- IP Access List Overview
- Creating an IP Access List and Applying It to an Interface
- Creating an IP Access List to Filter IP Options, TCP Flags, Noncontiguous Ports
- Configuring an FQDN ACL
- Refining an IP Access List
- IP Named Access Control Lists
- Commented IP Access List Entries
- Standard IP Access List Logging
- IP Access List Entry Sequence Numbering
- Configuring Lock-and-Key Security (Dynamic Access Lists)
- ACL IP Options Selective Drop
- Displaying and Clearing IP Access List Data Using ACL Manageability
- ACL Syslog Correlation
- IPv6 Access Control Lists
- IPv6 ACL Undetermined-Transport Support
- Configuring Template ACLs
- IPv6 Template ACL
- IPv4 ACL Chaining Support
- IPv6 ACL Chaining with a Common ACL
- IPv6 ACL Extensions for Hop by Hop Filtering
Security Configuration Guide: Access Control Lists, Cisco IOS XE Release 3S
- Updated:
- March 27, 2015
Chapter: Creating an IP Access List and Applying It to an Interface
- Finding Feature Information
- Restrictions for Creating an IP Access List and Applying It to an Interface on Cisco ASR 903 Routers
- Information About Creating an IP Access List and Applying It to an Interface
- How to Create an IP Access List and Apply It to an Interface
- Configuration Examples for Creating an IP Access List and Applying It to an Interface
- Example: Filtering on Host Source Address
- Example: Filtering on Subnet Source Address
- Example: Filtering on Source and Destination Addresses and IP Protocols
- Example: Filtering on Source Addresses Using a Numbered Access List
- Example: Preventing Telnet Access to a Subnet
- Example: Filtering on TCP and ICMP Using Port Numbers
- Example: Allowing SMTP E-mail and Established TCP Connections
- Example: Preventing Access to the Web by Filtering on Port Name
- Example: Filtering on Source Address and Logging the Packets
- Example: Limiting Debug Output
- Additional References Creating an IP Access List and Applying It to an Interface
- Feature Information for Creating an IP Access List and Applying It to an Interface
Creating an IP Access List and Applying It to an Interface
IP access lists provide many benefits for securing a network and achieving nonsecurity goals, such as determining quality of service (QoS) factors or limiting debug command output. This module describes how to create standard, extended, named, and numbered IP access lists. An access list can be referenced by a name or a number. Standard access lists filter on only the source address in IP packets. Extended access lists can filter on source address, destination address, and other fields in an IP packet.
After you create an access list, you must apply it to something in order for it to have any effect. This module describes how to apply an access list to an interface. However, there are many other uses for access lists, which are mentioned in this module and described in other modules and in other configuration guides for various technologies.
- Finding Feature Information
- Restrictions for Creating an IP Access List and Applying It to an Interface on Cisco ASR 903 Routers
- Information About Creating an IP Access List and Applying It to an Interface
- How to Create an IP Access List and Apply It to an Interface
- Configuration Examples for Creating an IP Access List and Applying It to an Interface
- Additional References Creating an IP Access List and Applying It to an Interface
- Feature Information for Creating an IP Access List and Applying It to an Interface
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table at the end of this module.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Restrictions for Creating an IP Access List and Applying It to an Interface on Cisco ASR 903 Routers
The following restrictions apply when configuring IPv4 and IPv6 access control lists (ACLs) on Cisco ASR 903 Series Aggregation Services Routers:
-
Application control engine (ACE)-specific counters are not supported.
-
Layer 3 IPv4 and IPv6 ACLs are not supported on the same interface.
-
MAC ACLs are not supported on Ethernet flow points (EFPs) or trunk EFP interfaces to which Layer 3 IPv4 or IPv6 ACLs are applied.
-
A maximum of 500 ACEs per ACL are supported.
-
IPv4 and IPv6 ACLs are not currently supported on EFP interfaces. IPv4 and IPv6 ACLs are supported on physical interfaces, bridge-domain interfaces, and port-channel interfaces.
Information About Creating an IP Access List and Applying It to an Interface
Helpful Hints for Creating IP Access Lists
-
Create the access list before applying it to an interface (or elsewhere), because if you apply a nonexistent access list to an interface and then proceed to configure the access list, the first statement is put into effect, and the implicit deny statement that follows could cause immediate access problems.
-
Another reason to configure an access list before applying it is because an interface with an empty access list applied to it permits all traffic.
