Maintenance Bus (MBUS) ROM agents below version 2.00 may render some line cards unstable.
A line card with a Layer 3 engine 2, engine 3, or engine 4 is never shipped from manufacturing with an MBUS ROM agent below version 2.00. If one is installed in a system with a Cisco IOS® software release 12.0(5)S or earlier and the upgrade all all command is issued, the MBUS agent in ROM will be downgraded to version 1.33. This earlier version of the MBUS agent may cause boot issues with the linecard.
If the MBUS ROM agent is accidentally downgraded to version 1.33, there is no way to upgrade to a newer version in the field.
Problem symptoms range from a warning message to a non-operational line card.
The warning message displayed is WARNING: MBUS agent in slot x is running from ROM.
Because it is a "race" condition when the MBUS is operating from ROM, a linecard might boot once, but not boot again for a number of cycles.
This issue can be avoided by not issuing the upgrade all all command with IOS 12.0(5) or earlier.
Rebooting the system or performing an online insertion/removal (OIR) of the affected line card may clear the condition, but there is no assurance that it will remain cleared after the next reboot or power on.
If the MBUS ROM agent in a linecard is changed, the recommended solution is to replace that linecard.
The Layer 3 engine of a linecard and the MBUS ROM version can be identified by issuing a show diag command as below. The linecard in the example below has an engine 2 and has MBUS ROM version 02.00.
GSR router#show diag 8
SLOT 8 (RP/LC 8 ): 1 Port SONET based SRP OC-48c/STM-16 Single Mode/SR SC-SC cr
MAIN: type 58, 800-5619-01 rev A0 dev 0
HW config: 0x04 SW key: 00-00-00
PCA: 73-4039-06 rev A0 ver 6
HW version 1.1 S/N SDK04391CZT
MBUS: Embedded Agent
Test hist: 0x00 RMA#: 00-00-00 RMA hist: 0x00
DIAG: Test count: 0x00000000 Test results: 0x00000000
FRU: Linecard/Module: OC48/SRP-SR-SC=
Route Memory: MEM-GRP/LC-128=
Packet Memory: MEM-LC1-PKT-256=
L3 Engine: 2 - Backbone OC48 (2.5 Gbps)
MBUS Agent Software version 01.46 (RAM) (ROM version is 02.00)
Using CAN Bus A
ROM Monitor version 10.05
Fabric Downloader version used 04.08 (ROM version is 04.08)
Primary clock is CSC 1
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: