@echo off&setlocal enabledelayedexpansion
set a=192.168.20.2
set v=1.inf
findstr "%a%6" "%v%">nul&&set b=6
findstr "%a%8" "%v%">nul&&set b=8
(if defined b for /f "usebackq eol=€ tokens=1* delims==" %%a in ("%v%") do if "%%b"=="" (echo %%a) else (
        set c=%%b
        if %b%==6 (set c=!c:%a%6=%a%8!) else set c=!c:%a%8=%a%6!
        echo %%a=!c!
))>temp.txt
del /q "%v%"
ren temp.txt %v%