DNS, the internet Domain Name System, is used to map a name to an IP address. Which statement best describes attributes of DNS: DNS allows an infinite number of names by allowing anyone to make up the root domain and selling the names to the highest bidder. The free market ensures the best operation of the naming system. Domain names are only based around an ISO 3166 country code and are thus regulated by governments around the world, with the exceptions of JE, GG, IM, BU and SU which do not have governments. Some DNS lookups are slower than others because the internet in the countries that operate those domains is slower than in the west. For those countries it is better to use an IP address. Some DNS lookups are slower than others because of local caching of DNS results in nearby computers. DNS lookups use a text file called hosts.txt located on each computer that contains the name and IP address of every computer on the internet to ensure quick lookups. What is the function of the TTL field in an IP datagram? TTL is used for Total Time Limit and indicates the time to wait for a resend packet to ensure reliable delivery TTL is used for Time to Live and indicates how many routers a packet can pass through before being deleted. The TTL count is decremented at each router and when reaches zero removed. The TTL is used to stop routing loops on an internet. It starts at zero and in incremented until the full count is reached, when a routing loop is detected. The TTL field is used to indicate if an IP datagram can be fragmented The TTL field is used to indicate if teh IP datagram contains TCP or UDP data An email message consists of several parts. Which is the correct set of parts standardised by RFC821 and RFC822: message body, message header, envelope headed notepaper, signature, envelope headed notepaper, letter, signature, envelope header, body, signature, envelope From, To, Date, Subject Why is locking required in a threaded server? Locking prevents two threads interfering with each other when accessing a static object, such as a dictionary or a file. If the lock was not used the values stored in the static object could become corrupted or overwritten by another concurrent thread. Locking prevent an unauthorised user from reading confidential data in a static object. Locking prevents the scheduler from swapping out a thread while it is processing a client transaction. Locking permits faster access to objects to ensuring they are in fats access memory. Locking is not required and servers can operate fine without them. FTP uses out-of band signalling. This is because it enables: file content not to be confused with FTP commands file transfers to third party machines very large files to be transferred files to be transferred very great distances the file transfer to recover from errors
