TCP/IP and DNS

Question 1

Explain UDP.

Answer 1

UDP is a connectionless communication - “fire and forget” - the sender doesn’t care if the recipient has bandwidth or receives the message.

Question 2

Explain TCP.

Answer 2

TCP is a connection-oriented communcation. It ensures packets arrive at the right time, and in the right order.

Question 3

Name some typical protocols which use UDP?

Answer 3

TFTP, DHCP, SNMP, DNS

Question 4

Name some typical protocols which use TCP?

Answer 4

FTP, HTTP, SSH, DNS

Question 5

What’s the TCP three-way handshake?

Answer 5

SYN, SYN/ACK, ACK.

Question 6

What’s the DNS namespace?

Answer 6

The area of the internet that a DNS server holds and manages the records for

Question 7

DNS is port 53. What would you use UDP and TCP for?

Answer 7

Name lookups UDP, zone transfers TCP

Question 8

Name the two servers that make up DNS and what they do.

Answer 8

Name resolver - answers requests. Authoritative server - holds the records for a namespace.

Question 9

What’s a DNS zone transfer?

Answer 9

When a DNS server passes a copy of part of its database (its “zone”) to another DNS server

Question 10

Here’s an example DNS zone transfer request: (2013090800 86400 900 1209600 3600). Name each of the components

Answer 10

2013090800 - the serial number
86400 - the refresh interval 
900 - retry time
1209600 - expiry time
3600 - TTL

Question 11

What’s the refresh interval?

Answer 11

How long before the secondary DNS server asks for an update

Question 12

What’s the retry time?

Answer 12

How long the secondary server will wait to retry if the transfer fails

Question 13

What’s the expiry time?

Answer 13

How long the secondary server will spend trying to complete a transfer

Question 14

What’s the TTL?

Answer 14

How long before the records are destroyed

Question 15

What’s an A record?

Answer 15

Points a name to a specific IP

Question 16

Whats a CNAME record?

Answer 16

Canonical name - an alias for the name, points a name at a name

Question 17

Whats an MX record?

Answer 17

Points at the mail exchange

Question 18

What’s an NS record?

Answer 18

Points to the authoritative name servers for the domain

Question 19

“How long before the secondary DNS server asks for an update”. What’s being described?

Answer 19

Refresh interval

Question 20

“How long the secondary server will wait to retry if the transfer fails”. What’s being described?

Answer 20

Retry time

Question 21

“How long the secondary server will spend trying to complete a transfer.” What’s being described?

Answer 21

Expiry time

Question 22

“How long before the records are destroyed”. What’s being described?

Answer 22

TTL