Published On: August 3ʳᵈ, 2020 08:22

Security Configuration Guide, Cisco IOS XE Amsterdam 17.3.x (Catalyst 9500 Switches)

Restrictions for IPv4 Access Control Lists

General Network Security

The following are restrictions for configuring network security with ACLs:

  • Not all commands that accept a numbered ACL accept a named ACL. ACLs for packet filters and route filters on interfaces can use a name. VLAN maps also accept a name.

  • A standard ACL and an extended ACL cannot have the same name.

  • Though visible in the command-line help strings, appletalk is not supported as a matching condition for the deny and permit MAC access-list configuration mode commands.

  • ACL wildcard is not supported in downstream client policy.

IPv4 ACL Network Interfaces

The following restrictions apply to IPv4 ACLs to network interfaces:

  • When controlling access to an interface, you can use a named or numbered ACL.

  • If you apply an ACL to a Layer 2 interface that is a member of a VLAN, the Layer 2 (port) ACL takes precedence over an input Layer 3 ACL applied to the VLAN interface or a VLAN map applied to the VLAN.

  • If you apply an ACL to a Layer 3 interface and routing is not enabled on the switch, the ACL only filters packets that are intended for the CPU, such as SNMP, Telnet, or web traffic.

  • If the preauth_ipv4_acl ACL is configured to filter packets, the ACL is removed after authentication.

  • You do not have to enable routing to apply ACLs to Layer 2 interfaces.

MAC ACLs on a Layer 2 Interface

After you create a MAC ACL, you can apply it to a Layer 2 interface to filter non-IP traffic coming in that interface. When you apply the MAC ACL, consider these guidelines:

  • You can apply no more than one IP access list and one MAC access list to the same Layer 2 interface. The IP access list filters only IP packets, and the MAC access list filters non-IP packets.

  • A Layer 2 interface can have only one MAC access list. If you apply a MAC access list to a Layer 2 interface that has a MAC ACL configured, the new ACL replaces the previously configured one.


Note

The mac access-group interface configuration command is only valid when applied to a physical Layer 2 interface. You cannot use the command on EtherChannel port channels.


IP Access List Entry Sequence Numbering

  • This feature does not support dynamic, reflexive, or firewall access lists.

Information About IPv4 Access Control Lists

ACL Overview

Packet filtering can help limit network traffic and restrict network use by certain users or devices. ACLs filter traffic as it passes through a device and permit or deny packets crossing specified interfaces. An ACL is a sequential collection of permit and deny conditions that apply to packets. When a packet is received on an interface, the switch compares the fields in the packet against any applied ACLs to verify that the packet has the required permissions to be forwarded, based on the criteria specified in the access lists. One by one, it tests packets against the conditions in an access list. The first match decides whether the switch accepts or rejects the packets. Because the switch stops testing after the first match, the order of conditions in the list is critical. If no conditions match, the switch rejects the packet. If there are no restrictions, the switch forwards the packet; otherwise, the switch drops the packet. The switch can use ACLs on all packets it forwards.

You configure access lists on a device to provide basic security for your network. If you do not configure ACLs, all packets passing through the switch could be allowed onto all parts of the network. You can use ACLs to control which hosts can access different parts of a network or to decide which types of traffic are forwarded or blocked at device interfaces. For example, you can allow e-mail traffic to be forwarded but not Telnet traffic.

Access Control Entries

An ACL contains an ordered list of access control entries (ACEs). Each ACE specifies permit or deny and a set of conditions the packet must satisfy in order to match the ACE. The meaning of permit or deny depends on the context in which the ACL is used.

ACL Supported Types

The device supports IP ACLs and Ethernet (MAC) ACLs:

  • IP ACLs filter IPv4 traffic, including TCP, User Datagram Protocol (UDP), Internet Group Management Protocol (IGMP), and Internet Control Message Protocol (ICMP).

  • Ethernet ACLs filter non-IP traffic.

This device also supports quality of service (QoS) classification ACLs.

Supported ACLs

The switch supports three types of ACLs to filter the traffic:

  • Port ACLs access-control traffic entering a Layer 2 interface. You can apply port ACLs to a Layer 2 interface in each direction to each access list type—IPv4 and MAC.

  • Router ACLs access-control traffic routed between VLANs and are applied to Layer 3 interfaces in a specific direction (inbound or outbound).

  • VLAN ACLs or VLAN maps are applied only to Layer 2 VLANs and impact bridged traffic only. You can use VLAN maps to filter traffic between devices in the same VLAN. VLAN maps are configured to provide access control based on Layer 3 addresses for IPv4. Unsupported protocols are access-controlled through MAC addresses using Ethernet ACEs. After a VLAN map is applied to a VLAN, all packets (routed or bridged) entering the VLAN are checked against the VLAN map. Packets can either enter the VLAN through a switch port or through a routed port after being routed.

ACL Precedence

When VLAN maps, Port ACLs, and router ACLs are configured on the same switch, the filtering precedence, from greatest to least for ingress traffic is port ACL, VLAN map, and then router ACL. For egress traffic, the filtering precedence is router ACL, VLAN map, and then port ACL.

The following examples describe simple use cases:

  • When both an input port ACL and a VLAN map are applied, incoming packets received on ports with a port ACL applied are filtered by the port ACL. Other packets are filtered by the VLAN map

  • When an input router ACL and input port ACL exist in a switch virtual interface (SVI), incoming packets received on ports to which a port ACL is applied are filtered by the port ACL. Incoming routed IP packets received on other ports are filtered by the router ACL. Other packets are not filtered.

  • When an output router ACL and input port ACL exist in an SVI, incoming packets received on the ports to which a port ACL is applied are filtered by the port ACL. Outgoing routed IP packets are filtered by the router ACL. Other packets are not filtered.

  • When a VLAN map, input router ACL, and input port ACL exist in an SVI, incoming packets received on the ports to which a port ACL is applied are only filtered by the port ACL. Incoming routed IP packets received on other ports are filtered by both the VLAN map and the router ACL. Other packets are filtered only by the VLAN map.

  • When a VLAN map, output router ACL, and input port ACL exist in an SVI, incoming packets received on the ports to which a port ACL is applied are only filtered by the port ACL. Outgoing routed IP packets are filtered by both the VLAN map and the router ACL. Other packets are filtered only by the VLAN map.

Port ACLs

Port ACLs are ACLs that are applied to Layer 2 interfaces on a switch. Port ACLs are supported on physical interfaces and on EtherChannel interfaces. Port ACLs can be applied to the interface in inbound direction. The following access lists are supported:

  • Standard IP access lists using source addresses

  • Extended IP access lists using source and destination addresses and optional protocol type information

  • MAC extended access lists using source and destination MAC addresses and optional protocol type information

The switch examines ACLs on an interface and permits or denies packet forwarding based on how the packet matches the entries in the ACL. In this way, ACLs control access to a network or to part of a network.

Figure 1. Using ACLs to Control Traffic in a Network. This is an example of using port ACLs to control access to a network when all workstations are in the same VLAN. ACLs applied at the Layer 2 input would allow Host A to access the Human Resources network, but prevent Host B from accessing the same network. Port ACLs can only be applied to Layer 2 interfaces in the inbound direction. Using ACLs to control traffic to a network.

When you apply a port ACL to a trunk port, the ACL filters traffic on all VLANs present on the trunk port. When you apply a port ACL to a port with voice VLAN, the ACL filters traffic on both data and voice VLANs.

With port ACLs, you can filter IP traffic by using IP access lists and non-IP traffic by using MAC addresses. You can filter both IP and non-IP traffic on the same Layer 2 interface by applying both an IP access list and a MAC access list to the interface.


Note

You cannot apply more than one IP access list and one MAC access list to a Layer 2 interface. If an IP access list or MAC access list is already configured on a Layer 2 interface and you apply a new IP access list or MAC access list to the interface, the new ACL replaces the previously configured one.


Router ACLs

You can apply router ACLs on switch virtual interfaces (SVIs), which are Layer 3 interfaces to VLANs; on physical Layer 3 interfaces; and on Layer 3 EtherChannel interfaces. You apply router ACLs on interfaces for specific directions (inbound or outbound). You can apply one router ACL in each direction on an interface.

The switch supports these access lists for IPv4 traffic:

  • Standard IP access lists use source addresses for matching operations.

  • Extended IP access lists use source and destination addresses and optional protocol type information for matching operations.

As with port ACLs, the switch examines ACLs associated with features configured on a given interface. As packets enter the switch on an interface, ACLs associated with all inbound features configured on that interface are examined. After packets are routed and before they are forwarded to the next hop, all ACLs associated with outbound features configured on the egress interface are examined.

