Access Control Lists (ACLs) | 85
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..
IP Prefix Lists
IP prefix lists control routing policy. An IP prefix list is a series of sequential filters that contain a matching
criterion (examine IP route prefix) and an action (permit or deny) to process routes. The filters are
processed in sequence so that if a route prefix does not match the criterion in the first filter, the second
filter (if configured) is applied. When the route prefix matches a filter, FTOS drops or forwards the packet
based on the filter’s designated action. If the route prefix does not match any of the filters in the prefix list,
the route is dropped (that is, implicit deny).
A route prefix is an IP address pattern that matches on bits within the IP address. The format of a route
prefix is A.B.C.D/X where A.B.C.D is a dotted-decimal address and /X is the number of bits that should be
matched of the dotted decimal address. For example, in 112.24.0.0/16, the first 16 bits of the address
112.24.0.0 match all addresses between 112.24.0.0 to 112.24.255.255.
Below are some examples that permit or deny filters for specific routes using the
le and ge parameters,
where x.x.x.x/x represents a route prefix:
• To deny only /8 prefixes, enter deny x.x.x.x/x ge 8 le 8
• To permit routes with the mask greater than /8 but less than /12, enter permit x.x.x.x/x ge 8
le 12
• To deny routes with a mask less than /24, enter deny x.x.x.x/x le 24
• To permit routes with a mask greater than /20, enter permit x.x.x.x/x ge 20
Task Command Syntax Command Mode
Apply Egress ACLs to IPv4 system
traffic.
ip control-plane [egress filter]
CONFIGURATION
Create a Layer 3 ACL using
permit
rules with the count option to describe
the desired CPU traffic
permit ip {source mask | any | host
ip-address} {destination mask | any |
host ip-address} count
CONFIG-NACL
FTOS Behavior: VRRP hellos and IGMP packets are not affected when you enable egress ACL
filtering for CPU traffic. Packets sent by the CPU with the source address as the VRRP virtual IP
address have the interface MAC address instead of VRRP virtual MAC address.
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