Snmp Binding

Documentation of the SNMP binding Bundle

Introduction

For installation of the binding, please see Wiki page Bindings.

NOTE: This page is updated for the SNMP binding in V1.3. The binding strings are not compatible with the older binding since there is a lot more functionality.

The SNMP binding allows SNMP GET (polling) and SNMP SET (commanding), and the reception of SNMP TRAPs (asynchronous events). SNMP is often found in network equipment, and the binding can be used to ensure your network is operating correctly. The out binding can be used to configure network settings.

Generic Item Binding Configuration

In order to bind an item to a SNMP OID (to be precise an OID prefix), you need to provide configuration settings. The easiest way to do so is to add some binding information in your item file (in the folder configurations/items`). The syntax for the SNMP binding configuration string is explained here:

in:   snmp="<[address:community:oid:update]"
out:  snmp=">[cmd:address:community:oid:value]"
trap: snmp="<[address:community:oid:0]"

• Address is the IP address of the SNMP device
• Community is the SNMP community string
• OID is the object id to GET or SET
• Value is the number to SET. This can only be an integer value.

Here are some examples of valid binding configuration strings:

in:   snmp="<[192.168.2.111:public:.1.3.6.1.2.1.2.2.1.10.10:10000]"
out:  snmp=">[OFF:192.168.2.111:private:.1.3.6.1.4.1.4526.11.16.1.1.1.3.1.2:2]"
trap: snmp="<[192.168.2.111:public:.1.3.6.1.2.1.2.2.1.10.10:0]"

Note: Config strings are only valid for Number and Switch items.

As a result, your lines in the items file might look like the following: Number Switch_POEState2 "PoE WiFi State [%s]" { snmp="<[192.168.2.111:public:.1.3.6.1.4.1.4526.11.16.1.1.1.6.1.2:10000]" }

Switch Switch_POEEnable2 "PoE WiFi Enable [%s]"  { snmp="<[192.168.2.111:public:.1.3.6.1.4.1.4526.11.16.1.1.1.3.1.2:10000] >[OFF:192.168.2.111:private:.1.3.6.1.4.1.4526.11.16.1.1.1.3.1.2:2] >[ON:192.168.2.111:private:.1.3.6.1.4.1.4526.11.16.1.1.1.3.1.2:1]" }

The above configuration allows reading the state of the Power over Ethernet on a Netgear switch, and to change the state of the power. In this configuration, it allows reading back the status, and turning on and off the power of a powered WiFi Access Point.

openhab.cfg configuration

The following configuration items can be set in the openhab file -:

• community: This is the default community for listening for traps (defaults to public).
• port: The listening port. Defaults to port 162 (see below).
• timeout: Sets the timeout period (in milliseconds) when polling SNMP GET and SET requests. Defaults to 1500ms.
• retries: Sets the number of retries before giving up. The retries will be sent every timeout milliseconds. Defaults to 0 (no retries).

Binding Port

By default the SNMP binding binds to localhost on Port 162 which is the SNMP default port. However on *nix Systems this port can only be bind by privileged users (root, sudo). Since openHAB won't be run under a privileged user a !BindException will be thrown.

As a workaround one could forward all traps to a port of your choice using snmptrapd. You should install snmptrapd (on Ubuntu as part of the snmpd-package) somewhere on your network and run it under a privileged user. snmptrapd forwards all traps to the machine openHAB is listening.

The /etc/snmp/snmptrapd.conf should be enhanced like this

disableAuthorization yes
forward default udp:<ip of openhab machine>:<port which is configured in openhab.cfg>

Don't forget to restart snmpd after reconfiguring by issuing /etc/init.d/snmpd restart