[mrtg] Dynamically determine SNMP OID from value of another

[Josh Hillman]

Is it possible in MRTG to dynamically reference an SNMP OID based on the 
value of another?

We monitor the following "rbnL2tpTCfgActSessCnt" SNMP OID in our Redback:
  .1.3.6.1.4.1.2352.2.28.1.2.1.12
which corresponds to
.iso.org.dod.internet.private.enterprises.redBackNetworks.rbnMgmt.rbnL2tpMib.rbnL2tpMibObjects.rbnL2tpTunnelCfgTable.rbnL2tpTunnelCfgEntry.rbnL2tpTCfgActSessCnt
(total number of sessions that are presently in the established state)

There's a separate instance value for each L2TP tunnel, such as:
  .11732
  .35387
  .35747
  .39342

The MRTG configuration lines would look like this:
Target[blah]: 
.1.3.6.1.4.1.2352.2.28.1.2.1.12.11732&.1.3.6.1.4.1.2352.2.28.1.2.1.12.11732:commname at devicename
  (etc.)

Unfortunately, those numbers periodically change--probably when the tunnel 
goes down and is re-established.  Because these numbers change periodically, 
MRTG is no longer able to get data for that particular instance.

The following "rbnL2tpTCfgTunnelNm" OID is the cross-reference between the 
consistant peer name and the inconsistent instance name (an ID of some 
sort):
  .1.3.6.1.4.1.2352.2.28.1.2.1.2
which corresponds to
.iso.org.dod.internet.private.enterprises.redBackNetworks.rbnMgmt.rbnL2tpMib.rbnL2tpMibObjects.rbnL2tpTunnelCfgTable.rbnL2tpTunnelCfgEntry.rbnL2tpTCfgTunnelNm
Each instance is represented like this:
  Instance   Value
  .11732     RBABCDEF01:11732
  .35387     RBGHIJKL01:35387
  .35747     RBMNOPQR01:35747
  .39342     RBSTUVWX01:39342

The first part of each value is the L2TP "peer name" (rbnL2tpTCfgPeerName):
  .1.3.6.1.4.1.2352.2.28.1.2.1.3
which corresponds to
.iso.org.dod.internet.private.enterprises.redBackNetworks.rbnMgmt.rbnL2tpMib.rbnL2tpMibObjects.rbnL2tpTunnelCfgTable.rbnL2tpTunnelCfgEntry.rbnL2tpTCfgPeerName
  Instance   Value
  .11732     RBABCDEF01
  .35387     RBGHIJKL01
  .35747     RBMNOPQR01
  .39342     RBSTUVWX01

Is it possible in MRTG to "SNMPwalk" either .1.3.6.1.4.1.2352.2.28.1.2.1.2 
(rbnL2tpTCfgTunnelNm) or .1.3.6.1.4.1.2352.2.28.1.2.1.3 
(rbnL2tpTCfgPeerName) to dynamically determine each instance value 
associated with .1.3.6.1.4.1.2352.2.28.1.2.1.12 (rbnL2tpTCfgActSessCnt) and 
use some kind of variable in the OID reference within the MRTG "Target" line 
configuration?

Josh