Missing memory

[shane.finn]

We have recently upgraded our Internet BGP routers from 2600XM (128M RAM) to 2821 with 256M RAM. However we have only gained an extra few more MB of RAM. Doing a "sh ver" and "sh mem" yields:

Cisco 2821 (revision 53.51) with 237568K/24576K bytes of memory.

Processor board ID FHK0925F1PP

2 Gigabit Ethernet interfaces

1 Virtual Private Network (VPN) Module

DRAM configuration is 64 bits wide with parity enabled.

239K bytes of non-volatile configuration memory.

62720K bytes of ATA CompactFlash (Read/Write)

Head Total(b) Used(b) Free(b) Lowest(b) Largest(b)

Processor 457B7080 151293824 116235932 35057892 34515920 34898852

I/O 3E800000 25165824 5297944 19867880 19856352 19853756

Analysing this shows that we can account for 175M of RAM usage (151M in processor and 25M in IO). What is the other missing 80M doing?

In this case an extra 128M RAM has only yielded a usable gain of near 40M.

Please help us understand or fix the issue.

[chfloyd]

The missing memory can be attributed to the image decompression process. You can look at the output from the following show commands

Sample Router

Cisco 2811 (revision xx.xx) with 772096K/14336K bytes of memory.

772096Kb*1024b/Kb = 790626304b of main memory

---------------------------------

OUTPUT from show stacks command

router#show stacks

.

.

.

0x40000000 0x6F1FFFFF 790626304 Local R/W main

0x4000F000 0x42DDFFFF 48041984 IText R/O main:text

0x42DE0000 0x454DD15F 40882528 IData R/W main:data

0x454DD160 0x45A2B4BF 5563232 IBss R/W main:bss

0x45A2B4C0 0x6F1FFFFF 696077120 Local R/W main:heap

----------------------------------------------

Main is the same amount as reported in show version. IText + IData + IBss + Local = Main memory amount. IText is the region of memory used to hold the decompressed image. IBss and IData are used to initialize store variable and structure information.

I suspect that you would see a much larger memory difference if you were to load an image of the same version and feature set on the 2600 router. In that case the 2600 would also need the memory associated with the new IOS images. My guess is that the memory difference would be more like 90Mb in that case. You will not see the full 128 difference as the 2800 images are larger than the 2600 imamges.

You may consider moving to a more limited feature set to free up memory if you are not using the addiational security features (IDS,IPS, etc.) that are poossible on this router.

--Brent