The cause of the issue is that the CIDR value /33 is invalid for an IPv4 address. The CIDR value represents the number of bits in the network prefix of an IP address, and it can range from 0 to 32 for IPv4 addresses. A CIDR value of /33 would imply a network prefix of more than 32 bits, which is impossible for an IPv4 address. To assign a temporary IP address/netmask of 192.168.168.1/255.255.255.255 to eth0, the CIDR value should be /32 instead, which means a network prefix of 32 bits and a host prefix of 0 bits. There is no route to 192.168.168.1/33 is not the cause of the issue, as the ip address add command does not check the routing table. The interface eth0 does not exist is not the cause of the issue, as the ip address add command would display a different error message if the interface does not exist. The IP address 192.168.168.1 is already in use is not the cause of the issue, as the ip address add command would display a different error message if the IP address is already in use. Reference: [CompTIA Linux+ (XK0-005) Certification Study Guide], Chapter 13: Networking Fundamentals, page 435.