Users Guide

You can activate ow-based monitoring for a monitoring session by entering the ow-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 — assign a lter to deny IP trac.
• deny udp — assign a lter to deny UDP trac.
deny udp (for Extended IP ACLs)
To drop user datagram protocol (UDP) packets meeting the lter criteria, congure a lter.
Syntax
deny udp {source mask | any | host ip-address} [operator port [port]]
{destination mask | any | host ip-address} [ttl operator] [dscp] [operator port
[port]] [count [byte]] [order] [fragments] [log [interval minutes] [threshold-
in-msgs [count]]
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 deny udp {source mask | any | host ip-address} {destination mask |
any | host ip-address} command.
Parameters
ttl Enter the keyword ttl to deny a packet based on the time to live value. The range is
from 1 to 255.
operator Enter one of the following logical operand:
• eq(equal to) — matches packets that contain a ttl value that is equal to the specied
ttl value.
• neq(not equal to) — matches packets that contain a ttl value that is not equal to the
specied ttl value.
•
gt(greater than) — matches packets that contain a ttl value that is greater than the
specied ttl value.
• lt (less than) — matches packets that contain a ttl value that is less than the
specied ttl value.
• range(inclusive range of values) — matches packets that contain a ttl value that
falls between the specied range of ttl values.
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 time interval range is from 1 to 10 minutes.
Access Control Lists (ACL) 317