WatchGuard x1000 参考指南

CHAPTER 1: Internet Protocol Reference

2

WatchGuard Firebox System

IP header number list

The IP Protocol header contains an 8-bit field that identifies the protocol 
for the transport layer for the datagram.

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.

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)

Keyword

Number

Protocol 

0 

Reserved 

ICMP

1 

Internet Control Message 

IGMP

2 

Internet Group Management 

GGP 

3 

Gateway-to-Gateway 

IP

4 

IP-within-IP (encapsulation)

ST

5 

Stream