Reference Guide

Access Control Lists (ACLs) | 115
Egress ACLs are applied to line cards and affect the traffic leaving the system. Configuring egress ACLs
onto physical interfaces protects the system infrastructure from attack—malicious and incidental—by
explicitly allowing only authorized traffic.These system-wide ACLs eliminate the need to apply ACLs
onto each interface and achieves the same results. By localizing target traffic, it is a simpler
implementation.
An egress ACL is used when users would like to restrict egress traffic. For example, when a DOS attack
traffic is isolated to one particular interface, you can apply an egress ACL to block that particular flow
from exiting the box, thereby protecting downstream devices.
To create an egress ACLs, use the
ip access-group command in the EXEC Privilege mode as shown in the
example below. This example also shows viewing the configuration, applying rules to the newly created
access group, and viewing the access list:
FTOS(conf)#interface gige 0/0
FTOS(conf-if-gige0/0)#ip access-group abcd out
FTOS(conf-if-gige0/0)#show config
!
gigethernet 0/0
no ip address
ip access-group abcd out
no shutdown
FTOS(conf-if-gige0/0)#end
FTOS#configure terminal
FTOS(conf)#ip access-list extended abcd
FTOS(config-ext-nacl)#permit tcp any any
FTOS(config-ext-nacl)#deny icmp any any
FTOS(config-ext-nacl)#permit 1.1.1.2
FTOS(config-ext-nacl)#end
FTOS#show ip accounting access-list
!
Extended Ingress IP access list abcd on gigethernet 0/0
seq 5 permit tcp any any
seq 10 deny icmp any any
seq 15 permit 1.1.1.2
Egress Layer 3 ACL Lookup for Control-plane IP Traffic
By default, packets originated from the system are not filtered by egress ACLs. If you initiate a ping
session from the system, for example, and apply an egress ACL to block this type of traffic on the
interface, the ACL does not affect that ping traffic. The Control Plane Egress Layer 3 ACL feature
enhances IP reachability debugging by implementing control-plane ACLs for CPU-generated and
CPU-forwarded traffic. Using
permit rules with the count option, you can track on a per-flow basis
whether CPU-generated and CPU-forwarded packets were transmitted successfully..
Task Command Syntax Command Mode
Apply Egress ACLs to IPv4 system
traffic.
ip control-plane [egress filter] CONFIGURATION
Apply Egress ACLs to IPv6 system
traffic.
ipv6 control-plane [egress filter] CONFIGURATION