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                                                             FREQUENTLY ASKED QUESTIONS

Improper Cabling (Most Common Support Issue - Please Read Carefully)

It is extremely important to utilize correct cabling for proper operation of the copper bypass switches, particularly in 10/100BaseT applications.  Cabling problems can result in confusing Link LED displays and the inability of the unit to function as a bypass switch.  In general, the copper units are designed for use with straight cables in the application shown in the figure below.  This target application is for use between a network switch and a router (or other NIC-type interface).  The application assumes that the Server 1 and Server 2 ports are connected to NIC-type interfaces such as the Cisco IPS 4200 Series appliances.  In the event that other network configurations are used, the cable polarity (NIC vs Switch or Straight vs Crossover) must be maintained.  For example, if both external ports (Router and Switch) are to be connected to network switches, then a crossover cable must be used on the Router interface (Net A) to reverse the switch pin mapping and present a NIC interface to the SM-2400.

To resolve cabling issues, it is often useful to verify that the Net A (Router) and Net B (Switch) interfaces can communicate in Bypass mode.  In Bypass mode, the SM-240x simply acts as a direct pin-to-pin patch panel.  Therefore in Bypass mode, one can simply connect the Net A and Net B interfaces and proper communication should be verified.  If the Bypass mode communication fails, one should try to directly connect the two external cables with a female-female RJ45 coupler.  

To further troubleshoot cabling issues, another technique is to only connect one cable to the SM-240X unit at a time and to look for Link LEDs to illuminate.  Due to the unique relay-based switching approach used in the SM-240x devices, the Link LEDs are driven by the link signal energy detected on specific RJ45 cable pairs (see figure above).  This fact is useful in troubleshooting since LEDs are direct indication of link activity on the "proper" wire pairs for the expected interface (NIC or Switch) type.  For example, in BYPASS mode, if the Router Link LED illuminates when only the Switch cable is connected, then the cable may be improperly crossed-over.  Likewise, if the Switch LED illuminating when only the Router cable is connected, then the cable may be improperly crossed-over.  If auto-MDIX (automatic polarity detection/correction) is enabled on a network interface, then both standard transmit and receive pairs are driven by the interface.  This condition causes both the Switch and Router Link LEDs to illuminate and flicker.  It is recommended that auto-MDIX not be used on interfaces attached to SM-240X devices.   

Please note that it is not sufficient to only verify that the network endpoints (Router and Switch ports) can communicate in Bypass mode.  For example, if a cross-over cable is used on a NIC connected to the Router port and a cross-over cable is used on a network switch connected to the Switch port, these endpoints will be able to communicate properly in Bypass mode since the two crossover cables cancel out each other.  However, if the SM-240X is switched to Online mode, then there will be two crossovers between the Router/Server1 interfaces (two NIC-type interfaces) and there will be one crossover between the Switch/Server2 interfaces (one NIC-type and one Switch-type interface).  In both cases, these systems will not communicate since both endpoints are transmitting on the same wire pairs.

In summary, cabling should be connected such that the Router port is connected with straight-thru cables to a DTE-type interface (NIC). Straight-thru cabling should also be used to connect the Switch port to a DCE-type interfaces (network switches). Similarly, straight-thru cabling should be used to connect the Server 1 and Server 2 ports to DTE-type (NIC) interfaces.  Crossover cables should be used where connection to the opposite equipment type is desired. Note that flickering of the Router and Switch link LEDs is normal when the link is not fully up and autonegotiation is in use.   

ButtonGenerator.comGigabit Ethernet Related Issues

All pairs are driven simultaneously by the Gigabit Ethernet interfaces.  If Gigabit Ethernet is used, it is normal (in the Bypass Mode with only one network cable connected to the Router or Switch port) for both the Router and Switch LEDs to flicker.  This indication is identical to the auto-MDIX case mentioned previously.  However, for Gigabit Ethernet, all cross-over functions are negotiated between the endpoints and crossover cables are not required for proper operation.  It is recommended that crossover cables be used as described above to ensure that proper operation will occur if the interfaces run at a reduced speec (10 or 100Mbit rather than 1Gb).

If the Server LEDs flicker in Bypass mode, increase the link filtering time with the SET FILTER command available through the RS-232 control  interface, until the link LEDs are steadily illuminated. Once the proper setting is found, save the configuration using the SAVECONFIG command. 

