The SNMP-polled discards are absolutely correct form what I've seen. (Sorry to hear you've been having issues w/this dennis - our Cisco 3750s report drops/errors completely correctly from what we've seen - have about 20 or so of these in the network). Note that we primarily use a combination of Juniper EX switches, MX core routers and the like. Whenever we see a transmit discard it's usually (as Pedro said):
1. QoS Settings. We have the wrong forwarding classes setup on the interface, and/or haven't applied the scheduler-map (HW queues) correctly. Note that this is 90% of what I normally see. I compare what IM says, and then check for drops on each of the forwarding queues; and yep - the numbers line up perfectly. This one is by far the most useful use of the "Tx Discards". 2. Saturated Links - Absolutely. Gotta drop somewhere; shaper or no shaper - you'll eventually tail-drop at >100% utilization. 3. Oversized frames/MTU problems, esp if the DF bit is set. Can't push a 9K frame down a 4K L2 pipe. 4. Downstream Customer is rate-limited, however we can usually shape it w/a deep enough buffer so that it's not dropped (just really delayed). =). If we want to police, then we do that via a hard policer in a firewall filter on the outbound IP interface; which goes into the polcier's counters and doesn't contribute to the interface's counters. (Nice and silent if we want it to be). > When I telnet to the switch and show stats on the interface the only errors > I see are 16 FCS errors. Not quite the 4000+ I expected to see. > I still wonder, what does IM see that the hardware won't show me directly? > And since IM is polling the hardware to get info to display bubbles - what > is actually happening - and what is to be believed? Thats because the frames are not errors. Somehow the "show interface" command being used isn't reporting the Tx discards - Somehow it's counting them, since Intermapper is reading this information from what the switch is telling it. =) (i.e. Intermapper is not making this up - it's just reading the Iface's SNMP Tx discard value, which is populated by the device). > > i have learned that if you are interested in discards choose your device > wisely. > some devices is just a mystery about discards.. Agreed on that =) - Chris. ____________________________________________________________________ List archives: http://www.mail-archive.com/intermapper-talk%40list.dartware.com/ To unsubscribe: send email to: [email protected]
