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Router Security Configuration Guide
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prints them according to a simple configuration file. This form of
logging is the best available for Cisco routers, because it can provide
protected long-term storage for logs.
5. SNMP trap logging –
For some kinds of events, Cisco routers can generate Simple Network
Management Protocol (SNMP) trap messages. This facility allows
routers to be monitored as part of an overall SNMP-based network
management infrastructure.
Cisco IOS messages are categorized by severity level. The lower the severity level
number, the more critical the message is. The severity levels are described in the
table below. Note that, when you are using logging levels in commands in IOS 11.3
and earlier, you must use the level name; in IOS 12.0 you may use the name or the
number.
Table 4-2 – Cisco Log Message Severity Levels
Level
Level Name
Description
Example
0
Emergencies
Router becoming unusable
IOS could not load
1
Alerts
Immediate action needed
Temperature too high
2
Critical
Critical condition
Unable to allocate memory
3
Errors
Error condition
Invalid memory size
4
Warnings
Warning condition
Crypto operation failed
5
Notifications
Normal but important
event
Interface changed state, up
or down
6
Informational
Information message
Packet denied by access
list
7
Debugging
Debug message
Appears only when
debugging is enabled
For example, the message below appears in the log when a user changes the running
configuration. It has a severity level of 5, as shown by the numeric field “-5-” in the
message name.
Figure 4-6: Format of a Cisco IOS Log Message
Mar 31 9:00:16 EST: %SYS-5-CONFIG_I: Configured from console by vty0 (14.2.9.6)
Time that message was generated
Message name and severity level
Message text
