HP 635n - JetDirect IPv6/IPsec Print Server Administrator's Manual page 152

For example, for LPD printing enabled with an IPsec rule, a local TCP, secure, port 515 would be
listed. Port 515 is a well-known port for LPD services. And if the print server is connected to a remote
application's port 25, it may list remote TCP, unsecure, port 25 of the client.
142 Chapter 8 HP Jetdirect Configuration Pages ENWW