Concept Guide

can congure ACL logging only on ACLs that are applied to ingress interfaces; you cannot enable logging for ACLs
that are associated with egress interfaces.
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 icmp
Congure a lter to allow all or specic ICMP messages.
Syntax
permit icmp {source mask | any | host ip-address} {destination mask | any |
host ip-address} [dscp] [message-type] [count [byte]] [order] [fragments]
[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 permit icmp {source mask | any | host ip-address} {destination mask
| any | host ip-address} command.
Parameters
source Enter the IP address of the network or host from which the packets were sent.
mask 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 noncontiguous.
any Enter the keyword any to match and drop specic Ethernet trac on the interface.
host ip-address Enter the keyword host and then enter the IP address to specify a host IP address.
destination Enter the IP address of the network or host to which the packets are sent.
dscp Enter the keyword dscp to deny a packet based on the DSCP value. The range is 0 to
63.
message-type (OPTIONAL) Enter an ICMP message type, either with the type (and code, if necessary)
numbers or with the name of the message type. The range is 0 to 255 for ICMP type and
0 to 255 for ICMP code.
count (OPTIONAL) Enter the keyword count to count packets the lter processes.
byte (OPTIONAL) Enter the keyword byte to count bytes the lter processes.
order (OPTIONAL) Enter the keyword order to specify the QoS priority for the ACL entry.
The range is 0 to 254 (where 0 is the highest priority and 254 is the lowest; lower-order
Access Control Lists (ACL) 173