Lesson 5.2 - DNS

Question 1

Purpose of DNS

Answer 1

Map human-readable names to IP addresses

-Human-readable is easier to remember but IP is needed to send traffic to intended destination

Question 2

gethostbyname()

Answer 2

Takes domain name as arg and returns IP address

Question 3

stub resolver

Answer 3

simple resolver handling all the DNS lookups for the OS. The resolver will send DNS queries (with recursive flag on) to a specified recursive resolver (name server) and stores the records in its cache based on their TTL (had to Google this one)

Question 4

Local DNS resolver

Answer 4

Typically configured automatically when your host is assigned an IP address, using a protocol called domain host configuration protocol (DHCP)

Question 5

Local host may have __ local DNS resolvers

Answer 5

2
-Tries the first one. If no response in certain preconfigured timeout, send query to second one as backup. Typically issued recursively.

Question 6

Local resolver performs _____ queries

Answer 6

Iterative

Question 7

Root of DNS hierarchy

Answer 7

Each fully-qualified domain name is presumed to end with a dot
-IP address for the root servers (those that are authoritative for the root) may already be configured in the local DNS resolver

Question 8

Cache on local resolver

Answer 8

Iterative process can be slow. Cache commonly queried/repeated mappings (like google.com)

Question 9

TTL

Answer 9

Time to live

• Indicates how long an answer can be saved (cached). Typically hours, days, or even weeks.
• Mapping of a local name (www.gatech.edu) on the other hand might change more infrequently. Thus, local TTL’s might need to be smaller.

Question 10

‘A’ record

Answer 10

maps an IP address to a domain name

Question 11

NS record

Answer 11

‘Name server’ record

• maps domain name to authoritative name server for that domain
• Referrals: if we ask the root for a mapping to an IP address, it doesn’t know the answer, but can issue a name server reply (NS record) referring the resolver to a different name server that could be responsible for that part of the domain namespace

Question 12

DNS is implemented as a _____

Answer 12

hierarchy

Question 13

MX record

Answer 13

shows the mail server for a particular domain

Question 14

CNAME

Answer 14

Canonical name. Like an alias. Basically a pointer from an alias to another domain name that needs to be looked up.

Question 15

PTR

Answer 15

Maps IP address to domain names (like a reverse lookup)

Question 16

AAAA

Answer 16

“Quad A record”: maps domain name to an IPv6 address

Question 17

Priorities

Answer 17

In addition to TTL, we can use priorities to allow a system admin to configure a primary and a backup mail server, for example. They can be the same level if no preference.

Question 18

Trace option

Answer 18

In dig, shows full lookup hierarchy

Question 19

in-addr.arpa

Answer 19

Maintains referrals to authoritative servers that are maintained by their respective internet routing registries such as ARIN, RIPE, etc. REVIEW THIS