The system encounters a bus error when the processor tries to access a memory location that either does not exist (a software error) or does not respond properly (a hardware problem). A bus error can be identified by looking at the output of the show version command. This is provided by the router, if not power cycled or manually reloaded.
To find out whether you have a Cisco IOS Software problem or a router hardware problem, you need to determine the memory location that the router tried to access when the bus error occurred.
You can find the memory location by looking at the address in the output of the show version command, as shown in this example:
Router uptime is 2 days, 21 hours, 30 minutes
System restarted by bus error at PC 0x30EE546, address 0xBB4C4
System image file is "flash:igs-j-l.111-24.bin", booted through Flash
With the address accessed by the router when the bus error occurred, determine the memory location that the address corresponds to by issuing the show region command.
If the address reported by the bus error does not fall within the ranges displayed in the output of the show region command, the router was trying to access an address that is not valid. This indicates that it is a Cisco IOS Software problem.
If the address falls within one of the ranges in the show region command output, it means that the router was accessing a valid memory address, but the hardware corresponding to that address is not responding properly.
This is the sample output:
Start End Size(b) Class Media Name
0x00000000 0x007FFFFF 8388608 Local R/W main
0x00001000 0x0001922F 98864 IData R/W main:data
0x00019230 0x000666B3 316548 IBss R/W main:bss
0x000666B4 0x007FEFFF 7965004 Local R/W main:heap
0x007FF000 0x007FFFFF 4096 Local R/W main:flhlog
0x00800000 0x009FFFFF 2097152 Iomem R/W iomem
0x03000000 0x037FFFFF 8388608 Flash R/O flash
0x0304033C 0x037A7D3F 7764484 IText R/O flash:text
This output indicates a hardware problem. The main corresponds to main memory or DRAM. The iomem corresponds to I/O memory, which means different parts for different platforms (such as DRAM for the Cisco 2500 series router and Shared RAM (SRAM) for the Cisco 4000 series router).