a touch overkill to get the hostname for sessions on your server perhaps?

select s.host_name

from sys.dm_exec_connections C

join sys.dm_exec_sessions S on S.session_id = C.session_ID

where C.client_net_address = '127.0.0.1'

will provide the same information a lot simpler and safer than allowing a CLR on your system with External_Access

However as an approach to allow a dns lookup from within sql server this is effective. I wrote something very similar 6 years ago when i was analysing web server logs associated with identifying click fraud and needed to do a lookup and at times a reverse lookup to fill the gaps in the data as provided by the logs.