-
All access lists need at least one permit statement; otherwise, all packets are denied and no traffic passes.
-
Organize your access list so that more specific references in a network or subnet appear before more general ones.
-
A packet will match the first ACE in the ACL. Thus, a permit ip any any will match all packets, ignoring all subsequent ACES.
-
Although all access lists end with an implicit deny statement, we recommend use of an explicit deny statement (for example, deny ip any any). On most platforms, you can display the count of packets denied by issuing the show access-list command, thus finding out more information about who your access list is disallowing. Only packets denied by explicit deny statements are counted, which is why the explicit deny statement will yield more complete data for you.
-
While you are creating an access list or after it is created, you might want to delete an entry. You can delete an entry from a named access list. Use the no permit or no deny command to delete the appropriate entry.
-
In order to make the purpose of individual statements more scannable and easily understood at a glance, you can write a helpful remark before or after any statement by using the remark command.
-
If you want to deny access to a particular host or network and find out if someone from that network or host is attempting to gain access, include the log keyword with the corresponding deny statement so that the packets denied from that source are logged for you.
-
This hint applies to the placement of your access list. When trying to save resources, remember that an inbound access list applies the filter conditions before the routing table lookup. An outbound access list applies the filter conditions after the routing table lookup.
Access List Remarks
You can include comments or remarks about entries in any IP access list. An access list remark is an optional remark before or after an access list entry that describes the entry so that you do not have to interpret the purpose of the entry. Each remark is limited to 100 characters in length.
The remark can go before or after a permit or deny statement. Be consistent about where you add remarks. Users may be confused if some remarks precede the associated permit or deny statements and some remarks follow the associated statements.
The following is an example of a remark that describes function of the subsequent deny statement:
ip access-list extended telnetting remark Do not allow host1 subnet to telnet out deny tcp host 172.16.2.88 any eq telnet
Additional IP Access List Features
Beyond the basic steps to create a standard or extended access list, you can enhance your access lists as mentioned below. Each of these methods is described completely in the Refining an IP Access List module.
-
You can impose dates and times when permit or deny statements in an extended access list are in effect, making your access list more granular and specific to an absolute or periodic time period.
-
After you create a named or numbered access list, you might want to add entries or change the order of the entries, known as resequencing an access list.
-
You can achieve finer granularity when filtering packets by filtering on noninitial fragments of packets.
How to Create an IP Access List and Apply It to an Interface
This section describes the general ways to create a standard or extended access list using either a name or a number. Access lists are very flexible; the tasks simply illustrate one permit command and one deny command to provide you the command syntax of each. Only you can determine how many permit and deny commands you need and their order.
 Note | The first two tasks in this module create an access list; you must apply the access list in order for it to function. If you want to apply the access list to an interface, perform the task “Applying the Access List to an Interface”. |
- Creating a Standard Access List to Filter on Source Address
- Creating an Extended Access List
- Applying an Access List to an Interface
Creating a Standard Access List to Filter on Source Address
If you want to filter on source address only, a standard access list is simple and sufficient. There are two alternative types of standard access list: named and numbered. Named access lists allow you to identify your access lists with a more intuitive name rather than a number, and they also support more features than numbered access lists.
- Creating a Named Access List to Filter on Source Address
- Creating a Numbered Access List to Filter on Source Address
Creating a Named Access List to Filter on Source Address
Use a standard, named access list if you need to filter on source address only. This task illustrates one permit statement and one deny statement, but the actual statements you use and their order depend on what you want to filter or allow. Define your permit and deny statements in the order that achieves your filtering goals.
1.
enable
2.
configure
terminal
3.
ip
access-list
standard
name
4.
remark
remark
5. deny {source [source-wildcard] | any} [log]
6.
remark
remark
7.
permit
{source
[source-wildcard] |
any} [log]
8. Repeat some combination of Steps 4 through 7 until you have specified the sources on which you want to base your access list.
9.
end
10.
show
ip
access-list
DETAILED STEPS
Creating a Numbered Access List to Filter on Source Address
Configure a standard, numbered access list if you need to filter on source address only and you prefer not to use a named access list.
IP standard access lists are numbered 1 to 99 or 1300 to 1999. This task illustrates one permit statement and one deny statement, but the actual statements you use and their order depend on what you want to filter or allow. Define your permit and deny statements in the order that achieves your filtering goals.
