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
ip access-list extended — creates an extended ACL.
permit tcp — assigns a permit lter for TCP packets.
permit udp — assigns a permit lter for UDP packets.
permit
To forward packets from a specic source MAC address, congure a lter.
Syntax
permit {any | mac-source-address [mac-source-address-mask]} [count [byte]] |
log [interval minutes] [threshold-in-msgs[count] [monitor]
To remove this lter, you have two choices:
• Use the no seq sequence-number command if you know the lter’s sequence number.
•
Use the no permit {any | mac-source-address mac-source-address-mask} command.
Parameters
any Enter the keyword any to forward all packets received with a MAC address.
mac-source-
address
Enter a MAC address in nn:nn:nn:nn:nn:nn format.
mac-source-
address-mask
(OPTIONAL) Specify which bits in the MAC address must match. If no mask is specied,
a mask of 00:00:00:00:00:00 is applied (in other words, the lter allows only MAC
addresses that match).
count (OPTIONAL) Enter the keyword count to count packets processed by the lter.
byte (OPTIONAL) Enter the keyword byte to count bytes processed by the lter.
log (OPTIONAL) Enter the keyword log to enable the triggering of ACL log messages.
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.
interval minutes (OPTIONAL) Enter the keyword interval followed by the time period in minutes at
which ACL logs must be generated. The interval range is from 1 to 10 minutes.
monitor (OPTIONAL) Enter the keyword monitor when the rule is describing the trac that you
want to monitor and the ACL in which you are creating the rule is applied to the
monitored interface
Defaults Not congured.
238 Access Control Lists (ACL)