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IPv4 Access Control Lists (ACLs)
Enable ACL “Deny” Logging
ACL Logging Operation
When the switch detects a packet match with an ACE and the ACE includes
both the deny action and the optional log parameter, an ACL log message is
sent to the designated debug destination. The first time a packet matches an
ACE with deny and log configured, the message is sent immediately to the
destination and the switch starts a wait-period of approximately five minutes.
(The exact duration of the period depends on how the packets are internally
routed.) At the end of the collection period, the switch sends a single-line
summary of any additional “deny” matches for that ACE (and any other “deny”
ACEs for which the switch detected a match). If no further log messages are
generated in the wait-period, the switch suspends the timer and resets itself
to send a message as soon as a new “deny” match occurs. The data in the
message includes the information illustrated in figure 9-33.
Feb 1 10:04:45 10.10.20.1 ACL:
ACL 02/01/07 10:04:45 List NO-TELNET, seq#10 denied
tcp 10.10.10.3(1612)->10.10.20.2(23) on vlan 1, port A7
Feb 1 10:04:45 10.10.20.1 ACL:
ACL 02/01/07 10:04:45 : ACL NO-TELNET seq#10 denied 6 packets
Example of
subsequent deny
events detected by
the switch for the
same ACE.
Example Syslog
report of the first
deny event
detected by the
switch for this ACE.
Figure 9-33. Content of a Message Generated by an ACL-Deny Action
9-97