Description of problem:
vsftpd DNS lookup cannot be disabled.
This bug have been resolv in 5.x with the option 'reverse_lookup_enable'
but in 6.2 this option is no longer available

https://rhn.redhat.com/errata/RHBA-2009-1282.html :
...
* the DNS reverse lookup feature was implemented without any way to disable
it. This update contains the parameter 'reverse_lookup_enable', which
allows users to enable or disable the DNS reverse lookup functionality.
(BZ#498548) 
...
Version-Release number of selected component (if applicable):
rpm -qi vsftpd
Name : vsftpd Relocations: (not relocatable)
Version : 2.2.2 
Release : 6.el6_2.1

How reproducible:
ALWAYS
Steps to Reproduce:
1. having 2(or more) nameserver in /etc/resolv.conf that is NOT reachable
2. and then try to connect to the ftp server.
  
Actual results:
Connection timed out

Expected results:
Connection succesfull

Additional info:
trying with "reverse_lookup_enable=NO"
service vsftpd restart
Shutting down vsftpd: [FAILED]
Starting vsftpd for vsftpd: 500 OOPS: unrecognised variable in config file: reverse_lookup_enable
                                                           [FAILED]