Users Guide

count for that new interval commences from zero. If ACL logging was stopped previously because the configured
threshold is exceeded, it is re-enabled for this new interval.
If ACL logging is stopped because the configured 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 configure 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 flow-based monitoring for a monitoring session by entering the flow-based enable command in
the Monitor Session mode. When you enable this capability, traffic with particular flows 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 specified traffic instead all
traffic on the interface. This feature is particularly useful when looking for malicious traffic. It is available for Layer
2 and Layer 3 ingress and egress traffic. You may specify traffic 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
• deny tcp — assign a filter to deny TCP packets.
• deny udp — assign a filter to deny UDP packets.
• ip access-list extended — create an extended ACL.
seq (for Standard IPv4 ACLs)
Assign a sequence number to a deny or permit filter in an IP access list while creating the filter.
Syntax
seq sequence-number {deny | permit} {source [mask] | any | host ip-address}}
[count [bytes]] [dscp value] [order] [fragments] [log [interval minutes]
[threshold-in-msgs [count]] [monitor]
To delete a filter, use the no seq sequence-number 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 interval range is from 1 to 10 minutes.
monitor (OPTIONAL) Enter the keyword monitor when the rule is describing the traffic 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 five minutes. By default, flow-based monitoring is not
enabled.
Command Modes CONFIGURATION-STANDARD-ACCESS-LIST
266 Access Control Lists (ACL)