Final answer:
There can be 126 Class A networks, 16,384 Class B networks, and 2,097,152 Class C networks in the IPv4 addressing architecture. However, the classful networking system has been mostly replaced by CIDR, allowing for a more efficient IP address allocation.
Step-by-step explanation:
The question "how many class A, B, and C networks can exist" refers to the IPv4 addressing system that categorizes IP addresses into different classes based on the leading bits and address size. These classes were part of the early Internet architecture designed for network classification.
Class A networks have a leading bit pattern of 0, allowing for a total of 27 - 2 (128 - 2) networks, because the highest and lowest network numbers are reserved.
Class B networks have a leading bit pattern of 10, resulting in 214 (16,384) possible networks.
Class C networks start with the bit pattern 110, and there can be 221 (2,097,152) possible networks.
Note that this classful networking system has largely been superseded by Classless Inter-Domain Routing (CIDR), which allows for more efficient allocation of IP addresses.