ACLs permit or deny packet forwarding based on how the packet matches the entries in the ACL, and can be used to control access to a network or to part of a network.

VLAN Maps

VLAN ACLs or VLAN maps are used to control the network traffic within a VLAN. You can apply VLAN maps to all packets that are bridged within a VLAN in the switch or switch stack. VACLs are strictly for the security packet filtering and for redirecting traffic to specific physical interfaces. VACLs are not defined by direction (ingress or egress).

All non-IP protocols are access-controlled through MAC addresses and Ethertype using MAC VLAN maps. (IP traffic is not access-controlled by MAC VLAN maps.) You can enforce VLAN maps only on packets going through the switch; you cannot enforce VLAN maps on traffic between hosts on a hub or on another switch that is connected to this switch.

With VLAN maps, forwarding of packets is permitted or denied, based on the action specified in the map.

Figure 2. Using VLAN Maps to Control Traffic. This figure shows how a VLAN map is applied to prevent a specific type of traffic from Host A in VLAN 10 from being forwarded. You can apply only one VLAN map to a VLAN. Using VLAN maps to control traffic.

ACEs and Fragmented and Unfragmented Traffic

IP packets can be fragmented as they cross the network. When this happens, only the fragment containing the beginning of the packet contains the Layer 4 information, such as TCP or UDP port numbers, ICMP type and code, and so on. All other fragments are missing this information.

Some access control entries (ACEs) do not check Layer 4 information and therefore can be applied to all packet fragments. ACEs that do test Layer 4 information cannot be applied in the standard manner to most of the fragments in a fragmented IP packet. When the fragment contains no Layer 4 information and the ACE tests some Layer 4 information, the matching rules are modified:

  • Permit ACEs that check the Layer 3 information in the fragment (including protocol type, such as TCP, UDP, and so on) are considered to match the fragment regardless of what the missing Layer 4 information might have been.


    Note

    For TCP ACEs with L4 Ops, the fragmented packets will be dropped per RFC 1858.


  • Deny ACEs that check Layer 4 information never match a fragment unless the fragment contains Layer 4 information.

Standard and Extended IPv4 ACLs

An ACL is a sequential collection of permit and deny conditions. One by one, the device tests packets against the conditions in an access list. The first match determines whether the device accepts or rejects the packet. Because the device stops testing after the first match, the order of the conditions is critical. If no conditions match, the device denies the packet.

The software supports these types of ACLs or access lists for IPv4:

  • Standard IP access lists use source addresses for matching operations.

  • Extended IP access lists use source and destination addresses for matching operations and optional protocol-type information for finer granularity of control.

IPv4 ACL Switch Unsupported Features

The following ACL-related features are not supported:

  • Non-IP protocol ACLs

  • IP accounting

  • Reflexive ACLs and dynamic ACLs are not supported.

Access List Numbers

The number you use to denote your ACL shows the type of access list that you are creating.

This lists the access-list number and corresponding access list type and shows whether or not they are supported in the switch. The switch supports IPv4 standard and extended access lists, numbers 1 to 199 and 1300 to 2699.

Table 1. Access List Numbers

Access List Number

Type

Supported

1–99

IP standard access list

Yes

100–199

IP extended access list

Yes

200–299

Protocol type-code access list

No

300–399

DECnet access list

No

400–499

XNS standard access list

No

500–599

XNS extended access list

No

600–699

AppleTalk access list

No

700–799

48-bit MAC address access list

No

800–899

IPX standard access list

No

900–999

IPX extended access list

No

1000–1099

IPX SAP access list

No

1100–1199

Extended 48-bit MAC address access list

No

1200–1299

IPX summary address access list

No

1300–1999

IP standard access list (expanded range)

Yes

2000–2699

IP extended access list (expanded range)

Yes

In addition to numbered standard and extended ACLs, you can also create standard and extended named IP ACLs by using the supported numbers. That is, the name of a standard IP ACL can be 1 to 99; the name of an extended IP ACL can be 100 to 199. The advantage of using named ACLs instead of numbered lists is that you can delete individual entries from a named list.

Numbered Standard IPv4 ACLs

When creating an ACL, remember that, by default, the end of the ACL contains an implicit deny statement for all packets that it did not find a match for before reaching the end. With standard access lists, if you omit the mask from an associated IP host address ACL specification, 0.0.0.0 is assumed to be the mask.

The device always rewrites the order of standard access lists so that entries with host matches and entries with matches having a don’t care mask of 0.0.0.0 are moved to the top of the list, above any entries with non-zero don’t care masks. Therefore, in show command output and in the configuration file, the ACEs do not necessarily appear in the order in which they were entered.

After creating a numbered standard IPv4 ACL, you can apply it to VLANs, to terminal lines, or to interfaces.

Numbered Extended IPv4 ACLs

Although standard ACLs use only source addresses for matching, you can use extended ACL source and destination addresses for matching operations and optional protocol type information for finer granularity of control. When you are creating ACEs in numbered extended access lists, remember that after you create the ACL, any additions are placed at the end of the list. You cannot reorder the list or selectively add or remove ACEs from a numbered list.

The device does not support dynamic or reflexive access lists. It also does not support filtering based on the type of service (ToS) minimize-monetary-cost bit.

Some protocols also have specific parameters and keywords that apply to that protocol.

You can define an extended TCP, UDP, ICMP, IGMP, or other IP ACL. The device also supports these IP protocols:


Note

ICMP echo-reply cannot be filtered. All other ICMP codes or types can be filtered.


These IP protocols are supported:

  • Authentication Header Protocol (ahp )

  • Encapsulation Security Payload (esp )

  • Enhanced Interior Gateway Routing Protocol (eigrp )

  • generic routing encapsulation (gre )

  • Internet Control Message Protocol (icmp )

  • Internet Group Management Protocol (igmp )

  • any Interior Protocol (ip )

  • IP in IP tunneling (ipinip )

  • KA9Q NOS-compatible IP over IP tunneling (nos )

  • Open Shortest Path First routing (ospf )

  • Payload Compression Protocol (pcp )

  • Protocol-Independent Multicast (pim )

  • Transmission Control Protocol (tcp )

  • User Datagram Protocol (udp )

Named IPv4 ACLs

You can identify IPv4 ACLs with an alphanumeric string (a name) rather than a number. You can use named ACLs to configure more IPv4 access lists in a device than if you were to use numbered access lists. If you identify your access list with a name rather than a number, the mode and command syntax are slightly different. However, not all commands that use IP access lists accept a named access list.


Note

The name you give to a standard or extended ACL can also be a number in the supported range of access list numbers. That is, the name of a standard IP ACL can be 1 to 99. The advantage of using named ACLs instead of numbered lists is that you can delete individual entries from a named list.


Consider these guidelines before configuring named ACLs:

  • Numbered ACLs are also available.

  • A standard ACL and an extended ACL cannot have the same name.

  • You can use standard or extended ACLs (named or numbered) in VLAN maps.

ACL Logging

The device software can provide logging messages about packets permitted or denied by a standard IP access list. That is, any packet that matches the ACL causes an informational logging message about the packet to be sent to the console. The level of messages logged to the console is controlled by the logging console commands controlling the syslog messages.


Note

ACL logging is only supported for RACL.



Note

Because routing is done in hardware and logging is done in software, if a large number of packets match a permit or deny ACE containing a log keyword, the software might not be able to match the hardware processing rate, and not all packets will be logged.


The first packet that triggers the ACL causes a logging message right away, and subsequent packets are collected over 5-minute intervals before they appear or logged. The logging message includes the access list number, whether the packet was permitted or denied, the source IP address of the packet, and the number of packets from that source permitted or denied in the prior 5-minute interval.


Note

The logging facility might drop some logging message packets if there are too many to be handled or if there is more than one logging message to be handled in 1 second. This behavior prevents the device from crashing due to too many logging packets. Therefore, the logging facility should not be used as a billing tool or an accurate source of the number of matches to an access list.

Hardware and Software Treatment of IP ACLs

ACL processing is performed in hardware. If the hardware reaches its capacity to store ACL configurations, all packets on that interface are dropped.


Note

If an ACL configuration cannot be implemented in hardware due to an out-of-resource condition on a device or stack member, then only the traffic in that VLAN arriving on that device is affected.


For router ACLs, other factors can cause packets to be sent to the CPU:

  • Using the log keyword

  • Generating ICMP unreachable messages

When you enter the show ip access-lists privileged EXEC command, the match count displayed does not account for packets that are access controlled in hardware. Use the show platform software fed switch { switch_num | active | standby } acl counters hardware privileged EXEC command to obtain some basic hardware ACL statistics for switched and routed packets.

Router ACLs function as follows:

  • The hardware controls permit and deny actions of standard and extended ACLs (input and output) for security access control.

