1. What is the maximum size of a DNS response packet (in bytes)?
- a) 512 bytes
- b) 1024 bytes
- c) 4096 bytes
- d) 2048 bytes
Answer: a) 512 bytes
Explanation: In traditional DNS, the maximum size of a DNS response is 512 bytes. If the response exceeds this size, DNS uses TCP instead of UDP for communication to allow for larger responses. DNS over TCP can support larger responses (up to 65,535 bytes), but the typical DNS response limit using UDP is 512 bytes.
2. In DNS, the TTL (Time To Live) value is typically set in seconds. What is the default TTL value for many DNS records?
- a) 30 seconds
- b) 60 seconds
- c) 86400 seconds (24 hours)
- d) 3600 seconds (1 hour)
Answer: c) 86400 seconds (24 hours)
Explanation: A common default TTL for many DNS records is 86400 seconds, which is equal to 24 hours. This means that DNS resolvers can cache the result for 24 hours before querying the authoritative DNS server again.
3. A DNS resolver performs 10 queries per second. How many queries will it make in 1 hour?
- a) 100
- b) 1,000
- c) 36,000
- d) 3,600,000
Answer: c) 36,000
Explanation: To find the total queries in 1 hour:
- 10 queries per second × 60 seconds per minute = 600 queries per minute
- 600 queries per minute × 60 minutes per hour = 36,000 queries per hour.
4. If a DNS resolver has a TTL value of 3600 seconds, how long will it cache a DNS record?
- a) 1 minute
- b) 1 hour
- c) 12 hours
- d) 1 day
Answer: b) 1 hour
Explanation: A TTL of 3600 seconds equals 1 hour. This means that the resolver will cache the DNS record for 1 hour before it needs to perform another lookup.
5. In DNS, the A record maps a domain name to an IP address. If a domain’s A record is configured as follows: “example.com. IN A 192.168.1.10”, what is the IP address for example.com?
- a) 192.168.1.1
- b) 192.168.1.10
- c) 10.0.0.1
- d) 10.1.1.10
Answer: b) 192.168.1.10
Explanation: The A record specifies that the domain “example.com” resolves to the IP address 192.168.1.10. This is how the domain name is associated with the IP address.
6. How many DNS root servers exist globally?
- a) 10
- b) 13
- c) 50
- d) 100
Answer: b) 13
Explanation: There are 13 root DNS servers globally, each of which is responsible for helping direct DNS queries to the correct authoritative DNS servers for top-level domains (TLDs).
7. If a DNS resolver receives a query for a domain name and there is a cached result with a TTL of 300 seconds, how long will the result remain in cache before it is expired?
- a) 2 minutes
- b) 5 minutes
- c) 10 minutes
- d) 1 hour
Answer: b) 5 minutes
Explanation: A TTL of 300 seconds equals 5 minutes. The DNS result will remain in the cache for this duration before it is considered expired and needs to be refreshed.
8. What is the maximum number of domain labels (components separated by dots) allowed in a fully qualified domain name (FQDN)?
- a) 128
- b) 255
- c) 253
- d) 64
Answer: b) 255
Explanation: The maximum length of a fully qualified domain name (FQDN) is 255 characters, which includes all domain labels separated by dots. Each individual label can be up to 63 characters long.
9. If a domain name has a CNAME record pointing to another domain, what does this mean?
- a) The domain is an alias for another domain.
- b) The domain is a top-level domain.
- c) The domain is a mail server.
- d) The domain does not exist.
Answer: a) The domain is an alias for another domain.
Explanation: A CNAME (Canonical Name) record allows one domain name to be an alias for another. When a user queries the alias domain, the DNS resolver is redirected to the canonical (real) domain.
10. If you want to configure a DNS record that points a subdomain (like “blog.example.com”) to the same IP address as the main domain (example.com), which type of DNS record would you use?
- a) A Record
- b) CNAME Record
- c) MX Record
- d) PTR Record
Answer: b) CNAME Record
Explanation: A CNAME record would be used for this purpose. It allows you to point “blog.example.com” to “example.com,” meaning they both resolve to the same IP address.
