In case anyone else stumbles upon this:
The OIDs above are still correct as of today (You have to do a snmpwalk to get all possible values).
1.3.6.1.4.1.2620.1.56.105.6.1.2 will give you all the interfaces available for TX traffic, eg.
iso.3.6.1.4.1.2620.1.56.105.6.1.2.2.0 = STRING: "eth2"
iso.3.6.1.4.1.2620.1.56.105.6.1.2.3.0 = STRING: "eth4
....
iso.3.6.1.4.1.2620.1.56.105.6.1.2.48.0 = STRING: "bond0.123"
iso.3.6.1.4.1.2620.1.56.105.6.1.2.49.0 = STRING: "eth2.345"
iso.3.6.1.4.1.2620.1.56.105.6.1.2.50.0 = STRING: "bond0.113"
....
iso.3.6.1.4.1.2620.1.56.105.6.1.2.59.0 = STRING: "eth0"
iso.3.6.1.4.1.2620.1.56.105.6.1.2.60.0 = STRING: "eth1"
iso.3.6.1.4.1.2620.1.56.105.6.1.2.61.0 = STRING: "TOTAL"
Those numbers (last 2 digits) are translated directly to the other OIDs with actual traffic values.
(Meaning 1.3.6.1.4.1.2620.1.56.105.6.1.9.2.0 as an example would be the TX-mbps of eth2)
I'm not really sure how those are numbered, I would assume it is by creation date and they are added at the end in front of TOTAL.
(Although eth0 and eth1 should always have been present, I really have no clue how this works)
I wanted to implement thropughput monitoring for our CP appliances, but unfortunately TOTAL is the last OID for either RX and TX.
What that means is that you can't have a general RX/TX Monitoring for your environment, since the TOTAL value I would need is dynamically adjusted and dependent on the number of interfaces and VLANs on the firewall.
If TOTAL would always be for example the first entry 1.3.6.1.4.1.2620.1.56.105.6.1.2.1.0 or any other "static" value this could work, but if it is always put at the end it is not really usable in this case unfortunately.