Before we can get started finding a OID we need to have a basic understanding of a few things. These topics are SNMP, MIB, OID and a MIB browser. If you understand these topics you can skip this.
Let’s first talk about SNMP. SNMP stands for Simple Network Management Protocol. SNMP is a protocol that is used to transport SNMP requests in the form of a Get or Set, as well as other types we won’t cover here. A SNMP Get is a request for data, and a SNMP Set is a request to change something. If we wanted to look at the sysname of a switch we would need to send a SNMP Get for “.220.127.116.11.18.104.22.168.0” to the device. This seemingly random number is called an Object Identifier (OID) for the sysname of a SNMP device defined by RFC1213 (MIB-II). If you wanted to change the sysname you would send a SNMP Set to “.22.214.171.124.126.96.36.199.0” with the new value for the sysname.
Now that we know enough about SNMP let’s move on to what an OID and a MIB file is. We know that an OID is an Object Identifier that can be defined by RFC’s. Extreme Networks also has a vendor specific OID’s for each EXOS version that covers more data collection points than what RFC1213 (MIB-II) covers. Im sure you’re asking yourself “How am I supposed to know that “.188.8.131.52.184.108.40.206.0” is for getting or changing the sysname. Well it’s not hard when you have a MIB file and a MIB browser.
A MIB file is a text file that defines all the OID’s available in that file. If you look at this file it will be hard to understand, which is fine. That is why MIB browsers where made. MIB browsers where made to interpreted MIB files and make it easier to understand each OID. Each OID will have a name, a description as well as if SNMP Get’s or Set’s are accepted. Most MIB browsers also have a built in feature to send SNMP Get's and Set's. This is great when looking for the right OID. Using the find feature "Ctrl+F" is very helpful in finding the correct OID you need.
1. Download any third party MIB browser. iReasoning
is free for non commercial use. iReasoning MIB browser and Extreme Management MIB Tools will have most of the RFC standard MIB files included.
2. Download the EXOS MIB. The EXOS MIB files are version specific so make sure you download the MIB file for the switch version you plan to poll. You can find the EXOS version using the "show version
" command in EXOS. You can also follow the "How to Obtain and Upgrade EXOS"
article to download the MIB file.
3. Once you have the MIB file you will need to import/load the MIB file into any third party MIB browser.
4. Once loaded you can look through the folder structure search with the key word until getting to the MIB. For example if OID for “extremeCpuAggregateUtilization” is should use "CPU" as search key
5. Once you have found the correct OID description in the MIB browser you should be able to see the OID value. If your looking for a specific port counter you can use the SNMP get bulk to see what OID it is.