DrayTek Vigor 2820 ADSL monitoring with SNMP, whats the line speed OID

One client with a DrayTek Vigor 2820n internet router has a problem with the ADSL upload speed slowing down to around 40-50% of normal on occasion. It has a big impact because there are staff out in the field needing to VPN in to the office to update the main database.

To keep an eye on performance we added SNMP monitoring to the Centrastage console for that client, with an alert to trigger if it fell below 80%. The upload line speed is typically just under 1.2Mbps with the Annex M fast upload option we have on that line. It seems to fluctuate 5-10% in normal operation anyway - possibly some dodgy wiring or just being quite a way from the exchange.

The key element of SNMP monitoring is knowing what object identifier (OID) to monitor. We used snmpwalk to dump them all out to CSV. Then matched the known line speed values to the relevant OIDs:
 .1.3.6.1.2.1.2.2.1.5.4  --- ADSL download line speed
 .1.3.6.1.2.1.10.94.1.1.5.1.2.4  --- ADSL upload line speed

DrayTek have a list of some useful Vigor router OIDs

Have you got any other useful parameters or OIDs to monitor on a DrayTek router ?