ZyXEL Communications P-660 series Betriebsanweisung PDF herunterladen (Seite 96)

Chapter 7 Firewalls

P-660R-F1 Series User’s Guide

The following table describes the labels in this screen.

7.4 The Firewall Threshold Screen

For DoS attacks, the ZyXEL Device uses thresholds to determine when to start dropping sessions

that do not become fully established (half-open sessions). These thresholds apply globally to all

sessions.

For TCP, half-open means that the session has not reached the established state-the TCP three-way

handshake has not yet been completed. Under normal circumstances, the application that initiates

a session sends a SYN (synchronize) packet to the receiving server. The receiver sends back an ACK

(acknowledgment) packet and its own SYN, and then the initiator responds with an ACK

(acknowledgment). After this handshake, a connection is established.

Figure 59 Three-Way Handshake

For UDP, half-open means that the firewall has detected no return traffic. An unusually high number

(or arrival rate) of half-open sessions could indicate a DOS attack.

Table 35 Security > Firewall > Rules: Edit: Edit Customized Services: Config

LABEL DESCRIPTION

Config

Service Name Type a unique name for your custom port.

Service Type Choose the IP port (TCP, UDP or TCP/UDP) that defines your customized port

from the drop down list box.

Port Configuration

Type Click Single to specify one port only or Range to specify a span of ports that define

your customized service.

Port Number Type a single port number or the range of port numbers that define your

customized service.

Back Click this to return to the previous screen without saving.

Apply Click this to save your changes.

Cancel Click this to restore your previously saved settings.

Delete Click this to delete the current rule.

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ZyXEL Communications P-660 series Betriebsanweisung Seite 96