ZyXEL ZyWALL USG 2000 User Guide - Page 582

Chapter 34 IDP Table 157 IP v4 Packet Headers (continued) HEADER DESCRIPTION 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. 34.8 Configuring Custom Signatures 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. 582 ZyWALL USG 2000 User's Guide