RE: SNMP Protocol

Ok – let’s try this another way – rather than think of a MIB as a database in the traditional sense of a repository where information is placed, think of it more as a specification of how data is stored or ‘mapped’. In this way, a SNMP agent (software – typically a daemon or background process which runs on a host such as a server, router, etc. ) is coded to the MIB specifications.

In a similar way, a management station may load a MIB in order to understand what the returned information ‘means’ in human-readable form. Let’s take an example from RFC1155-SMI &RFC1213 (MIB II):

RFC1155 defines the root of the tree:
internet      OBJECT IDENTIFIER ::= { iso org(3) dod(6) 1 }
directory     OBJECT IDENTIFIER ::= { internet 1 }
mgmt          OBJECT IDENTIFIER ::= { internet 2 }
experimental  OBJECT IDENTIFIER ::= { internet 3 }
private       OBJECT IDENTIFIER ::= { internet 4 }
enterprises   OBJECT IDENTIFIER ::= { private 1 }
mib-2      OBJECT IDENTIFIER ::= { mgmt 1 }
system       OBJECT IDENTIFIER ::= { mib-2 1 }A

RFC1213 begins to add branches after importing RFC1155
sysDescr OBJECT-TYPE
    SYNTAX  DisplayString (SIZE (0..255))
    ACCESS  read-only
    STATUS  mandatory
    DESCRIPTION
            "A textual description of the entity.  This value
            should include the full name and version
            identification of the system's hardware type,
            software operating-system, and networking
            software.  It is mandatory that this only contain
            printable ASCII characters."
    ::= { system 1 }

We can express the object identifier (OID) sysDescr as: 1.3.6.1.2.1.1.1 OR as RFC1213-MIB::sysDescr
In other words, the MIB is used to define the structure of the information.

As a SNMP agent is being built, it makes use of the MIB structure to define that when a management station requests 1.3.6.1.2.1.1.1.0, the software is supposed to return a description of the software running on the host.  Without having the MIB loaded in a management station, it would be perfectly possible to retrieve the information, but it’s a whole lot easier to understand this:

RFC1213-MIB::sysDescr.0 = STRING: "Cisco Internetwork Operating System Software”
RFC1213-MIB::sysObjectID.0 = OID: CISCO-PRODUCTS-MIB::ciscoWSC6509neba
RFC1213-MIB::sysContact.0 = "Me"
RFC1213-MIB::sysName.0 = STRING: “myrouter"
RFC1213-MIB::sysLocation.0 = "Under my desk"
RFC1213-MIB::sysServices.0 = INTEGER: 78
SNMPv2-MIB::sysORLastChange.0 = Timeticks: (0) 0:00:00.00

Than:
1.3.6.1.2.1.1.1 = STRING: "Cisco Internetwork Operating System Software”
1.3.6.1.2.1.1.2=1.3.6.1.4.1.9.5.1.3.1.1.2.291
1.3.6.1.2.1.1.3= "Me"
1.3.6.1.2.1.1.4= STRING: “myrouter"
1.3.6.1.2.1.1.5= "Under my desk"
1.3.6.1.2.1.1.6= INTEGER: 78
1.3.6.1.2.1.1.7= Timeticks: (0) 0:00:00.00

Hope this is helpful


From: Alex [mailto:[email protected]]
Sent: Thursday, April 10, 2014 4:23 PM
To: [email protected]
Subject: Re: SNMP Protocol

Hi,

Thank you for input.
I don't understand. I've read specification RFC 2741 and RFC 1157, not full though, just important moments. My understanding is that SNMP is protocol, SNMP agent is plain daemon that run on the background, and MIB files is a sort of centralized database, where agent sends a request. Therefore MIB database must be installed somewhere. If MIB files is not installed, where SNMP agent will take information about OID values?
Well, suppose it depends on application and network device.  Where the MIB files resides on cable modem or set-top box, for example? Is it hard-coded into their program code or they are located on a management station? If its hard-coded inside program code, then to add a new MIB file requires replacement of the entire software, if its on management station, then we just need add new MIB to database which is more easy?


Thanks






----- Original Message -----

From: Joel Hansell

Sent: 04/10/14 06:37 PM

To: [email protected]<mailto:[email protected]>

Subject: Re: SNMP Protocol

Dear Anonymous,

In principle, the MIB files don't have to be installed anywhere. They are only a specification. The describe which objects are available on the agent, and which notifications the agent may send.

Some SNMP managers let the user "load" MIB files, in order to better present the data fetched from the agents. But this is not mandatory.

Some SNMP agents let the user "load" MIB files, to alter structure of the data which is published, but this is more unusual. Many SNMP agents in industrial use have the MIB structure hard-coded into their program code.

I'm sure such an answer will lead to more questions, please go ahead. :-)

Regards,
Joel Hansell

On Thu, Apr 10, 2014 at 4:25 PM, <[email protected]<mailto:[email protected]>> wrote:
question about SNMP Protocol: where is installed MIB files (vendor-specific): on the Network management station (NMS) or on the network devices (network node)?




------------------------------------------------------------------------------
Put Bad Developers to Shame
Dominate Development with Jenkins Continuous Integration
Continuously Automate Build, Test & Deployment
Start a new project now. Try Jenkins in the cloud.
http://p.sf.net/sfu/13600_Cloudbees
_______________________________________________
Net-snmp-users mailing list
[email protected]<mailto:[email protected]>
Please see the following page to unsubscribe or change other options:
https://lists.sourceforge.net/lists/listinfo/net-snmp-users




T. Rowe Price (including T. Rowe Price Group, Inc. and its affiliates) and its associates do not provide legal or tax advice.  Any tax-related discussion contained in this e-mail, including any attachments, is not intended or written to be used, and cannot be used, for the purpose of (i) avoiding any tax penalties or (ii) promoting, marketing, or recommending to any other party any transaction or matter addressed herein.  Please consult your independent legal counsel and/or professional tax advisor regarding any legal or tax issues raised in this e-mail.

The contents of this e-mail and any attachments are intended solely for the use of the named addressee(s) and may contain confidential and/or privileged information. Any unauthorized use, copying, disclosure, or distribution of the contents of this e-mail is strictly prohibited by the sender and may be unlawful. If you are not the intended recipient, please notify the sender immediately and delete this e-mail.

------------------------------------------------------------------------------
Put Bad Developers to Shame
Dominate Development with Jenkins Continuous Integration
Continuously Automate Build, Test & Deployment 
Start a new project now. Try Jenkins in the cloud.
http://p.sf.net/sfu/13600_Cloudbees

_______________________________________________
Net-snmp-users mailing list
[email protected]
Please see the following page to unsubscribe or change other options:
https://lists.sourceforge.net/lists/listinfo/net-snmp-users