Cisco ASA 5500 Series Configuration Guide using the CLI, 8.2
Adding an EtherType Access List
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Adding an EtherType Access List

Table Of Contents

Adding an EtherType Access List

Information About EtherType Access Lists

Supported EtherTypes

Implicit Permit of IP and ARPs Only

Implicit and Explicit Deny ACE at the End of an Access List

Allowing MPLS

Licensing Requirements for EtherType Access Lists

Guidelines and Limitations

Default Settings

Configuring EtherType Access Lists

Task Flow for Configuring EtherType Access Lists

Adding EtherType Access Lists

Adding Remarks to Access Lists

What to Do Next

Monitoring EtherType Access Lists

Configuration Examples for EtherType Access Lists

Feature History for EtherType Access Lists


Adding an EtherType Access List


This chapter describes how to configure EtherType access lists and includes the following topics:

Information About EtherType Access Lists

Licensing Requirements for EtherType Access Lists

Guidelines and Limitations

Default Settings

Configuring EtherType Access Lists

Monitoring EtherType Access Lists

What to Do Next

Configuration Examples for EtherType Access Lists

Feature History for EtherType Access Lists

Information About EtherType Access Lists

An EtherType access list is made up of one or more Access List Entries (ACEs) that specify an EtherType. This section includes the following topics:

Supported EtherTypes

Implicit Permit of IP and ARPs Only

Implicit and Explicit Deny ACE at the End of an Access List

Allowing MPLS

Supported EtherTypes

An EtherType ACE controls any EtherType identified by a 16-bit hexadecimal number. You can apply only one access list of each type (extended and EtherType) to each direction of an interface. You can also apply the same access lists on multiple interfaces.

Implicit Permit of IP and ARPs Only

IPv4 traffic is allowed through the transparent firewall automatically from a higher security interface to a lower security interface, without an access list. ARPs are allowed through the transparent firewall in both directions without an access list. ARP traffic can be controlled by ARP inspection.

However, to allow any traffic with EtherTypes other than IPv4 and ARP, you need to apply an EtherType access list, even from a high security to a low security interface.

Because EtherTypes are connectionless, you need to apply the access list to both interfaces if you want traffic to pass in both directions.

Implicit and Explicit Deny ACE at the End of an Access List

For EtherType access lists, the implicit deny at the end of the access list does not affect IP traffic or ARPs; for example, if you allow EtherType 8037, the implicit deny at the end of the access list does not now block any IP traffic that you previously allowed with an extended access list (or implicitly allowed from a high security interface to a low security interface). However, if you explicitly deny all traffic with an EtherType ACE, then IP and ARP traffic is denied.

Allowing MPLS

If you allow MPLS, ensure that Label Distribution Protocol and Tag Distribution Protocol TCP connections are established through the ASA by configuring both MPLS routers connected to the ASA to use the IP address on the ASA interface as the router-id for LDP or TDP sessions. (LDP and TDP allow MPLS routers to negotiate the labels [addresses] used to forward packets.)

On Cisco IOS routers, enter the appropriate command for your protocol, either LDP or TDP. The interface is the interface connected to the ASA.

hostname(config)# mpls ldp router-id interface force
 
   

Or

hostname(config)# tag-switching tdp router-id interface force
 
   

Licensing Requirements for EtherType Access Lists

The following table shows the licensing requirements for this feature:

Model
License Requirement

All models

Base License.


Guidelines and Limitations

This section includes the guidelines and limitations for this feature:

Context Mode Guidelines

Firewall Mode Guidelines

Additional Guidelines and Limitations

Context Mode Guidelines

Available in single and multiple context modes.

Firewall Mode Guidelines

Supported in transparent firewall mode only.

Additional Guidelines and Limitations

The following guidelines and limitations apply to EtherType access lists:

When you enter the access-list command for a given access list name, the ACE is added to the end of the access list.

EtherType access lists support Ethernet V2 frames.

802.3-formatted frames are not handled by the access list because they use a length field as opposed to a type field. Bridge protocol data units, which are allowed by default, are the only exception; they are SNAP-encapsulated, and the adaptive security appliance is designed to specifically handle BPDUs.

Because EtherTypes are connectionless, you need to apply the ACL to both interfaces if you want traffic to pass in both directions.

If you allow MPLS, ensure that LDP and TDP TCP connections are established through the adaptive security appliance by configuring both MPLD routers connected to the adaptive security appliance to use the IP address on the adaptive security appliance interface as the router-ID for LDP or TDP sessions. (LDP and TDP allow MPLS routers to negotiate the labels, or addresses, used to forward packets.)

For EtherType access lists, the implicit deny at the end of the access list does not affect IP traffic or ARPs; for example, if you allow EtherType 8037, the implicit deny at the end of the access list does not now block any IP traffic that you previously allowed with an extended access list (or implicitly allowed from a high security interface to a low security interface). However, if you explicitly deny all traffic with an EtherType ACE, then IP and ARP traffic is denied.

You can apply only one access list of each type (extended and Ethertype) to each direction of an interface. You can also apply the same access lists on multiple interfaces.

Default Settings

Table 12-1 lists the default settings for EtherType access lists parameters.

