Create a text filter in rsyslog.conf

Here is an example how to filter some messages from your rsyslog:

# Save Cisco Messages (filter known junk messages)

:msg, contains, "System clock" ~
:msg, contains, "changed state to down" ~
:msg, contains, "changed state to up" ~
:msg, contains, "LINK STATUS CHANGE" ~
:msg, contains, "FIB synchro state" ~
local7.*                                                -/var/log/cisco.log