Catalyst 3750 Software Configuration Guide, Release 12.2(55)SE

Supported ACLs

• Port ACLs access-control traffic entering a Layer 2 interface. The switch does not support port ACLs in the outbound direction. You can apply only one IP access list and one MAC access list to a Layer 2 interface. For more information, see the “Port ACLs” section.
• Router ACLs access-control routed traffic between VLANs and are applied to Layer 3 interfaces in a specific direction (inbound or outbound). For more information, see the “Router ACLs” section.
• VLAN ACLs or VLAN maps access-control all packets (bridged and routed). 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. For more information, see the “VLAN Maps” section.

You can use input port ACLs, router ACLs, and VLAN maps on the same switch. However, a port ACL takes precedence over a router ACL or VLAN map.

• 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.

If IEEE 802.1Q tunneling is configured on an interface, any IEEE 802.1Q encapsulated IP packets received on the tunnel port can be filtered by MAC ACLs, but not by IP ACLs. This is because the switch does not recognize the protocol inside the IEEE 802.1Q header. This restriction applies to router ACLs, port ACLs, and VLAN maps. For more information about IEEE 802.1Q tunneling, see Chapter17, “Configuring IEEE 802.1Q and Layer 2 Protocol Tunneling”

Port ACLs

Port ACLs are ACLs that are applied to Layer 2 interfaces on a switch. Port ACLs are supported only on physical interfaces and not on EtherChannel interfaces and can be applied only on interfaces in the inbound direction. These 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 associated with all inbound features configured on a given 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 34-1 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.

Figure 34-1 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.

An ACL can be used with multiple features for a given interface, and one feature can use multiple ACLs. When a single router ACL is used by multiple features, it is examined multiple times.

Supported 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 information for matching operations.

As with port ACLs, the switch examines ACLs associated with features configured on a given interface. However, you can apply only inbound port ACLs, while router ACLs are supported in both directions. 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. In Figure 34-1, ACLs applied at the router input allow Host A to access the Human Resources network but prevent Host B from accessing the same network.

VLAN Maps

Use VLAN ACLs or VLAN maps to access-control all traffic. You can apply VLAN maps to all packet s that are routed into or out of a VLAN or are bridged within a VLAN in the stack.

Use VLAN maps for security packet filtering. VLAN maps are not defined by direction (input or output).

You can configure VLAN maps to match Layer 3 addresses for IPv4 traffic.

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 connected to this switch.

With VLAN maps, forwarding of packets is permitted or denied, based on the action specified in the map. Figure 34-2 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.

Figure 34-2 Using VLAN Maps to Control Traffic

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

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

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.

ACLs and Switch Stacks

ACL support is the same for a switch stack as for a standalone switch. ACL configuration information is propagated to all switches in the stack. All switches in the stack, including the stack master, process the information and program their hardware. (For information about switch stacks, see Chapter5, “Configuring the Switch Stack”)

The stack master performs these ACL functions:

• It processes the ACL configuration and propagates the information to all stack members.
• It distributes the ACL information to any switch that joins the stack.
• If packets must be forwarded by software for any reason (for example, not enough hardware resources), the master switch forwards the packets only after applying ACLs on the packets.
• It programs its hardware with the ACL information it processes.

Stack members perform these ACL functions:

• They receive the ACL information from the master switch and program their hardware.
• They act as standby switches, ready to take over the role of the stack master if the existing master were to fail and they were to be elected as the new stack master.

When a stack master fails and a new stack master is elected, the newly elected master reparses the backed up running configuration. (See Chapter5, “Configuring the Switch Stack”) The ACL configuration that is part of the running configuration is also reparsed during this step. The new stack master distributes the ACL information to all switches in the stack.

Creating Standard and Extended IPv4 ACLs

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

These sections describe access lists and how to create them:

• Access List Numbers
• ACL Logging
• Creating a Numbered Standard ACL
• Creating a Numbered Extended ACL
• Resequencing ACEs in an ACL
• Creating Named Standard and Extended ACLs
• Using Time Ranges with ACLs
• Including Comments in ACLs

Access List Numbers

The number you use to denote your ACL shows the type of access list that you are creating. Table 34-1 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.

