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HP ProCurve Switch 2124 - FAQs

These FAQs apply to the J4868A HHP ProCurve Switch 2124.

Click on the question below to jump to the answer lower on the page.

Q1: Does the HP ProCurve Switch 2124 support IEEE 802.3u auto-negotiation?

The HP ProCurve Switch 2124 supports full IEEE 802.3u auto-negotiation, except for the 100Base-FX Transceiver Module. Note that the device connected to the Switch 2124 must be compliant with the IEEE 802.3u standard. A non-standard device may experience some problems. If the device is older, or is using pre-standard drivers, the device may have difficulty in auto-negotiating with the HP ProCurve Switch 2124. If you experience problems, you should check with the manufacturer of the device and if necessary, update the drivers for that device.

Note: The ProCurve Networking by HP 100-FX SC Transceiver (product number J4853A), which is supported as an accessory in the switch, operates in full duplex mode only and uses flow control packets. This port will therefore not auto-negotiate and it is important to configure the device to which it connects with the same port parameters (that is: full duplex).

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Q2: Is 10/100Mbps auto-negotiation the same as Plug-n-Play?

No. The following configuration will cause severe network problems:

The hub, switch, or router will correctly sense (not auto-negotiate) the 10Mbps or 100Mbps speed. Since the end node was configured for a specific speed and duplex state, and therefore does not negotiate, the hub, switch, or router will choose the communication mode specified by the 802.3u standard, namely half-duplex.

With one device running at half-duplex and the device on the other end of the connection at full-duplex, the connection will work reasonably well at low levels of traffic. At high levels of traffic the full-duplex device (end node, in this case) will experience an abnormally high level of CRC or alignment errors. The end users usually describe this situation as, "Performance seems to be approximately 1Mbps!". Often, end nodes will drop connections to their servers.

In this same situation, the half-duplex device will experience an abnormally high level of late collisions.

The network administrator must take care to verify the configuration of each network device during installation. Also, check the operational mode of each network device. That is, check both how you configured it and also that it comes up as you expect, for example, at 10Mbps/half-duplex.

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Q3: What cables are used with the HP ProCurve Switch 2124?

The HP ProCurve Switch 2124 supports HP Auto-MDIX on all twisted pair parts, so either "straight-through" or "cross-over" cables can be used.

For connections to the 10 Mbps ports, you can use Category 3, 4 or 5 unshielded twisted-pair cable, as supported by the IEEE 802.3 Type 10Base-T standard.

For connections to the 100 Mbps ports, use Category 5 only, as defined by the IEEE 802.3u Type 100Base-TX standard. Only twisted-pair cables with solid conductors are supported to the full 100 meters; do not use braided or drop cables.

All twisted-pair wires must be twisted through the entire length of the cable. The wiring sequence must conform to AT&T 2588 (not USOC). Here is a "straight through" cable:

Here is a "crossover" cable:

Fiber-optic cables connected to an ProCurve Networking by HP 100-FX SC Transceiver (product number J4853A) installed in the switch's transceiver slot must be 62.5/125 µm or 50/125 µm (core/cladding) diameter, graded-index, multimode fiber-optic cables, complying with the ITU-T G.651 and ISO/IEC 793-2 Type A1b or A1a respectively, fitted with SC connectors and not exceeding 2 kilometers in length.

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Q4: Does the HP ProCurve Switch 2124 support full duplex?

The HP ProCurve Switch 2124 will auto-negotiate half or full duplex, except for the 100Base-FX Transceiver Module. If a full-duplex auto-negotiating device is connected to the switch, it chooses full-duplex. Note that the device connected to the HP ProCurve Switch 2124 must be compliant with the IEEE 802.3u standard. A non-standard device may experience some problems. If you experience problems, you should check with the manufacturer of the device and if necessary, update the drivers for that device.

