OSI Model Summary

OSI Layers – Summary
 
Layer 2 – Data Link – Frame (802.3/Ethernet)
Dst MAC (6 bytes) Src MAC (6 bytes) 802.1q (4 bytes) [opt] Type/Leng (2 bytes)
Layer 3 – Network – Packet (IPv4)
Version/IHL (1 byte) DSCP/ECN (1 byte) Leng (2 bytes)
Identification (2 bytes) Flags/Frag Offset (2 bytes)
TTL (1 byte) Protocol (1 byte) Header Checksum (2 bytes)
Src IP (4 bytes)
Dst IP (4 bytes)
Layer 4 – Transport – Segment (UDP)
Src Port (2 bytes) Dst Port (2 bytes)
Leng (2 bytes) Checksum (2 bytes)
 
Layer 4 – Transport – Segment (TCP)
Src Port (2 bytes) Dst Port (2 bytes)
Leng (2 bytes) Checksum (2 bytes)
Sequence Number (4 bytes)
Acknowledgment Number (4 bytes)
Data Offset (1 byte) Flags (1 byte)
SYN/ACK/RST/FIN
Window Size (2 bytes)
Layer 5/6/7 – Application – Data (DHCP/DNS/SSH/HTTP)
Payload
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OSI Model Summary

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