[nsp] OT? When do log messages get created?

[Furnish, Trever G]

This may be considered off-topic - hopefully not, but if so, any pointers to
more appropriate forums would be appreciated.

I've configured our routers and switches to log to syslog servers at
'informational' level and done some scripting to process the resulting logs.
Everything seems to be working ok, BUT...  I'm having difficulty finding
documentation on what exactly triggers a log message.

Trial and error indicates it's not a one-to-one relationship - one error of
pretty much any type (crc, framing, overrun, collision, etc) doesn't always
cause an error report to be logged (to syslog or the buffer).  I'm guessing
there's a threshold of some sort that defines when to log a message in the
buffer/console/term/trap logs.

On at least one switch (looking for others) the collisions increased by
about 800 within 5 minutes without the switch deciding that needed an error
message in the buffer log or sent via syslog.  The same switch logs other
messages with no problems.  Logging level is informational for all
destinations.

Any advice or pointers to where this is documented?

-t.