Which version of RIP only advertises classful addresses?

RIP version 1 (RIPv1) is the protocol that only advertises classful addresses. This means that it recognizes only the traditional classful IP address formats (Class A, Class B, and Class C) and does not support any form of subnetting or Variable Length Subnet Masking (VLSM). In RIPv1, this lack of support for classless routing means that it cannot provide precise subnet information, limiting its usability in more complex or modern network environments.

In contrast, RIPv2 and RIPng are updated versions of the protocol that do support classless routing. RIPv2 allows for the use of VLSM and can advertise subnet masks along with the IP addresses, enabling more efficient use of IP address space. RIPng, which stands for Routing Information Protocol next generation, is designed for IPv6 and also offers classless addressing features.

As for RIPv3, it does not exist as a formalized version of the RIP protocol, making the option irrelevant. Thus, RIPv1 is clearly identifiable as the only version of RIP that operates within the constraints of classful addressing only.