Using Multicast IP Addresses for Cross-Subnet Communication

D

Multicast is a networking protocol where one host can send a message to a special multicast IP address and one or more network devices can listen for and receive those messages. Multicast works by taking advantage of the existing IPv4 networking infrastructure, and it does so in something of a weird fashion. As you read, keep in mind that things are a little confusing because multicast was "shoe-horned" in to an existing technology. For the rest of this article, let's use the multicast IP address of 239.255.0.1. We'll not worry about port numbers yet, but make a mental note that they are used in multicast.

The correct answer is D. 239.255.0.1

Explanation: To send a message to multiple devices across different subnets, a host can use multicast addressing. Multicast addressing allows a host to send a single message to a group of hosts that have expressed interest in receiving the message. The group of hosts can be located on different subnets.

The Internet Assigned Numbers Authority (IANA) has reserved a range of IP addresses for multicast addressing. The range of multicast addresses is 224.0.0.0 through 239.255.255.255. The first 224 addresses in the range (224.0.0.0 through 224.0.0.255) are reserved for specific multicast addresses, such as all hosts on a local network segment. The remaining addresses (224.0.1.0 through 239.255.255.255) are available for general use.

In this case, the destination IP address 239.255.0.1 is a multicast address that can be used to send a message to multiple devices across different subnets. It is not a reserved address and can be used for general multicast purposes.

Option A (172.20.1.0) is a network address and cannot be used as a destination address.

Option B (127.0.0.1) is the loopback address and is used for communication within a host.

Option C (192.168.0.119) is a unicast address and can only be used to send a message to a single host.