This document provides an overview of the maintenance bus, power
supplies and blowers, and alarm cards of the Cisco 120000 Series Internet
There are no specific requirements for this document.
The information in this document is based on the software and hardware
The information in this document was created from the devices in a
specific lab environment. All of the devices used in this document started with
a cleared (default) configuration. If your network is live, make sure that you
understand the potential impact of any command.
For more information on document conventions, see the
Cisco Technical Tips
The Maintenance Bus (MBUS) is a 1 Mbps redundant Controller Area
Network (CAN) serial bus that connects the route processor (RP), the line cards
(LCs), the switch fabric cards (SFCs), the power supplies, and the fans (except
for the 12008). Due to its high fault-tolerant design, the CAN bus is commonly
used in the industrial control area.
Each line card supports an MBUS module, which provides an interface to
the master GRP. Use the show diag command to view
the MBUS Agent Software version running on your switch fabric card or line
SLOT 17 (CSC 1): Clock Scheduler Card
MAIN: type 17, 800-2353-02 rev A0 dev 16777215
HW config: 0xFF SW key: FF-FF-FF
PCA: 73-2148-02 rev C0 ver 2
HW version 1.0 S/N CAB03191T45
MBUS: MBUS Agent (1) 73-2146-07 rev B0 dev 0
HW version 1.2 S/N CAB03181N2S
Test hist: 0xFF RMA#: FF-FF-FF RMA hist: 0xFF
DIAG: Test count: 0xFFFFFFFF Test results: 0xFFFFFFFF
EEPROM contents (hex):
00: 01 00 01 00 49 00 08 62 07 58 00 00 00 FF FF FF
10: 43 41 42 30 33 31 38 31 4E 32 53 00 00 00 00 00
20: 01 02 00 00 00 00 00 FF FF FF FF FF FF FF FF FF
30: A5 A5 A5 A5 A5 A5 FF A5 A5 A5 A5 A5 A5 A5 A5 A5
40: 00 11 01 00 00 49 00 08 64 02 60 02 00 03 FF FF
50: 03 20 00 09 31 02 50 FF FF FF FF FF FF FF FF FF
60: 43 41 42 30 33 31 39 31 54 34 35 00 00 00 00 00
70: FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF
80: 01 02 04 08 10 20 40 80 01 02 04 08 10 20 40 80
90: 01 02 04 08 10 20 40 80 01 02 04 08 10 20 40 80
MBUS Agent Software version 01.43 (RAM) (ROM version is 01.33)
Using CAN Bus A
ROM Monitor version 0
Primary clock is CSC 1
The MBUS is mainly used for the following purposes:
Initial bootup - On initial load, the primary GRP uses the MBUS to
instruct the MBUS modules on the line cards and switch cards to power on their
cards. A bootstrap image is then downloaded to the line cards across the MBUS.
The MBUS is also used to gather revision numbers, environmental information,
and general maintenance information. In addition, the GRPs exchange redundancy
messages over the MBUS, which report the results of GRP arbitration, as
illustrated in the following log messages:
00:00:14: %MBUS-6-GRP_STATUS: GRP in Slot 0 Mode = MBUS Primary
00:00:20: %MBUS-6-GRP_STATUS: GRP in Slot 11 Mode = MBUS Secondary
The primary GRP periodically restates its mastership through the
MBUS. The secondary GRP re-enters the arbitration phase after failing to detect
the primary's ownership claims for a configurable period.
Environmental statistic monitoring
Out-of-band console access to the LCs using the attach
Download of the field diagnostics image.
Note: Data traffic never goes through the MBUS, but across the switch
fabric. The MBUS is used exclusively to manage components within the Cisco
12000 series router.
The MBUS also transports log and debug messages from LCs to the GRP.
Access control list (ACL) logging can produce a large number of messages that
overwhelm the MBUS and can result in LCLOG-3-INVSTATE and MBUS_SYS-3-SEQUENCE
errors. A similar problem may occur when logging Border Gateway Protocol (BGP)
neighbor changes. Cisco IOS® Software Release 12.0(20)S resolves this problem
by allowing log messages to be transferred through the switch fabric using
Inter-Process Communication (IPC) messages (CSCdu00535). It introduces the
following new commands:
logging method mbus <severity> -
Selects the severity of the message sent through the MBUS. Cisco IOS Software
Release 12.0(20)S changes the default logging configuration of the GSR. Log
messages with severity 0-4 are sent through the MBUS and log messages with
severity 5-7 are sent through IPC, so ACL and BGP neighbor logs are sent
through IPC. The logging method mbus 7 command sends
all logs through the MBUS.
show logging method - Displays the current
severity settings of which log messages are sent through
logging sequence-nums - Configures LCs to
add a sequence number to transmitted log messages to ensure that the GRP
process messages sent by either IPC or the MBUS are in sequential order. When
this command is enabled, logs are sent to the GRP in the format: "SLOT <slot
num>:<seq num>: <HH:MM:SS:MM>: <message text>".
In rare cases, the GSR reports the following MBUS-related error
%MBUS_SYS-3-NOCHANNEL: Failed to allocate MBUS channel for over 10 secs
This message has been seen when the router has a faulty power supply
and when LCs are upgraded incorrectly. In the latter case, you should remove
all LCs from the chassis and reboot the Cisco 12000 router. Once the GRP is up,
introduce the LCs one at a time. As each LC boots up successfully, issue the
upgrade all command on the slot with the LC from
enable mode. When all the LCs are upgraded, it is extremely unlikely that you
will run into this issue again since, on subsequent reboots, you can download
the LC image over the switch fabric rather than the MBUS.
The Cisco 12000 Series Router is available in either an AC or a DC
configuration. All power supplies are load-sharing and hot-swappable.
Both the 12008 and 12012 need at least one AC or one DC power supply to
The 12016 and the 12416 power modules do not have MBUS modules. They
are monitored through the Busboard. The 12016 and the 12416 are divided into
two load zones for power. There are two AC power supply configurations, one
with three power supply modules, the other with four power supply modules. When
using a DC power supply system, there are four DC power supply modules (A1, A2,
To completely power the system, you need to power both load zones. The
second load zone covers the switch fabric card cage, the lower card cage, and
the lower blower module, while the first load zone covers the top card cage and
the top blower module. In an AC system, this is done by connecting any two
power modules to a source. For the DC system, A1 and B1 power the upper load
zone while A2 and B2 power the lower load zone. To fully power a 12016/12416
with DC power supplies, the minimum that must be connected is A1&A2,
B1&B2, A1&B2, or A2&B1.
The links below provide information, per chassis, about the power
supply location and how to replace it.
There are different types of alarm cards depending on the type of 12000
chassis. On the Cisco 12008 and the 12016/12416, alarm cards power the LCs, so
make sure that at least one alarm card is present. The 12008 needs an alarm
card because that alarm card is integrated with the Card Scheduler and Clock
(CSC). The 12016 and 12416 have slots for two alarm cards (for redundancy). The
two alarm cards do not have segmented service zones like the DC power supply on
The Cisco 12404 supports a Consolidated Switch Fabric Card that
includes the switch fabric, alarm, and clock and schedule functions on one
The links below provide information related to alarm cards and
replacement instructions for each alarm card.