Addendum
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 corresponding flow processor to
perform the action specified for that port. If mirroring action is set in the flow processor entry, the
destination port details, which indicates the port on the device to which the mirrored information must
be sent, are sent to the destination port.
When a stack unit is reset or a stack unit undergoes a failure, the ACL agent registers with the port
mirroring application. The port mirroring utility downloads the monitoring configuration to the ACL
agent. The interface manager notifies the port mirroring application about the removal of an interface
when an interface to which an ACL entry is associated is deleted.
Behavior of Flow-Based Monitoring
You can enter 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 interfaces are examined and, appropriate ACLs can be
applied in the ingress direction. By default, flow-based monitoring is not enabled.
You must specify the monitor option with the permit, deny, or seq command for ACLs that are
assigned to the source or the monitored port (MD) to enable the evaluation and replication of traffic that
is destined to the source port to the destination port. Enter the keyword monitor with the seq, permit
and deny ACL rules to allow or drop IPv4, IPv6, ARP, UDP, EtherType, ICMP, and TCP packets when the
rule is describing the traffic that you want to monitor and the ACL in which you are creating the rule will
be applied to the monitored interface. Flow monitoring is supported for standard and extended IPv4
ACLs, standard and extended IPv6 ACLs, and standard and extended MAC ACLs.
CONFIG-STD-NACL mode
seq sequence-number {deny | permit} {source [mask] | any | host ip-address}
[count [byte]] [order] [fragments] [log [threshold-in-msgs count] ]
If the number of monitoring sessions increases, inter-process communication (IPC) bandwidth utilization
will be high. ACL manager might require a large bandwidth when you assign an ACL with many entries to
an interface.
The ACL agent module saves monitoring details in its local database and also in the CAM region to
monitor packets which match the specified criterion. The ACL agent maintains data on the source port,
destination port, and the endpoint to which the packet must be forwarded when a match occurs with the
ACL entry.
If you configure the flow-based enable command and do not apply an ACL on the source port or the
monitored port, both flow-based monitoring and port mirroring do not function. Flow-based monitoring
is supported only for ingress traffic and not for egress packets.
The port mirroring application maintains database that contains all monitoring sessions (including port
monitor sessions). It has information regarding the sessions that are enabled for flow-based monitoring
and those sessions that are not enabled for flow-based monitoring. It downloads monitoring
configuration to the ACL agent whenever the ACL agent is registered with the port mirroring application
or when flow-based monitoring is enabled.
The show monitor session session-id command has been enhanced to display the Type field in
the output, which indicates whether a particular session is enabled for flow-monitoring.
Example Output of the show Command
E1200-maa-01#show running-config monitor session
!
monitor session 11
flow-based enable
source GigabitEthernet 13/0 destination GigabitEthernet 13/1 direction both
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