  • If log has not been specified, the flows that match a deny statement in a security ACL are dropped by the hardware if ip unreachables is disabled. The flows matching a permit statement are switched in hardware.

  • Adding the log keyword to an ACE in a router ACL causes a copy of the packet to be sent to the CPU for logging only. If the ACE is a permit statement, the packet is still switched and routed in hardware.

VLAN Map Configuration Guidelines

VLAN maps are the only way to control filtering within a VLAN. VLAN maps have no direction. To filter traffic in a specific direction by using a VLAN map, you need to include an ACL with specific source or destination addresses. If there is a match clause for that type of packet (IP or MAC) in the VLAN map, the default action is to drop the packet if the packet does not match any of the entries within the map. If there is no match clause for that type of packet, the default is to forward the packet.

The following are the VLAN map configuration guidelines:

  • If there is no ACL configured to deny traffic on an interface and no VLAN map is configured, all traffic is permitted.

  • Each VLAN map consists of a series of entries. The order of entries in an VLAN map is important. A packet that comes into the device is tested against the first entry in the VLAN map. If it matches, the action specified for that part of the VLAN map is taken. If there is no match, the packet is tested against the next entry in the map.

  • If the VLAN map has at least one match clause for the type of packet (IP or MAC) and the packet does not match any of these match clauses, the default is to drop the packet. If there is no match clause for that type of packet in the VLAN map, the default is to forward the packet.

  • Logging is not supported for VLAN maps.

  • When a device has an IP access list or MAC access list applied to a Layer 2 interface, and you apply a VLAN map to a VLAN that the port belongs to, the port ACL takes precedence over the VLAN map.

  • If a VLAN map configuration cannot be applied in hardware, all packets in that VLAN are dropped.

VLAN Maps with Router ACLs

To access control both bridged and routed traffic, you can use VLAN maps only or a combination of router ACLs and VLAN maps. You can define router ACLs on both input and output routed VLAN interfaces, and you can define a VLAN map to access control the bridged traffic.

If a packet flow matches a VLAN-map deny clause in the ACL, regardless of the router ACL configuration, the packet flow is denied.


Note

When you use router ACLs with VLAN maps, packets that require logging on the router ACLs are not logged if they are denied by a VLAN map.


If the VLAN map has a match clause for the type of packet (IP or MAC) and the packet does not match the type, the default is to drop the packet. If there is no match clause in the VLAN map, and no action specified, the packet is forwarded if it does not match any VLAN map entry.

VLAN Maps and Router ACL Configuration Guidelines

These guidelines are for configurations where you need to have an router ACL and a VLAN map on the same VLAN. These guidelines do not apply to configurations where you are mapping router ACLs and VLAN maps on different VLANs.

If you must configure a router ACL and a VLAN map on the same VLAN, use these guidelines for both router ACL and VLAN map configuration:

  • You can configure only one VLAN map and one router ACL in each direction (input/output) on a VLAN interface.

  • Whenever possible, try to write the ACL with all entries having a single action except for the final, default action of the other type. That is, write the ACL using one of these two forms:

    permit...
permit...
permit...
deny ip any any

    or

    deny...
deny...
deny...
permit ip any any

  • To define multiple actions in an ACL (permit, deny), group each action type together to reduce the number of entries.

  • Avoid including Layer 4 information in an ACL; adding this information complicates the merging process. The best merge results are obtained if the ACLs are filtered based on IP addresses (source and destination) and not on the full flow (source IP address, destination IP address, protocol, and protocol ports). It is also helpful to use don’t care bits in the IP address, whenever possible.

    If you need to specify the full-flow mode and the ACL contains both IP ACEs and TCP/UDP/ICMP ACEs with Layer 4 information, put the Layer 4 ACEs at the end of the list. This gives priority to the filtering of traffic based on IP addresses.

Time Ranges for ACLs

You can selectively apply extended ACLs based on the time of day and the week by using the time-range global configuration command. First, define a time-range name and set the times and the dates or the days of the week in the time range. Then enter the time-range name when applying an ACL to set restrictions to the access list. You can use the time range to define when the permit or deny statements in the ACL are in effect, for example, during a specified time period or on specified days of the week. The time-range keyword and argument are referenced in the named and numbered extended ACL task tables.

These are some benefits of using time ranges:

  • You have more control over permitting or denying a user access to resources, such as an application (identified by an IP address/mask pair and a port number).

  • You can control logging messages. ACL entries can be set to log traffic only at certain times of the day. Therefore, you can simply deny access without needing to analyze many logs generated during peak hours.

Time-based access lists trigger CPU activity because the new configuration of the access list must be merged with other features and the combined configuration loaded into the hardware memory. For this reason, you should be careful not to have several access lists configured to take affect in close succession (within a small number of minutes of each other.)


Note

The time range relies on the device system clock; therefore, you need a reliable clock source. We recommend that you use Network Time Protocol (NTP) to synchronize the device clock.


IPv4 ACL Interface Considerations

When you apply the ip access-group interface configuration command to a Layer 3 interface (an SVI, a Layer 3 EtherChannel, or a routed port), the interface must have been configured with an IP address. Layer 3 access groups filter packets that are routed or are received by Layer 3 processes on the CPU. They do not affect packets bridged within a VLAN.

For inbound ACLs, after receiving a packet, the device checks the packet against the ACL. If the ACL permits the packet, the device continues to process the packet. If the ACL rejects the packet, the device discards the packet.

For outbound ACLs, after receiving and routing a packet to a controlled interface, the device checks the packet against the ACL. If the ACL permits the packet, the device sends the packet. If the ACL rejects the packet, the device discards the packet.

By default, the input interface sends ICMP Unreachable messages whenever a packet is discarded, regardless of whether the packet was discarded because of an ACL on the input interface or because of an ACL on the output interface. ICMP Unreachables are normally limited to no more than one every one-half second per input interface, but this can be changed by using the ip icmp rate-limit unreachable global configuration command.

When you apply an undefined ACL to an interface, the device acts as if the ACL has not been applied to the interface and permits all packets. Remember this behavior if you use undefined ACLs for network security.

How to Configure IPv4 Access Control Lists

Configuring IPv4 ACLs

These are the steps to use IP ACLs on the switch:

Procedure


Step 1

Create an ACL by specifying an access list number or name and the access conditions.

Step 2

Apply the ACL to interfaces or terminal lines. You can also apply standard and extended IP ACLs to VLAN maps.


Creating a Numbered Standard ACL

Follow these steps to create a numbered standard ACL:

Procedure

  Command or Action Purpose
Step 1

enable

Example:


Device> enable


Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal


Enters global configuration mode.

Step 3

access-list access-list-number {deny | permit} source source-wildcard ]

Example:


Device(config)# access-list 2 deny your_host


Defines a standard IPv4 access list by using a source address and wildcard.

The access-list-number is a decimal number from 1 to 99 or 1300 to 1999.

Enter deny or permit to specify whether to deny or permit access if conditions are matched.

The source is the source address of the network or host from which the packet is being sent specified as:

  • The 32-bit quantity in dotted-decimal format.

  • The keyword any as an abbreviation for source and source-wildcard of 0.0.0.0 255.255.255.255. You do not need to enter a source-wildcard.

  • The keyword host as an abbreviation for source and source-wildcard of source 0.0.0.0.

(Optional) The source-wildcard applies wildcard bits to the source.

Note 

Logging is supported only on ACLs attached to Layer 3 interfaces.

Step 4

end

Example:


Device(config)# end


Exits global configuration mode and returns to privileged EXEC mode.

Creating a Numbered Extended ACL

Follow these steps to create a numbered extended ACL:

Procedure

  Command or Action Purpose
Step 1

enable

Example:


Device> enable


Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal


Enters global configuration mode.

Step 3

access-list access-list-number 
{deny | permit} protocol source source-wildcard destination destination-wildcard [precedence precedence] [tos tos] [fragments] [time-range time-range-name] [dscp dscp]

Example:


Device(config)# access-list 101 permit ip host 10.1.1.2 any precedence 0 tos 0 log


Defines an extended IPv4 access list and the access conditions.

The access-list-number is a decimal number from 100 to 199 or 2000 to 2699.

Enter deny or permit to specify whether to deny or permit the packet if conditions are matched.

Source, source-wildcard, destination, and destination-wildcard can be specified as:

  • The 32-bit quantity in dotted-decimal format.

  • The keyword any for 0.0.0.0 255.255.255.255 (any host).

  • The keyword host for a single host 0.0.0.0.

The other keywords are optional and have these meanings:

  • precedence —Enter to match packets with a precedence level specified as a number from 0 to 7 or by name: routine (0), priority (1), immediate (2), flash (3), flash-override (4), critical (5), internet (6), network (7).

