Another possibility (more error checking is left as an excercise):

my $key;
while (<IN>) {
  chomp;
  if ( my $status = /^interface Vlan/.../^!/ ) {
    $key = $_ if $status == 1;
    if ( /^\s*ip address (?:[\d.]+)/ ) {
      my ($value) = $key =~ /(\d+)/;
      $hash{$key} = $value;
    }
  }
}
[download]

or

my $key;
while (<IN>) {
  if ( /^(interface Vlan(\d+))/ ) {
      $key = $1;
      $hash{$1} = $2;
  }
  delete $hash{$key} if /no ip address/;
}
[download]