Note that applications can set and override the keep-alive values. We just spent 6 months resolving a problem with keep-alive timeouts and it turned out that an application running on a Windows server was setting the values and overriding TCP/IP and firewall settings (another place where they set keep-alive). Mainframe applications can also set the value.
-----Original Message----- From: IBM Mainframe Discussion List [mailto:ibm-m...@bama.ua.edu] On Behalf Of Chris Mason Sent: Tuesday, June 02, 2009 7:32 AM To: IBM-MAIN@bama.ua.edu Subject: Re: TCPIP Default keep alive question Vic The best list to use for questions concerning the Communications Server IP component (even the Communications Server SNA component given that Enterprise Extender is so often the subject) is the IBMTCP-L list: For IBMTCP-L subscribe / signoff / archive access instructions, send email to lists...@vm.marist.edu with the message: INFO IBMTCP-L - Your precise answer is at the end of the post. If there were such an API, it would be one of the options of either the getsockopt() call or the getibmsockopt() call and the equivalent in languages other than C. You may be aware that the matter of TCP keep-alive is not quite as straightforward as it might be. To be sure I cover the topic correctly - as best I can - I'll quote what is said in the CS IP Configuration Reference regarding the value in which you are interested, the one that shows up in the NETSTAT CONFIG output as DefaultKeepALive specified by the PROFILE TCPCONFIG statement INTERVAL parameter: <quote> INTERVAL default_keepalive_interval The default TCP keepalive interval for applications that enable the SO_KEEPALIVE socket option and do not override the interval using the TCP_KEEPALIVE socket option. The range is 0 - 35 791 minutes, and the default is 120. A value of 0 disables the keepalive function, so that sockets for which SO_KEEPALIVE is specified do not perform TCP keepalive. In this case, sockets specifying a specific interval using TCP_KEEPALIVE continue to send keepalive probes. TCP keepalive probes end TCP connections after a period of inactivity. TCP keepalive is disabled by default for a connection, but can be enabled by issuing the SO_KEEPALIVE or TCP_KEEPALIVE socket options. The TCP_KEEPALIVE socket option enables the application to specify the keepalive probe interval, while the SO_KEEPALIVE socket option uses default_keepalive_interval as the interval. After the interval has expired, TCP sends a single keepalive probe to the peer. If the TCP_KEEPALIVE socket option is not used to specify the probe interval, a total of ten probes are then sent at 75-second intervals if no response is received from the peer. If no response has been received 75 seconds after the last probe, the connection is reset. If TCP_KEEPALIVE is used to specify the keepalive probe interval, the number of probes and the interval between the probes might differ depending on the interval specified. </quote> It was only after I read the last sentence that I realised the topic was even more complicated than I had initially supposed! OK, INTERVAL sets a node-wide "keepalive" interval for those TCP sockets which have decided to call upon the "keepalive" service by requesting it by means of the setsockopt() SO_KEEPALIVE option. The default is for the service to be disabled. The value of the SO_KEEPALIVE option can be obtained by means of the getsockopt() call. Note that, even if the program requests that the service is enabled, it can effectively be disabled on a node-wide basis, by setting "0" as the value for the INTERVAL parameter. But there is also the TCP_KEEPALIVE option of the setsockopt() and getsockopt() calls. This requests the service and sets a value for the interval. Moreover it sets up a regime for conducting the keepalive testing should it be called upon - that's the unexpected complication in that last sentence! <quote> TCP_KEEPALIVE Use this option to set or determine whether a socket-specific timeout value (in seconds) is to be used in place of a configuration-specific value whenever keep alive timing is active for that socket. When activated, the socket- specified timer value remains in effect until respecified by SETSOCKOPT or until the socket is closed. See the z/OS Communications Server: IP Programmer's Guide and Reference for more information about the socket option parameters. </quote> The "configuration-specific value" is the value of the INTERVAL parameter when the service is enabled using the SO_KEEPALIVE option rather than the TCP_KEEPALIVE option. For reasons best known to the manual authors the section you need now to consult for the specifics of how the TCP_KEEPALIVE option works is tucked away as the last section of the last chapter of the CS IP Programmer's Guide and Reference manual! When you have read this section you may decide that the TCP_KEEPALIVE option better satisfies your needs that the mechanism associated with the PROFILE TCPCONFIG statement INTERVAL parameter and the SO_KEEPALIVE option. - Finally, to answer your question, I am not aware of an easy-to-use API which yields the value configured on the PROFILE TCPCONFIG statement INTERVAL parameter. It is possible to extract the value as an SNMP manager accessing the MIB variable ibmMvsTcpKeepAliveTimer, 1.3.6.1.4.1.2.6.19.2.2.2.4. If there's an easier way, I hope someone will jump in with the answer. I suspect some technique able to extract the value from the output of the NETSTAT CONFIG output might be the easiest. Chris Mason On Mon, 1 Jun 2009 12:16:28 -0500, Vic Petrone <v...@bell.net> wrote: >Is there a programming interface to extract the DefaultKeepALive value that is >stored the TCP Configuration Table? > >This is the same value that the TSO NETSTAT CONFIG command displays. > >Thanks, >Vic ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@bama.ua.edu with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@bama.ua.edu with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
