ZyXEL Communications USG 2000 User Manual

Chapter 34 IDP

ZyWALL USG 2000 User’s Guide

Select Configuration > Anti-X > IDP > Custom Signatures. 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 signature or click the Edit icon 
to edit an existing signature. You can also delete custom signatures here or save 
them to your computer.

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.

Table 157   IP v4 Packet Headers  (continued)