Set to yes, the Restrict Source IP parameter of your device to prevent your device responding to DoS attacks.
If set to no, the device may crash with an out of memory error.
If you use a configuration file to configure your devices, edit the Restrict_Source_IP_N_ parameter
For example to secure Line 1 of a SPA2102, edit the configuration file as follows:
<Restrict_Source_IP_1_ ua="na">Yes</Restrict_Source_IP_1_>
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