Note 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.

ACL Logging

The switch 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 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.

Creating a Numbered Standard ACL

Beginning in privileged EXEC mode, follow these steps to create a numbered standard ACL:

Use the no access-list access-list-number global configuration command to delete the entire ACL. You cannot delete individual ACEs from numbered access lists.

Note 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.

This example shows how to create a standard ACL to deny access to IP host 171.69.198.102, permit access to any others, and display the results.

Switch(config)# end

The switch 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 terminal lines (see the “Applying an IPv4 ACL to a Terminal Line” section), to interfaces (see the “Applying an IPv4 ACL to an Interface” section), or to VLANs (see the “Configuring VLAN Maps” section).

Creating a Numbered Extended ACL

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.

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

These IP protocols are supported (protocol keywords are in parentheses in bold):

Authentication Header Protocol (ahp), Enhanced Interior Gateway Routing Protocol (eigrp), Encapsulation Security Payload (esp), 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), or User Datagram Protocol (udp).

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

For more details on the specific keywords for each protocol, see these command references:

• Cisco IOS IP Command Reference, Volume 1 of 3: Addressing and Services, Release 12.2
• Cisco IOS IP Command Reference, Volume 2 of 3: Routing Protocols, Release 12.2
• Cisco IOS IP Command Reference, Volume 3 of 3: Multicast, Release 12.2

These documents are available from the Cisco.com page under Documentation > Cisco IOS Software > 12.2 Mainline > Command References.

Note The switch 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.

Supported parameters can be grouped into these categories: TCP, UDP, ICMP, IGMP, or other IP.

Beginning in privileged EXEC mode, follow these steps to create an extended ACL:

Use the no access-list access-list-number global configuration command to delete the entire access list. You cannot delete individual ACEs from numbered access lists.

This example shows how to create and display an extended access list to deny Telnet access from any host in network 171.69.198.0 to any host in network 172.20.52.0 and to permit any others. (The eq keyword after the destination address means to test for the TCP destination port number equaling Telnet.)

Switch(config)# access-list 102 deny tcp 171.69.198.0 0.0.0.255 172.20.52.0 0.0.0.255 eq telnet

Switch(config)# access-list 102 permit tcp any any

Switch(config)# end

After an ACL is created, any additions (possibly entered from the terminal) are placed at the end of the list. You cannot selectively add or remove access list entries from a numbered access list.

Note When you are creating an ACL, remember that, by default, the end of the access list contains an implicit deny statement for all packets if it did not find a match before reaching the end.

After creating a numbered extended ACL, you can apply it to terminal lines (see the “Applying an IPv4 ACL to a Terminal Line” section), to interfaces (see the “Applying an IPv4 ACL to an Interface” section), or to VLANs (see the “Configuring VLAN Maps” section).

Resequencing ACEs in an ACL

Sequence numbers for the entries in an access list are automatically generated when you create a new ACL. You can use the ip access-list resequence global configuration command to edit the sequence numbers in an ACL and change the order in which ACEs are applied. For example, if you add a new ACE to an ACL, it is placed at the bottom of the list. By changing the sequence number, you can move the ACE to a different position in the ACL.

For information about the ip access-list resequence command:
http://www.cisco.com/en/US/docs/ios/12_2s/feature/guide/fsaclseq.html#wp1027188

Creating Named Standard and Extended 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 router 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 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.

Consider these guidelines and limitations before configuring named 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.
• Numbered ACLs are also available, as described in the “Creating Standard and Extended IPv4 ACLs” section.
• You can use standard and extended ACLs (named or numbered) in VLAN maps.

Beginning in privileged EXEC mode, follow these steps to create a standard ACL using names:

To remove a named standard ACL, use the no ip access-list standard name global configuration command.

Beginning in privileged EXEC mode, follow these steps to create an extended ACL using names:

To remove a named extended ACL, use the no ip access-list extended name global configuration command.

When you are creating standard 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. This example shows how you can delete individual ACEs from the named access list border-list :

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

After creating a named ACL, you can apply it to interfaces (see the “Applying an IPv4 ACL to an Interface” section) or to VLANs (see the “Configuring VLAN Maps” section).

