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In order to block ping or other unwanted traffic, you should use the firewall, see the User Guide section here:
Also, I would suggest you to look at this guide as well: https://ftp1.digi.com/support/documentation/AN_018_TransPort_Security_Lockdown.pdf
I hope this helps, if you need any further assistance please send us an email to email@example.com.
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Digi Technical Support