Avaya Business Secure Router 252 Configuration - Basics Uživatelský manuál stáhnout pdf (Strana 162)

100

101

162 Chapter 10 Firewalls

NN47923-500

• Allows all sessions originating from the LAN (local network) to the WAN

(Internet).

• Denies all sessions originating from the WAN to the LAN.

Figure 49 Stateful inspection

Figure 49 shows the Business Secure Router default firewall rules in action, and

demonstrates how stateful inspection works. User A can initiate a Telnet session

from within the LAN and responses to this request are allowed. However, other

Telnet traffic initiated from the WAN is blocked.

Stateful inspection process

In the following example, the following sequence of events occurs when a TCP

packet leaves the LAN network through the firewall's WAN interface. The TCP

packet is the first in a session, and the packet's application layer protocol is

configured for a firewall rule inspection:

1 The packet travels from the firewall's LAN to the WAN.

2 The packet is evaluated against the interface's existing outbound access list,

and the packet is permitted (a denied packet is dropped at this point).

3 The packet is inspected by a firewall rule to determine and record information

about the state of the packet's connection. This information is recorded in a

new state table entry created for the new connection. If there is not a firewall

Business Secure Router

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