CODEWITHSUNDEEP
snmpnet-snmpint64oid
zjyuan
zjyuan

Reputation: 21

using int64 type for snmp v2c oid?

I am debugging some snmp code for an integer overflow problem. Basically we use an integer to store disk/raid capacity in KB. However when a disk/raid of more than 2TB is used, it'll overflow.

I read from some internet forums that snmp v2c support integer64 or unsigned64. In my test it'll still just send the lower 32 bits even though I have set the type to integer64 or unsigned64.

Here is how I did it:

  1. a standalone program will obtain the capacity and write the data to a file. example lines for raid capacity

    my-sub-oid
Counter64
7813857280

  2. /etc/snmp/snmpd.conf has a clause to pass thru the oids:

    pass_persist mymiboid /path/to/snmpagent

  3. in the mysnmpagent source, read the oidmap into oid/type/value structure from the file, and print to stdout.

    printf("%s\n", it->first.c_str());
printf("%s\n", it->second.type.c_str());
printf("%s\n", it->second.value.c_str());
fflush(stdout);

  4. use snmpget to get the sub-oid, and it returns:

    mysuboid = Counter32: 3518889984

  5. I use tcpdump and the last segment of the value portion is:

    41 0500 d1be 0000

41 should be the tag, 05 should be the length, and the value is only carrying the lower 32-bit of the capacity. (note 7813857280 is 0x1.d1.be.00.00)

I do find that using string type would send correct value (in octetstring format). But I want to know if there is a way to use 64-bit integer in snmp v2c.

I am running NET-SNMP 5.4.2.1 though. thanks a lot.

Update:

Found the following from snmpd.conf regarding pass (and probably also pass_persist) in net-snmp doc page. I guess it's forcing the Counter64 to Counter32.

Note:
The SMIv2 type counter64 and SNMPv2 noSuchObject exception are not supported.

Upvotes: 1

Views: 4611

Answers (2)

xte
xte

Reputation: 171

You are supposed to use two Unsigned32 for lower and upper bytes of your large number.

Counter64 is not meant to be used for large numbers this way.

For reference : 17 Common MIB Design Errors (last one)

Upvotes: 3

Lex Li
Lex Li

Reputation: 63243

SNMP SMIv2 defines a new type Counter64,

https://www.rfc-editor.org/rfc/rfc2578#page-24

which is in fact unsigned 64 bit integer. So if your data fall into the range, using Counter64 is proper.

"In my test it'll still just send the lower 32 bits even though I have set the type to integer64 or unsigned64" sounds like a problem, but unless you show more details (like showing some code) on how you tested it out and received the result, nobody might help further.

Upvotes: 1

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