1.
enable
2.
configure
terminal
3.
access-list
access-list-number
permit {source [source-wildcard] |
any} [log]
4.
access-list
access-list-number
deny {source [source-wildcard] |
any} [log]
5. Repeat some combination of Steps 3 through 6 until you have specified the sources on which you want to base your access list.
6.
end
7.
show
ip
access-list
DETAILED STEPS
Creating an Extended Access List
If you want to filter on anything other than source address, you need to create an extended access list. There are two alternative types of extended access list: named and numbered. Named access lists allow you to identify your access lists with a more intuitive name rather than a number, and they also support more features.
For details on how to filter something other than source or destination address, see the syntax descriptions in the command reference documentation.
Creating a Named Extended Access List
Create a named extended access list if you want to filter the source and destination address or filter a combination of addresses and other IP fields.
1.
enable
2.
configure
terminal
3.
ip
access-list
extended
name
4.
deny
protocol
source
[source-wildcard]
destination
[destination-wildcard] [option
option-name]
[precedence
precedence]
[tos
tos] [established] [log |
log-input]
[time-range
time-range-name] [fragments]
5.
permit
protocol
source
[source-wildcard]
destination
[destination-wildcard] [option
option-name]
[precedence
precedence]
[tos
tos] [established] [log |
log-input]
[time-range
time-range-name] [fragments]
6. Repeat some combination of Steps 4 through 7 until you have specified the fields and values on which you want to base your access list.
7.
end
8.
show
ip
access-list
DETAILED STEPS
Creating a Numbered Extended Access List
Create a numbered extended access list if you want to filter on source and destination address, or a combination of addresses and other IP fields, and you prefer not to use a name. Extended IP access lists are numbered 100 to 199 or 2000 to 2699.
1.
enable
2.
configure
terminal
3.
access-list
access-list-number
remark
remark
4.
access-list
access-list-number
permit
protocol
{source [source-wildcard] |
any} {destination [destination-wildcard] |
any} [precedence
precedence]
[tos
tos] [established] [log |
log-input]
[time-range
time-range-name] [fragments]
5.
access-list
access-list-number
remark
remark
6.
access-list
access-list-number
deny
protocol
{source
[source-wildcard] |
any} {destination [destination-wildcard] |
any} [precedence
precedence]
[tos
tos] [established] [log |
log-input]
[time-range
time-range-name] [fragments]
7. Repeat some combination of Steps 3 through 6 until you have specified the fields and values on which you want to base your access list.
8.
end
9.
show
ip
access-list
DETAILED STEPS
Applying an Access List to an Interface
1.
enable
2.
configure
terminal
3.
interface
type number
4.
ip
access-group
{access-list-number |
access-list-name} {in |
out}
5.
end
DETAILED STEPS
Configuration Examples for Creating an IP Access List and Applying It to an Interface
- Example: Filtering on Host Source Address
- Example: Filtering on Subnet Source Address
- Example: Filtering on Source and Destination Addresses and IP Protocols
- Example: Filtering on Source Addresses Using a Numbered Access List
- Example: Preventing Telnet Access to a Subnet
- Example: Filtering on TCP and ICMP Using Port Numbers
- Example: Allowing SMTP E-mail and Established TCP Connections
- Example: Preventing Access to the Web by Filtering on Port Name
- Example: Filtering on Source Address and Logging the Packets
- Example: Limiting Debug Output
Example: Filtering on Host Source Address
In the following example, the workstation belonging to user1 is allowed access to gigabitethernet 0/0/0, and the workstation belonging to user2 is not allowed access:
interface gigabitethernet 0/0/0 ip access-group workstations in ! ip access-list standard workstations remark Permit only user1 workstation through permit 172.16.2.88 remark Do not allow user2 workstation through deny 172.16.3.13
Example: Filtering on Subnet Source Address
In the following example, the user1 subnet is not allowed access to gigabitethernet interface 0/0/0, but the Main subnet is allowed access:
interface gigabitethernet 0/0/0 ip access-group prevention in ! ip access-list standard prevention remark Do not allow user1 subnet through deny 172.22.0.0 0.0.255.255 remark Allow Main subnet permit 172.25.0.0 0.0.255.255
Example: Filtering on Source and Destination Addresses and IP Protocols
The following configuration example shows an interface with two access lists, one applied to outgoing packets and one applied to incoming packets. The standard access list named Internet-filter filters outgoing packets on source address. The only packets allowed out the interface must be from source 172.16.3.4.
