[j-nsp] Interface tail drops vs. ifOutDiscards

[Antti Ristimäki]

Hi,
 
> On Wed, Jan 30, 2013 at 03:44:42PM +0400, Nick Kritsky wrote:
> > You can use counters in jnx-cos MIB ( 1.3.6.1.4.1.2636.3.15 ).
> > They will give you per-queue drop counters for each interface.
> > I use jnxCosIfqTailDropPkts for monitoring interfaces on EX switches.
> These
> > are the counters you see in "show interface extensive" - dropped
> packets
> > for for each queue.
> 
> Unlike EX-series MX does report total number of dropped packets
> (sum of drops in each queue) in standard ifOutDiscards OID:
> 
> snar at router> show snmp mib walk ifOutDiscards | except " = 0"
> ifOutDiscards.522 = 62118
> ifOutDiscards.529 = 82824
> ifOutDiscards.545 = 2350808
> ifOutDiscards.548 = 2518889
> ifOutDiscards.558 = 2465225
> 
> Not sure if packets dropped by deeper QoS functions like RED are
> reported here however.

ifOutDiscards counter seems to include packets dropped by RED, at least in MX series. In our case the ifOutDiscards counter is most of the time equal to jnxCosIfqTotalRedDropPkts given that all the dropped packets were in the same forwarding class.

Antti