Reference Guide
1
CHAPTER 1
Internet Protocol Reference
Internet Protocol (IP) specifies the format of packets and the addressing scheme for
sending data over the Internet. By itself, it functions like a postal system allowing you
to address a package and drop it into the system. There is, however, no direct link
between you and the recipient. In other words, there is no package.
Most networks combine IP with higher-level protocols like Transmission Control
Protocol (TCP). Unlike simple IP, TCP/IP establishes a connection between two host
servers so that they can send messages back and forth. TCP/IP provides the
“packaging.”
Internet Protocol header
Internet Protocol (IP) is an Internet standard and enables the shipment of datagrams
– self-contained packets of information that include their own address and delivery
instructions. IP prepends a header to each datagram. The IP header contains a
minimum of twelve attributes as well as additional optional attributes.
Attribute
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 generally
under-utilized because few application layers can set it.
Tot_Len
16 bits
Total length of packet measured in octets. It is used in
reassembling fragments.
ID
16 bits
Packet ID, used for reassembling 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.
Summary of Contents for Firebox X20E
Page 1: ...WatchGuard Firebox System Reference Guide Firebox System 4 6...
Page 12: ...Standard ports and random ports 8...
Page 32: ...Well known services list 28...
Page 36: ...Searching for Blocked Sites 32...
Page 42: ...Newsgroups 38...
Page 50: ...Managing flash disk memory 46...