11. How many queries per second would a DNS resolver process if it receives 5,000 queries every 10 minutes?
- a) 5
- b) 8
- c) 50
- d) 833
Answer: b) 8
Explanation:
To calculate the number of queries per second:
5,000 queries / (10 minutes * 60 seconds) = 5,000 / 600 = 8 queries per second.
12. If a DNS resolver is configured with a TTL of 7200 seconds, how long will it cache a record before it expires?
- a) 1 hour
- b) 30 minutes
- c) 2 hours
- d) 12 hours
Answer: c) 2 hours
Explanation:
7200 seconds = 2 hours. This is the amount of time the DNS resolver will keep the cached record before expiring and needing to refresh it.
13. A DNS query is sent for a domain that has 3 DNS servers listed in its NS (Name Server) record. If each DNS server responds within 50 milliseconds, how long will it take (in milliseconds) to get a response from all servers?
- a) 50 ms
- b) 150 ms
- c) 200 ms
- d) 100 ms
Answer: a) 50 ms
Explanation:
DNS queries are typically sent in parallel to multiple servers. Since the servers respond simultaneously, it will only take 50 milliseconds for the first response, regardless of the number of servers listed.
14. If a DNS resolver receives a response with a TTL of 1800 seconds, and the query is received at 2:00 PM, when will the DNS record expire?
- a) 2:30 PM
- b) 2:45 PM
- c) 3:00 PM
- d) 3:30 PM
Answer: a) 2:30 PM
Explanation:
1800 seconds = 30 minutes. If the query was received at 2:00 PM, the DNS record will expire at 2:30 PM.
15. If a domain has 2 authoritative name servers with a round-robin DNS configuration and each server is handling 100 queries per second, how many total queries are being processed by both servers per minute?
- a) 2,000
- b) 3,000
- c) 12,000
- d) 60,000
Answer: c) 12,000
Explanation:
Each server processes 100 queries per second.
Total queries per minute = 100 queries per second × 60 seconds per minute = 6,000 queries per server.
For both servers: 6,000 × 2 = 12,000 queries per minute.
16. A DNS response exceeds the standard 512-byte limit and switches to TCP. If the response is 700 bytes, how many additional bytes are used for the TCP header (assuming a standard TCP header size of 20 bytes)?
- a) 10 bytes
- b) 20 bytes
- c) 50 bytes
- d) 700 bytes
Answer: b) 20 bytes
Explanation:
The size of the TCP header is typically 20 bytes. This is the overhead added to the DNS response when switching from UDP to TCP.
17. In DNS, what is the maximum length of an individual domain label (each part of a domain name separated by periods)?
- a) 63 characters
- b) 128 characters
- c) 255 characters
- d) 256 characters
Answer: a) 63 characters
Explanation:
Each individual domain label (e.g., in “example.com,” “example” and “com” are domain labels) can be up to 63 characters long.
18. If a DNS query is sent for a domain and the TTL is set to 43200 seconds, how many hours will the DNS resolver cache the record?
- a) 1 hour
- b) 12 hours
- c) 24 hours
- d) 48 hours
Answer: b) 12 hours
Explanation:
43200 seconds = 12 hours. This is the duration for which the DNS resolver will cache the record before it expires.
19. If a DNS resolver receives 20 queries per second, how many queries will it receive in 5 minutes?
- a) 600
- b) 1,200
- c) 3,600
- d) 6,000
Answer: b) 1,200
Explanation:
To calculate the total number of queries:
20 queries per second × 60 seconds per minute = 1,200 queries per minute.
1,200 queries per minute × 5 minutes = 1,200 queries.
20. If the maximum size of a DNS response over UDP is 512 bytes, and the DNS response is 450 bytes, how much space is left for additional data?
- a) 450 bytes
- b) 50 bytes
- c) 512 bytes
- d) 100 bytes
Answer: b) 50 bytes
Explanation:
The maximum response size is 512 bytes, and the response is 450 bytes, so the remaining space is:
512 bytes – 450 bytes = 50 bytes.
