how to show DNS recursive resolution

If I am asked to explain the concept of DNS recursive resolution, I would prepare a sketch like this one below :

There is an altenative. In a Linux/Unix shell, just issue the command "dig +trace FQDN" can do the same. Dig makes iterative queries to resolve the name being looked up and will follow referrals from the root servers,showing the answer from each server that was used to resolve the lookup.


Using different port number for SSH, SFTP and SCP clients

How could I access hosts running SSH daemon with a different port number such as 747 ? SSH can support SFTP and SCP on the same daemon so the commad syntax for SSH, SFTP and SCP should also be remembered. The answers are here below :

#ssh -p 747 user@abc.com
#sftp -oPort=747 user@abc.com
#scp -P 747 user@abc.com:/directory/file .

The small and capital letter of p means different things, in SCP, -p means preserving modification times, access times of file whereas -P specifies a port number. For SSH, no -P exist, just -p will be ok for port number.