A fix is available
APAR status
Closed as program error.
Error description
Netstat conn will show that there are connections in a CLOSWAIT state. This happens when TCPIP processes an inbound FIN and the window size goes to zero. The FIN is acked, but if there is unsent data, TCPIP will not try to send it. The data buffers will stay allocated in storage. If there are many connections in this state, especially if they are connections with the FTP server (which utilize 180K ECSA CSM buffers), you could see a storage problem. This could cause CSM to be constrained. . KEYWORDS: closewait close wait idle ftp netstat . ADDITIONAL SYMPTOMS: If this causes CSM to be constrained, TRACERTE could fail with a EZA0486E RawIPOpen(ICMP): No more space for data currently available (8539) OMPROUTE could also see EZZ7840I SENDTO() ERROR, ERRNO=1122:EDC8122I NO BUFFER SPACE AVAILABLE, ERRNO2=74420324 . VERIFICATION STEPS: Looking at the hung TCB in a dump of TCPIP, you will see that the TCB_SND_WND is zero. The TCB_TIMING PROBE will not be initialized (will not have a TID eyecatcher). You can determine how long the connection has been idle from the TCB_LAST_ACTIVITY timestamp. . A packet trace will show that a FIN is received with a window size of zero.
Local fix
Issue a netstat conn. If there are connections in a closewait state, use the drop command to drop the connection. This will also clean up storage associated with the connection.
Problem summary
**************************************************************** * USERS AFFECTED: All users of the IBM Communications Server * * for OS/390 Release 10 IP * **************************************************************** * PROBLEM DESCRIPTION: TCP connections remain in CLOSEWAIT * * state indefinitely. * **************************************************************** * RECOMMENDATION: * **************************************************************** TCP connections may remain in CLOSEWAIT state indefinitely. The connection will have no data in the pipe so the retransmit timer will not be running. The send queue will have data to be sent, the window size will be zero, and the probe timer will be off. The connection has no timers running that will cause any data on the send queue to be sent, so there will be no outbound data packets sent unless the remote end sends a non-zero window update. The probe timer should be started when the window goes to zero, the pipe is empty, and there is data on the send queue. This problem only occurs when the inbound TCP layer receives a zero window update and a FIN during the same pass. This can occur in the same packet or separate packets that arrive over the network interface in the same read operation. The specific case where this problem was reported involved a TCPIP stack that allowed the remote socket to close without reading all of the data. The connection should have been reset by the remote end when the socket was closed. The fact that the remote socket was closed means there will never be an unsolicited window update received on the local side of the connection. +-------------------------------------------------------------+ + Please check our Communications Server for OS/390 homepages + + for common networking tips and fixes. The URL for these + + homepages can be found in Informational APAR II11334. + +-------------------------------------------------------------+
Problem conclusion
TCSNDINT has been amended to convert a request to send an ACK to a PROBE request when there is no data in the pipe, the window is zero, there is data on the send queue and there is no probe timer already running. * Cross Reference between External and Internal Names
Temporary fix
Comments
APAR Information
APAR number
PQ72868
Reported component name
TCP/IP V3 MVS
Reported component ID
5655HAL00
Reported release
50A
Status
CLOSED PER
PE
NoPE
HIPER
NoHIPER
Special Attention
NoSpecatt / Xsystem
Submitted date
2003-04-04
Closed date
2003-04-25
Last modified date
2003-06-05
APAR is sysrouted FROM one or more of the following:
APAR is sysrouted TO one or more of the following:
UQ76331
Modules/Macros
EZBTCFWR EZBTCSND TCSNDINT
Fix information
Fixed component name
TCP/IP V3 MVS
Fixed component ID
5655HAL00
Applicable component levels
R50A PSY UQ76331
UP03/05/15 P F305
Fix is available
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Document Information
Modified date:
05 June 2003