client wait 30s befor send SYN to ftp server on the passive port

edit

https://oracle-base.com/dba/miscellan...
Can you add logging with timestamps to FUNCTION get_passive ?
The PASV request and TCP connection to the new port are in that function.

yes, i had do that. it show 30s waiting time at client. the pic: https://c-t.work/s/06b4d08403c448

You get the delay on both TCP connection opens.
The reference says REMOTE_HOST is a name which gets resolved somewhere.
Can you run nslookup on the ftp client machine with the IP address of the FTP server to see if there is a delay in name resolution.

16:51:27:start Open_Connection 10.x.x.x:21
28 second delay
16:51:55:conned Open_Connection
.
.
.
16:51:55:start Open_Connection 10.x.x.x:30938
29 second delay
16:52:24:conned Open_Connection

https://docs.oracle.com/cd/E11882_01/appdev.112/e40758/u_tcp.htm#ARPLS075

UTL_TCP.OPEN_CONNECTION  (
   remote_host          IN VARCHAR2,
<snip>

Table 238-12 OPEN_CONNECTION Function Parameters

Parameter   Description
remote_host Name of the host providing the service. When remote_host is NULL, it connects to the local host.

I has used the ip adress of ftp server as "remote_host" in UTL_TCP.OPEN_CONNECTION. I has added the hostname and ip address to /etc/hosts on both ftp client and server. And, i had checked the config file /etc/netsvc.conf : hosts=local,bind,nis @bubbasnmp

Have you tried UTL_INADDR to test name resolution - IP -> name and name -> IP.
https://oracle-base.com/articles/misc...