Online Mode Problems 

Verify that the cables are fully inserted. Then directly connect the Server 2 endpoint (IPS) directly to the Switch endpoint and verify that link is established. Similarly directly connect the Router endpoint to the Server 1 endpoint (IPS) and verify the connection. Disable the SM-240X, and place it online (see command reference or switch operation). If the links are OK while directly connected, and bad while connected through the SM-240X, the unit may need servicing.  

Cisco- Specific Settings

Based on testing with Cisco IPS products, SM-240X units are pre-configured at the factory with the following non-default option settings.  These settings should be restored if the SM-240X units are ever returned to factory default option settings.


    Singleport Units (Syntax shown in parentheses):

  • Gigabit  (SET GIGABIT ENA)
  • Mode 3  (SET MODE 3)
  • Link Filter (SET FILTER 5.0)
  • Saveconfig  (SAVECONFIG)

    Multiport Units (Syntax shown in parentheses - some commands may generate syntax errors depending on option settings at the beginning of this command sequence. The "A" in the following PA commands must be capitalized for proper effect):

  • Echo - Port 1 (SET ECHO ENA)
  • Multiport  (SET MULTIPORT ENA)
  • Echo - Other ports   (PASET ECHO ENA)
  • Gigabit  (PASET GIGABIT ENA)
  • Mode 3  (PASET MODE 3)
  • Link Filter (PASET FILTER 5.0)
  • Saveconfig  (PASAVECONFIG)

For support on programming multiple units, follow the links below:

To setup the USB Windows driver for the SM-2402/4 USB interface, please click here.

To setup the SM-2402/4 for Cisco Operation using Hyperterm, please click here.

Mode 3 Port Switching

In Mode 3, if the unit will not switch to Bypass when Server Links are Down, an adjustment of link filter parameters may be necessary. This may happen when the Router and Switch ports are using automatic crossover detection (MIDI-X). This causes the switch and router connected equipment to send link pulses on the alternate wire pair, causing a false link detect on the SM-240X Server ports. Increase the filter setting on the server ports (see the SET FILTER xx.x command) should resolve this condition. Note that link detection is not used in Mode 1 so filter settings will not affect the SM-240X operation. Filter setting adjustment affect the display LEDs only in this case.

Startup Procedure for Cisco IPS and SM-240X 

The Cisco IPS appliance should be fully booted and operational before power is applied to the SM-240X units.  When the SM-240X is powered down, it maintains connectivity between the Router and Switch ports.  Once fully booted and operational, the SM-240X should be powered up and the unit should switch to Online mode within 2-3 seconds.  If the SM-240X unit is powered up before the Cisco IPS is fully operational, the SM-240X will switch to Online mode before the IPS is capable of processing packets and a brief network outage could occur. 

No Serial Communications with SM-240X

Check that a correct RS-232 cable is used. For connecting to a PC or terminal, a straight cable is required. For connecting to a modem, a null modem must be used. Make sure that the terminal or PC is set for 9600 bps, 8 bit data, 1 stop bit, no parity, and no hardware flow control. Reboot the SM-240X by pressing the reset switch (on single port units) or by cycling its power. Observe the LEDs on the RJ45  connectors.  All LEDs should illuminate briefly (lamp test) and then switch to status indication (i.e. alarm, bypass, and any link LEDs on). You may have to disconnect all RJ45 cables to observe this more clearly. Check that there is no intermediate status indication between the lamp test and the status indication. This indication is a brief illumination of the ALARM LED, and one or both Server 1 or Server 2 Link LEDs. For example, after power up, all LEDs illuminate, then the ALARM LED illuminates, and then the steady status indication is displayed.  This indicates that the unit may be in test mode.  To cancel test mode: If the ALARM LED illuminates with one or both Server Link test LEDS, check that there are no jumpers present on the circuit board option jumper headers JP3 and JP4. If this is the case, remove the jumpers. If ALARM LED only illuminates briefly after lamp test, cancel test mode by typing: PASYSRESET, wait about 10 seconds and then type PAREBOOT. The unit should then reboot and print a standard power up banner message to the terminal. 

Other Communication Problems: 

If using the RJ11 console connector is used, check that the pinout of the cable you are using is correct.  This information is listed in the SM-240X User Manual.