5.2.a [i] VACL, PACL
VLAN ACLs (VACLs) can provide access control for all packets that are bridged within a VLAN or that are routed into or out of a VLAN or a WAN interface for VACL capture. Unlike Cisco IOS ACLs that are applied on routed packets only, VACLs apply to all packets and can be applied to any VLAN or WAN interface. VACLs are processed in the ACL TCAM hardware. VACLs ignore any Cisco IOS ACL fields that are not supported in hardware.
You can configure VACLs for IP and MAC-layer traffic. VACLs applied to WAN interfaces support only IP traffic for VACL capture. If a VACL is configured for a packet type, and a packet of that type does not match the VACL, the default action is to deny the packet.
The port ACL (PACL) feature provides the ability to perform access control on specific Layer 2 ports. A Layer 2 port is a physical LAN or trunk port that belongs to a VLAN . Port ACLs are applied only on the ingress traffic. The port ACL feature is supported only in hardware (port ACLs are not applied to any packets routed in software). They apply to both voice and data VLANs. When you create a port ACL, an entry is created in the ACL TCAM. You can use the show tcam counts command to see how much TCAM space is available. The PACL feature does not affect Layer 2 control packets received on the port. You can use the access-group mode command to change the way that PACLs interact with other ACLs. PACLs use the following modes:
Prefer port mode—If a PACL is configured on a Layer 2 interface, the PACL takes effect and overwrites the effect of other ACLs (Cisco IOS ACL and VACL). If no PACL feature is configured on the Layer 2 interface, other features applicable to the interface are merged and are applied on the interface.
Merge mode—In this mode, the PACL, VACL, and Cisco IOS ACLs are merged in the ingress direction following the logical serial. This is the default access group mode.
You configure the access-group mode command on each interface . The default is merge mode.
Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 5181-5184). . Kindle Edition.