Prestige 652H/HW Series User’s Guide
Firewalls
12-5
Figure 12-2 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 12-3 SYN Flood
Содержание Prestige 652H series
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Страница 173: ...Prestige 652H HW Series User s Guide Firewall Screens 13 11 Figure 13 5 Insert Append A Firewall Rule ...
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Страница 197: ...VPN IPSec V Part V VPN IPSec This part provides information about configuring VPN IPSec for secure communications ...
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Страница 493: ...XII Part XII Appendices and Index This part contains additional background information and an index or key terms ...
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