  • fragments —Enter to check non-initial fragments.

  • tos —Enter to match by type of service level, specified by a number from 0 to 15 or a name: normal (0), max-reliability (2), max-throughput (4), min-delay (8).

  • time-range —Specify the time-range name.

  • dscp —Enter to match packets with the DSCP value specified by a number from 0 to 63, or use the question mark (?) to see a list of available values.

Note 

If you enter a dscp value, you cannot enter tos or precedence . You can enter both a tos and a precedence value with no dscp .

Step 4

access-list access-list-number {deny | permit} tcp source source-wildcard [operator port] destination destination-wildcard [operator port] [established] [precedence precedence] [tos tos] [fragments] [time-range time-range-name] [dscp dscp] [flag]

Example:


Device(config)# access-list 101 permit tcp any any eq 500


Defines an extended TCP access list and the access conditions.

The parameters are the same as those described for an extended IPv4 ACL, with these exceptions:

(Optional) Enter an operator and port to compare source (if positioned after source source-wildcard ) or destination (if positioned after destination destination-wildcard ) port. Possible operators include eq (equal), gt (greater than), lt (less than), neq (not equal), and range (inclusive range). Operators require a port number (range requires two port numbers separated by a space).

Enter the port number as a decimal number (from 0 to 65535) or the name of a TCP port. Use only TCP port numbers or names when filtering TCP.

The other optional keywords have these meanings:

  • established —Enter to match an established connection. This has the same function as matching on the ack or rst flag.

  • flag —Enter one of these flags to match by the specified TCP header bits: ack (acknowledge), fin (finish), psh (push), rst (reset), syn (synchronize), or urg (urgent).

Step 5

access-list access-list-number 
{deny | permit} udp source source-wildcard [operator port] destination destination-wildcard [operator port] [precedence precedence] [tos tos] [fragments] [time-range time-range-name] [dscp dscp]

Example:


Device(config)# access-list 101 permit udp any any eq 100


(Optional) Defines an extended UDP access list and the access conditions.

The UDP parameters are the same as those described for TCP except that the [operator [port]] port number or name must be a UDP port number or name, and the flag and established keywords are not valid for UDP.

Step 6

access-list access-list-number 
{deny | permit} icmp source source-wildcard destination destination-wildcard [icmp-type | [[icmp-type icmp-code] | [icmp-message]] [precedence precedence] [tos tos] [fragments] [time-range time-range-name] [dscp dscp]

Example:


Device(config)# access-list 101 permit icmp any any 200


Defines an extended ICMP access list and the access conditions.

The ICMP parameters are the same as those described for most IP protocols in an extended IPv4 ACL, with the addition of the ICMP message type and code parameters. These optional keywords have these meanings:

  • icmp-type—Enter to filter by ICMP message type, a number from 0 to 255.

  • icmp-code—Enter to filter ICMP packets that are filtered by the ICMP message code type, a number from 0 to 255.

  • icmp-message—Enter to filter ICMP packets by the ICMP message type name or the ICMP message type and code name.

Step 7

access-list access-list-number 
{deny | permit} igmp source source-wildcard destination destination-wildcard [igmp-type] [precedence precedence] [tos tos] [fragments] [time-range time-range-name] [dscp dscp]

Example:


Device(config)# access-list 101 permit igmp any any 14


(Optional) Defines an extended IGMP access list and the access conditions.

The IGMP parameters are the same as those described for most IP protocols in an extended IPv4 ACL, with this optional parameter.

igmp-type—To match IGMP message type, enter a number from 0 to 15, or enter the message name: dvmrp , host-query , host-report , pim , or trace .

Step 8

end

Example:


Device(config)# end


Exits global configuration mode and returns to privileged EXEC mode.

Creating Named Standard ACLs

Follow these steps to create a standard ACL using names:

Procedure

  Command or Action Purpose
Step 1

enable

Example:


Device> enable


Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal


Enters global configuration mode.

Step 3

ip access-list standard name

Example:


Device(config)# ip access-list standard 20


Defines a standard IPv4 access list using a name, and enter access-list configuration mode.

The name can be a number from 1 to 99.

Step 4

Use one of the following:

  • deny {source [source-wildcard] | host source | any} [log]
  • permit {source [source-wildcard] | host source | any} [log]

Example:


Device(config-std-nacl)# deny 192.168.0.0 0.0.255.255 255.255.0.0 0.0.255.255


or


Device(config-std-nacl)# permit 10.108.0.0 0.0.0.0 255.255.255.0 0.0.0.0


In access-list configuration mode, specify one or more conditions denied or permitted to decide if the packet is forwarded or dropped.

  • host source —A source and source wildcard of source 0.0.0.0.

  • any —A source and source wildcard of 0.0.0.0 255.255.255.255.

Step 5

end

Example:


Device(config-std-nacl)# end


Exits access-list configuration mode and returns to privileged EXEC mode.

Creating Extended Named ACLs

Follow these steps to create an extended ACL using names:

Procedure

  Command or Action Purpose
Step 1

enable

Example:


Device> enable


Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal


Enters global configuration mode.

Step 3

ip access-list extended name

Example:


Device(config)# ip access-list extended 150


Defines an extended IPv4 access list using a name, and enter access-list configuration mode.

The name can be a number from 100 to 199.

Step 4

{deny | permit} protocol {source [source-wildcard] | host source | any} {destination [destination-wildcard] | host destination | any} [precedence precedence] [tos tos] [established] [log] [time-range time-range-name]

Example:


Device(config-ext-nacl)# permit 0 any any


In access-list configuration mode, specify the conditions allowed or denied. Use the log keyword to get access list logging messages, including violations.

  • host source —A source and source wildcard of source 0.0.0.0.

  • host destintation —A destination and destination wildcard of destination 0.0.0.0.

  • any—A source and source wildcard or destination and destination wildcard of 0.0.0.0 255.255.255.255.

Step 5

end

Example:


Device(config-ext-nacl)# end


Exits access-list configuration mode and returns to privileged EXEC mode.

When you are creating extended ACLs, remember that, by default, the end of the ACL contains an implicit deny statement for everything if it did not find a match before reaching the end. For standard ACLs, if you omit the mask from an associated IP host address access list specification, 0.0.0.0 is assumed to be the mask.

After you create an ACL, any additions are placed at the end of the list. You cannot selectively add ACL entries to a specific ACL. However, you can use no permit and no deny access-list configuration mode commands to remove entries from a named ACL.

Being able to selectively remove lines from a named ACL is one reason you might use named ACLs instead of numbered ACLs.

What to do next

After creating a named ACL, you can apply it to interfaces or to VLANs .

Configuring Time Ranges for ACLs

Follow these steps to configure a time-range parameter for an ACL:

Procedure

  Command or Action Purpose
Step 1

enable

Example:


Device> enable


Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal


Enters global configuration mode.

Step 3

time-range time-range-name

Example:


Device(config)# time-range workhours


Assigns a meaningful name (for example, workhours) to the time range to be created, and enters time-range configuration mode. The name cannot contain a space or quotation mark and must begin with a letter.

Step 4

Use one of the following:

  • absolute [start time date] 
[end time date]
  • periodic day-of-the-week hh:mm to [day-of-the-week] hh:mm
  • periodic {weekdays | weekend | daily} hh:mm to hh:mm

Example:


Device(config-time-range)# absolute start 00:00 1 Jan 2006 end 23:59 1 Jan 2006


or


Device(config-time-range)# periodic weekdays 8:00 to 12:00


Specifies when the function it will be applied to is operational.

  • You can use only one absolute statement in the time range. If you configure more than one absolute statement, only the one configured last is executed.

  • You can enter multiple periodic statements. For example, you could configure different hours for weekdays and weekends.

Step 5

end

Example:


Device(config-time-range)# end


Exits time-range configuration mode and returns to privileged EXEC mode.

What to do next

Repeat the steps if you have multiple items that you want in effect at different times.

Applying an IPv4 ACL to a Terminal Line

You can use numbered ACLs to control access to one or more terminal lines. You cannot apply named ACLs to lines. You must set identical restrictions on all the virtual terminal lines because a user can attempt to connect to any of them.

Follow these steps to restrict incoming and outgoing connections between a virtual terminal line and the addresses in an ACL:

Procedure

  Command or Action Purpose
Step 1

enable

Example:


Device> enable


Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal


Enters global configuration mode.

Step 3

line [console | vty] line-number

Example:


Device(config)# line console 0


Identifies a specific line to configure, and enter in-line configuration mode.

  • console—Specifies the console terminal line. The console port is DCE.

  • vty—Specifies a virtual terminal for remote console access.

The line-number is the first line number in a contiguous group that you want to configure when the line type is specified. The range is from 0 to 16.

