Concept Guide

Applying Egress Layer 3 ACLs (Control-Plane)
By default, packets originated from the system are not ltered by egress ACLs.
For example, if you initiate a ping session from the system and apply an egress ACL to block this type of trac on the interface, the ACL
does not aect that ping trac. The Control Plane Egress Layer 3 ACL feature enhances IP reachability debugging by implementing
control-plane ACLs for CPU-generated and CPU-forwarded trac. Using permit rules with the
count option, you can track on a per-ow
basis whether CPU-generated and CPU-forwarded packets were transmitted successfully.
NOTE: The ip control-plane [egress filter] and the ipv6 control-plane [egress filter] commands are
not supported.
1 Apply Egress ACLs to IPv4 system trac.
CONFIGURATION mode
ip control-plane [egress filter]
2 Apply Egress ACLs to IPv6 system trac.
CONFIGURATION mode
ipv6 control-plane [egress filter]
3 Create a Layer 3 ACL using permit rules with the count option to describe the desired CPU trac.
CONFIG-NACL mode
permit ip {source mask | any | host ip-address} {destination mask | any | host ip-address}
count [monitor [session-id]]
Dell EMC Networking OS Behavior: Virtual router redundancy protocol (VRRP) hellos and internet group management protocol (IGMP)
packets are not aected when you enable egress ACL ltering for CPU trac. 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.
IP Prex Lists
IP prex lists control routing policy. An IP prex list is a series of sequential lters that contain a matching criterion (examine IP route prex)
and an action (permit or deny) to process routes. The lters are processed in sequence so that if a route prex does not match the criterion
in the rst lter, the second lter (if congured) is applied. When the route prex matches a lter, Dell EMC Networking OS drops or
forwards the packet based on the lter’s designated action. If the route prex does not match any of the lters in the prex list, the route is
dropped (that is, implicit deny).
A route prex is an IP address pattern that matches on bits within the IP address. The format of a route prex 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 rst 16 bits of the address 112.24.0.0 match all addresses between 112.24.0.0 to 112.24.255.255.
The following examples show permit or deny lters for specic routes using the le and ge parameters, where x.x.x.x/x represents a route
prex:
• To deny only /8 prexes, 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.
• 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.
The following rules apply to prex lists:
• A prex list without any permit or deny lters allows all routes.
• An “implicit deny” is assumed (that is, the route is dropped) for all route prexes that do not match a permit or deny lter in a
congured prex list.
Access Control Lists (ACLs)
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