Concept Guide

You can activate ow-based monitoring for a monitoring session by entering the flow-based enable
command in the Monitor Session mode. When you enable this capability, trac with particular ows 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 specied trac
instead all trac on the interface. This feature is particularly useful when looking for malicious trac. It is available
for Layer 2 and Layer 3 ingress and egress trac. You may specify trac 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 — assigns a IP ACL lter to deny IP packets.
ip access-list standard — creates a standard ACL.
seq
Assign a sequence number to a deny or permit lter in an extended IP access list while creating the lter.
Syntax
seq sequence-number {deny | permit} {source [mask] | any | host ip-address}}
[count [byte] [dscp value] [order] [fragments] [threshold-in-msgs [count]
Parameters
sequence-number Enter a number from 0 to 4294967290. The range is from 0 to 65534.
deny Enter the keyword deny to congure a lter to drop packets meeting this condition.
permit Enter the keyword permit to congure a lter to forward packets meeting this criteria.
source Enter an IP address in dotted decimal format of the network from which the packet was
received.
mask (OPTIONAL) Enter a network mask in /prex format (/x) or A.B.C.D. The mask, when
specied in A.B.C.D format, may be either contiguous or non-contiguous.
any Enter the keyword any to specify that all routes are subject to the lter.
count (OPTIONAL) Enter the keyword count to count packets the lter processes.
byte (OPTIONAL) Enter the keyword byte to count bytes the lter processes.
dscp (OPTIONAL) Enter the keyword dcsp to match to the IP DCSCP values.
order (OPTIONAL) Enter the keyword order to specify the QoS order for the ACL entry. The
range is from 0 to 254 (where 0 is the highest priority and 254 is the lowest; lower-order
numbers have a higher priority). If you do not use the keyword order, the ACLs have the
lowest order by default (
255).
fragments Enter the keyword fragments to use ACLs to control packet fragments.
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.
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 ve minutes. By default, ow-based monitoring is not enabled.
Command Modes CONFIGURATION-IP ACCESS-LIST-STANDARD
Access Control Lists (ACL) 161