Note: The ProCurve Networking by HP 100-FX SC Transceiver (product number J4853A), which is supported as an accessory in the switch, operates in full duplex mode only and uses flow control packets. This port will therefore not auto-negotiate and it is important to configure the device to which it connects with the same port parameters (that is: full duplex).

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Q5: Does the HP ProCurve Switch 2124 support IEEE 802.3u auto-negotiation?

The HP ProCurve Switch 2124 supports full IEEE 802.3u auto-negotiation, except for the 100Base-FX Transceiver Module. Note that the device connected to the Switch 2124 must be compliant with the IEEE 802.3u standard. A non-standard device may experience some problems. If the device is older, or is using pre-standard drivers, the device may have difficulty in auto-negotiating with the HP ProCurve Switch 2124. If you experience problems, you should check with the manufacturer of the device and if necessary, update the drivers for that device.

Note: The ProCurve Networking by HP 100-FX SC Transceiver (product number J4853A), which is supported as an accessory in the switch, operates in full duplex mode only and uses flow control packets. This port will therefore not auto-negotiate and it is important to configure the device to which it connects with the same port parameters (that is: full duplex).

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Q6: Does the HP ProCurve Switch 2124 support 802.1Q/802.1p?

The HP ProCurve Switch 2124 allows 1522 byte size packets tagged with an 802.1Q tag but does not decode the VLAN ID. The switch does not participate in VLAN tagging or VLAN priorities. The packets will be forwarded without any problems.

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Q7: What transceivers can be used in the HP ProCurve Switch 2124 (product number J4868A)?

There is one transceiver module slot in the HP ProCurve Switch 2124. The only transceiver supported in that slot is the ProCurve Networking by HP 100-FX SC Transceiver (product number J4853A). If a non-supported transceiver is installed in the switch, such as the HP Advancestack 100Base-TX UTP Transceiver Module, the port 25 LED and the switch Fault LED will blink simultaneously.

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Q8: Can the HP ProCurve Switch 2124 be used as a desktop switch?

Yes, the HP ProCurve Switch 2124 is designed to be used primarily as a desktop switch to which end nodes, printers and other peripherals, and servers are directly connected, as shown in the illustration below. Notice that the end node devices are connected to the switch by "straight-through" or "cross-over" twisted pair cables. Either cable type can be used because of the "HP Auto-MDIX" feature on the Switch 2124.

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Q9: Can the HP ProCurve Switch 2124 be used as a segment switch?

Yes, the HP ProCurve Switch 2124 can be used as a segment switch. Although it was designed as a desktop switch, with its high performance and large address table, it can be used for interconnecting network segments by simply connecting the network hubs that form those segments to the switch.

In the illustration below, two Ethernet hubs with PCs, printers, and local servers attached, are both connected to an HP ProCurve Switch 2124. The devices attached to the two hubs can now communicate with each other through the switch. They can also all communicate with the server that is connected to the switch. Connecting the server through a 100 Mbps connection allows a large number of users to access the server without causing network congestion.

The switch is connected to a network backbone through fiber-optic cabling connected to a 100Base-FX transceiver installed in the switch. Now, all the devices on these network segments can access other network resources that are connected elsewhere on the network backbone.

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Q10: Can the HP ProCurve Switch 2124 be used to connect to a backbone?

The simpler desktop and segment networks shown in previous HP ProCurve Switch 2124 FAQs can easily be combined and expanded. For example, you could use an HP ProCurve Switch 8000m to interconnect each of your smaller switched workgroups to form a larger switched network. All the devices in this network can communicate with each other. With an HP ProCurve Switch Gigabit-SX Module, for example, installed in the HP ProCurve Switch 8000m, the entire switched topology could be connected to a campus backbone, as shown in the illustration below.

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Q11: Why won't my iMac, which is directly attached to an ProCurve Networking by HP switch, NetBoot from an OS X Server, even though it worked correctly when my iMac was plugged directly into a hub?

