Lost DNS Registration

This is a re-post since I received no responses to my query. For the past
several months I have been losing my DNS name registration settings
intermittently while using my DSL Internet connection. Because "Repair this
Connection" works, and as per other advice in this forum I ran through the
repair procedure manually to determine exactly what was being repaired. I
have discovered that the Command "ipconfig /registerdns" is the command that
fixes my connection. Now I need some advice on why this is happening or how
to fix the problem so that I do not lose the connection in the first place.
Is this a problem on my machine or with my ISP's server?

My setup is an Ethernet connection to a Cisco DSL router/modem. Integrated
3Com 3C920 Fast Ethernet Controller in a Dell P4 1.5 gig machine w/512 Ram.

TIA
GWL