SNMP and interfaces
- Last UpdatedFeb 13, 2023
- 1 minute read
- PI System
- PI Interface for SNMP 1.7.0.37
- Interfaces
Under SNMP, the interfaces in a router are indexed by an Object Identifier (OID) called ifIndex. This index is a positive integer, and allows the user to reference and correlate other interface OID variables (e.g., interface speed). The SNMP Agent on the router automatically assigns the value of ifIndex.
Examples of interface descriptions (interfaces.ifTable.ifEntry.ifDescr) and speeds ( interfaces.ifTable.ifEntry.ifSpeed) in our first example are:
|
ifIndex |
OID variable |
OID value |
|---|---|---|
|
3 |
OID=interfaces.ifTable.ifEntry.ifDescr.3 |
Serial1/0 |
|
4 |
OID=interfaces.ifTable.ifEntry.ifDescr.4 |
Ethernet0 |
|
5 |
OID=interfaces.ifTable.ifEntry.ifDescr.5 |
Ethernet1 |
|
100 |
OID=interfaces.ifTable.ifEntry.ifDescr.100 |
FastEthernet |
|
3 |
OID=interfaces.ifTable.ifEntry.ifSpeed.3 |
512,000 |
|
4 |
OID=interfaces.ifTable.ifEntry.ifSpeed.4 |
10,000,000 |
|
5 |
OID=interfaces.ifTable.ifEntry.ifSpeed.5 |
10,000,000 |
|
100 |
OID=interfaces.ifTable.ifEntry.ifSpeed.100 |
100,000,000 |
For the example ISP:
|
ifIndex |
OID variable |
OID value |
|---|---|---|
|
101 |
OID=interfaces.ifTable.ifEntry.ifDescr.101 |
ATM2/0.1 |
|
102 |
OID=interfaces.ifTable.ifEntry.ifDescr.102 |
ATM2/0.2 |
|
103 |
OID=interfaces.ifTable.ifEntry.ifDescr.103 |
ATM2/0.3 |
|
200 |
OID=interfaces.ifTable.ifEntry.ifDescr.200 |
Serial2 |
|
101 |
OID=interfaces.ifTable.ifEntry.ifSpeed.101 |
512,000 |
|
102 |
OID=interfaces.ifTable.ifEntry.ifSpeed.102 |
384,000 |
|
103 |
OID=interfaces.ifTable.ifEntry.ifSpeed.103 |
384,000 |
|
200 |
OID=interfaces.ifTable.ifEntry.ifSpeed.200 |
1,544,000 |
For PI Server receiving data, examples may be:
|
ifIndex |
OID variable |
OID value |
|---|---|---|
|
1 |
OID=interfaces.ifTable.ifEntry.ifDescr.1 |
Ethernet0 |
|
2 |
OID=interfaces.ifTable.ifEntry.ifDescr.2 |
Ethernet1 |
|
3 |
OID=interfaces.ifTable.ifEntry.ifDescr.3 |
Ethernet2 |
|
4 |
OID=interfaces.ifTable.ifEntry.ifDescr.4 |
Ethernet3 |
|
1 |
OID=interfaces.ifTable.ifEntry.ifSpeed.1 |
10,000,000 |
|
2 |
OID=interfaces.ifTable.ifEntry.ifSpeed.2 |
10,000,000 |
|
3 |
OID=interfaces.ifTable.ifEntry.ifSpeed.3 |
10,000,000 |
|
4 |
OID=interfaces.ifTable.ifEntry.ifSpeed.4 |
10,000,000 |
Be aware that the value of ifIndex does not have to start at 1, and that these indices are not necessarily consecutive. Also, note that the value for the OID variable
interfaces.ifTable.ifEntry.ifSpeed.X,
where X is an ifIndex value, reflects engineering units of bits per second.