This issue is not specific to HP switches. Rather, it is a timing problem in early versions of the iMac Boot ROM. Apple Computer, Inc has fixed this NetBoot issue by releasing both an updated Boot ROM image and Mac OS X Server version 1.2. Please advise customers with iMac NetBoot issues to contact Apple Computer, Inc Technical Support.

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Q12: How can the LEDs on the front of the HP ProCurve Switch 2124 be used to troubleshoot networking problems?

The following is a chart with an explanation of the LED behavior.
Indication: The power cord is plugged in and the Power LED is not lit.
Problem: The switch is not plugged into an active AC power source, or the switch's power supply may have failed.
Solution:
  1. Verify that the power cord is plugged into an active power source and to the switch. Make sure these connections are snug.
  2. Try power cycling the switch by unplugging and plugging in the power.
  3. If the Power LED is still not on, verify that the AC power source works by plugging another device into the outlet. Or try plugging the switch into a different outlet or try a different power cord.
If the power source and power cord are OK and this condition persists, the switch power supply may have failed. Call your HP Authorized Reseller, or use the electronic support services from HP to get assistance. Refer to your Customer Support/Warranty booklet for more information.
Indication:The Power LED is ON and the Fault LED is on for a prolonged period of time.
Problem: A switch hardware failure has occurred during self-test.
Solution: Try power cycling the switch. If the fault indication reoccurs, the switch may have failed. Call your HP Authorized Reseller, or use the electronic support services from HP to get assistance. Refer to your Customer Support/Warranty booklet for more information.
Indication:The Power LED is ON and the Fault LED is Blinking.
Problem: The switch has experienced a failure during self-test or operation.
Solution: Try resetting the switch by pressing the Reset button on the front of the switch, or by power cycling the switch. If this does not resolve the problem, contact your HP Authorized Reseller, or use the electronic support services from HP to get assistance. Refer to your Customer Support/Warranty booklet for more information.
Indication: The Power LED is ON, the Fault LED is OFF, and the Port Link LED is OFF with a cable connected.
Problem: The network connection is not working properly.
Solution: Try the following procedures:
  1. For the indicated port, verify that both ends of the cabling, at the switch and the connected device, are snug.
  2. Verify that the connected device and switch are both powered on and operating correctly.
  3. Verify that you have used the correct cable type for the connection. For fiber-optic connections, verify that the transmit port on the switch is connected to the receive port on the connected device, and that the switch receive port is connected to the transmit port on the connected device.
  4. Verify that the connected devices comply with the IEEE 802.3 standard, including transmission of the Link Beat signal. See "Testing Twisted-Pair Cabling" on page 3-5 of the HP ProCurve Switch 2124 Installation Guide.
  5. Try the "Testing End-to-End Network Communications" procedures on page 3-6 of the HP ProCurve Switch 2124 Installation Guide.
  6. If the other procedures don't resolve the problem, try using a different port or a different cable.
  7. For Port 25 (transceiver port), it may indicate that the transceiver has failed. Contact your local HP authorized reseller or your local HP Customer Care Center.
Indication:The Power LED is ON, the Fault LED is Blinking, and the Port Link LED is Blinking for Port 25.
Problem: An unsupported transceiver module has been installed in the transceiver slot.
Solution: The Switch 2124 supports installation of only the HP J4853A 100-FX SC Transceiver. If you have installed any other transceiver, the Port 25 Link LED will blink simultaneously with the switch Fault LED.

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Q13: What causes the Activity LED for a port to flash continuously, even though there is no traffic, or little traffic, going through that port?

The Switch 2124 transmits flow control by default. These packets do not impact performance because the packet rate is very low. The switch sends flow control packets at a rate of approximately one every 50 milliseconds. While these are multicast packets, they are sent from switch to switch only and not throughout the entire network. These flow control packets may cause the Switch 2124 Activity LED to flicker or remain on constantly and may also cause a device attached to the Switch 2124 to indicate activity (in terms of received packet statistics).

