[erlang-questions] SNMP v3 usmStatsNotInTimeWindows error
Dominik Pawlak
dominik_pawlak@REDACTED
Wed Sep 14 22:52:33 CEST 2016
Hi Devangana,
I see that you use AES for encryption. There was a related bug in the
snmp library:
http://erlang.org/pipermail/erlang-bugs/2014-August/004551.html
I don't know if it's fixed in newer snmp library versions. I attached
the patch that we used to fix snmp 4.25.1.
Or maybe you can live with DES encryption?
Best
Dominik
On 14.09.2016 20:41, Devangana Tarafdar wrote:
> Hi Dominik,
>
> So I was able look at the wireshark stream decoded after entering snmp
> credentials (that was very helpful, thanks !) and compared the 2
> streams : One from the snmp get tool and the other from the erlang script.
>
> Wireshark is not able to decode the encrypted pdu in the erlang
> stream but it can decode the snmpget stream.
>
> The message is clear enough I suppose but I don't know what I am doing
> wrong with the key.
>
> I changed my local key generation to :
>
> %Priv_key_local = snmp:passwd2localized_key(sha, Priv_key ,
> Agent_engine_id),
>
> % since auth protocol is SHA
> Priv_key_local = lists:sublist(snmp:passwd2localized_key(sha,
> Priv_key , Agent_engine_id),16),
>
> but it did not help.
>
>
> msgData: encryptedPDU (1)
> encryptedPDU: 8a3e7fc633c531d2747782a6fc8d89187c452929426e4b6e...
> Decrypted data not formatted as expected, wrong key?
> [Expert Info (Warn/Malformed): Decrypted data not
> formatted as expected]
> [Message: Decrypted data not formatted as expected]
> [Severity level: Warn]
> [Group: Malformed]
>
>
> Attaching good wireshark trace from snmpget and a bad one from erlang.
>
> Also tried putting a context name but did not work but snmpget does
> not put one and it works.
>
> Thanks,
> Devangana
>
>
>
> On Sun, Sep 11, 2016 at 4:09 PM, Devangana Tarafdar
> <devangana@REDACTED <mailto:devangana@REDACTED>> wrote:
>
> Hi Dominik,
>
> I have not looked into the context. Will check all the items that
> you mention. I have been able to connect to the agent using
> snmpwalk and snmpget though I have not studied the wireshark
> output of those in detail.
> Thanks again for all these tips and I will get back to you .
>
> Devangana
>
>
> On Sep 11, 2016 3:08 PM, "Dominik Pawlak"
> <dominik_pawlak@REDACTED <mailto:dominik_pawlak@REDACTED>>
> wrote:
>
> Hello Devangana,
> Hard to tell, but I see that you haven't specified any context
> in your sync_get. Are you sure it is not needed? I would also
> double check the engine id and security configuration.
> Have you managed to connect to that agent from something other
> than OTP (say snmpb, snmpget)?
> If so, you can compare in Wireshark, the snmp requests from
> erlang and from that tool. You can even enter your snmp
> credentials in Wireshark and it will decode encrypted messages.
> I hope any of this helps.
>
> Best
> Dominik
>
> On 11.09.2016 16:46, Devangana Tarafdar wrote:
>> Hello Dominik,
>>
>> Thanks you for the reply.
>>
>> I sent another sync_get after the first as you suggested.
>> The wireshark trace shows the manager has updated the
>> 'msgAuthoritativeEngineBoots' and
>> 'msgAuthoritativeEngineTime' to the values sent by the Agent
>> as you pointed out. But now the agent does not respond at all
>> and the sync_get fails with a timeout. I tried adding a
>> second's sleep between the 2 gets as well. I don't have
>> access currently to the agent's logs or configuration but
>> have you seen this before ?
>>
>> Thanks !
>> Devangana
>>
>>
>> On Sat, Sep 10, 2016 at 6:09 PM, Dominik Pawlak
>> <dominik_pawlak@REDACTED
>> <mailto:dominik_pawlak@REDACTED>> wrote:
>>
>> Hello Devangana,
>> Basically, you just have to perform the sync_get once
>> more. I observed similar behavior in OTP 17.1 (snmp
>> 4.25.1). The first request will always fail because the
>> manager is not fully configured to communicate with the
>> agent (more on that below).
>>
>> A longer explanation:
>>
>> In snmp v3 there is a process called 'discovery', which
>> should be performed before secure communication with the
>> agent can be established. It is described here:
>>
>> https://tools.ietf.org/html/rfc3414#section-4
>> <https://tools.ietf.org/html/rfc3414#section-4>
>>
>> The snmp library in OTP does not implement that process
>> (at least not as described in the RFC).
>> This process has two steps: 'snmpEngineID discovery' and
>> 'time synchronization'.
>> The first step is skipped altogether in OTP - you have to
>> provide engine id upfront.
