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WatchGuard System Manager
Internet Protocol Header
Internet Protocol (IP) is an Internet standard that enables the sending of datagrams — packets of
information that include an address and instructions on how to send the datagram to its destination.
IP prepends a header to each datagram. The IP header contains a minimum of 12 properties, and other
optional properties.
Property
Size
Description
Version
4 bits
IP format number (Current version = 4)
IHL
4 bits
Header length in 32-bit words (Minimum = 5)
TOS
8 bits
Type of service sets routing priorities. It is usually not used because not many
application layers can set it.
Tot_Len
16 bits
Total length of packet measured in octets. It is used to assemble fragments.
ID
16 bits
Packet ID, used to assemble fragments.
Flags
3 bits
Miscellaneous flags
Frag_Off
13 bits
Identifies fragment part for this packet.
TTL
8 bits
Time to live. It sets the maximum time the datagram remains alive in the system.
Protocol
8 bits
IP protocol number. Indicates which of TCP, UDP, ICMP, IGMP, or other Transport
protocol is inside.
Check
16 bits
Checksum for the IP header
Sour_Addr
32 bits
Source IP address
Dest_Addr
32 bits
Destination IP address
Options
24 bits
IP Options (Present if IHL is 6)