FTP Client Delay Connecting to Linux FTP Server

 
 APAR Identifier ...... PQ77414      Last Changed ........ 03/08/26
 FTP CLIENT DELAY CONNECTING TO LINUX FTP SERVER
 
 Symptom ...... IN INCORROUT         Status ........... CLOSED  PER
 Severity ................... 3      Date Closed ......... 03/08/22
 Component .......... 5735FAL00      Duplicate of ........
 Reported Release ......... 440      Fixed Release ............ 999
 Component Name TCP/IP V2 FOR V      Special Notice
 Current Target Date ..              Flags
 SCP ...................
 Platform ............
 
 Status Detail: SHIPMENT - Packaged solution is available for
                           shipment.
 
 PE PTF List:
 
 PTF List:
 Release 440   : UQ79640 available 03/08/26 (1000 )
 
 Parent APAR:
 Child APAR list:
 
 ERROR DESCRIPTION:
 User initiates an FTP connection via the VM FTP client to
 connect to a Linux FTP sever.  When this connection is being
 established, a 5 to 10 second delay is experienced before a
 user login prompt is presented.  Once this prompt is produced,
 no further delay issues are encountered during the FTP process.
 
 
 LOCAL FIX:
 
 PROBLEM SUMMARY:
 ****************************************************************
 * USERS AFFECTED: Users with inbound TCP connections to        *
 *                 inactive ports                               *
 ****************************************************************
 * PROBLEM DESCRIPTION:                                         *
 ****************************************************************
 * RECOMMENDATION: APPLY PTF                                    *
 ****************************************************************
 If an incoming TCP connection is directed to a port on which
 there is no listener, the SYN packet is simply dropped. This
 causes the client to delay until eventually it times out.
 
 In this particular case, an FTP client connection is initiated
 to a Linux system. The FTP server on Linux attempts to identify
 the client using the Ident protocol. This causes an incoming
 connection to z/VM TCP/IP but there is no listener on port 113
 (the Ident port).
 
 PROBLEM CONCLUSION:
 Code has been changed to send a RST in response to a SYN that is
 directed to a port without a listener.
 
 TEMPORARY FIX:
 
 COMMENTS:
 
 MODULES/MACROS:   FPTCPUP  TCPIP
 
 SRLS:      NONE
 
 RTN CODES:
 
 CIRCUMVENTION:
 
 MESSAGE TO SUBMITTER: