Communications limits

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The IBM i system limits for communications include general communications configuration limits, SNA limits, TCP/IP limits, and communications trace service tool limits.

Table 1. General communications configuration limits
General communications configuration limits Value
Maximum number of communications configuration objects that can be in a varied on state1 Approximately 100 000
Recommended maximum number of devices that are allocated to a communications subsystem 250 to 300
Maximum number of device descriptions for display devices per subsystem2 Approximately 74 000
Maximum number of virtual devices that can be specified as automatically configured (QAUTOVRT system value) 32 500 or *NOMAX
Maximum communications/LAN hardware capabilities See Power Systems Technical Guide on the Redbooks® Web site Link to PDF.
Notes:
  1. A maximum of 32 767 communications configuration objects can be varied online at initial program load (IPL) per communications arbiter system job (see QCMNARB system value).
  2. Removing generic workstation types in workstation entries can help avoid this limit. For example, the *ALL workstation type allows the subsystem to allocate all of the valid workstations on the system. Note that WRKSTNTYP(*ALL) is the default for some IBM-supplied subsystem descriptions.
Table 2. SNA communication limits
SNA communication limits Value
Maximum number of communication arbiters (maximum value of QCMNARB system value) 99
Maximum number of active sessions per APPC node 512
Maximum number of modes per APPC device (or APPN location)1 14
Maximum combined number of APPC devices (in any state) and APPN devices (in varied on state) 25 300
Maximum number of APPN intermediate sessions 9999
Maximum number of devices per APPC controller 254
Maximum number of switched lines per APPC controller 64
Maximum size of APPN local location list 476
Maximum size of APPN remote location list 1898
Maximum size of asynchronous network address list 294
Maximum size of asynchronous remote location list 32 000
Maximum size of retail pass-through list 450
Maximum size of SNA pass-through group 254
Note:
  1. An APPN location refers to all the devices that have the same values for RMTLOCNAME, RMTNETID, and LCLLOCNAME.
Table 3. TCP/IP communication limits
TCP/IP communication limits Value
Maximum number of interfaces per line 2048
Maximum number of interfaces per system 16 384
Maximum number of routes per system 65 535
Maximum number of ports for TCP 65 535
Maximum number of ephemeral ports for TCP per address family (IPv4 or IPv6)2 60 536
Maximum number of ports for UDP 65 535
Maximum number of ephemeral ports for UDP per address family (IPv4 or IPv6)2 60 536
Maximum TCP receive buffer size 8MB
Maximum TCP send buffer size 8MB
Maximum size of a transmission unit on an interface 16 388 bytes
Maximum number of TELNET server jobs 200
Maximum number of pass-through server jobs 100
Maximum number of TELNET server sessions Maximum number of virtual devices
Default maximum number of socket and file descriptors per job 1 200
Maximum number of socket and file descriptors per job 2 500 000
Maximum number of socket descriptors on the system Approximately 46 420 000
Maximum size of database files for FTP 1 terabyte
Maximum size of integrated file system files for FTP Amount of storage
Maximum number of simultaneous inbound connections for SMTP Configurable using the CHGSMTPA command, the limit is the system resources
Maximum number of simultaneous outbound connections for SMTP Configurable using the CHGSMTPA command, the limit is the system resources
Maximum number of MX records handled by MX resolver (Client) for SMTP 80
Maximum document size for SMTP 2.1 GB
Maximum number of active threads per HTTP server 9999
Maximum number of connections that can be displayed using WRKTCPSTS or NETSTAT commands 32 767
Start of changeMaximum number of TCP connections that can be displayed using the QtocLstNetCnn API and QSYS2.NETSTAT_INFO or QSYS2.NETSTAT_JOB_INFOEnd of change Start of change
  • IPv4: 55173
  • IPv6: 65535
End of change
Start of changeMaximum number of UDP connections that can be displayed using the QtocLstNetCnn API and QSYS2.NETSTAT_INFO or QSYS2.NETSTAT_JOB_INFOEnd of change Start of change
  • IPv4: 77359
  • IPv6: 58254
End of change
Maximum number of L2TP tunnels per system 200
Maximum number of calls per L2TP tunnel 200
Notes:
  1. Default can be changed with DosSetRelMaxFH() - Change the Maximum Number of File Descriptors (see UNIX-Type APIs in the information center).
  2. The default ephemeral port range on the IBM i is 5000 through 65 535 for both TCP and UDP. Within this range, the System Service Tools (SST) Advanced Analysis command IPCONFIG can be used to set the lowest and highest valid ephemeral port to be used by TCP or UDP, respectively. An ephemeral port in this range can be simultaneously in use once per IP address family regardless of the number of IP interfaces configured.
Table 4. Communications trace service tool limits
Communications trace service tool limits Value
Maximum amount of storage allocated for a single communications trace buffer 4 GB
Maximum total amount of storage allocated for all communications trace buffers 16 GB
Maximum record size when using the TRCTCPAPP trace tool for Host Server and DDM/DRDA Server 6000 bytes