Chapter 38 IDP
ZyWALL USG Series User’s Guide
727
Figure 506
IP v4 Packet Headers
The header fields are discussed in the following table.
Select
Configuration > UTM Profile > IDP >
Custom Signature
s. The first screen shows a summary of all
custom signatures created. Click the
SID
or
Name
heading to sort. Click the
Add
icon to create a new
Table 264 IP v4 Packet Headers
HEADER
DESCRIPTION
Version
The value 4 indicates IP version 4.
IHL
IP Header Length is the number of 32 bit words forming the total length of the header
(usually five).
Type of Service
The Type of Service, (also known as Differentiated Services Code Point (DSCP)) is
usually set to 0, but may indicate particular quality of service needs from the network.
Total Length
This is the size of the datagram in bytes. It is the combined length of the header and
the data.
Identification
This is a 16-bit number, which together with the source address, uniquely identifies this
packet. It is used during reassembly of fragmented datagrams.
Flags
Flags are used to control whether routers are allowed to fragment a packet and to
indicate the parts of a packet to the receiver.
Fragment Offset
This is a byte count from the start of the original sent packet.
Time To Live
This is a counter that decrements every time it passes through a router. When it
reaches zero, the datagram is discarded. It is used to prevent accidental routing
loops.
Protocol
The protocol indicates the type of transport packet being carried, for example, 1 =
ICMP; 2= IGMP; 6 = TCP; 17= UDP.
Header Checksum
This is used to detect processing errors introduced into the packet inside a router or
bridge where the packet is not protected by a link layer cyclic redundancy check.
Packets with an invalid checksum are discarded by all nodes in an IP network.
Source IP Address
This is the IP address of the original sender of the packet.
Destination IP Address
This is the IP address of the final destination of the packet.
Options
IP options is a variable-length list of IP options for a datagram that define IP
Security
Option, IP Stream Identifier
, (security and handling restrictions for the military),
Record
Route
(have each router record its IP address),
Loose Source Routing
(specifies a list of
IP addresses that must be traversed by the datagram),
Strict Source Routing
(specifies
a list of IP addresses that must ONLY be traversed by the datagram),
Timestamp
(have
each router record its IP address and time),
End of IP List
and
No IP Options
.
Padding
Padding is used as a filler to ensure that the IP packet is a multiple of 32 bits.
Summary of Contents for USG110
Page 27: ...27 PART I User s Guide ...
Page 195: ...195 PART II Technical Reference ...
Page 309: ...Chapter 10 Interfaces ZyWALL USG Series User s Guide 309 ...
Page 313: ...Chapter 10 Interfaces ZyWALL USG Series User s Guide 313 ...
Page 358: ...Chapter 10 Interfaces ZyWALL USG Series User s Guide 358 ...
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