A fix is available
APAR status
Closed as program error.
Error description
A Telnet is configured with shared LUs, so it is acting as a LUNR. Another Telnet running on a different TCPIP stack is acting as a LUNS. When the LUNR and LUNS are communicating, the Nagle algorithm is preventing small packets from being sent individually. This can slow down the assignment of LUs as the data will not be sent until the delayACK timer expires, which can be 200ms. This delay can grow to over 30 seconds in configuration with a large number of LUGroups mapped to a connection and the client includes a LU group name when establishing the connection. The Telnet client will see a delay before being presented with the MSG10 screen. VERIFICATION STEPS: 1) Slow response time for LU requests from LUNR system on different TCPIP stacks than the LUNS. The delay may grow to be over 30 seconds. 2) LU requests from a LUNR on the same TCPIP stack as the LUNS are not delayed 3) A packet trace of the connection between the LUNR and LUNS will show delayed acks or data being sent after a 200ms gap on the connection.
Local fix
Coding NoDelayAck on the PORT reservation for the Telnet LUNS port and on the TCPCONFIG statement can reduce the delay some.
Problem summary
**************************************************************** * USERS AFFECTED: All users of the IBM Communications Server * * for z/OS Version 1 Release(s) 10, 11, 12, * * and 13 IP: Telnet facilities using the * * Telnet LU Name Server ( LUNS ) and LU Name * * Requestor ( LUNR ). * **************************************************************** * PROBLEM DESCRIPTION: Slow performance in LU assignment * * from LUNS server due to Nagle * * algorithm. * **************************************************************** * RECOMMENDATION: * **************************************************************** The problem may be summarized as follows: 1. A Telnet LUNR running on one TCPIP stack established a connection to a Telnet LUNS server running on a different TCPIP stack. 2. The Telnet LUNR was configured with a large number of shared LU groups containing a single LU such as in the following example: SLUGROUP GROUP01 TCPM1151 ENDSLUGROUP LUMAP GROUP01 ALLIPGROUP SPECIFIC SLUGROUP GROUP02 TCPM1152 ENDSLUGROUP LUMAP GROUP02 ALLIPGROUP SPECIFIC 3. A TN3270E client connected to the LUNR. The client was configured with a specific LUGROUP name (e.g. GROUP02). LUNR handshake processing with the LUNS occurred during the connection establishment. The handshake took an excessive amount of time, delaying presentation of the USSMSG10 screen at the client. Packet trace analysis revealed that the delay was due to the LUNS/LUNR connection being subject to the Nagle algorithm. +-------------------------------------------------------------+ + 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
Modules EZBTXLUR and EZBTXLUS have been amended to issue a SETSOCKOPT specifying the TCP_NODELAY option to disable Nagle for the LUNS/LUNR connection. Macro EZBZTXCF has been amended to add an internal serviceability indicator. * Cross Reference between External and Internal Names
Temporary fix
Comments
APAR Information
APAR number
PM44234
Reported component name
TCP/IP V3 MVS
Reported component ID
5655HAL00
Reported release
1B0
Status
CLOSED PER
PE
NoPE
HIPER
NoHIPER
Special Attention
NoSpecatt
Submitted date
2011-07-21
Closed date
2011-08-09
Last modified date
2011-10-03
APAR is sysrouted FROM one or more of the following:
APAR is sysrouted TO one or more of the following:
UK70617 UK70618 UK70619 UK70620
Modules/Macros
EZBTXLUR EZBTXLUS EZBZTXCF
Fix information
Fixed component name
TCP/IP V3 MVS
Fixed component ID
5655HAL00
Applicable component levels
R1A0 PSY UK70617
UP11/09/20 P F109
R1B0 PSY UK70618
UP11/09/20 P F109
R1C0 PSY UK70619
UP11/09/20 P F109
R1D0 PSY UK70620
UP11/09/20 P F109
Fix is available
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Document Information
Modified date:
03 October 2011