Users Guide

Flow-Based Monitoring Support for ACLs
Flow-based monitoring is supported on the platform.
Flow-based monitoring conserves bandwidth by monitoring only the specified traffic instead of all traffic on the interface. It is available for
Layer 2 and Layer 3 ingress traffic. You can specify traffic using standard or extended access-lists. This mechanism copies incoming
packets that matches the ACL rules applied on the ingress 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).
The port mirroring application maintains and performs all the monitoring operations on the chassis. ACL information is sent to the ACL
manager, which in turn notifies the ACL agent to add entries in the CAM area. Duplicate entries in the ACL are not saved.
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.
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 ACL entry associated with that interface to is deleted.
Behavior of Flow-Based Monitoring
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 traversing to the destination port. Enter the keyword
monitor with the seq, permit, or deny command for the ACL rules to allow or drop IPv4, IPv6, ARP, UDP, EtherType, ICMP, and
TCP packets. The ACL rule describes 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]] [monitor]
If the number of monitoring sessions increases, inter-process communication (IPC) bandwidth utilization will be high. The 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 that match the
specified criterion. The ACL agent maintains data on the source port, the 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 a 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
Dell(conf-mon-sess-0)#do show monitor session 0
SessID Source Destination Dir Mode Source IP Dest IP
------ ------ ----------- --- ---- --------- --------
0 Gi 1/1 Gi 1/2 rx Flow N/A N/A
The show config command has been modified to display monitoring configuration in a particular session.
Access Control Lists (ACLs)
121