Administrator Guide
If ACL logging is stopped because the congured threshold is exceeded, it is re-enabled after the logging interval
period elapses. ACL logging is supported for standard and extended IPv4 ACLs, IPv6 ACLs, and MAC ACLs. You
can congure ACL logging only on ACLs that are applied to ingress interfaces; you cannot enable logging for ACLs
that are associated with egress interfaces.
You can activate ow-based monitoring for a monitoring session by entering the ow-based enable command in
the Monitor Session mode. When you enable this capability, trac with particular ows that are traversing through
the ingress and egress interfaces are examined and, appropriate ACLs can be applied in both the ingress and
egress direction. Flow-based monitoring conserves bandwidth by monitoring only specied trac instead all trac
on the interface. This feature is particularly useful when looking for malicious trac. It is available for Layer 2 and
Layer 3 ingress and egress trac. You may specify trac using standard or extended access-lists. This mechanism
copies all incoming or outgoing packets on one port and forwards (mirrors) them to another port. The source port
is the monitored port (MD) and the destination port is the monitoring port (MG).
Related Commands
• ip access-list standard — congure a standard ACL.
• permit — congure a permit lter.
deny (for Extended IP ACLs)
Congure a lter that drops IP packets meeting the lter criteria.
Syntax
deny {ip | ip-protocol-number} {source mask | any | host ip-address}
{destination mask | any | host ip-address} [count [byte]] [dscp value] [order]
[monitor] [fragments] [log [interval minutes] [threshold-in-msgs [count]]
[monitor]
To remove this lter, you have two choices:
• Use the no seq sequence-number command if you know the lter’s sequence number.
• Use the no deny {ip | ip-protocol-number} {source mask | any | host ip-address}
{destination mask | any | host ip-address} command.
Parameters
log (OPTIONAL) Enter the keyword log to enable the triggering of ACL log messages.
threshold-in msgs
count
(OPTIONAL) Enter the threshold-in-msgs keyword followed by a value to indicate
the maximum number of ACL logs that can be generated, exceeding which the generation
of ACL logs is terminated. with the seq, permit, or deny commands. The threshold
range is from 1 to 100.
interval minutes (OPTIONAL) Enter the keyword interval followed by the time period in minutes at
which ACL logs must be generated. The time interval range is from 1 to 10 minutes.
monitor (OPTIONAL) Enter the keyword monitor when the rule is describing the trac that you
want to monitor and the ACL in which you are creating the rule is applied to the
monitored interface.
Defaults
By default, 10 ACL logs are generated if you do not specify the threshold explicitly.
The default frequency at which ACL logs are generated is ve minutes. By default, ow-based monitoring is not
enabled.
Command Modes CONFIGURATION-EXTENDED-ACCESS-LIST
272 Access Control Lists (ACL)