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Cisco IGX 8400 Series Switches

Field Notice: Possible Cause Identified for Intermittent Bus Errors on IGX


Updated April 27, 2000

Updated February 9, 2000

February 2, 2000


Products Affected

Product

Comments

IGX-ALM/A

If any UFM or UXM is in the same bus timing group.

IGX-ALM/B

If any UFM or UXM is in the same bus timing group.

IGX-BTM

If any UFM or UXM is in the same bus timing group.

IGX-BTM/B

If any UFM or UXM is in the same bus timing group.

IGX-CVM

If any UFM or UXM is in the same bus timing group.

IGX-FRM

If any UFM or UXM is in the same bus timing group.

IGX-FRM-31

If any UFM or UXM is in the same bus timing group.

IGX-HDM

If any UFM or UXM is in the same bus timing group.

IGX-LDM

If any UFM or UXM is in the same bus timing group.

IGX-NPM-32

If any UFM or UXM is in the same bus timing group.

IGX-NPM-64

If any UFM or UXM is in the same bus timing group.

IGX-NPM-64B

If any UFM or UXM is in the same bus timing group.

IGX-NTM

If any UFM or UXM is in the same bus timing group.

IGX-NTM/B

If any UFM or UXM is in the same bus timing group.

IGX-UVM

If any UFM or UXM is in the same bus timing group.

Problem Description

In rare instances, the physical arrangement of modules in an IGX8400 node may cause infrequent Universal Bandwidth Unit (UBU) bus errors. These errors are very rare, and when they occur, they are almost always minor and do not affect service.

Following is example output of the event log record when the problem occurs. This output shows when you use the dsplog command.

Info   Bus B Reports 1 Error(s) on Slot 8 HWY 1 (UBU)  12/06/99 18:34:57
Info   Bus A Reports 1 Error(s) on Slot 8 HWY 1 (UBU)  12/06/99 16:05:41

Notice that the error type is classified as "Info" and not "Minor" because isolated UBU errors normally do not noticeably affect traffic.

Background

The IGX 8400 Cell Bus is physically located in the IGX8400 backplane and carries data between modules in the chassis. The system clock is organized in groups of four contiguous module slots. A unique copy of the system clock is distributed to each of these groups of four slots. For example, in an IGX8420 (16-slot chassis), a copy of the system clock is given to slots 1 through 4, and another distinct copy of the system clock is given to slots 5 through 8, a third copy is used in slots 9 through 12, and a fourth copy is shared between slots 13 through 16. This design reduces clock race problems between slots.

The presence of either a UXM or a UFM card type, including IGX-UFM-4C, IGX-UFM-8C, IGX-UFM-U, IGX-UXM, and IGX-UXME, in the same bus timing group as the cards listed in the "Products Affected" section may cause infrequent cell bus errors. The following chart shows which slots share a unique copy of the system clock.

IGX8410
[1,2,3,4]
[5,6,7,8]

IGX8420
[1,2,3,4]
[5,6,7,8]
[9,10,11,12]
[13,14,15,16]

IGX8430
[1,2,3,4]
[5,6,7,8]
[9,10,11,12]
[13,14,15,16]
[17,18,19,20]
[21,22,23,24]
[25,26,27,28]
[29,30,31,32]

The problem may occur when one the modules listed in the "Products Affected" section is combined with any UFM-C, UFM-U, UXM, or UXME in the same timing group. For example, if slots [1,2,3,4] are populated, respectively, with [NPM, NPM, Empty, UXM], the problem may occur. Similarly, if slots [5, 6, 7, 8] are populated, respectively, with [Empty, HDM, Empty, UXM], the problem may occur. The frequency of the problem is rare, and in instances when it does occur, user traffic is not normally impacted.

Problem Symptoms

If this problem is occurring, the network maintenance staff will see node event log entries similar to the one that follows. The dsplog command shows log entries.

Info   Bus B Reports 1 Error(s) on Slot 8 HWY 1 (UBU)  12/06/99 18:34:57
Info   Bus A Reports 1 Error(s) on Slot 8 HWY 1 (UBU)  12/06/99 16:05:41

The slot number referenced in the log entry must be occupied by one of the module types listed in the "Products Affected" section of this Field Notice. The problem may be exhibited on either Cell Bus A, Cell Bus B, or both.

If this problem occurs, most often the symptom is an isolated packet or cell with an error that does not degrade application performance. In the rarest of instances, the problem may cause a momentary flicker or glitch in video or audio traffic.

If the IGX 8400 event log (use dsplog) does not record bus errors (UBU), it is not recommended that you move cards. As discussed above, it is not necessary to restrict the card configuration on the new IGX8400 installations.

Note: UBU errors may also be caused by failed cards. These hardware failure modes should not be confused with the intermittent bus errors that may be caused by the sharing of timing groups by UXMs or UFMs with other card types as described in this field notice. Card failures that result in bus errors on UBUs tend to have continual, rapidly-logged bus errors, not intermittently logged, as in this problem. This type of card failure is severe enough to cause a switch to the redundant bus and are logged in the event log as "Bus A Failed" or "Bus B Failed". These failures are resolved by card replacement through the standard Return Material Authorization (RMA) process.

Workaround/Solution

If a workaround is absolutely necessary, the recommended solution is to move the affected modules to another timing group.

Rearrange the cards if (and only if) all five of the following conditions are met:

  • Intermittent bus errors (UBU)are reported against one of the card types listed in the "Products Affected" section

  • The card reporting the error shares a timing group with an UFM or UXM card type

  • Service degradation is experienced

  • Other causes for bus errors (UBU) are eliminated

  • The disruption caused by the workaround can be justified given the extremely remote possibility of noticeable service-affecting errors.

For newly installed IGX8400 systems, the configuration guidelines in the workaround need not be followed if this results in any substantial customer implementation restrictions.

If the workaround is used, then only the cards in the timing groups exhibiting this problem should be moved. Either the card reporting the error may be moved, or the UXM or UFM in the same timing group as the card reporting the problem may be moved to another timing group.

If a workaround must be used, the procedure described above is the only one available. RMAs of chassis or cards will not resolve this trouble.

For More Information

If you require further assistance, or if you have any further questions regarding this field notice, please contact the Cisco Systems Technical Assistance Center (TAC) by one of the following methods:

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