Avaya Business Secure Router 252 Configuration - Basics Manual de usuario descargar pdf (Pagina 191)

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.

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Avaya Business Secure Router 252 Configuration - Basics Manual de usuario Pagina 191