[mrtg] cisco switches, etherchannel, and artificially low graph values?

[Kettler, Matt]

I've got an odd problem with my interface graphs never reaching their
proper peak.. They all seem to be scaled down inappropriately.

 

For starters, I've pointed cfgmaker at a variety of ordinary Cisco
switches.  I'll be using examples from a Cisco 4948 running
12.2(20r)EW1, but I've seen the same affects on 3750's 12.2(25r)SE1.

 

I've got MRTG running in daemon mode at 5 minute intervals.

 

When I run cfgmaker, I use this basic form:

 

cfgmaker --global 'WorkDir: /var/mrtg/work' --global
'Options[_]:bits,growright' --global 'WithPeak[_]: wmy' --no-down
--show-op-down --output  switchname.cfg community at switchname

 

This generates me a nice little switchname.cfg file, so far so good.

 

It properly adds the global Options[_]: bits, growright, which makes
MRTG graph in bits, not bytes, which I prefer, etc..

 

Cfgmaker generates an entry for each port (ie: gi1/3, gi1/4), and one
for the combined port (ie: po7). However, MRTG seems to handle the
combined ports strangely.

 

This particular example is a 2gbit/sec LACP port made of 2 gig-e
interfaces. cfgmaker understands this port and generated:

 

MaxBytes[switch_96]: 250000000

 

And pagetop contains:

                                        <td>Max Speed:</td>

                                        <td>2000.0 Mbits/s</td>

 

 

Which is all as it should be. When MRTG runs, it generates the graphs
which claim to be in bits, but the values never reach as high as they
should.

 

When I log into the switch and use sho int I get:

 

5 minute output rate 208729000 bits/sec, 17265 packets/sec

 

 

That's 208mbit/sec, or perhaps 199 mbit/sec if you count by 1024's. This
is a port to my backup server, and it sustains rates around
300-500mbit/sec pretty readily.

 

However, MRTG is reporting this on the daily graph:

            Max      Average             Current

Out       143.0 Mb/s (0.9%)         23.9 Mb/s (0.1%)           75.1 Mb/s
(0.5%)

 

Earlier I had the switch reporting 463mbit/sec for an extended period of
time, and I've not gotten a report out of the switch below 200mbit/sec
in repeated queries over the past hour minutes or so. However, even the
24hr max doesn't line up with my current measurements.....

 

Both are operating on 5 minute averages, and the load is fairly
sustained, so why the low numbers in MRTG?

 

 

Also, in the same graph update MRTG reports:

                                    Max      Average             Current

Gi1/3                Out       106.8 Mb/s (1.3%)         18.9 Mb/s
(0.2%)           96.3 Mb/s (1.2%)

Gi1/4                Out       165.6 Mb/s (2.1%)         16.7 Mb/s
(0.2%)           46.7 Mb/s (0.6%) 

Po7                  Out       143.0 Mb/s (0.9%)         24.3 Mb/s
(0.2%)           46.2 Mb/s (0.3%)

 

How does an etherchannel have a lower current output rate than either of
its children?

 

Is there a known issue on cisco switches and their reporting of
etherchannel interfaces over SNMP?

 

In general I seem to be having anomalous numbers on all my switch ports,
but they're most noticeable on etherchannels

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.oetiker.ch/pipermail/mrtg/attachments/20080321/ce96b19c/attachment-0001.html