curious

I have a question- NOT WORRIED ABOUT SECURITY ISSUE WITH THIS ONE

 

I use NAV2008 so when I look at the internet connection logs, it will show the remote IP address in number format and when I click on that particular entry it will in words say hat it is

 

example connection log shows

 remote IP as 208.74.204.196

when I click the entry it says community.norton.com

 

so that makes sense

but sometimes it will still only show the number even when I click the entry

 

why is that?then sometimes if I go to webyield.net and put in the IP ( example 206.16.246.184) I get a result that says no reverse DNS for this IP

 

why is that?