Chapter 11 Firewall screens
191
Nortel Business Secure Router 252 Configuration — Basics
The Business Secure Router measures both the total number of existing half-open
sessions and the rate of session establishment attempts. Both TCP and UDP
half-open sessions are counted in the total number and rate measurements.
Measurements are made once a minute.
After the number of existing half-open sessions rises above a threshold
(
max-incomplete high
), the Business Secure Router starts deleting half-open
sessions as required to accommodate new connection requests. The Business
Secure Router continues to delete half-open requests as necessary, until the
number of existing half-open sessions drops below another threshold
(
max-incomplete low
).
After the rate of new connection attempts rises above a threshold (
one-minute
high
), the Business Secure Router starts deleting half-open sessions to
accommodate new connection requests as required. The Business Secure Router
continues to delete half-open sessions, as necessary, until the rate of new
connection attempts drops below another threshold (
one-minute low
). The rate is
the number of new attempts detected in the last one minute sample period.
TCP maximum incomplete and blocking period
An unusually high number of half-open sessions with the same destination host
address indicates that a Denial of Service attack is being launched against the
host.
Whenever the number of half-open sessions with the same destination host
address rises above a threshold (
TCP Maximum Incomplete
), the Business
Secure Router starts deleting half-open sessions according to one of the following
methods:
•
If the
Blocking Period
timeout is 0 (the default), the Business Secure Router
deletes the oldest existing half-open session for the host for every new
connection request to the host. This ensures that the number of half-open
sessions to a given host never exceeds the threshold.
•
If the
Blocking Period
timeout is greater than 0, the Business Secure Router
blocks all new connection requests to the host giving the server time to handle
the present connections. The Business Secure Router continues to block all
new connection requests until the
Blocking Period
expires.
Summary of Contents for BSR252
Page 28: ...28 Tables NN47923 500 ...
Page 44: ...44 Chapter 1 Getting to know your Business Secure Router NN47923 500 ...
Page 52: ...52 Chapter 2 Introducing the WebGUI NN47923 500 ...
Page 70: ...70 Chapter 3 Wizard setup NN47923 500 ...
Page 96: ...96 Chapter 5 System screens NN47923 500 ...
Page 114: ...114 Chapter 7 WAN screens NN47923 500 Figure 27 WAN IP ...
Page 120: ...120 Chapter 7 WAN screens NN47923 500 Figure 31 Dial Backup Setup ...
Page 128: ...128 Chapter 7 WAN screens NN47923 500 ...
Page 152: ...152 Chapter 9 Static Route screens NN47923 500 ...
Page 194: ...194 Chapter 11 Firewall screens NN47923 500 ...
Page 210: ...210 Chapter 13 VPN NN47923 500 Figure 67 Summary IP Policies ...
Page 222: ...222 Chapter 13 VPN NN47923 500 Figure 71 VPN Branch Office rule setup ...
Page 256: ...256 Chapter 13 VPN NN47923 500 Figure 81 VPN Client Termination advanced ...
Page 260: ...260 Chapter 13 VPN NN47923 500 ...
Page 264: ...264 Chapter 14 Certificates NN47923 500 Figure 83 My Certificates ...
Page 270: ...270 Chapter 14 Certificates NN47923 500 Figure 85 My Certificate create ...
Page 274: ...274 Chapter 14 Certificates NN47923 500 Figure 86 My Certificate details ...
Page 282: ...282 Chapter 14 Certificates NN47923 500 Figure 89 Trusted CA details ...
Page 298: ...298 Chapter 14 Certificates NN47923 500 ...
Page 316: ...316 Chapter 16 IEEE 802 1x NN47923 500 ...
Page 320: ...320 Chapter 17 Authentication server NN47923 500 Figure 106 Local User database edit ...
Page 328: ...328 Chapter 17 Authentication server NN47923 500 ...
Page 376: ...376 Chapter 20 Logs Screens NN47923 500 Figure 150 Log settings ...
Page 386: ...386 Chapter 20 Logs Screens NN47923 500 ...
Page 393: ...Chapter 21 Call scheduling screens 393 Nortel Business Secure Router 252 Configuration Basics ...
Page 394: ...394 Chapter 21 Call scheduling screens NN47923 500 ...
Page 410: ...410 Chapter 22 Maintenance NN47923 500 ...