Using Time Ranges with 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 in the previous sections, the “Creating Standard and Extended IPv4 ACLs” section, and the “Creating Named Standard and Extended ACLs” section.

These are some of the many possible 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 TCAM. 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 switch system clock; therefore, you need a reliable clock source. We recommend that you use Network Time Protocol (NTP) to synchronize the switch clock. For more information, see the “Managing the System Time and Date” section.

Beginning in privileged EXEC mode, follow these steps to configure a time-range parameter for an ACL:

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

To remove a configured time-range limitation, use the no time-range time-range-name global configuration command.

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

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.

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

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 Jones is allowed access, and the workstation that belongs to Smith is not allowed access:

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 Jones subnet is not allowed to use outbound Telnet:

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.

For procedures for applying ACLs to interfaces, see the “Applying an IPv4 ACL to an Interface” section. For applying ACLs to VLANs, see the “Configuring VLAN Maps” section.

Beginning in privileged EXEC mode, follow these steps to restrict incoming and outgoing connections between a virtual terminal line and the addresses in an ACL:

To remove an ACL from a terminal line, use the no access-class access-list-number { in | out } line configuration command.

Applying an IPv4 ACL to an Interface

Note these guidelines:

• Apply an ACL only to inbound Layer 2 ports.
• Apply an ACL to either outbound or inbound Layer 3 interfaces.
• When controlling access to an interface, you can use a named or numbered ACL.
• If you apply an ACL to a port that is a member of a VLAN, the port ACL takes precedence over an ACL applied to the VLAN interface.
• 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. The port ACL always filters incoming packets received on the Layer 2 port.
• If you apply an ACL to a Layer 3 interface and routing is not enabled, the ACL only filters packets that are intended for the CPU, such as SNMP, Telnet, or web traffic. You do not have to enable routing to apply ACLs to Layer 2 interfaces.
• When private VLANs are configured, you can apply router ACLs only on the primary-VLAN SVIs. The ACL is applied to both primary and secondary VLAN Layer 3 traffic.

Note By default, the router sends Internet Control Message Protocol (ICMP) unreachable messages when a packet is denied by an access group. These access-group denied packets are not dropped in hardware but are bridged to the switch CPU so that it can generate the ICMP-unreachable message.

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

To remove the specified access group, use the no ip access-group { access-list-number | name } { in | out } interface configuration command.

This example shows how to apply access list 2 to a port to filter packets entering the port:

Note 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 switch checks the packet against the ACL. If the ACL permits the packet, the switch continues to process the packet. If the ACL rejects the packet, the switch discards the packet.

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

Hardware and Software Treatment of IP ACLs

ACL processing is primarily accomplished in hardware, but requires forwarding of some traffic flows to the CPU for software processing. If the hardware reaches its capacity to store ACL configurations, packets are sent to the CPU for forwarding. The forwarding rate for software-forwarded traffic is substantially less than for hardware-forwarded traffic.

Note If an ACL configuration cannot be implemented in hardware due to an out-of-resource condition on a stack member, then only the traffic in that VLAN arriving on that switch is affected (forwarded in software). Software forwarding of packets might adversely impact the performance of the switch stack, depending on the number of CPU cycles that this consumes.

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

• Using the log keyword
• Generating ICMP unreachable messages

When traffic flows are both logged and forwarded, forwarding is done by hardware, but logging must be done by software. Because of the difference in packet handling capacity between hardware and software, if the sum of all flows being logged (both permitted flows and denied flows) is of great enough bandwidth, not all of the packets that are forwarded can be logged.

If router ACL configuration cannot be applied in hardware, packets arriving in a VLAN that must be routed are routed in software, but are bridged in hardware. If ACLs cause large numbers of packets to be sent to the CPU, the switch performance can be negatively affected.

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 access-lists hardware counters privileged EXEC command to obtain some basic hardware ACL statistics for switched and routed packets.

Troubleshooting ACLs

If this ACL manager message appears and [chars] is the access-list name,

The switch has insufficient resources to create a hardware representation of the ACL. The resources include hardware memory and label space but not CPU memory. A lack of available logical operation units or specialized hardware resources causes this problem. Logical operation units are needed for a TCP flag match or a test other than eq (ne, gt, lt, or range) on TCP, UDP, or SCTP port numbers.