Step 4

access-class access-list-number {in | out}

Example:


Device(config-line)# access-class 10 in


Restricts incoming and outgoing connections between a particular virtual terminal line (into a device) and the addresses in an access list.

Step 5

end

Example:


Device(config-line)# end


Exits line configuration mode and returns to privileged EXEC mode.

Applying an IPv4 ACL to an Interface

This section describes how to apply IPv4 ACLs to network interfaces.

Beginning in privileged EXEC mode, follow these steps to control access to an interface:

Procedure

  Command or Action Purpose
Step 1

enable

Example:


Device> enable


Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal


Enters global configuration mode.

Step 3

interface interface-id

Example:


Device(config)# interface gigabitethernet1/0/1


Identifies a specific interface for configuration, and enters interface configuration mode.

The interface can be a Layer 2 interface (port ACL), or a Layer 3 interface (router ACL).

Step 4

ip access-group {access-list-number | name} {in | out}

Example:


Device(config-if)# ip access-group 2 in


Controls access to the specified interface.

Step 5

end

Example:


Device(config-if)# end


Exits interface configuration mode and returns to privileged EXEC mode.

Creating Named MAC Extended ACLs

You can filter non-IPv4 traffic on a VLAN or on a Layer 2 interface by using MAC addresses and named MAC extended ACLs. The procedure is similar to that of configuring other extended named ACLs.

Follow these steps to create a named MAC extended ACL:

Procedure

  Command or Action Purpose
Step 1

enable

Example:


Device> enable


Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal


Enters global configuration mode.

Step 3

mac access-list extended name

Example:


Device(config)# mac access-list extended mac1


Defines an extended MAC access list using a name.

Step 4

{deny | permit} {any | host source MAC address | source MAC address mask} {any | host destination MAC address | destination MAC address mask} [type mask | lsap lsap mask | aarp | amber | dec-spanning | decnet-iv | diagnostic | dsm | etype-6000 | etype-8042 | lat | lavc-sca | mop-console | mop-dump | msdos | mumps | netbios | vines-echo | vines-ip | xns-idp | 0-65535] [cos cos]

Example:


Device(config-ext-macl)# deny any any decnet-iv


or


Device(config-ext-macl)# permit any any


In extended MAC access-list configuration mode, specifies to permit or deny any source MAC address, a source MAC address with a mask, or a specific host source MAC address and any destination MAC address, destination MAC address with a mask, or a specific destination MAC address.

(Optional) You can also enter these options:

  • type mask —An arbitrary EtherType number of a packet with Ethernet II or SNAP encapsulation in decimal, hexadecimal, or octal with optional mask of don’t care bits applied to the EtherType before testing for a match.

  • lsap lsap mask —An LSAP number of a packet with IEEE 802.2 encapsulation in decimal, hexadecimal, or octal with optional mask of don’t care bits.

  • aarp | amber | dec-spanning | decnet-iv | diagnostic | dsm | etype-6000 | etype-8042 | lat | lavc-sca | mop-console | mop-dump | msdos | mumps | netbios | vines-echo | vines-ip | xns-idp —A non-IP protocol.

  • cos cos —An IEEE 802.1Q cost of service number from 0 to 7 used to set priority.

Step 5

end

Example:


Device(config-ext-macl)# end


Exits extended MAC access-list configuration mode and returns to privileged EXEC mode.

Applying a MAC ACL to a Layer 2 Interface

Follow these steps to apply a MAC access list to control access to a Layer 2 interface:

Procedure

  Command or Action Purpose
Step 1

enable

Example:


Device> enable


Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal


Enters global configuration mode.

Step 3

interface interface-id

Example:


Device(config)# interface gigabitethernet1/0/2


Identifies a specific interface, and enters interface configuration mode. The interface must be a physical Layer 2 interface (port ACL).

Step 4

mac access-group {name} {in | out }

Example:


Device(config-if)# mac access-group mac1 in


Controls access to the specified interface by using the MAC access list.

Port ACLs are supported in the outbound and inbound directions .

Step 5

end

Example:


Device(config-if)# end


Exits interface configuration mode and returns to privileged EXEC mode.

Step 6

show mac access-group [interface interface-id]

Example:


Device# show mac access-group interface gigabitethernet1/0/2


Displays the MAC access list applied to the interface or all Layer 2 interfaces.

After receiving a packet, the device checks it against the inbound ACL. If the ACL permits it, the device continues to process the packet. If the ACL rejects the packet, the device discards it. When you apply an undefined ACL to an interface, the device acts as if the ACL has not been applied and permits all packets. Remember this behavior if you use undefined ACLs for network security.

Configuring VLAN Maps

To create a VLAN map and apply it to one or more VLANs, perform these steps:

Before you begin

Create the standard or extended IPv4 ACLs or named MAC extended ACLs that you want to apply to the VLAN.

Procedure

  Command or Action Purpose
Step 1

enable

Example:


Device> enable


Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal


Enters global configuration mode.

Step 3

vlan access-map name [number]

Example:


Device(config)# vlan access-map map1 20


Creates a VLAN map, and give it a name and (optionally) a number. The number is the sequence number of the entry within the map.

When you create VLAN maps with the same name, numbers are assigned sequentially in increments of 10. When modifying or deleting maps, you can enter the number of the map entry that you want to modify or delete.

VLAN maps do not use the specific permit or deny keywords. To deny a packet by using VLAN maps, create an ACL that would match the packet, and set the action to drop. A permit in the ACL counts as a match. A deny in the ACL means no match.

Entering this command changes to access-map configuration mode.

Step 4

match {ip | mac} address {name | number} [name | number]

Example:


Device(config-access-map)# match ip address ip2


Match the packet (using either the IP or MAC address) against one or more standard or extended access lists. Note that packets are only matched against access lists of the correct protocol type. IP packets are matched against standard or extended IP access lists. Non-IP packets are only matched against named MAC extended access lists.

Note 

If the VLAN map is configured with a match clause for a type of packet (IP or MAC) and the map action is drop, all packets that match the type are dropped. If the VLAN map has no match clause, and the configured action is drop, all IP and Layer 2 packets are dropped.

Step 5

Enter one of the following commands to specify an IP packet or a non-IP packet (with only a known MAC address) and to match the packet against one or more ACLs (standard or extended):

  • action { forward}
    
    Device(config-access-map)# action forward
    
    
    
  • action { drop}
    
    Device(config-access-map)# action drop
    
    
    

Sets the action for the map entry.

Step 6

exit

Example:


Device(config-access-map)# exit


Exits access-map configuration mode. and returns to global configuration mode.

Step 7

vlan filter mapname vlan-list list

Example:


Device(config)# vlan filter map1 vlan-list 20-22


Applies the VLAN map to one or more VLAN IDs.

The list can be a single VLAN ID (22), a consecutive list (10-22), or a string of VLAN IDs (12, 22, 30). Spaces around the comma and hyphen are optional.

Step 8

end

Example:


Device(config)# end


Exits global configuration mode and returns to privileged EXEC mode.

Applying a VLAN Map to a VLAN

To apply a VLAN map to one or more VLANs, perform these steps.

Procedure

  Command or Action Purpose
Step 1

enable

Example:

Device> enable

Enables privileged EXEC mode.

Enter your password, if prompted.

Step 2

configure terminal

Example:

Device# configure terminal

Enters global configuration mode.

Step 3

vlan filter mapname vlan-list list

Example:


Device(config)# vlan filter map 1 vlan-list 20-22


Applies the VLAN map to one or more VLAN IDs.

The list can be a single VLAN ID (22), a consecutive list (10-22), or a string of VLAN IDs (12, 22, 30). Spaces around the comma and hyphen are optional.

Step 4

end

Example:

Device(config)# end

Exits global configuration mode and returns to privileged EXEC mode.

Monitoring IPv4 ACLs

You can monitor IPv4 ACLs by displaying the ACLs that are configured on the device, and displaying the ACLs that have been applied to interfaces and VLANs.

When you use the ip access-group interface configuration command to apply ACLs to a Layer 2 or 3 interface, you can display the access groups on the interface. You can also display the MAC ACLs applied to a Layer 2 interface. You can use the privileged EXEC commands as described in this table to display this information.

Table 2. Commands for Displaying Access Lists and Access Groups
Command Purpose

show access-lists [number | name]

Displays the contents of one or all current IP and MAC address access lists or a specific access list (numbered or named).

show ip access-lists [number | name]

Displays the contents of all current IP access lists or a specific IP access list (numbered or named).

show ip interface interface-id

Displays detailed configuration and status of an interface. If IP is enabled on the interface and ACLs have been applied by using the ip access-group interface configuration command, the access groups are included in the display.

show running-config [interface interface-id]

Displays the contents of the configuration file for the device or the specified interface, including all configured MAC and IP access lists and which access groups are applied to an interface.

show mac access-group [interface interface-id]

Displays MAC access lists applied to all Layer 2 interfaces or the specified

Layer 2 interface.

