put r write the content of the register named r on a new line after the current line.
nput r write the content of the register named r on a new line after line n (for example 17put r puts the content of @r on line 18).
.put puts text after the current line (. usually indicates the current line).
Instead of a named register, = can be used which evaluates the expression up to the end of the line and inserts the evaluated value. For example, :put =line('.') puts the current line number onto the next line. :put=g:foo puts the value of the variable g:foo after the current line.
After putting a value on a line, the cursor is placed on the line where text was inserted.
So, the range of ip numbers from 10.0.0.1 through 10.0.0.255 can be inserted from the current with
:for i in range(1,255) | .put='10.0.0.'.i | endfor