Use one of these workarounds:

• Modify the ACL configuration to use fewer resources.
• Rename the ACL with a name or number that alphanumerically precedes the ACL names or numbers.

To determine the specialized hardware resources, enter the show platform layer4 acl map privileged EXEC command. If the switch does not have available resources, the output shows that index 0 to index 15 are not available.

For more information about configuring ACLs with insufficient resources, see CSCsq63926 in the Bug Toolkit.

For example, if you apply this ACL to an interface:

And if this message appears:

The flag-related operators are not available. To avoid this issue,

• Move the fourth ACE before the first ACE by using ip access-list resequence global configuration command:

or

• Rename the ACL with a name or number that alphanumerically precedes the other ACLs (for example, rename ACL 79 to ACL 1).

You can now apply the first ACE in the ACL to the interface. The switch allocates the ACE to available mapping bits in the Opselect index and then allocates flag-related operators to use the same bits in the TCAM.

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.

IPv4 ACL Configuration Examples

This section provides examples of configuring and applying IPv4 ACLs. For detailed information about compiling ACLs, see the Cisco IOS Security Configuration Guide, Release 12.2 and to the Configuring IP Services” section in the “IP Addressing and Services” chapter of the Cisco IOS IP Configuration Guide, Release 12.2.

Figure 34-3 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.

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.

Figure 34-3 Using Router ACLs to Control Traffic

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.

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 applied 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.

Numbered ACLs

In this example, network 36.0.0.0 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 36.0.0.0 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 36.0.0.0 subnets. The ACL is applied to packets entering a port.

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 128.88.1.2. The third line permits incoming ICMP messages for error feedback.

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. Outbound packets have the port numbers reversed. Because the secure system of the network always accepts mail connections on port 25, the incoming and outgoing services are separately controlled. The ACL must be configured as an input ACL on the outbound interface and an output ACL on the inbound interface.

In this example, the network is a Class B network with the address 128.88.0.0, and the mail host address is 128.88.1.2. 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 on stack member 1 is the interface that connects the router to the Internet.

Named 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 1.2.3.4.

The marketing_group ACL allows any TCP Telnet traffic to the destination address and wildcard 171.69.0.0 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 171.69.0.0 through 179.69.255.255 with a destination port less than 1024, denies any other IP traffic, and provides a log of the result.

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

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).

Commented IP ACL Entries

In this example of a numbered ACL, the workstation that belongs to Jones is allowed access, and the workstation that belongs to Smith is not allowed access:

In this example of a numbered ACL, the Winter and Smith workstations are not allowed to browse the web:

In this example of a named ACL, the Jones subnet is not allowed access:

In this example of a named ACL, the Jones subnet is not allowed to use outbound Telnet:

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.

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.

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

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:

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

Applying a MAC ACL to 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:

• 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. Incoming packets received on the Layer 2 port are always filtered by the port ACL.
• 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.

Beginning in privileged EXEC mode, follow these steps to apply a MAC access list to control access to a Layer 2 interface:

To remove the specified access group, use the no mac access-group { name} interface configuration command.

This example shows how to apply MAC access list mac1 to a port to filter packets entering the port:

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.

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

VLAN Map Configuration Guidelines

Follow these guidelines when configuring VLAN maps:

• 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 switch 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.
• The system might take longer to boot up if you have configured a very large number of ACLs.
• Logging is not supported for VLAN maps.
• When a switch 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 VLAN map configuration cannot be applied in hardware, all packets in that VLAN must be bridged and routed by software.
• You can configure VLAN maps on primary and secondary VLANs. However, we recommend that you configure the same VLAN maps on private-VLAN primary and secondary VLANs.
• When a frame is Layer-2 forwarded within a private VLAN, the same VLAN map is applied at the ingress side and at the egress side. When a frame is routed from inside a private VLAN to an external port, the private-VLAN map is applied at the ingress side.

– For frames going upstream from a host port to a promiscuous port, the VLAN map configured on the secondary VLAN is applied.

