What is RFC 1918?

What is RFC 1918?

• A standar for HTTP
• An IRC channel for network admins
• A standard for private IPv4 addresses
• A random UDP port number               

EXPLANATION

Wikipedia entry: Addresses in the private space are not allocated to any specific organization and anyone may use these addresses without approval from a regional Internet registry. However, IP packets addressed from them cannot be transmitted through the public Internet, and so if such a private network needs to connect to the Internet, it must do so via a network address translator (NAT) gateway, or a proxy server.

IETF documentation for RFC 1918

IPv6 equivalent RFC 4193

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If you wanted to retrieve all the records from TableA and only those records from TableB that matched, which query would you use?

 If you wanted to retrieve all the records from TableA and only those records from TableB that matched, which query would you use?

• SELECT TableA.*, TableB.* FROM TableA INNER JOIN TableB ON TableA.PK = TableB.FK
• SELECT TableA.*, TableB.* FROM TableA RIGHT JOIN TableB ON TableA.PK = TableB.FK
• SELECT TableA.*, TableB.* FROM TableA LEFT JOIN TableB ON TableA.PK = TableB.FK
• SELECT * FROM TableA UNION ALL SELECT * FROM TableB         

EXPLANATION

In this question we are joining TableA to TableB

An INNER JOIN will give you the results where there is a match between TableA and TableB on the join criteria.

A LEFT JOIN will return every record from the table on the left (TableA in this case) and only those records from TableB where there is a match on the join criteria.

A RIGHT JOIN does the exact opposite of the LEFT JOIN. It will return every record from the table on the right (TableB in this case) and only those records from TableA where there is a match on the join criteria.

A UNION ALL statement takes the results of two or more queries and returns them as one dataset. The only caveat is that the columns being returned must match for all queries.

SOURCE

https://www.w3schools.com/sql/sql_join.asp, https://www.w3schools.com/sql/sql_union.asp      

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Which of the following is a non-volatile memory ?

Which of the following is a non-volatile memory ?

• RAM
• LSI
• VLSI
• ROM   

EXPLANATION

ROM stands for Read-Only-Memory. This type of memory is static with regards to the storage in that the changes to the ROM are not allowed (in most cases). 

SOURCE

https://en.wikipedia.org/wiki/Read-only_memory            

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A DHCP assigned IP address has a lease duration of 6 days. After how many days does the client start to try to renew the address if it is not rebooted?

A DHCP assigned IP address has a lease duration of 6 days. After how many days does the client start to try to renew the address if it is not rebooted?

• 4 days
• 3 days
• 5 days
• 6 days        

EXPLANATION

After half the lease time is over, the client will start to try to renew and extend the current lease with the DHCP server he got the address from. If he is unsuccessful, he will try again when 87.5% of the lease time is up, trying to find any server that can renew and extend the lease. If no server is found, the client releases the address after the lease time is up and the administrator is in trouble...

More info here.       

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Which of the following is the default port used for POP3 SSL Traffic?

 Which of the following is the default port used for POP3 SSL Traffic?

• 995
• 25
• 587
• 110

EXPLANATION

POP uses port 110, but SSL/TLS encrypted POP uses port 995.

SOURCE

https://www.fastmail.com/help/technical/ssltlsstarttls.html               

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