Problem Description:
test environment a FTP, login user feedback connection is very slow, and some even connect.
Description:
ftp server using vsftpd. Operating system centos7.4.
Analysis and Testing:
1. First in native FTP test, and troubleshoot the FTP server firewall, selinux problem (no problem).
2. ftp Native landing soon, other machines (the same network segment) access is very slow.
3. The window access the office network, not connected, the network is OK (telnet, firewalls are no problem)
Ethereal:
Ethereal found, in fact, already landed, the account password, no problem, but after a successful landing, do not know why every 20s before landing a success.
filezilla client default 20s no activity, so disconnected.
Online inquiry vsftpd problem of slow connection, it was suggested that found reverse_lookup_enable parameters could be greater delay. Information about the number of man as follows:
reverse_lookup_enable Set to YES if you want vsftpd to transform the ip address into the hostname, before pam authentication. This is useful if you use pam_access including the hostname. If you want vsftpd to run on the environment where the reverse lookup for some hostname is available and the name server doesn’t respond for a while, you should set this to NO to avoid a performance issue. Default: YES
Since the default is YES, but it will try to counter-resolution, here under modification, increase in /etc/vsftpd/vsftpd.conf file
reverse_lookup_enable=NO
After the restart vsftpd and services, the problem is solved.
This is just one example, does not mean that all land is slow or can not connect this reason, the test for reference only.