An Ethernet services access control lists (ACLs) consist of one or more access control entries (ACE) that collectively define the Layer 2 network traffic profile. This profile can then be referenced by Cisco IOS XR software features. Each Ethernet services ACL includes an action element (permit or deny) based on criteria such as source and destination address, Class of Service (CoS), ether-type, or 802.1ad DEI.

Layer 2 ACLs are supported on ingress traffic only. Layer 2 ACLs are not supported on egress traffic.

Layer 2 access control lists are also known as Ethernet services control access lists.

This prerequisite applies to configuring the access control lists and prefix lists:

You must be in a user group associated with a task group that includes the proper task IDs. The command reference guides include the task IDs required for each command.

If you suspect user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

Layer 2 access control lists perform packet filtering to control which packets move through the network and where. Such controls help to limit incoming and outgoing network traffic and restrict the access of users and devices to the network at the port level.

A Layer 2 access control list is a sequential list consisting of permit and deny statements that apply to Layer 2 configurations. The access list has a name by which it is referenced.

An access list can be configured and named, but it is not in effect until the access list is referenced by a command that accepts an access list. Multiple commands can reference the same access list. An access list can control Layer 2 traffic arriving at the router, but not traffic originating at the router and leaving the router.

Use this process and rules when configuring Layer 2 access control list:

• The software tests the source or destination address of each packet being filtered against the conditions in the access list, one condition (permit or deny statement) at a time.

• If a packet does not match an access list statement, the packet is then tested against the next statement in the list.

• If a packet and an access list statement match, the remaining statements in the list are skipped and the packet is permitted or denied as specified in the matched statement. The first entry that the packet matches determines whether the software permits or denies the packet. That is, after the first match, no subsequent entries are considered.

• If the access list denies the address or protocol, the software discards the packet.

• If no conditions match, the software drops the packet because each access list ends with an unwritten or implicit deny statement. That is, if the packet has not been permitted or denied by the time it was tested against each statement, it is denied.

• The access list should contain at least one permit statement or else all packets are denied.

• Because the software stops testing conditions after the first match, the order of the conditions is critical. The same permit or deny statements specified in a different order could result in a packet being passed under one circumstance and denied in another circumstance.

• Inbound access lists process packets arriving at the router. An inbound access list is efficient because it saves the overhead of routing lookups if the packet is to be discarded because it is denied by the filtering tests. If the packet is permitted by the tests, it is then processed for routing. For inbound lists, permit means continue to process the packet after receiving it on an inbound interface; deny means discard the packet.

• An access list can not be removed if that access list is being applied by an access group in use. To remove an access list, remove the access group that is referencing the access list and then remove the access list.

• An access list must exist before you can use the ethernet-services access-group command.

Consider these when creating a Layer 2 access control list:

• Create the access list before applying it to an interface.

• Organize your access list so that more specific references appear before more general ones.

These restrictions apply to configuring Layer 2 access control lists:

• Layer 2 access control lists are not supported over management interfaces.

• NetIO (software slow path) is not supported for Layer 2 access control lists.

• Layer 2 access control lists attachment is possible only in ingress direction on an interface.

• Only COS (Class of Service) and dei (Discard Eligibility Indication) are supported for Layer 2 access control lists.

This section describes how you can configure Layer 2 access control lists.

Router# configure 
Router(config)# ethernet-services access-list es_acl_1 
Router(config-es-acl)# deny 00ff.eedd.0010 ff00.0000.00ff 0000.0100.0001 0000.0000.ffff
Router(config-es-acl)# permit host 000a.000b.000c host 00aa.ab99.1122 cos 1 dei
Router(config-es-acl)# deny host 000a.000b.000c host 00aa.dc11.ba99 cos 7 dei
Router(config-es-acl)# commit
Router(config)# interface tengige0/0/0/4 
Router(config-if)# l2transport
Router(config-if-l2)# commit
Router(config-if-l2)# exit
Router(config-if)# ethernet-services access-group es_acl_1 ingress
Router(config-if)# commit