X.25 Switch for Linux


The FarSync X.25 Switch allows a Linux based system to act as an X.25 switch with XOT support whilst also supporting all the standard functions available with Linux. The FarSync X25 cards used by the Switch daemon and other applications simultaneously.


The FarSync Switch daemon can support up to 500 simultaneous connections from 1 to 16 or more X.25 and XOT (X.25 over IP) ports. The port limit is only restricted by the number of free PCI or PCIe slots available to install X.25 cards.

1, 2 and 4 port X.25 cards are available. For most small servers a typical maximum is 16 lines, however, some server support over 12 cards (48 X.25 lines!). The network connections using the FarSync X25 cards can be a mixture of RS232, X.21, V.35, EIA530, RS449 and E1 with a maximum line speed of 2 Mbits/s per port. Ports are configurable for both DCE and DTE operation.

Routing for the X.25 connections is controlled using the standard Linux route commands. Connections and disconnections of X.25 calls are logged to a daily rotating log file.

The FarSync X.25 Switch software for Linux is provided as a free of charge downloadable application for purchasers of the FarSync X.25 range of products.

Typical Uses

  • X.25 concentrator to connect several X.25 devices to an external network
  • Routing of data between X.25 and XOT
  • Low cost X.25 switch for systems testing


The X.25 Switch daemon is very simple to use and configure. The configuration commands are in the command line, options include:

+t<trace level> set the trace level
-z<message size> set the size of the message buffer to use in a call to the receive function


The standard Linux routing table is used to route X.25 calls through the Switch. The routing table can contain routes for all sorts of protocols, not just X.25. Routes for the X.25 Switch Daemon are added as follows:

route add -Ax25 <address> <device>

for example:

route add -Ax25 1234 fsxsk0
route add -Ax25 5678 x25tap0


The X.25 Switch daemon writes to a log file, a new log file is created each day. The previous days log file is renamed to x25Switch.yyy, where yyy are the first three letters of the day of the week. This schema provides for a log file for the current day, plus a log file for each day of the week. The log file contents will depend on the level of trace set when the daemon is started.

Example log entries for when a new call is switched.
Wed Feb 4 09:02:01 2004 : Incoming X.25 call from Null NUA to 123, adapter=0, line=0, socket=5
Wed Feb 4 09:02:01 2004 : Connecting to 123
Wed Feb 4 09:02:01 2004 : Call routed: Null NUA to 123, adapter=255, line=255, socket=6

Example log entries for when a call is terminated.
Wed Feb 4 09:42:05 2004 : Zero length Rx Data - socket=6, cause=0x00, diag=0x00
Wed Feb 4 09:42:05 2004 : Connection closed, sockets 5 & 6, cause=0x00, diag=0x00

Systems Requirements

The X.25 Switch daemon requires the FarSync X.25 driver version 2.0 or later. The switch will run on version 2.6 and later Kernels, see the FarSync X.25 driver Readme file for further details of specific Kernel versions. For XOT support the XOT Extension option must be purchased.

Technical Specifications
Product Name FarSync X.25 Switch for Linux
Product code FS9601
Switch Features
Maximum connections 500
Connection types supported SVC
Maximum X.25 ports No limit, dependent on the number of FarSync X.25 cards installed
Logging Optional logging of X.25 call connections and disconnections, daily rotating log file
Data packet size range 0 to 4096 bytes
Routing Routes configured using Linux standard route command
Kernel versions supported 2.6 and onward
FarSync X.25 Features(using the FarSync X25 T-Series cards)
DTE/DCE Operation Both
Line clocking Both Internal and External
Lines per card From 1 to 4 X.25 lines per card, cards per server only limited by available PCI slots
Line Interfaces RS232, X.21, V.35, EIA530, RS449 - 2 Mbits/s per line maximum
Maximum SVCs (all types) 254 per card using the standard FarSync X25 T-Series cards
4095 per line with the addition of the FarSync X.25 High Capacity Pack
XOT (IP over x.25) Supported and accessible by the FarSync X.25 Switch when installed in conjunction with the FarSync X.25 High Capacity Pack version 1.02 and above
Data Packet size range 16 to 4096 bytes
Reverse Charging option Yes
Closed User Group (CUG) option Yes
Network User Identifier (NUI) Yes
Fast Select Yes
Packet & Window size negotiation Yes
Throughput class negotiation Yes
Extended sequence numbering (128) Yes

Download X.25 Switch

The X.25 Switch daemon software can be downloaded from here. Remember you will need to install FarSync X25 T-Series cards to use the product.