[c-nsp] 3750 input packet counts (CSCec35100)

[David DeSimone]

While browsing I happened to stumble across this bug report:

    Cat3750: Frames not counted as input packets on a dot1Q trunk

    Symptoms:

    On a Catalyst 3750, packets of size 64 to 67 bytes (including the
    dot1Q tag) that ingress the switch on a dot1Q trunk will not be
    counted under the show interface command as input packets.

    Workaround:

    There is no workaround

I remember being vaguely aware of this issue, that the hardware will
treat these frames as "runts" after the dot-1q header is stripped away
from the packet.  I also remember that this doesn't affect forwarding in
the least; it only affects how packets are counted at the interface.

However, it started me thinking...  Are there further ramifications to
this "cosmetic" problem?

For instance, will the counters reported up to SNMP be likewise
affected?  Will all the 64-byte packets be missed completely when
building my RRD graphs showing packets/sec over units of time?  Will the
bits/sec speeds reported be lower, because the 64-byte packets are not
counted towards those totals, as well?

Suppose that some miscreant is sending thousands of tiny packets through
my switch's trunk ports?  Will I be unable to see them reflected in my
packet counters?  Will I be unable to notice the bandwidth surge in my
graphs?

Essentially my question boils down to:  Is it ONLY the "show interface"
command that will give incorrect results?  Or will the SNMP counters and
bandwidth counters be likewise incorrect?

-- 
David DeSimone == Network Admin == fox at verio.net
  "I don't like spinach, and I'm glad I don't, because if I
   liked it I'd eat it, and I just hate it." -- Clarence Darrow


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