bits
Payload Data begins...
Variable
Version
4 bits
IHL
4 bits
Type of Service (DSCP/ECN)
8 bits
Total Length
16 bits
Identification
16 bits
Flags
3 bits
Fragment Offset
13 bits
Time to Live (TTL)
8 bits
Protocol
8 bits
Header Checksum
16 bits
Source IP Address
32 bits
Destination IP Address
32 bits
Options (If IHL > 5) & Padding
Variable
Source Port
16 bits
Destination Port
16 bits
Sequence Number
32 bits
Acknowledgment Number
32 bits
Data Offset
4 bits
Reserved
3 bits
Flags (NS, CWR, ECE, URG, ...)
9 bits
Window Size
16 bits
Checksum
16 bits
Urgent Pointer
16 bits
Options & Padding
Variable
Source Port
16 bits
Destination Port
16 bits
Length
16 bits
Checksum
16 bits
Method (e.g. GET)
Text
URI (e.g. /index.html)
Text
Version (e.g. HTTP/1.1)
Text
HTTP Headers (Host, User-Agent, Accept, etc.)
Key: Value format
CRLF (Blank Line)
Separator
Message Body / Data Payload
HTML, JSON, Image, etc.
Select a Field

Size: -

Click on any field in the header diagram to see its detailed explanation, purpose, and usage in networking.