DNS

DNS resolves names through root → TLD → authoritative servers, usually via a caching local resolver (host query recursive, resolver queries iterative). Lookup time = sum of the RTTs actually needed; a full uncached lookup is 8 messages. Records: A (IPv4), AAAA (IPv6), NS (name server), CNAME (alias), MX (mail). UDP port 53, TCP 53 for zone transfers.

1. NAT · 1 mark

   Iterative, cold cache, RTTs: host↔local 3, local↔root 60, local↔TLD 40, local↔authoritative 25 (ms). Lookup time?

   Write your answer before opening the key.

2. MCQ · 1 mark

   Which record type tells which server is authoritative for a domain?

   1. A
   2. NS
   3. MX
   4. CNAME
3. MCQ · 1 mark

   Default transport for a DNS query:

   1. TCP port 53
   2. UDP port 53
   3. TCP port 80
   4. UDP port 80
4. NAT · 1 mark

   Total DNS messages in a full uncached lookup through root, TLD and authoritative servers, including the host↔resolver pair?

   Write your answer before opening the key.

5. MSQ · 1 mark

   Which statements are correct?

   1. A local resolver caches answers.
   2. Recursive resolution makes the queried server do the chasing.
   3. The TLD server returns the A record of www.example.com.
   4. TTL limits how long a record may be cached.
6. NAT · 2 marks

   Same RTTs as Q1 but the TLD server's referral is cached (skip root). Lookup time in ms?

   Write your answer before opening the key.

7. MCQ · 1 mark

   www.store.com is an alias of store.cdn.net. The record stored for www.store.com is:

   1. A
   2. CNAME
   3. MX
   4. NS
8. MCQ · 1 mark

   Why does DNS normally use UDP?

   1. UDP is reliable
   2. One small query and reply need no connection setup
   3. TCP cannot carry names
   4. Routers block TCP