Use ifAlias to ensure data collection after router reboot

RFC 2233 specifies that if an SNMP agent supports the ifAlias OID variable, its value must not change during a router reboot: "... the ifAlias name is non-volatile, and thus an interface must retain its assigned ifAlias value across reboots, even if an agent chooses a new ifAlias value for the interface."

The interface obtains all the ifAlias names from the router. It then matches the IFALIAS value of tag1 with these ifAlias names to determine the interface index number. If the interface number is 2, the SNMP interface constructs the following OID:

interfaces.ifTable.ifEntry.ifInOctets.2

and sends the appropriate request to the router.

If the router restarts and the SNMP agent reassigns interface indexes, the interface still can read correct values for the tag, because it constructs the following OID to get the data from the router:

interfaces.ifTable.ifEntry.ifInOctets.3

Because a particular device must be specified at startup, this configuration limits data collection to a single device. When configured for a single device, the interface groups all tags into sets, regardless of the value of location3. The specified router must support the system.sysUptime.0 OID. If this OID is not supported, the interface exits.

1. Configure PI points for the interface instance by setting the extended descriptor attribute keywords as follows:

   • Inbound traffic

     OID_I=ifInOctets; IFALIAS="ifAlias_name_of_the_interface"

   • Outbound traffic

     OID_I=ifOutOctets; IFALIAS="ifAlias_name_of_the_interface"

     Note: Omit the host and cs parameters.

2. Using PI ICU, go to the PISNMP tab and configure the interface instance.

3. Check Get data from one device and specify the device IP address or host name.

4. Check Read community string from pisnmp#.pwd instead of Exdesc.

5. Click Edit pisnmp#.pwd file and specify the host and community string settings.

   For example:

   host=10.8.10.1;
   cs=public; community string for 10.8.10.1

6. Save your entries, return to PI ICU, and then click Apply.