Brocade Communications Systems ServerIron ADX 12.4.00a - Manual (Page 129)

ServerIron ADX Security Guide 115
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Configuring Syn-Proxy
5
ServerIronADX(config)# interface ethernet 2/1
ServerIronADX(config-if-e1000-2/1)# ip tcp syn-proxy in
Syntax: interface ethernet <slot number/port number>
Syntax: ip tcp syn-proxy in
The ip tcp syn-proxy command can be configured for either a physical interface (as shown) or a
ve interface.
Setting Attack-Rate-Threshold
A DoS attack threshold specifies the number of SYNs, without corresponding ACKs, the ServerIron
ADX accepts before writing a warning message to the system log (every 60 seconds for the duration
of the attack).
To configure a threshold value for the SYN attack rate, use the following command:
ServerIronADX(config)# server syn-cookie-attack-rate-threshold 2000
Syntax: server syn-cookie-attack-rate-threshold <threshold value>
<threshold value> is a number between 1 and 10,000,000. The default is 1000.
NOTE
If you do not configure a threshold, the ServerIron ADX does not write SYN attack messages to the
log file.
If the number of SYNs (without corresponding ACKs), received on the ServerIron ADX exceeds the
specified threshold of 2000, the ServerIron ADX writes the following message to the log file every
60 seconds for the duration of the attack:
"CRITICAL: syn-cookie attack rate 2005 exceeds attack rate threshold 2000"
Setting SYN-Ack-Window-Size
To globally set the TCP window size that the ServerIron ADX uses on a SYN-ACK packet sent back to
a client with SYN-Cookie, use the following command:
ServerIronADX(config)# server syn-proxy-syn-ack-window-size 5000
Syntax: [no] server syn-proxy-syn-ack-window-size <value>
<value> is the window size. The range from 1 to 65536. The default is 8192.
This command works with a syn-proxy configuration. By having syn-ack-window-size configured, the
window size of the SYN-ACK packet sent from ServerIron ADX to client will have the configured
<value>.
This feature can be used to prevent the client from sending HTTP-Gets before the server side 3-way
handshake is established.
Setting Reset-Using-Client-MAC
NOTE
In this rare corner-case, the reset-using-client-mac command is needed to send a reset to the client.
To globally send a Reset to the client using the client MAC address on the interfaces where
Syn-Proxy is enabled, use the following command: