Thanks Dave, here is some more information on our bug.

Dave Shield wrote:
> On 31/08/06, Mike Varley wrote:
>> we are seeing an snmptable command respond with question
>> marks ('?') as the result for some of the column entries; and I am
>> wondering if this is normal behaviour if net-snmp encounters an error
>> while trying to interpret a response.

> Not an error as such, but it's the way snmptable displays "gaps" in a
> table,
> where a particular row is missing one or more column values.

Don't you hate it when people withhold information? I'm sorry, I
forgot to specify that that table is double-indexed by both the 'id' and
a numeric value. So here is a more accurate sample of the output:

id(index1) num(index2) ipaddress someotherinfo
0FB 1 abc
078 1 def
095 1 hij
095 2 klm
DE8 ? ?
(repeat (x) times in output)
9D8 1 qrs

So, as you can see, our secondary index is one of those 'gaps' -- we did
a test to see what happens if you perform a GETNEXT and provide
(a) just the 1st index (index1), or
(b) a secondary index (index1.index2) that is valid but non-existant,
and the response is the first entry...

so if a request for 'GETNEXT DE8' is returning a bogus secindary index,
subsequent GETNEXT requests would return the same row: with a bogus
secondary index ... infinite loop! (or until the bogus secondary index
is corrected).

So here's the important question:
By 'gaps' do you mean the MIB code is replying with NULL? Or just an
incosistant value? (like, out of range, or an int when it should be a
string) -- I believe there is a case where we could be sending NULL back
as a column value...

> It might occur if the MIB-code is returning inconsistent data - e.g.
> if the table is changing while it's being retrieved. How are you
> implementing the table? Which helper? Is the table data cached at
> all, or is it retrieved afresh for each separate request?

We are using the old- UCD style MIB implementation, and the table is
maintained using the Initialise_Table, Search_Table, Add_Entry methods
found in net-snmp/agent/mibgroup/util_funcs.c

Thanks Dave, I will see if we can find the 'gaps'. But if you could help
me out by giving me an example of a 'gap' (like, returning NULL, or
out of range data or something) that would be great.

> Dave

Mike Varley -= SOMA Networks =- 416-348-1578

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