
160
Chapter 10 Firewalls
NN47922-500
2
Weaknesses in the TCP/IP specification leave it open to SYN Flood and
LAND attacks. These attacks are executed during the handshake that initiates
a communication session between two applications.
Figure 47
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.
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 ignores all incoming SYN requests, making the
system unavailable for legitimate users.
Содержание BSR222
Страница 28: ...28 Tables NN47922 500 ...
Страница 50: ...50 Chapter 2 Introducing the WebGUI NN47922 500 ...
Страница 66: ...66 Chapter 3 Wizard setup NN47922 500 ...
Страница 87: ...Chapter 5 System screens 87 Nortel Business Secure Router 222 Configuration Basics Figure 17 Time and Date ...
Страница 92: ...92 Chapter 5 System screens NN47922 500 ...
Страница 96: ...96 Chapter 6 LAN screens NN47922 500 Configuring IP Click LAN to open the IP screen Figure 19 LAN IP ...
Страница 104: ...104 Chapter 6 LAN screens NN47922 500 ...
Страница 115: ...Chapter 7 WAN screens 115 Nortel Business Secure Router 222 Configuration Basics Figure 27 WAN IP ...
Страница 123: ...Chapter 7 WAN screens 123 Nortel Business Secure Router 222 Configuration Basics Figure 32 Dial Backup Setup ...
Страница 154: ...154 Chapter 9 Static Route screens NN47922 500 ...
Страница 196: ...196 Chapter 11 Firewall screens NN47922 500 ...
Страница 212: ...212 Chapter 13 VPN NN47922 500 Figure 68 Summary IP Policies ...
Страница 223: ...Chapter 13 VPN 223 Nortel Business Secure Router 222 Configuration Basics Figure 72 VPN Branch Office rule setup ...
Страница 249: ...Chapter 13 VPN 249 Nortel Business Secure Router 222 Configuration Basics Figure 79 VPN Client Termination ...
Страница 256: ...256 Chapter 13 VPN NN47922 500 Figure 82 VPN Client Termination advanced ...
Страница 260: ...260 Chapter 13 VPN NN47922 500 ...
Страница 264: ...264 Chapter 14 Certificates NN47922 500 Figure 84 My Certificates ...
Страница 273: ...Chapter 14 Certificates 273 Nortel Business Secure Router 222 Configuration Basics Figure 87 My Certificate details ...
Страница 281: ...Chapter 14 Certificates 281 Nortel Business Secure Router 222 Configuration Basics Figure 90 Trusted CA details ...
Страница 290: ...290 Chapter 14 Certificates NN47922 500 Figure 95 Trusted remote host details ...
Страница 314: ...314 Chapter 16 IEEE 802 1x NN47922 500 ...
Страница 318: ...318 Chapter 17 Authentication server NN47922 500 Figure 107 Local User database edit ...
Страница 326: ...326 Chapter 17 Authentication server NN47922 500 ...
Страница 374: ...374 Chapter 20 Logs Screens NN47922 500 Figure 151 Log settings ...
Страница 384: ...384 Chapter 20 Logs Screens NN47922 500 ...
Страница 390: ...390 Chapter 21 Call scheduling screens NN47922 500 Figure 158 Applying Schedule Sets to a remote node ...
Страница 402: ...402 Chapter 22 Maintenance NN47922 500 Figure 170 Restart screen ...
Страница 422: ...422 Appendix A Troubleshooting NN47922 500 ...