>> The second step is performed by the first request - it
>> will always fail with the 'usmStatsNotInTimeWindows'
>> error report message, but it will set the required
>> 'msgAuthoritativeEngineBoots' and
>> 'msgAuthoritativeEngineTime' in the manager.
>>
>> Best,
>> Dominik
>>
>>
>> On 10.09.2016 06:48, Devangana Tarafdar wrote:
>>> Hello,
>>>
>>> I am trying to connect to a third party SNMP agent,
>>> using snmp manager (snmp v3) ( in the erlang 19 release
>>> snmp 5.2.3) and I am running into a problem where the
>>> agent is returning this error on the manager calling
>>> sync_get:
>>>
>>>
>>> *** [2016:09:08 21:26:00 830] SNMP M-SERVER TRACE ***
>>> handle_snmp_report -> entry with
>>> Domain: snmpUDPDomain
>>> Addr: {{xx,xxx,xxx,xxx},161}
>>> ReqId: 37078226
>>> Rep: {invalid_sec_info,[{sec_level,3,1},
>>> {request_id,37078226,2147483647 <tel:2147483647>}]}
>>> Pdu: {pdu,report,2147483647 <tel:2147483647>,noError,0,
>>> [{varbind,[1,3,6,1,6,3,15,1,1,2,0],'Counter32',33,1}]}
>>> *** [2016:09:08 21:26:00 830] SNMP M-SERVER DEBUG ***
>>> handle_snmp_report -> found corresponding request:
>>> reply to sync request
>>> Ref: #Ref<0.0.4.210>
>>> ModRef: #Ref<0.0.4.211>
>>> From: {<0.3.0>,#Ref<0.0.4.202>}
>>> *** [2016:09:08 21:26:00 830] SNMP M-SERVER TRACE ***
>>> handle_snmp_pdu(get-response) -> Remaining: 4979
>>> *** [2016:09:08 21:26:00 830] SNMP M-SERVER TRACE ***
>>> handle_snmp_report -> deliver reply
>>>
>>> {error,{invalid_sec_info,[{sec_level,3,1},{request_id,37078226,2147483647
>>> <tel:2147483647>}],{noError,0,[{varbind,[1,3,6,1,6,3,15,1,1,2,0],'Counter32',33,1}]}}}
>>>
>>> *** [2016:09:08 21:26:00 831]
>>>
>>> Where [1,3,6,1,6,3,15,1,1,2,0] maps to
>>> "usmStatsNotInTimeWindows" (from http://www.oid-info.com/)
>>>
>>> I have attached a wireshark trace for the snmp part of
>>> this exchange.
>>>
>>> I am invoking the snmpm module functions through a basic
>>> script as follows (using tips from the tutorial at
>>> https://erlangcentral.org/wiki/index.php?title=SNMP_Quick_Start
>>> <https://erlangcentral.org/wiki/index.php?title=SNMP_Quick_Start>
>>> )
>>> .........
>>> ..........
>>> ok = application:start(crypto),
>>> ok = application:start(snmp),
>>>
>>> Userid = "snmp3user",
>>> Agent_target = "testagent",
>>> Agent_engine_id = [128,0,0,8,2,0,0,26,84,40,108,176],
>>> Agent_ip = {xx,xxx,xxx,xxx},
>>> Agent_port = 161 ,
>>> Secure_name= Userid,
>>>
>>> Security_level = 'authPriv',
>>> Security_model = 'usm',
>>> Agent_version = 'v3',
>>> Auth_protocol = 'usmHMACSHAAuthProtocol',
>>> Priv_protocol = 'usmAesCfb128Protocol',
>>>
>>> % this is 16 in length
>>> Priv_key_local = snmp:passwd2localized_key(md5, Priv_key , Agent_engine_id),
>>>
>>> % this is 20 in length
>>> Auth_key_local = snmp:passwd2localized_key(sha, Auth_key , Agent_engine_id),
>>>
>>> ok = snmpm:register_user(Userid,snmpm_user_default,[]),
>>> ok = snmpm:register_usm_user(Agent_engine_id, Userid, [
>>> {auth, Auth_protocol},
>>> {auth_key,Auth_key_local},
>>> {priv, Priv_protocol},
>>> {priv_key,Priv_key_local },
>>> {sec_name, Secure_name}
>>> ]),
>>> ok = snmpm:register_agent(Userid, Agent_target ,[
>>> {engine_id,Agent_engine_id},
>>> {address, Agent_ip},
>>> {port, Agent_port},
>>> {version,Agent_version},
>>> {sec_model,Security_model},
>>> {sec_name,Secure_name},
>>> {sec_level, Security_level}
>>> ]),
>>> Res0 = snmpm:sync_get(Userid, Agent_target, [[1,3,6,1,4,1,9,10,19,1,1,9,1,3,7,2]]),
>>> ........................
>>> ........................
>>> Can anyone please tell me what I am doing wrong here ? Any tips would be appreciated !
>>> Thanks, Devangana
>>>
>>> _______________________________________________
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>>
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