Users Guide

Table Of Contents
Access Control Lists 689
In the last column of the table (Optimized), a Yes entry means the rule is
never processed in hardware because the action, if any, is to fall through to the
next match criteria. The system optimizes out deny ACL match clauses and
never processes them in the system hardware. Counters for these match
clauses will always show 0.
ACLs and Policy Interaction
Within this paragraph, the word policy refers to both DiffServ Policy and
Policy Based Routing. A more specific term may be use when the statement
only applies to one of the policy types.
PBR can be configured only on VLAN routing interfaces. However, ACLs can
be configured on all types of interfaces, including physical interfaces, port-
channels, and VLANs. DiffServ policies can be defined on Ethernet interfaces
and port channels (with or without VLAN match criteria). When processing
packets on which both policy and ACLs are configured, policy matching is
performed only after the application of all VLAN and interface ACLs
matches, including the implicit deny all match at the end of ACL processing.
Only packets that match a user-defined ingress permit ACL rule configured
on an incoming interface are eligible for processing by policy. This is due to
the implicit deny all rule that takes effect at the end of ACL processing and
prior to PBR and DiffServ Policy processing. Interface ACLs have a higher
precedence than VLAN ACLs or PBR ACLs. In the case of conflicting actions,
the interface ACL takes precedence. Specifically, if an interface ACL drops a
packet (explicit or implicit deny), policy is not applied to the packet.
Likewise, if a VLAN interface ACL drops a packet, policy is not applied to the
packet.
In many cases, the switch is capable of taking multiple actions on a packet,
irrespective of whether the action is configured in a policy or in an ACL
configured on a port. For example, the system can both rate limit packets on
ingress with an interface ACL and set the ip precedence on packets that do
not exceed the rate limit with a PBR ACL or DiffServ Policy.
The following table describes the action resolution mechanism when a packet
matches both the policy rules configured on a VLAN routing interface and a
permit ACL rule configured on a physical interface (the deny ACL action is
included for emphasis):