Running Raddle (2): snmpd & Replay Custom Private Enterprise MIB

In General Linux on 18 August 2011 with no comments flame_ico 117 views

Net-SNMP wiki gives tutorial on extending snmpd using Perl. In basic run of Raddle (previous post) this involves r1.pl called by r1.conf fed to snmpd. Private enterprise MIB i.e. Microchip’s in this example can be replayed without really ever captured the real device’s SNMP data. This is necessary when the actual device is yet existed; normal situation when developing. There are two simple ways of replaying this artificial SNMP data over which either way requires correct OID.

First put the Microchip.TXT (the MIB file) under /usr/share/snmp/mibs to easily exchange OID canonical form and name vice versa while making dummy. In this case I’ve modify the MIB to have some additional object i.e. name:
$ snmptranslate -m +Microchip -On Microchip::name .1.3.6.1.4.1.17095.1.1
so we can then use this correct OID for our dummy.

How?

use SetMIBValue() in r1.pl

$agent->SetMIBValue( '.1.3.6.1.4.1.17095.1.1', ASN_OCTET_STR, "Microchip");
$agent->SetMIBValue( '.1.3.6.1.4.1.17095.3.13', ASN_INTEGER, 82);

Feed r1.snmp for playing as in

$agent->ParseDataFile( '/usr/local/etc/snmp-emulator/r1.snmp', 0 )

with the content of

.1.3.6.1.4.1.17095.1.1 = STRING: Microchip
.1.3.6.1.4.1.17095.3.13 = INTEGER: 82

In all above two examples we can only GET for Raddle to return an answer for each OID. GETNEXT as in bulk snmpwalk won’t give output because they are not sequenced.

A sample of sequenced data inside a real snmpwalk dump is:

$ snmpwalk -v 1 -c public -On localhost
 
.1.3.6.1.2.1.1.1.0 = STRING: Linux xp-racy 2.6.38-10-generic #46~lucid1-Ubuntu SMP Wed Jul 6 18:40:11 UTC 2011 i686
.1.3.6.1.2.1.1.2.0 = OID: .1.3.6.1.4.1.8072.3.2.10
.1.3.6.1.2.1.1.3.0 = Timeticks: (496371) 1:22:43.71
.1.3.6.1.2.1.1.4.0 = STRING: Root  (configure /etc/snmp/snmpd.local.conf)
.1.3.6.1.2.1.1.5.0 = STRING:
.1.3.6.1.2.1.1.6.0 = STRING: Unknown (configure /etc/snmp/snmpd.local.conf)
.1.3.6.1.2.1.1.8.0 = Timeticks: (0) 0:00:00.00
.1.3.6.1.2.1.1.9.1.2.1 = OID: .1.3.6.1.6.3.10.3.1.1
.1.3.6.1.2.1.1.9.1.2.2 = OID: .1.3.6.1.6.3.11.3.1.1

thus, we can only

$ snmpget -m +Microchip -v 1 -c public localhost Microchip::control.13
Microchip::control.13 = INTEGER: 82

or from other system with no Microchip MIB use

$ snmpget -v 1 -c public 192.168.40.105 .1.3.6.1.4.1.17095.3.13
SNMPv2-SMI::enterprises.17095.3.13 = INTEGER: 82

The tree below may visually explains sequenced data for GETNEXT where our Microchip is branched at private.enterprises.microchip :

$ snmptranslate -m +Microchip -Tp
 
+--iso(1)
   |
   +--org(3)
      |
      +--dod(6)
         |
         +--internet(1)
            |
            +--directory(1)
            |
            +--mgmt(2)
            |  |
            |  +--mib-2(1)
            |     |
            |     +--system(1)
            |     |  |
...
            +--private(4)
            |  |
...
            |  +--enterprises(1)
            |     |
...
            |     +--microchip(17095)
            |        |
            |        +--product(1)
            |        |  |

How GET and GETNEXT appeared in SNMP can be viewed by running snmpd in debug mode with this options:

$ snmpd -m +Microchip -f -L -V -C -I vacm_vars -c /usr/local/etc/snmp-emulator/r1.conf
NET-SNMP version 5.3.1
Connection from UDP: [127.0.0.1]:32770
Received SNMP packet(s) from UDP: [127.0.0.1]:32770
  GET message
    -- control.13

logIt Log Around The Clock