Table 12-1 Default EtherType Access Lists Parameters 

Parameters
Default

bpdu

By default, BPDUs are permitted.

deny | permit

The adaptive security appliance denies all packets on the originating interface unless you specifically permit access.

deny

Access list logging generates system log message 106023 for denied packets. Deny packets must be present to loge denied packets.

log

When the log optional keyword is specified, the default severity level for system log message 106100 is 6 (informational).


Configuring EtherType Access Lists

This section includes the following topics:

Task Flow for Configuring EtherType Access Lists

Adding EtherType Access Lists

Adding Remarks to Access Lists

Task Flow for Configuring EtherType Access Lists

Use the following guidelines to create and implement an access list:

Create an access list by adding an ACE and applying an access list name, as shown in the "Adding EtherType Access Lists" section.

Apply the access list to an interface. (See the "Applying an Access List to an Interface" section for more information.)

Adding EtherType Access Lists

To configure an access list that controls traffic based upon its EtherType, enter the following command:

Command
Purpose

access-list access_list_name ethertype {deny | permit} {ipx | bpdu | mpls-unicast | mpls-multicast | any | hex_number}

Example:

hostname(config)# hostname(config)# 
access-list ETHER ethertype permit ipx

Adds an EtherType ACE.

The access_list_name argument lists the name or number of an access list. When you specify an access list name, the ACE is added to the end of the access list. Enter the access_list_name in upper case letters so that the name is easy to see in the configuration. You might want to name the access list for the interface (for example, INSIDE) or for the purpose (for example, MPLS or PIX).

The any keyword specifies access to anyone.

The bpdu keyword specifies access to bridge protocol data units, which are permitted by default.

The deny keyword denies access if the conditions are matched. If an EtherType access list is configured to deny all, all ethernet frames are discarded. Only physical protocol traffic, such as auto-negotiation, is still allowed.

The hex_number argument indicates any Ethertype that can be identified by a 16-bit hexadecimal number greater than or equal to 0x600. (See RFC 1700, "Assigned Numbers," at http://www.ietf.org/rfc/rfc1700.txt for a list of EtherTypes.)

The ipx keyword specifies access to IPX.

The mpls-multicast keyword specifies access to MPLS multicast.

The mpls-unicast keyword specifies access to MPLS unicast.

The permit keyword permits access if the conditions are matched.


Note To remove an EtherType ACE, enter the no access-list command with the entire command syntax string as it appears in the configuration.



Example

The following sample access list allows common EtherTypes originating on the inside interface:

hostname(config)# access-list ETHER ethertype permit ipx
hostname(config)# access-list ETHER ethertype permit mpls-unicast
hostname(config)# access-group ETHER in interface inside

Adding Remarks to Access Lists

You can include remarks about entries in any access list, including extended, EtherType, IPv6, standard, and Webtype access lists. The remarks make an access list easier to understand.

To add a remark after the last access-list command you entered, enter the following command:

Command
Purpose
access-list access_list_name remark text
 
        
Example:
hostname(config)# access-list OUT remark - 
this is the inside admin address
 
        

Adds a remark after the last access-list command you entered.

The text can be up to 100 characters in length. You can enter leading spaces at the beginning of the text. Trailing spaces are ignored.

If you enter the remark before any access-list command, then the remark is the first line in the access list.

If you delete an access list using the no access-list access_list_name command, then all remarks are also removed.


Example

You can add remarks before each ACE, and the remarks appear in the access list in these locations. Entering a dash (-) at the beginning of a remark helps to set it apart from the ACE.

hostname(config)# access-list OUT remark - this is the inside admin address
hostname(config)# access-list OUT extended permit ip host 209.168.200.3 any
hostname(config)# access-list OUT remark - this is the hr admin address
hostname(config)# access-list OUT extended permit ip host 209.168.200.4 any

What to Do Next

Apply the access list to an interface. (See the "Applying an Access List to an Interface" section for more information.)

Monitoring EtherType Access Lists

To monitor EtherType access lists, enter one of the following commands:

Command
Purpose
show access-list

Displays the access list entries by number.

show running-config access-list

Displays the current running access-list configuration.


Configuration Examples for EtherType Access Lists

The following example shows how to configure EtherType access lists:

The following access list allows some EtherTypes through the ASA, but it denies IPX:

hostname(config)# access-list ETHER ethertype deny ipx
hostname(config)# access-list ETHER ethertype permit 0x1234
hostname(config)# access-list ETHER ethertype permit mpls-unicast
hostname(config)# access-group ETHER in interface inside
hostname(config)# access-group ETHER in interface outside
 
   

The following access list denies traffic with EtherType 0x1256, but it allows all others on both interfaces:

hostname(config)# access-list nonIP ethertype deny 1256
hostname(config)# access-list nonIP ethertype permit any
hostname(config)# access-group ETHER in interface inside
hostname(config)# access-group ETHER in interface outside

Feature History for EtherType Access Lists

Table 12-2 lists the release history for this feature.

Table 12-2 Feature History for EtherType Access Lists 

Feature Name
Releases
Feature Information

EtherType access lists

7.0

EtherType access lists control traffic based upon its EtherType.

The feature and the following command were introduced: access-list ethertype.