[c-nsp] SNMP/bit-bucket question

[Sargon]

We have a GRE tunnel connecting a 6509 to a 7513 via a PIX 525. The 
tunnel source is the IP addressing for the VLAN which carries all our 
Internet traffic, and the destination is the GigE in the 7513. The 
tunnel is used to carry all our multicast and BGP traffic through the 
PIX.

We are attempting to graph (via MRTG) the traffic levels of the 
tunnel. What we see, however, looks identical to the traffic graph 
for that VLAN (100Mbps or so). If I specifically graph non-unicast 
packets, the graph drops to zero.

Is there an order in which bit buckets are parsed for SNMP values? It 
certainly appears that VLAN-tagged packets are parsed before anything 
else, which means I probably will never get the values from the 6509. 
I get them from the 7513 (no VLANs in that router).

All ideas/pointers are appreciated.