ZyXEL 4-port Prestige 792H Router 91-004-342001 Manual Do Utilizador

Prestige 792H G.SHDSL Router 

Firewalls  

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4.  Based on the obtained state information, a firewall rule creates a temporary access list entry that is 

inserted at the beginning of the WAN interface's inbound extended access list. This temporary 
access list entry is designed to permit inbound packets of the same connection as the outbound 
packet just inspected. 

5.  The outbound packet is forwarded out through the interface. 

6.  Later, an inbound packet reaches the interface. This packet is part of the connection previously 

established with the outbound packet. The inbound packet is evaluated against the inbound access 
list, and is permitted because of the temporary access list entry previously created. 

7.  The packet is inspected by a firewall rule, and the connection's state table entry is updated as 

necessary. Based on the updated state information, the inbound extended access list temporary 
entries might be modified, in order to permit only packets that are valid for the current state of the 
connection. 

8.  Any additional inbound or outbound packets that belong to the connection are inspected to update 

the state table entry and to modify the temporary inbound access list entries as required, and are 
forwarded through the interface. 

9. 

When the connection terminates or times out, the connection's state table entry is deleted and the 
connection's temporary inbound access list entries are deleted.

 

Additional rules may be defined to extend or override the default rules. For example, a rule may be created 
which will: 

i.  Block all traffic of a certain type, such as IRC (Internet Relay Chat), from the LAN to the Internet. 

ii.  Allow certain types of traffic from the Internet to specific hosts on the LAN. 

iii.  Allow access to a Web server to everyone but competitors. 

iv.  Restrict use of certain protocols, such as Telnet, to authorized users on the LAN. 

These custom rules work by evaluating the network traffic’s Source IP address, Destination IP address, IP 
protocol type, and comparing these to rules set by the administrator.