TCPIP Packet Format

This tutorial covers everything one like to know about networking basics including circuit switching vs packet switching, TCP/IP protocol fields, ARP/RARP protocol fields, what is IP address ,what is MAC address, networking devices which include hub, switch, bridge, router, gateway and firewall. This page covers This page covers TCPIP packet including fields in Ethernet header,IP header and TCP header.

• Circuit Switching vs Packet switching
• LAN vs WAN vs MAN
• What is an IP address
• What is MAC Address
• Basics of OSI and TCP-IP Layers
• What is Hub
• What is Switch
• What is Bridge
• What is Router
• What is Gateway
• Firewall basics
• TCP-IP Packet format
• ARP Protocol format

No. of bytes Field type Description Header type
1-6 DA Destination address Ethernet Header
7-12 SA Source Address Ethernet Header
13-14 Type Type Field 0x800-
IP 0x806 ARP
Ethernet Header
15 Ver Ver=4, No. of 4 byte words in the header IP header
16 Type Type of Service(typically 0) IP header
17-18 T-len Total length of packet in
bytes including IP header
IP header
19-20 ID Unique Identification of packet IP header
21 Flags 3 bits (0-DF-MF)
DF=0 May fragment,MF=0 last fragment
IP header
21-22 Offset Fragment offset in 64 bit blocks IP header
23 TTL Time to live IP header
24 Protocol Upper layer protocol carried
in data(TCP/UDP)
IP header
25-26 Checksum Checksum of the header IP header
27-30 IP SA IP source address IP header
31-34 IP DA IP destination address IP header
35-36 S-port Source port TCP header
37-38 D-port destination port TCP header
39-42 Seq. Num. Sequence Number TCP header
43-46 ACK Acknowledgement number TCP header
47 Len 4 bit size of TCP header
in 4 byte words
TCP header
47-48 Reserved 6 bits not used TCP header
48 Flags UAPRSF(U=Urgent,A=Ack,P=Push,
TCP header
49-50 Window TCP Window(for flow control) TCP header
51-52 Checksum Checksum for header and data TCP header
53-54 Urgent Urgent pointer TCP header
55 to N DATA TCP Data Data Payload part
N+1 FCS CRC(4 byte) Ethernet Header

Networking related links

What is Bridge
What is Router
What is Gateway
Firewall basics
TCP-IP Packet format
Difference between OSI and TCPIP layers
Difference between TCP UDP

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