Configuration Examples for IPv4 Access Control Lists

ACLs in a Small Networked Office

Figure 3. Using Router ACLs to Control Traffic. This shows a small networked office environment with routed Port 2 connected to Server A, containing benefits and other information that all employees can access, and routed Port 1 connected to Server B, containing confidential payroll data. All users can access Server A, but Server B has restricted access.Using Router ACLs to Control Traffic

Use router ACLs to do this in one of two ways:

  • Create a standard ACL, and filter traffic coming to the server from Port 1.

  • Create an extended ACL, and filter traffic coming from the server into Port 1.

Examples: ACLs in a Small Networked Office

This example uses a standard ACL to filter traffic coming into Server B from a port, permitting traffic only from Accounting’s source addresses 172.20.128.64 to 172.20.128.95. The ACL is applied to traffic coming out of routed Port 1 from the specified source address.


Device> enable
Device# configure terminal
Device(config)# access-list 6 permit 172.20.128.64 0.0.0.31
Device(config)# exit
Device# show access-lists

Standard IP access list 6
    10 permit 172.20.128.64, wildcard bits 0.0.0.31

Device# configure terminal
Device(config)# interface gigabitethernet1/0/1
Device(config-if)# ip access-group 6 out
Device(config-if)# end


This example uses an extended ACL to filter traffic coming from Server B into a port, permitting traffic from any source address (in this case Server B) to only the Accounting destination addresses 172.20.128.64 to 172.20.128.95. The ACL is appliDeviceed to traffic going into routed Port 1, permitting it to go only to the specified destination addresses. Note that with extended ACLs, you must enter the protocol (IP) before the source and destination information.


Device(config)# access-list 106 permit ip any 172.20.128.64 0.0.0.31
Device(config)# exit
Device# show access-lists

Extended IP access list 106
    10 permit ip any 172.20.128.64 0.0.0.31


Device# configure terminal
Device(config)# interface gigabitethernet1/0/1
Device(config-if)# ip access-group 106 in
Device(config-if)# end

Example: Numbered ACLs

In this example, network 10.0.0.0 is a Class A network whose second octet specifies a subnet; that is, its subnet mask is 255.255.0.0. The third and fourth octets of a network 10.0.0.0 address specify a particular host. Using access list 2, the switch accepts one address on subnet 48 and reject all others on that subnet. The last line of the list shows that the switch accepts addresses on all other network 10.0.0.0 subnets. The ACL is applied to packets entering a port.


Device> enable
Device# configure terminal
Device(config)# access-list 2 permit 10.48.0.3
Device(config)# access-list 2 deny 10.48.0.0 0.0.255.255
Device(config)# access-list 2 permit 10.0.0.0 0.255.255.255 
Device(config)# interface gigabitethernet2/0/1
Device(config-if)# ip access-group 2 in
Device(config-if)# end


Examples: Extended ACLs

In this example, the first line permits any incoming TCP connections with destination ports greater than 1023. The second line permits incoming TCP connections to the Simple Mail Transfer Protocol (SMTP) port of host 172.16.0.0. The third line permits incoming ICMP messages for error feedback.

Device> enable
Device# configure terminal
Device(config)# access-list 102 permit tcp any 172.16.0.0 0.0.255.255 gt 1023
Device(config)# access-list 102 permit tcp any host 172.16.1.2 eq 25
Device(config)# access-list 102 permit icmp any any
Device(config)# interface gigabitethernet 2/0/1
Device(config-if)# ip access-group 102 in
Device(config-if)# end

In this example, suppose that you have a network connected to the Internet, and you want any host on the network to be able to form TCP connections to any host on the Internet. However, you do not want IP hosts to be able to form TCP connections to hosts on your network, except to the mail (SMTP) port of a dedicated mail host.

SMTP uses TCP port 25 on one end of the connection and a random port number on the other end. The same port numbers are used throughout the life of the connection. Mail packets coming in from the Internet have a destination port of 25. Because the secure system of the network always accepts mail connections on port 25, the incoming sevices are separately controlled.

Device> enable
Device# configure terminal
Device(config)# access-list 102 permit tcp any 172.16.0.0 0.0.255.255 eq 23
Device(config)# access-list 102 permit tcp any 172.16.0.0 0.0.255.255 eq 25
Device(config)# interface gigabitethernet 1/0/1
Device(config-if)# ip access-group 102 in
Device(config-if)# end

In this example, the network is a Class B network with the address 172.16.0.0, and the mail host address is 172.16.1.2. The established keyword is used only for the TCP to show an established connection. A match occurs if the TCP datagram has the ACK or RST bits set, which show that the packet belongs to an existing connection. Gigabit Ethernet interface 1 is the interface that connects the device to the Internet.

Device> enable
Device# configure terminal
Device(config)# access-list 102 permit tcp any 172.16.0.0 0.0.255.255 established
Device(config)# access-list 102 permit tcp any host 172.16.1.2 eq 25
Device(config)# interface gigabitethernet 1/0/1
Device(config-if)# ip access-group 102 in
Device(config-if)# end

Examples: Named ACLs

Creating named standard and extended ACLs

This example creates a standard ACL named internet_filter and an extended ACL named marketing_group. The internet_filter ACL allows all traffic from the source address 10.2.3.4.

Device> enable
Device# configure terminal
Device(config)# ip access-list standard Internet_filter
Device(config-ext-nacl)# permit 10.2.3.4
Device(config-ext-nacl)# exit
Device(config-ext-nacl)# end

The marketing_group ACL allows any TCP Telnet traffic to the destination address and wildcard 172.16.0.0 0.0.255.255 and denies any other TCP traffic. It permits ICMP traffic, denies UDP traffic from any source to the destination address range 172.16.0.0 through 172.16.255.255 with a destination port less than 1024, denies any other IP traffic, and provides a log of the result.

Device> enable
Device# configure terminal
Device(config)# ip access-list extended marketing_group
Device(config-ext-nacl)# permit tcp any 172.16.0.0 0.0.255.255 eq telnet
Device(config-ext-nacl)# deny tcp any any
Device(config-ext-nacl)# permit icmp any any
Device(config-ext-nacl)# deny udp any 172.16.0.0 0.0.255.255 lt 1024
Device(config-ext-nacl)# deny ip any any log
Device(config-ext-nacl)# end


The Internet_filter ACL is applied to outgoing traffic and the marketing_group ACL is applied to incoming traffic on a Layer 3 port.

Device> enable
Device# configure terminal
Device(config)# interface gigabitethernet3/0/2
Device(config-if)# no switchport
Device(config-if)# ip address 10.0.5.1 255.255.255.0
Device(config-if)# ip access-group Internet_filter out
Device(config-if)# ip access-group marketing_group in
Device(config-if)# end

Deleting Individual ACEs from Named ACLs

This example shows how to delete individual ACEs from the named access list border-list:

Device> enable
Device# configure terminal
Device(config)# ip access-list extended border-list
Device(config-ext-nacl)# no permit ip host 10.1.1.3 any
Device(config-ext-nacl)# end

Examples: ACL Logging

Two variations of logging are supported on router ACLs. The log keyword sends an informational logging message to the console about the packet that matches the entry; the log-input keyword includes the input interface in the log entry.

In this example, standard named access list stan1 denies traffic from 10.1.1.0 0.0.0.255, allows traffic from all other sources, and includes the log keyword.


Device> enable
Device# configure terminal
Device(config)# ip access-list standard stan1
Device(config-std-nacl)# deny 10.1.1.0 0.0.0.255 log
Device(config-std-nacl)# permit any log
Device(config-std-nacl)# exit
Device(config)# interface gigabitethernet1/0/1
Device(config-if)# ip access-group stan1 in
Device(config-if)# end
Device# show logging

Syslog logging: enabled (0 messages dropped, 0 flushes, 0 overruns)
    Console logging: level debugging, 37 messages logged
    Monitor logging: level debugging, 0 messages logged
    Buffer logging: level debugging, 37 messages logged
    File logging: disabled
    Trap logging: level debugging, 39 message lines logged

Log Buffer (4096 bytes):

00:00:48: NTP: authentication delay calculation problems

<output truncated>

00:09:34:%SEC-6-IPACCESSLOGS:list stan1 permitted 0.0.0.0 1 packet
00:09:59:%SEC-6-IPACCESSLOGS:list stan1 denied 10.1.1.15 1 packet
00:10:11:%SEC-6-IPACCESSLOGS:list stan1 permitted 0.0.0.0 1 packet


This example is a named extended access list ext1 that permits ICMP packets from any source to 10.1.1.0 0.0.0.255 and denies all UDP packets.


