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Unsupported DIMM

I have a 2811 with 512 of memory installed (two by 256).  The router has been sitting spare for sometime and I know there was once a memory problem with it long ago.  It has two 256M Non ECC DIMMs installed and seems to work fine.  I recently tried to install a 512M DIMM ECC and all I get is 'Unsupported DIMM" error - same if I remove the other 256M DIMM leaving just the 512M.   I have tried three different DIMMs - and all have the same error message.  One of the DIMMs is 'cisco supported' and based on what I can find in the web - seems to be the correct spec.  I have also tried non ECC 512 DIMM and 'unsupported DIMM" error message is still coming up.  If I did not know better, I would say that there was something that needed changing in the config to allow 512M DIMMs to be installed.

I'm a bit new to this router (kind of inherited it) and a bit lost as to what to try next?

Reza Sharifi
Hall of Fame Expert


The maximum supported memory for a 2811 is 768MB.  Is your case one module is 512 and the other is 256 for a total of 768.  Have you try putting the 512 module in the second slot?

Hi - thanks for the reply

Yes - have tried both slots - same error message (but with other bank number given)

Pins could be dirty.

Not on all three DIMMs.  Is there any 'config' settings needed to allow the 2811 to support 512M DIMMs?

No, no config change setting needed it at all.  When the memory is good and the router is booted, you will see the total amount of memory in "sh ver"

Q. Can the Cisco 2811, 2821, and 2851 router DRAM be used in the Cisco 2801 platform?
A. No, the Cisco 2811, 2821, and 2851 router DRAM is SDRAM DDR, whereas the Cisco 2801 router memory is SDRAM extended data output (EDO). The SDRAM DRR and SDRAM EDO are not compatible.

So, is your 512 memory SDRAM DDR?

Yes - double checked them: DDR 266 ECC

Steve Wood

Did you get a resolution to this issue as I am experiencing the same problem

Spec states 512MB DDR PC2100 CL2.5 ECC


System Bootstrap, Version 12.4(13r)T, RELEASE SOFTWARE (fc1)

Technical Support:

Copyright (c) 2006 by cisco Systems, Inc.


ERROR: Unsupported DIMM memories in DIMM SLOT:00000000


Nope - never did fix it.  Ended up using the Router anyway.  It still booted (was slow to boot) but worked .  I wonder if the issue was the DIMM or the motherboard.  

Thanks for the update. Think I will punt it back to my supplier and see their response. need to get it on 15.1 to support call manager 9.1


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It might be Cisco is looking for a proprietary tag in something like the SPD.

Got the same "ERROR: Unsupported DIMM memories in DIMM SLOT:00000000" error. With two different 512MB DDR 2100 ECC DIMMs from different manufacturers! I know specs say 768MB max but i couldn't find a cisco part number for 512MB stick!