Hi and welcome to Digi Forum!
In order to block ping or other unwanted traffic, you should use the firewall, see the User Guide section here:
https://www.digi.com/resources/documentation/digidocs/90001019/default.htm#references/r_firewall.htm%3FTocPath%3DConfiguring%2520security%2520%7CFirewall%2520%7C_____0
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 tech.support@digi.com.
You can find details on available Support options here: https://www.digi.com/support.
Thanks,
Anny
Digi Technical Support