Concept Guide

Table Of Contents
A maximum of 125 ACL entries with permit action can be logged. A maximum of 126 ACL entries with deny action can be
logged.
For virtual ACL entries, the same match rule number is reused. Similarly, when an ACL entry is deleted that was previously
enabled for ACL logging, the match rule number used by it is released back to the pool or available set of match indices so
that it can be reused for subsequent allocations.
If you enabled the count of packets for the ACL entry for which you configured logging, and if the logging is deactivated in
a specific interval owing to the threshold having exceeded, the count of packets that exceeded the logging threshold value
during that interval is logged when the subsequent log record (in the next interval) is generated for that ACL entry.
When you delete an ACL entry, the logging settings associated with it are also removed.
ACL logging is supported for standard and extended IPv4 ACLs, IPv6 ACLs, and standard and extended MAC ACLs.
For ACL entries applied on port-channel interfaces, one match index for every member interface of the port-channel
interface is assigned. Therefore, the total available match indices of 251 are split (125 match indices for permit action and
126 match indices for the deny action).
You can configure ACL logging only on ACLs that are applied to ingress interfaces; you cannot enable logging for ACLs on
egress interfaces.
The total available match rule indices is 255 with four match indices used by other modules, leaving 251 indices available for
ACL logging.
Configuring ACL Logging
This functionality is supported on the platform.
To configure the maximum number of ACL log messages to be generated and the frequency at which these messages must be
generated, perform the following steps:
NOTE:
This example describes the configuration of ACL logging for standard IP access lists. You can enable the logging
capability for standard and extended IPv4 ACLs, IPv6 ACLs, and standard and extended MAC ACLs.
1. Specify the maximum number of ACL logs or the threshold that can be generated by using the threshold-in-msgs
count option with the seq, permit, or deny commands. Upon exceeding the specified maximum limit, the generation of ACL
logs is terminated. You can enter a threshold in the range of 1-100. By default, 10 ACL logs are generated if you do not
specify the threshold explicitly.
CONFIG-STD-NACL mode
seq sequence-number {deny | permit} {source [mask] | any | host ip-address} [log
[threshold-in-msgs count] ]
2. Specify the interval in minutes at which ACL logs must be generated. You can enter an interval in the range of 1-10 minutes.
The default frequency at which ACL logs are generated is 5 minutes. If ACL logging is stopped because the configured
threshold has exceeded, it is re-enabled after the logging interval period elapses. ACL logging is supported for standard
and extended IPv4 ACLs, IPv6 ACLs, and standard and extended MAC ACLs. Configure ACL logging only on ACLs that are
applied to ingress interfaces; you cannot enable logging for ACLs that are associated with egress interfaces.
CONFIG-STD-NACL mode
seq sequence-number {deny | permit} {source [mask] | any | host ip-address} [log
[interval minutes]]
Flow-Based Monitoring
Flow-based monitoring conserves bandwidth by monitoring only the specified traffic instead of all traffic on the interface. It
is available for Layer 3 ingress traffic. You can specify the traffic that needs to be monitored using standard or extended
access-lists. The flow-based monitoring mechanism copies packets that matches the ACL rules applied on the 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).
When a packet arrives at a port that is being monitored, the packet is validated against the configured ACL rules. If the packet
matches an ACL rule, the system examines the corresponding flow processor to perform the action specified for that port. If the
mirroring action is set in the flow processor entry, the destination port details, to which the mirrored information must be sent,
are sent to the destination port.
124
Access Control Lists (ACLs)