Avaya Business Secure Router 252 Configuration - Basics Instrukcja Użytkownika Pobierz pdf (Strona 163)

Chapter 10 Firewalls 163

Nortel Business Secure Router 252 Configuration — Basics

rule for this packet and it is not an attack, the Action for packets that don’t

match firewall rules field determines the action for this packet.

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. You can modify the inbound extended access

list temporary entries based on the updated state information, 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.

Stateful inspection and the Business Secure Router

Additional rules can be defined to extend or override the default rules. For

example, a rule can be created that will:

• Block all traffic of a certain type, such as IRC (Internet Relay Chat), from the

LAN to the Internet.

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

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

• Restrict use of certain protocols, such as Telnet, to authorized users on the

LAN.

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Avaya Business Secure Router 252 Configuration - Basics Instrukcja Użytkownika Strona 163