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:
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