Variable length subnet masks
RIP VERSIONV1 can be seen to exclude subnet information from routing updates, this is because ripv1 is a classful routing protocol and does not support VSLM, this was corrected in RIPv2 where ripv2 does send out subnet mask's in the form of a prefix eg /24 which is the subnet mask of 255.255.255.0 or a class c address.
RIP version 2 (RIPv2) supports Variable Length Subnet Masking (VLSM) through the use of subnet masks in its routing updates. Unlike its predecessor, RIPv1, which only supports classful routing, RIPv2 includes the subnet mask with each route advertisement, allowing for more efficient use of IP address space and the implementation of subnets of different sizes within the same network. This feature enables networks to optimize address allocation and enhance routing flexibility.