– For frames going downstream from a promiscuous port to a host port, the VLAN map configured on the primary VLAN is applied.

To filter out specific IP traffic for a private VLAN, you should apply the VLAN map to both the primary and secondary VLANs. For more information about private VLANs, see Chapter16, “Configuring Private VLANs”

For configuration examples, see the “Using VLAN Maps in Your Network” section.

For information about using both router ACLs and VLAN maps, see the “VLAN Maps and Router ACL Configuration Guidelines” section.

Creating a VLAN Map

Each VLAN map consists of an ordered series of entries. Beginning in privileged EXEC mode, follow these steps to create, add to, or delete a VLAN map entry:

Use the no vlan access-map name global configuration command to delete a map. Use the no vlan access-map name number global configuration command to delete a single sequence entry from within the map.

Use the no action access-map configuration command to enforce the default action, which is to forward.

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.

Examples of ACLs and VLAN Maps

These examples show how to create ACLs and VLAN maps that for specific purposes.

Example 1

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.

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.

Example 2

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

Example 3

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

Example 4

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

Applying a VLAN Map to a VLAN

Beginning in privileged EXEC mode, follow these steps to apply a VLAN map to one or more VLANs:

To remove the VLAN map, use the no vlan filter mapname vlan-list list global configuration command.

This example shows how to apply VLAN map 1 to VLANs 20 through 22:

Using VLAN Maps in Your Network

These sections describes some typical uses for VLAN maps:

• Wiring Closet Configuration
• Denying Access to a Server on Another VLAN

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. In Figure 34-4, 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.

Figure 34-4 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.

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

Then, apply VLAN access map map2 to VLAN 1.

Denying 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 (see Figure 34-5):

• 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.

Figure 34-5 Deny Access to a Server on Another a 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.

Step 1 Define the IP ACL that will match the correct packets.

Step 2 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.

Step 3 Apply the VLAN map to VLAN 10.

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.

The switch hardware provides one lookup for security ACLs for each direction (input and output); therefore, you must merge a router ACL and a VLAN map when they are configured on the same VLAN. Merging the router ACL with the VLAN map might significantly increase the number of ACEs.

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.

Examples of Router ACLs and VLAN Maps Applied to VLANs

This section gives examples of applying router ACLs and VLAN maps to a VLAN for switched, bridged, routed, and multicast packets. Although the following illustrations show packets being forwarded to their destination, each time the packet’s path crosses a line indicating a VLAN map or an ACL, it is also possible that the packet might be dropped, rather than forwarded.

ACLs and Switched Packets

Figure 34-6 shows how an ACL is applied on packets that are switched within a VLAN. Packets switched within the VLAN without being routed or forwarded by fallback bridging are only subject to the VLAN map of the input VLAN.

Figure 34-6 Applying ACLs on Switched Packets

ACLs and Bridged Packets

Figure 34-7 shows how an ACL is applied on fallback-bridged packets. For bridged packets, only Layer 2 ACLs are applied to the input VLAN. Only non-IP, non-ARP packets can be fallback-bridged.

Figure 34-7 Applying ACLs on Bridged Packets

ACLs and Routed Packets

Figure 34-8 shows how ACLs are applied on routed packets. For routed packets, the ACLs are applied in this order:

1. VLAN map for input VLAN

2. Input router ACL

3. Output router ACL

4. VLAN map for output VLAN

Figure 34-8 Applying ACLs on Routed Packets

ACLs and Multicast Packets

Figure 34-9 shows how ACLs are applied on packets that are replicated for IP multicasting. A multicast packet being routed has two different kinds of filters applied: one for destinations that are other ports in the input VLAN and another for each of the destinations that are in other VLANs to which the packet has been routed. The packet might be routed to more than one output VLAN, in which case a different router output ACL and VLAN map would apply for each destination VLAN.

The final result is that the packet might be permitted in some of the output VLANs and not in others. A copy of the packet is forwarded to those destinations where it is permitted. However, if the input VLAN map (VLAN 10 map in Figure 34-9) drops the packet, no destination receives a copy of the packet.

Figure 34-9 Applying ACLs on Multicast Packets