tcp syn-cookies

Last Updated : Nov 06, 2012 |

Enables the TCP SYN cookies defense mechanism against SYN attacks. Use no tcp syn-cookies to disable the TCP SYN cookies defense mechanism against SYN attacks.

Note:

SYN cookies are disabled by default.

When enabling or disabling SYN cookies, you are prompted to copy the running configuration to the start-up configuration using the copy running-config startup-config command, and then to reset the device.

This command applies to IPv4 only.

Syntax

[no] tcp syn-cookies

User level

read-write

Context

general

Examples

To enable SYN cookies:

Gxxx-001(config)# tcp syn-cookies
To enable tcp syn-cookies copy the running configuration to the 
start-upconfiguration file, and reset the device.
Gxxx-001(config)# copy running-config startup-config
Gxxx-001(config)# reset
...
! Coming up from reset - syn-cookies are now enabled

To disable SYN cookies:

Gxxx-001(config)# no tcp syn-cookies
To disable tcp syn-cookies copy the running configuration to the 
start-upconfiguration file, and reset the device.