Note that ProCurve Networking by HP switches provide an Activity LED persistence of 5 milliseconds per flash so that extremely low levels of traffic are easy to detect visually. As a result, the traffic level on a 100 Mbps link will appear (according to the Activity LED) to be higher than it really is.

Because of the low impact on the inter-switch traffic level these flow control packets should not cause concern. Even so, it is possible to turn them off in certain types of devices connected to the Switch 2124:
  • Switch 2124. When two Switch 2124 units are connected to each other, flow control will always be on. Because these switches are unmanaged there is no way to turn off the flow control packets.
  • 10/100Base-T. When a Switch 2124 is connected to a device other than a Switch 2124 using 10Base-T or 100Base-T cabling, you may choose to disable flow control on the remote device. The Switch 2124 will detect this setting during auto-negotiation and transmit no flow control packets.
  • 100Base-FX. The Switch 2124 does not auto-negotiate on the 100Base-FX port. That port always operates at 100 Mbps, full duplex, with flow control on. You may disable flow control on the remote device to prevent it from sending flow control packets to the Switch 2124. The Switch 2124 will still transmit flow control packets out its 100Base-FX port, though.

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Q14: Why are the multicast packet counters incrementing on a device connected to the HP ProCurve Switch 2124, even though there is no traffic going through the network?

The Switch 2124 transmits flow control by default. These packets do not impact performance because the packet rate is very low. The switch sends flow control packets at a rate of approximately one every 50 milliseconds. While these are multicast packets, they are sent from switch to switch only and not throughout the entire network. These flow control packets may cause the Switch 2124 Activity LED to flicker or remain on constantly and may also cause a device attached to the Switch 2124 to indicate activity (in terms of received packet statistics).

Note that ProCurve Networking by HP switches provide an Activity LED persistence of 5 milliseconds per flash so that extremely low levels of traffic are easy to detect visually. As a result, the traffic level on a 100 Mbps link will appear (according to the Activity LED) to be higher than it really is.

Because of the low impact on the inter-switch traffic level these flow control packets should not cause concern. Even so, it is possible to turn them off in certain types of devices connected to the Switch 2124:
  • Switch 2124. When two Switch 2124 units are connected to each other, flow control will always be on. Because these switches are unmanaged there is no way to turn off the flow control packets.
  • 10/100Base-T. When a Switch 2124 is connected to a device other than a Switch 2124 using 10Base-T or 100Base-T cabling, you may choose to disable flow control on the remote device. The Switch 2124 will detect this setting during auto-negotiation and transmit no flow control packets.
  • 100Base-FX. The Switch 2124 does not auto-negotiate on the 100Base-FX port. That port always operates at 100 Mbps, full duplex, with flow control on. You may disable flow control on the remote device to prevent it from sending flow control packets to the Switch 2124. The Switch 2124 will still transmit flow control packets out its 100Base-FX port, though.

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Q15: Why won't my Xircom Realport-REM56G-100BTX Notebook NIC operate properly with my ProCurve Networking by HP switch in full duplex mode at 100Mbps?

HP knows that this Xircom NIC, at full duplex over 100Mbps, does not operate with our ProCurve Networking by HP switches. HP has no reports of any other vendors' NIC having a similar issue with our ProCurve switches. While this NIC's data sheet states support of full duplex, HP has not been able to get this NIC to operate at full duplex over a 100Mbps connection, regardless whether it is configured to Auto-negotiate or full duplex, fixed configuration.

We are not aware of any fixes for this issue.

Failure symptoms include poor performance and lost connections. See the discussion of " Is 10/100Mbps auto-negotiation the same as Plug-n-Play? " on this same page for more details on the problem symptoms.

The workaround is to operate the NIC in half-duplex mode or to use a different NIC.

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Q16: Does the HP ProCurve Switch 2124 support 802.1Q/802.1p?

The HP ProCurve Switch 2124 allows 1522 byte size packets tagged with an 802.1Q tag but does not decode the VLAN ID. The switch does not participate in VLAN tagging or VLAN priorities. The packets will be forwarded without any problems.

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