Dell PowerSwitch S4820T Configuration Guide for the S4820T System 9.14.1.0 - Page 141

Behavior of Flow-Based Monitoring

Page 141 highlights

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. Behavior of Flow-Based Monitoring You can activate flow-based monitoring for a monitoring session using the flow-based enable command in the Monitor Session mode. When you enable this flow-based monitoring, traffic with particular flows that are traversing through the interfaces are examined in accordance with the applied ACLs. By default, flow-based monitoring is not enabled. There are two ways in which you can enable flow-based monitoring in Dell EMC Networking OS. You can create an ACL and apply that ACL either to an interface that needs to be monitored or apply it in the monitor session context. If you apply the monitor ACL to an interface, the Dell EMC Networking OS mirrors the ingress traffic with an implicit deny applied at the end of the ACL. If you apply the ACL to the monitor section context, the Dell EMC Networking OS mirrors the ingress and known unicast egress traffic with an implicit permit applied at the end of the ACL. This enables the other traffic to flow without being blocked by the ACL. When you apply an ACL within the monitor session, it is applied to all source interfaces configured in the monitor session. The Dell EMC Networking OS honors any permit or deny actions of the ACL rules used for flow-based mirroring. Packets that match a mirror ACL rule is denied or forwarded depending on the rule but the packet is mirrored. However, the user ACL has precedence over the mirror ACL. The same source interface can be part of multiple monitor sessions. Flow-based monitoring is supported for SPAN, RSPAN, and ERSPAN sessions. If there are overlapping rules between ACLs applied on different monitor sessions, the session with the highest monitor session ID takes precedence. NOTE: You can apply only IPv4 ACL rules under monitor session context. 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 is 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 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. You cannot apply the same ACL to an interface or a monitoring session context simultaneously. 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. Access Control Lists (ACLs) 141

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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.
Behavior of Flow-Based Monitoring
You can activate
flow-based
monitoring for a monitoring session using the
flow-based enable
command in the Monitor Session mode.
When you enable this
flow-based
monitoring,
traffic
with particular
flows
that are traversing through the interfaces are examined in
accordance with the applied ACLs. By default,
flow-based
monitoring is not enabled.
There are two ways in which you can enable
flow-based
monitoring in Dell EMC Networking OS. You can create an ACL and apply that ACL
either to an interface that needs to be monitored or apply it in the monitor session context. If you apply the monitor ACL to an interface,
the Dell EMC Networking OS mirrors the ingress
traffic
with an implicit deny applied at the end of the ACL. If you apply the ACL to the
monitor section context, the Dell EMC Networking OS mirrors the ingress and known unicast egress
traffic
with an implicit permit applied
at the end of the ACL. This enables the other
traffic
to
flow
without being blocked by the ACL.
When you apply an ACL within the monitor session, it is applied to all source interfaces
configured
in the monitor session.
The Dell EMC Networking OS honors any permit or deny actions of the ACL rules used for
flow-based
mirroring. Packets that match a
mirror ACL rule is denied or forwarded depending on the rule but the packet is mirrored. However, the user ACL has precedence over the
mirror ACL.
The same source interface can be part of multiple monitor sessions.
Flow-based monitoring is supported for SPAN, RSPAN, and ERSPAN sessions. If there are overlapping rules between ACLs applied on
different
monitor sessions, the session with the highest monitor session ID takes precedence.
NOTE:
You can apply only IPv4 ACL rules under monitor session context.
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 is 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 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.
You cannot apply the same ACL to an interface or a monitoring session context simultaneously.
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.
Access Control Lists (ACLs)
141