Automated Ping Test error - batch-file

Question

I am trying to create an automated ping test using a .cmd file that pulls the ip addresses from a file called computers. It looks like it works for the most part but all the ping test after the first come back negative or dead.
#echo off
set fnm=C:\Users\jelliott\Desktop\computers.txt
set lnm=C:\Users\jelliott\Desktop\results.txt
if exist %fnm% goto Label1
echo.
echo Cannot find %fnm%
echo.
Pause
goto :eof
:Label1
echo PingTest STARTED on %date% at %time% > %lnm%
echo ================================================= >> %lnm%
echo.
for /f %%i in (%fnm%) do call :Sub %%i
echo.
echo ================================================= >> %lnm%
echo PingTest ENDED on %date% at %time% >> %lnm%
echo ... now exiting
goto :eof
:Sub
echo Testing %1
set state=alive
ping -n 1 %1
if errorlevel 1 set state=dead
echo %1 is %state% >> %lnm%

Answer 1

I don't know if this is the source of the problem but the errorlevel after a ping request is not reliable: it is not always set on 0 after a successful ping. The most reliable way to check a successful ping is to search for "TTL=" in the output of the ping command. The output of a successful ping always contains the TTL of the ping answer. In other cases, the output won't conain "TTL=".
Check the errorlevel of this command instead:
ping -n 1 %1 | find "TTL="
find allows to search for a literal string in some text. It will set the errorlevel on 0 if it is found and 1 otherwise. You can also use findstr instead of find.
EDIT: This is only in case the addresses you're pinging to are IPv4. For IPv6 addresses, the errorlevel is set correctly. For IPv6 no TTL is printed so the errorlevel must be used to check if the ping succeeded or not. [Here] you can find a general way to check if the ping was successful or not (either it is IPv4 or IPv6). Thank you MC ND for the remark and the link. If you ever want to force IPv4 or IPv6, you can use respectively the -4 or the -6 flags of ping.