Device> enable
Device# configure terminal
Device(config)# ip access-list extended ext1
Device(config-ext-nacl)# permit icmp any 10.1.1.0 0.0.0.255 log
Device(config-ext-nacl)# deny udp any any log
Device(config-std-nacl)# exit
Device(config)# interface gigabitethernet1/0/2
Device(config-if)# ip access-group ext1 in
Device(config)# end

This is a an example of a log for an extended ACL:


01:24:23:%SEC-6-IPACCESSLOGDP:list ext1 permitted icmp 10.1.1.15 -> 10.1.1.61 (0/0), 1 packet
01:25:14:%SEC-6-IPACCESSLOGDP:list ext1 permitted icmp 10.1.1.15 -> 10.1.1.61 (0/0), 7 packets
01:26:12:%SEC-6-IPACCESSLOGP:list ext1 denied udp 0.0.0.0(0) -> 255.255.255.255(0), 1 packet
01:31:33:%SEC-6-IPACCESSLOGP:list ext1 denied udp 0.0.0.0(0) -> 255.255.255.255(0), 8 packets


Note that all logging entries for IP ACLs start with %SEC-6-IPACCESSLOG with minor variations in format depending on the kind of ACL and the access entry that has been matched.

This is an example of an output message when the log-input keyword is entered:


00:04:21:%SEC-6-IPACCESSLOGDP:list inputlog permitted icmp 10.1.1.10 (Vlan1 0001.42ef.a400) -> 
10.1.1.61 (0/0), 1 packet


A log message for the same sort of packet using the log keyword does not include the input interface information:


00:05:47:%SEC-6-IPACCESSLOGDP:list inputlog permitted icmp 10.1.1.10 -> 10.1.1.61 (0/0), 1 packet


Example: ACEs and Fragmented and Unfragmented Traffic

Consider access list 102, configured with these commands, applied to three fragmented packets:

Device> enable
Device# configure terminal
Device(config)# access-list 102 permit tcp any host 10.1.1.1 eq smtp
Device(config)# access-list 102 deny tcp any host 10.1.1.2 eq telnet
Device(config)# access-list 102 permit tcp any host 10.1.1.2
Device(config)# access-list 102 deny tcp any any
Device(config)# end



Note

In the first and second ACEs in the examples, the eq keyword after the destination address means to test for the TCP-destination-port well-known numbers equaling Simple Mail Transfer Protocol (SMTP) and Telnet, respectively.


  • Packet A is a TCP packet from host 10.2.2.2., port 65000, going to host 10.1.1.1 on the SMTP port. If this packet is fragmented, the first fragment matches the first ACE (a permit) as if it were a complete packet because all Layer 4 information is present. The remaining fragments also match the first ACE, even though they do not contain the SMTP port information, because the first ACE only checks Layer 3 information when applied to fragments. The information in this example is that the packet is TCP and that the destination is 10.1.1.1.

  • Packet B is from host 10.2.2.2, port 65001, going to host 10.1.1.2 on the Telnet port. If this packet is fragmented, the first fragment matches the second ACE (a deny) because all Layer 3 and Layer 4 information is present. The remaining fragments in the packet do not match the second ACE because they are missing Layer 4 information. Instead, they match the third ACE (a permit).

    Because the first fragment was denied, host 10.1.1.2 cannot reassemble a complete packet, so packet B is effectively denied. However, the later fragments that are permitted will consume bandwidth on the network and resources of host 10.1.1.2 as it tries to reassemble the packet.

  • Fragmented packet C is from host 10.2.2.2, port 65001, going to host 10.1.1.3, port ftp. If this packet is fragmented, the first fragment matches the fourth ACE (a deny). All other fragments also match the fourth ACE because that ACE does not check any Layer 4 information and because Layer 3 information in all fragments shows that they are being sent to host 10.1.1.3, and the earlier permit ACEs were checking different hosts.

Examples: Using Time Ranges with ACLs

This example shows how to verify after you configure time ranges for workhours and to configure January 1, 2006, as a company holiday.


Device# show time-range

time-range entry: new_year_day_2003 (inactive)
   absolute start 00:00 01 January 2006 end 23:59 01 January 2006
time-range entry: workhours (inactive)
   periodic weekdays 8:00 to 12:00
   periodic weekdays 13:00 to 17:00


To apply a time range, enter the time-range name in an extended ACL that can implement time ranges. This example shows how to create and verify extended access list 188 that denies TCP traffic from any source to any destination during the defined holiday times and permits all TCP traffic during work hours.


Device> enable
Device# configure terminal
Device(config)# access-list 188 deny tcp any any time-range new_year_day_2006
Device(config)# access-list 188 permit tcp any any time-range workhours
Device(config)# exit
Device# show access-lists

Extended IP access list 188
   10 deny tcp any any time-range new_year_day_2006 (inactive)
   20 permit tcp any any time-range workhours (inactive)


This example uses named ACLs to permit and deny the same traffic.

Device> enable
Device# configure terminal
Device(config)# ip access-list extended deny_access
Device(config-ext-nacl)# deny tcp any any time-range new_year_day_2006
Device(config-ext-nacl)# exit
Device(config)# ip access-list extended may_access
Device(config-ext-nacl)# permit tcp any any time-range workhours
Device(config-ext-nacl)# end
Device# show ip access-lists

Extended IP access list lpip_default
    10 permit ip any any
Extended IP access list deny_access
    10 deny tcp any any time-range new_year_day_2006 (inactive)
Extended IP access list may_access
    10 permit tcp any any time-range workhours (inactive)


Examples: Time Range Applied to an IP ACL

This example denies HTTP traffic on IP on Monday through Friday between the hours of 8:00 a.m. and 6:00 p.m (18:00). The example allows UDP traffic only on Saturday and Sunday from noon to 8:00 p.m. (20:00).


Device> enable
Device# configure terminal
Device(config)# time-range no-http
Device(config)# periodic weekdays 8:00 to 18:00
Device(config)# time-range udp-yes
Device(config)# periodic weekend 12:00 to 20:00
Device(config)# ip access-list extended strict
Device(config-ext-nacl)# deny tcp any any eq www time-range no-http
Device(config-ext-nacl)# permit udp any any time-range udp-yes
Device(config-ext-nacl)# exit
Device(config)# interface gigabitethernet2/0/1
Device(config-if)# ip access-group strict in
Device(config-if)# end


Examples: Including Comments in ACLs

You can use the remark keyword to include comments (remarks) about entries in any IP standard or extended ACL. The remarks make the ACL easier for you to understand and scan. Each remark line is limited to 100 characters.

The remark can go before or after a permit or deny statement. You should be consistent about where you put the remark so that it is clear which remark describes which permit or deny statement. For example, it would be confusing to have some remarks before the associated permit or deny statements and some remarks after the associated statements.

To include a comment for IP numbered standard or extended ACLs, use the access-list access-list number remark remark global configuration command. To remove the remark, use the no form of this command.

In this example, the workstation that belongs to user1 is allowed access, and the workstation that belongs to user2 is not allowed access:


Device> enable
Device# configure terminal
Device(config)# access-list 1 remark Permit only user1 workstation through
Device(config)# access-list 1 permit 171.69.2.88
Device(config)# access-list 1 remark Do not allow user2 through
Device(config)# access-list 1 deny 171.69.3.13
Device(config)# end

For an entry in a named IP ACL, use the remark access-list configuration command. To remove the remark, use the no form of this command.

In this example, the subnet1 subnet is not allowed to use outbound Telnet:

Device> enable
Device# configure terminal
Device(config)# ip access-list extended telnetting
Device(config-ext-nacl)# remark Do not allow subnet1 subnet to telnet out
Device(config-ext-nacl)# deny tcp host 171.69.2.88 any eq telnet
Device(config-ext-nacl)# end

Example: Creating an ACL and a VLAN Map to Deny a Packet

This example shows how to create an ACL and a VLAN map to deny a packet. In the first map, any packets that match the ip1 ACL (TCP packets) would be dropped. You first create the ip1 ACL to permit any TCP packet and no other packets. Because there is a match clause for IP packets in the VLAN map, the default action is to drop any IP packet that does not match any of the match clauses.


Device> enable
Device# configure terminal
Device(config)# ip access-list extended ip1
Device(config-ext-nacl)# permit tcp any any
Device(config-ext-nacl)# exit
Device(config)# vlan access-map map_1 10
Device(config-access-map)# match ip address ip1
Device(config-access-map)# action drop
Device(config-access-map)# end


Example: Creating an ACL and a VLAN Map to Permit a Packet

This example shows how to create a VLAN map to permit a packet. ACL ip2 permits UDP packets and any packets that match the ip2 ACL are forwarded. In this map, any IP packets that did not match any of the previous ACLs (that is, packets that are not TCP packets or UDP packets) would get dropped.


