Can't call method "prepare" on an undefined value at ./update.pl line 22.

#!/usr/bin/perl -w
#DatenbankAbfragen

use strict;
use warnings;
use DBI;
use Net::Telnet::Cisco;
use Digest::MD5;
my $session = Net::Telnet::Cisco-> new (Host => '10.200.2.100');
my $dbh;
my $raw_data;
my $sqldata;
my $filename;
my $id;
my $neid;
my $datacisco;
my $MD5;
my $query;
my $sth;

$query = "INSERT INTO Tabelle1(ID,NEID,BState,Data_Cisco,MD5) VALUES(?,?,now(),?,?,?)";
$sth = $dbh->prepare($query) or die "Error in query prepare: $DBI::errstr\n";
$sth->execute($id,$neid,'UP',$datacisco,$MD5) or die "Error executing query: $DBI::errstr\n";
$sth->finish();