[mrtg] Re: To low traffic in vlan graph??!! can't make sense.

[Rich Adamson]

> When i add all vlan together the sum will be lower than the total output
> graph (meashuring on FW). The hardware is cisco catalyst.
> 
> Anyone know where the lost traffic goes? Can i measure it?

Over the past several years, this same question has come up in several
different network management forums. Don't know if these comments 
apply to your environment. Some of the differences have included:
1) snmp interface stats only count data that passes "through" an
interface. If packets exist on the wire that don't pass through (for
example Firewall ARPs), those are not counted by the switch.
2) overhead bytes are typically not counted (eg, ethernet header)
3) vlan overhead bytes not counted
4) BPDU (spanning tree) packets not counted
5) broadcasts originated by the Firewall that are not handled by the
switch are not counted
6) multicast packets not counted if the switch is ignoring those
7) etc, etc.

Also, some vendors will count the same packet in two or more different
snmp counters causing a distorting from expected results.



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