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
Summary of Contents for Prestige 652H series
Page 32: ......
Page 50: ......
Page 66: ......
Page 68: ......
Page 76: ......
Page 80: ......
Page 120: ...Prestige 652H HW Series User s Guide 8 12 WAN Setup Figure 8 6 Advanced WAN Backup ...
Page 128: ......
Page 146: ......
Page 148: ......
Page 162: ......
Page 178: ...Prestige 652H HW Series User s Guide 13 16 Firewall Screens Figure 13 8 Rule Edit Example ...
Page 196: ......
Page 198: ......
Page 204: ......
Page 214: ...Prestige 652H HW Series User s Guide 16 10 VPN Screens Figure 16 5 VPN IKE ...
Page 227: ...Prestige 652H HW Series User s Guide VPN Screens 16 23 Figure 16 8 Manual Setup ...
Page 238: ......
Page 258: ......
Page 277: ...Maintenance VIII Part VIII Maintenance This part covers the maintenance screens ...
Page 278: ......
Page 296: ......
Page 298: ......
Page 308: ......
Page 324: ......
Page 330: ......
Page 386: ......
Page 406: ......
Page 418: ......
Page 428: ......
Page 450: ......
Page 454: ......
Page 464: ......
Page 470: ......
Page 486: ......
Page 494: ......
Page 500: ......
Page 512: ......
Page 516: ......
Page 520: ......
Page 560: ......
Page 574: ......