How we discover Interfaces

This is implemented in _get_interface-data()

We read the “Interface MIBs” data from the device. This is really stored in two locations, the original MIB-II “ifTable” branch, and the more modern IF-MIB branch.

For performance reasons, we are reading only specific entries from these MIBs:

ifIndex (.1.3.6.1.2.1.2.2.1.1) gets us the ID of an interface. We start with this, and then fill in the rest of the interface data from the others.

ifType (.1.3.6.1.2.1.2.2.1.3) tells us what kind of interface this is, e.g Ethernet, virtual, serial, etc.

ifAdminStatus (.1.3.6.1.2.1.2.2.1.7) gets the status of the interface, admin up/down

ifOperStatus (.1.3.6.1.2.1.2.2.1.8) tells us the link status of an interface that is Admin-UP.

ifName (.1.3.6.1.2.1.31.1.1.1.1) is what is says :-) This value comes from the newer IF-MIB. If this is not found, we then look to get the name from the older MIB-II ifDescr entry (.1.3.6.1.2.1.2.2.1.2), which is actually not what is says!

ifAlias in IF-MIB (.1.3.6.1.2.1.31.1.1.1.18) is actually the interface description!

The new IF-MIB has interface speed in ifHighSpeed (.1.3.6.1.2.1.31.1.1.1.15), in Mbps, to handle higher speed interface 10g, 100g, 400g, etc.

If that does not exist, we read the older MIB-II ifSpeed (.1.3.6.1.2.1.2.2.1.5), which reports as is (eg. 1000 is 1kbps)

Finally, dot3StatsDuplexStatus (.1.3.6.1.2.1.10.7.2.1.19) from the ETHERLIKE-MIB gives us information about half- or full-duplex status of an interface.

We now have the interface-id, aka ifIndex, and most information about the interfaces.