You could use the errmode method of Net::Telnet. The default error mode is "die", which you are experiencing. The alternative is "return", in which case Net::Telnet (or, in your case Net::Telnet::Cisco) will return and you will have to check for errors.

Something like the following might work:

    if ( $session )
    {
       $session->errmode('return');
         ### Login to privileged exec mode ###
        $session->login( Name => $uid , Password => $pawd );
       # $session->enable( $pawd );
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Another solution, particularly if Net::Telent::Cisco is dieing despite setting the error mode to 'return', is to use eval to catch that. Maybe something like:

foreach $entry (@iplist) {
    chomp ($entry);
    eval { &SDM };
    if($@) {
        # log the error
        open ( ERROR_LOG, ">>$dte-error.txt")
            or die "Could not open $dte-error.txt.\n";
        print "$entry: failed with $@ !\n";
        print ERROR_LOG "$entry: failed with $@ !\n";
        close ERROR_LOG;
    }
}
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