Re: Getting Too Long Error

2008/6/19 Rucha <rucha_mahajan@persistent.co.in>:
> I checked the size of pdu which I am sending, its size of just 4bytes.

An SNMP PDU of just 4 bytes!!?
Can you please post a packet dump of this request.


> Any other reason for getting this error ?

Given that a GET PDU will typically be at *least* 30 bytes in size,
and the absolute minimum size of a completely empty GET
request is (I think) 18 bytes - if your GET request is just 4 bytes,
then it's almost certainly invalid.
If it's malformed, then the parsing code might well be reading
the length as over-size, and returning a tooLong error.


Dave

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Hi Dave,

Here is the dump of pdu.

(gdb) p pdu
$1 = (netsnmp_pdu *) 0x951b398
(gdb) p *$1
$2 = {version = -1, command = 160, reqid = 713309340, msgid = 1415423209,
transid = 0, sessid = 0, errstat = -1,
errindex = -1, time = 0, flags = 0, securityModel = -1, securityLevel = 0,
msgParseModel = 0, transport_data = 0x0,
transport_data_length = 0, tDomain = 0x0, tDomainLen = 0, variables = 0x0,
community = 0x0, community_len = 0,
enterprise = 0x0, enterprise_length = 0, trap_type = 0, specific_type = 0,
agent_addr = "\000\000\000",
contextEngineID = 0x0, contextEngineIDLen = 0, contextName = 0x0,
contextNameLen = 0, securityEngineID = 0x0,
securityEngineIDLen = 0, securityName = 0x0, securityNameLen = 0, priority
= 0, range_subid = 0, securityStateRef = 0x0}

135 int length = sizeof(pdu);
(gdb) n
137 printf("PDU Length = %d\n", length);
(gdb) n
PDU Length = 4
139 status = snmp_synch_response(ss, pdu, &response);
(gdb) p length
$4 = 4

Regards,
Rucha

-----Original Message-----
From: dave.shield@googlemail.com [mailto:dave.shield@googlemail.com] On
Behalf Of Dave Shield
Sent: Thursday, June 19, 2008 8:18 PM
To: Rucha
Cc: Pranesh Kulkarni; Net-snmp-users@lists.sourceforge.net
Subject: Re: Getting Too Long Error

2008/6/19 Rucha <rucha_mahajan@persistent.co.in>:
> I checked the size of pdu which I am sending, its size of just 4bytes.

An SNMP PDU of just 4 bytes!!?
Can you please post a packet dump of this request.


> Any other reason for getting this error ?

Given that a GET PDU will typically be at *least* 30 bytes in size,
and the absolute minimum size of a completely empty GET
request is (I think) 18 bytes - if your GET request is just 4 bytes,
then it's almost certainly invalid.
If it's malformed, then the parsing code might well be reading
the length as over-size, and returning a tooLong error.


Dave


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2008/6/20 Rucha <rucha_mahajan@persistent.co.in>:
> Here is the dump of pdu.
>
> (gdb) p pdu
> $1 = (netsnmp_pdu *) 0x951b398
> (gdb) p *$1

No - we're not interested in the internal data structure.
What it relevant here is the size of the PDU that's
put out over the wire.

Try running the application with the '-d' option,
to dump the raw incoming/outgoing packets.
*That* is the dump that I was talking about.


> 135 int length = sizeof(pdu);
> (gdb) n
> 137 printf("PDU Length = %d\n", length);
> (gdb) n
> PDU Length = 4

The variable 'pdu' is a pointer.
So yes - the size of it is almost certainly going to be 4.
(assuming a 32-bit O/S). That's not useful information.


What does the traffic on the wire look like.

Also - how are you setting up the administrative
settings for this request? (Community string,
or SNMPv3 user)

It also looks as if you are sending a GET request with
an empty varbind list. I.e. you are asking for nothing?

Dave

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2008/6/21 xiao ren <reign99@21cn.com>:
> I'm learning to use net-snmp lib to write client program just like snmpget,
> but sourceforge only provide one demo app example on this
> (http://net-snmp.sourceforge.net/tuto...oolkit/demoapp) .
> Could anybody give some other examples on how to write client side
> code to fetch information from agent, Especially for snmp v2c?

Remember that you've also got the source code for the command-line
applications (snmpget, etc), in the 'apps' directory of the source tree.

They should illustrate all the basic techniques you'll need.

Dave

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