Device> enable
Device# configure terminal
Device(config)# ip access-list extended ip2
Device(config-ext-nacl)# permit udp any any
Device(config-ext-nacl)# exit
Device(config)# vlan access-map map_1 20
Device(config-access-map)# match ip address ip2
Device(config-access-map)# action forward
Device(config-access-map)# exit

Example: Default Action of Dropping IP Packets and Forwarding MAC Packets

In this example, the VLAN map has a default action of drop for IP packets and a default action of forward for MAC packets. Used with standard ACL 101 and extended named access lists igmp-match and tcp-match , the map will have the following results:

  • Forward all UDP packets

  • Drop all IGMP packets

  • Forward all TCP packets

  • Drop all other IP packets

  • Forward all non-IP packets


Device> enable
Device# configure terminal
Device(config)# access-list 101 permit udp any any
Device(config)# ip access-list extended igmp-match
Device(config-ext-nacl)# permit igmp any any
Device(config)# action forward
Device(config-ext-nacl)# permit tcp any any
Device(config-ext-nacl)# exit
Device(config)# vlan access-map drop-ip-default 10
Device(config-access-map)# match ip address 101
Device(config-access-map)# action forward
Device(config-access-map)# exit
Device(config)# vlan access-map drop-ip-default 20
Device(config-access-map)# match ip address igmp-match
Device(config-access-map)# action drop
Device(config-access-map)# exit
Device(config)# vlan access-map drop-ip-default 30
Device(config-access-map)# match ip address tcp-match
Device(config-access-map)# action forward
Device(config-access-map)# end


Example: Default Action of Dropping MAC Packets and Forwarding IP Packets

In this example, the VLAN map has a default action of drop for MAC packets and a default action of forward for IP packets. Used with MAC extended access lists good-hosts and good-protocols , the map will have the following results:

  • Forward MAC packets from hosts 0000.0c00.0111 and 0000.0c00.0211

  • Forward MAC packets with decnet-iv or vines-ip protocols

  • Drop all other non-IP packets

  • Forward all IP packets


Device> enable
Device# configure terminal
Device(config)# mac access-list extended good-hosts
Device(config-ext-macl)# permit host 000.0c00.0111 any
Device(config-ext-macl)# permit host 000.0c00.0211 any
Device(config-ext-nacl)# exit
Device(config)# action forward
Device(config-ext-macl)# mac access-list extended good-protocols
Device(config-ext-macl)# permit any any vines-ip
Device(config-ext-nacl)# exit
Device(config)# vlan access-map drop-mac-default 10
Device(config-access-map)# match mac address good-hosts
Device(config-access-map)# action forward
Device(config-access-map)# exit
Device(config)# vlan access-map drop-mac-default 20
Device(config-access-map)# match mac address good-protocols
Device(config-access-map)# action forward
Device(config-access-map)# end

Example: Default Action of Dropping All Packets

In this example, the VLAN map has a default action of drop for all packets (IP and non-IP). Used with access lists tcp-match and good-hosts from Examples 2 and 3, the map will have the following results:

  • Forward all TCP packets

  • Forward MAC packets from hosts 0000.0c00.0111 and 0000.0c00.0211

  • Drop all other IP packets

  • Drop all other MAC packets


Device> enable
Device# configure terminal
Device(config)# vlan access-map drop-all-default 10
Device(config-access-map)# match ip address tcp-match
Device(config-access-map)# action forward
Device(config-access-map)# exit
Device(config)# vlan access-map drop-all-default 20
Device(config-access-map)# match mac address good-hosts
Device(config-access-map)# action forward
Device(config-access-map)# end


Example: Using VLAN Maps in a Network

Example: Wiring Closet Configuration

Figure 4. Wiring Closet Configuration. In a wiring closet configuration, routing might not be enabled on the switch. In this configuration, the switch can still support a VLAN map and a QoS classification ACL. Assume that Host X and Host Y are in different VLANs and are connected to wiring closet switches A and C. Traffic from Host X to Host Y is eventually being routed by Switch B, a Layer 3 switch with routing enabled. Traffic from Host X to Host Y can be access-controlled at the traffic entry point, Switch A.Wiring Closet Configuration

If you do not want HTTP traffic switched from Host X to Host Y, you can configure a VLAN map on Switch A to drop all HTTP traffic from Host X (IP address 10.1.1.32) to Host Y (IP address 10.1.1.34) at Switch A and not bridge it to Switch B.

First, define the IP access list http that permits (matches) any TCP traffic on the HTTP port.


Device> enable
Device# configure terminal
Device(config)# ip access-list extended http
Device(config-ext-nacl)# permit tcp host 10.1.1.32 host 10.1.1.34 eq www
Device(config-ext-nacl)# end


Next, create VLAN access map map2 so that traffic that matches the http access list is dropped and all other IP traffic is forwarded.

Device> enable
Device# configure terminal
Device(config)# vlan access-map map2 10
Device(config-access-map)# match ip address http
Device(config-access-map)# action drop
Device(config-access-map)# exit
Device(config)# ip access-list extended match_all
Device(config-ext-nacl)# permit ip any any
Device(config-ext-nacl)# exit
Device(config)# vlan access-map map2 20
Device(config-access-map)# match ip address match_all
Device(config-access-map)# action forward
Device(config-access-map)# end


Then, apply VLAN access map map2 to VLAN 1.


Device> enable
Device# configure terminal
Device(config)# vlan filter map2 vlan 1
Device(config)# end

Example: Restricting Access to a Server on Another VLAN

Figure 5. Restricting Access to a Server on Another VLAN.
You can restrict access to a server on another VLAN. For example, server 10.1.1.100 in VLAN 10 needs to have access denied to these hosts:


  • Hosts in subnet 10.1.2.0/8 in VLAN 20 should not have access.


  • Hosts 10.1.1.4 and 10.1.1.8 in VLAN 10 should not have access.

Denying access to a server on another VLAN.

Example: Denying Access to a Server on Another VLAN

This example shows how to deny access to a server on another VLAN by creating the VLAN map SERVER 1 that denies access to hosts in subnet 10.1.2.0.8, host 10.1.1.4, and host 10.1.1.8 and permits other IP traffic. The final step is to apply the map SERVER1 to VLAN 10.

Define the IP ACL that will match the correct packets.


Device> enable
Device# configure terminal
Device(config)# ip access-list extended SERVER1_ACL
Device(config-ext-nacl)# permit ip 10.1.2.0 0.0.0.255 host 10.1.1.100
Device(config-ext-nacl)# permit ip host 10.1.1.4 host 10.1.1.100
Device(config-ext-nacl)# permit ip host 10.1.1.8 host 10.1.1.100
Device(config-ext-nacl)# end


Define a VLAN map using this ACL that will drop IP packets that match SERVER1_ACL and forward IP packets that do not match the ACL.

Device> enable
Device# configure terminal
Device(config)# vlan access-map SERVER1_MAP
Device(config-access-map)# match ip address SERVER1_ACL
Device(config-access-map)# action drop
Device(config)# vlan access-map SERVER1_MAP 20
Device(config-access-map)# action forward
Device(config-access-map)# end


Apply the VLAN map to VLAN 10.

Device> enable
Device# configure terminal
Device(config)# vlan filter SERVER1_MAP vlan-list 10
Device(config)# end

Additional References for IPv4 Access Control Lists

Related Documents

Related Topic

Document Title

Cisco IOS commands

Cisco IOS Master Command List, All Releases

IPv6 ACLs

IPv6 ACLs chapter of the Security Configuration Guide

Technical Assistance

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Feature History for IPv4 Access Control Lists

This table provides release and related information for features explained in this module.

These features are available on all releases subsequent to the one they were introduced in, unless noted otherwise.

Release

Feature

Feature Information

Cisco IOS XE Everest 16.5.1a

IPv4 Access Control Lists

This chapter describes how to configure network security on the switch by using ACLs. Packet filtering can help limit network traffic and restrict network use by certain users or devices. ACLs filter traffic as it passes through device and permit or deny packets crossing specified interfaces.

Support for this feature was introduced on all the models of the Cisco Catalyst 9500 Series Switches.

Cisco IOS XE Fuji 16.8.1a

IPv4 Access Control Lists

Support for this feature was introduced on the C9500-32C, C9500-32QC, C9500-48Y4C, and C9500-24Y4C models of the Cisco Catalyst 9500 Series Switches.

Use Cisco Feature Navigator to find information about platform and software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn.