N10-009 Question 121
Single answerIPv4 address classes: Class A, Class B, Class C, Class D, Class EA network technician is reviewing firewall logs for a training lab after several students reported unusual traffic. The logs show packets destined for 239.10.10.10, 10.25.4.8, 172.20.14.9, 192.168.50.12, and 250.1.1.1. The instructor asks which destination address is being used for IPv4 multicast traffic so the team can verify whether the application is intentionally sending one-to-many streams. Which address should the technician identify?
- A
10.25.4.8
- B
172.20.14.9
- C
192.168.50.12
- D
239.10.10.10
- E
250.1.1.1
Show answer and explanation
Correct answer: D
Explanation
IPv4 address classes can still appear on Network+ as a way to identify broad address purposes, even though modern networking primarily relies on CIDR. In the classful model, Class A uses first octets 1-126, Class B uses 128-191, Class C uses 192-223, Class D uses 224-239 for multicast, and Class E uses 240-255 for experimental or reserved purposes. In this scenario, the technician must identify multicast traffic in logs, which requires recognizing that 239.10.10.10 is in the Class D range. The other listed addresses are either private unicast addresses defined in RFC 1918 or a reserved Class E address. As a best practice, technicians analyzing packet captures or firewall events should distinguish between private unicast, multicast, and reserved address spaces to quickly determine whether traffic behavior is expected. References: RFC 791 for IPv4 addressing and RFC 1918 for private IPv4 address space.
- A. Incorrect.
10.25.4.8 is a Class A private IPv4 address from the 10.0.0.0/8 range defined in RFC 1918. It is used for unicast addressing inside private networks, not multicast. A candidate might choose it if they remember it is a special-purpose range, but its special purpose is private addressing, not one-to-many delivery.
- B. Incorrect.
172.20.14.9 is a Class B private IPv4 address within the RFC 1918 range 172.16.0.0 through 172.31.255.255. Like other private addresses, it is used for unicast communication on internal networks. It is not part of the multicast range.
- C. Incorrect.
192.168.50.12 is a Class C private IPv4 address from the RFC 1918 192.168.0.0/16 block. It is commonly used on LANs for standard host addressing. It is not a multicast address, although many candidates recognize 192.168.x.x as special and may confuse private-use addresses with other reserved classes.
- D. Correct.
239.10.10.10 is correct because IPv4 Class D addresses, used for multicast, span 224.0.0.0 through 239.255.255.255. The first octet 239 places this address in the Class D range. In a real environment, traffic sent to this destination could indicate multicast applications such as streaming, routing protocol messaging, or service discovery.
- E. Incorrect.
250.1.1.1 falls within the 240.0.0.0 through 255.255.255.254 range historically identified as Class E, which is reserved for experimental use and not used for normal host or multicast addressing. This is a plausible distractor because it is also outside the common unicast classes, but Class E is not the multicast range.