ASA 5510, 7.2(3), 0-byte memory block?

[Patrick0711]

Unfortunately I cannot share much of the configuration details other than that I have a ASA 5510 with 256MB RAM running 7.2(3) code.  I was troubleshooting a sharp spike in memory utilization (from 41% used to 91% used in the span of 2 hours) when I noticed the following:

  SIZE    MAX    LOW    CNT

     0    100     35    100

     4    300    299    299

    80    100     57    100

   256   4148   3968   4148

  1550   9251   7208   7722

  2048   2100   2100   2100

  2560      1      0      1

16384      2      2      2

Has anyone ever seen a 0-byte memory block before? I cannot seem to find documentation on this anywhere. 

[mirober2]

Hi Patrick,

The 0-byte blocks are used for copying/duplicating existing blocks in memory. The documentation for the different block sizes can be found here:

http://www.cisco.com/en/US/docs/security/asa/asa84/command/reference/s2.html#wp1435964

Hope that helps.

-Mike

[brquinn]

Memory depletion is not necessarily related to the block utilization. The 'show memory detail' output will give you an idea of what memory fragment sizes are in use. Note that these are not the same as the blocks in the 'show blocks' output.

In version 7.2.3, I wouldn't be surprised if you are experiencing a memory leak. You can open a TAC case to troubleshoot the issue or if you have an upcoming maintenance window, you may just want to try an upgrade.

Thanks,

Brendan

[Patrick0711]

Thank you both for your responses.  I know that given the information there is little that can be done to troubleshoot the cause of the memory spike.  I was simply unaware of what purpose the 0-byte block served.  If the issue persists/reoccurs I will certainly open a TAC case. 

[mirober2]

Hi Patrick,

Just to clarify: the presence of the 0-byte blocks is not a problem, it is normal for those to be there. The problem would come in if the count (CNT) column on any of the block sizes ever goes to 0. This would indicate a block depletion for that particular block size.

As Brendan said, if you suddenly see a rise in memory utilization it is very possibly a memory leak in the old 7.2(3) code and should be investigated by TAC.

-Mike