ZyWALL Series Internet Security Gateway
Firewalls
11-5
Figure 11-2 Three-Way Handshake
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.
2-a
SYN Attack
floods a targeted system with a series of SYN packets. Each packet causes the
targeted system to issue a SYN-ACK response. While the targeted system waits for the ACK that
follows the SYN-ACK, it queues up all outstanding SYN-ACK responses on what is known as a
backlog queue. SYN-ACKs are moved off the queue only when an ACK comes back or when an
internal timer (which is set at relatively long intervals) terminates the three-way handshake. Once
the queue is full, the system will ignore all incoming SYN requests, making the system unavailable
for legitimate users.
Figure 11-3 SYN Flood
Содержание Internet Security Gateway ZyWALL 100
Страница 1: ...ZyWALL 10W 30W 50 100 Internet Security Gateway User s Guide Version 3 62 February 2004 ...
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Страница 52: ...ZyWALL Series Internet Security Gateway 1 10 Getting to Know Your ZyWALL Figure 1 2 VPN Application ...
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Страница 103: ...DMZ and WAN III Part III DMZ and WAN This part covers configuration of the DMZ and WAN screens ...
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Страница 124: ...ZyWALL Series Internet Security Gateway 8 16 WAN Screens Figure 8 10 Dial Backup Setup ...
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Страница 217: ...VPN IPSec VI Part VI VPN IPSec This part provides information on how to configure Virtual Private Networks ...
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Страница 235: ...ZyWALL Series Internet Security Gateway VPN Screens 15 11 Figure 15 5 VPN IKE ...
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Страница 282: ...ZyWALL Series Internet Security Gateway 16 20 Certificates Figure 16 9 Trusted CA Details ...
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Страница 302: ...ZyWALL Series Internet Security Gateway 17 2 Authentication Server Figure 17 1 Local User Database ...
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Страница 351: ...Logs IX Part IX Logs This part provides information and instructions for the logs and reports ...
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Страница 356: ...ZyWALL Series Internet Security Gateway 20 4 Log Screens Figure 20 2 Log Settings ...
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Страница 365: ...Maintenance X Part X Maintenance This part covers the maintenance screens ...
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Страница 386: ...ZyWALL Series Internet Security Gateway 22 6 Introducing the SMT Figure 22 5 Advanced Management SMT Menus ...
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