The extended access list named marketing-group filters incoming packets. The access list permits Telnet packets from any source to network 172.26.0.0 and denies all other TCP packets. It permits any ICMP packets. It denies UDP packets from any source to network 172.26.0 0 on port numbers less than 1024. Finally, the access list denies all other IP packets and performs logging of packets passed or denied by that entry.
interface gigabitethernet 0/0/0 ip address 172.20.5.1 255.255.255.0 ip access-group Internet-filter out ip access-group marketing-group in ! ip access-list standard Internet-filter permit 172.16.3.4 ip access-list extended marketing-group permit tcp any 172.26.0.0 0.0.255.255 eq telnet deny tcp any any permit icmp any any deny udp any 172.26.0.0 0.0.255.255 lt 1024 deny ip any any
Example: Filtering on Source Addresses Using a Numbered Access List
In the following 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 Cisco IOS XE software would accept one address on subnet 48 and reject all others on that subnet. The last line of the list shows that the software would accept addresses on all other network 10.0.0.0 subnets.
interface gigabitethernet 0/0/0 ip access-group 2 in ! access-list 2 permit 10.48.0.3 access-list 2 deny 10.48.0.0 0.0.255.255 access-list 2 permit 10.0.0.0 0.255.255.255
Example: Preventing Telnet Access to a Subnet
In the following example, the user1 subnet is not allowed to telnet out of gigabitethernet interface 0/0/0:
interface gigabitethernet 0/0/0 ip access-group telnetting out ! ip access-list extended telnetting remark Do not allow user1 subnet to telnet out deny tcp 172.20.0.0 0.0.255.255 any eq telnet remark Allow Top subnet to telnet out permit tcp 172.33.0.0 0.0.255.255 any eq telnet
Example: Filtering on TCP and ICMP Using Port Numbers
In the following example, the first line of the extended access list named acl1 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 172.28.1.2. The last line permits incoming ICMP messages for error feedback.
interface gigabitethernet 0/0/0 ip access-group acl1 in ! ip access-list extended acl1 permit tcp any 172.28.0.0 0.0.255.255 gt 1023 permit tcp any host 172.28.1.2 eq 25 permit icmp any 172.28.0.0 255.255.255.255
Example: Allowing SMTP E-mail and Established TCP Connections
Suppose you have a network connected to the Internet, and you want any host on an Ethernet 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 the gigabitethernet 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 two port numbers are used throughout the life of the connection. Mail packets coming in from the Internet will have a destination port of 25. Outbound packets will have the port numbers reversed. The fact that the secure system behind the router always will accept mail connections on port 25 is what makes possible separate control of incoming and outgoing services. The access list can be configured on either the outbound or inbound interface.
In the following example, the gigabitethernet network is a Class B network with the address 172.18.0.0, and the address of the mail host is 172.18.1.2. The established keyword is used only for the TCP protocol to indicate an established connection. A match occurs if the TCP datagram has the ACK or RST bits set, which indicate that the packet belongs to an existing connection.
interface gigabitethernet 0/0/0 ip access-group 102 in ! access-list 102 permit tcp any 172.18.0.0 0.0.255.255 established access-list 102 permit tcp any host 172.18.1.2 eq 25
Example: Preventing Access to the Web by Filtering on Port Name
In the following example, the w1and w2 workstations are not allowed web access; other hosts on network 172.20.0.0 are allowed web access:
interface gigabitethernet0/0/0 ip access-group no-web out ! ip access-list extended no-web remark Do not allow w1 to browse the web deny host 172.20.3.85 any eq http remark Do not allow w2 to browse the web deny host 172.20.3.13 any eq http remark Allow others on our network to browse the web permit 172.20.0.0 0.0.255.255 any eq http
Example: Filtering on Source Address and Logging the Packets
The following example defines access lists 1 and 2, both of which have logging enabled:
interface gigabitethernet 0/0/0 ip address 172.16.1.1 255.0.0.0 ip access-group 1 in ip access-group 2 out ! access-list 1 permit 172.25.0.0 0.0.255.255 log access-list 1 deny 172.30.0.0 0.0.255.255 log ! access-list 2 permit 172.27.3.4 log access-list 2 deny 172.17.0.0 0.0.255.255 log
If the interface receives 10 packets from 172.25.7.7 and 14 packets from 172.17.23.21, the first log will look like the following:
list 1 permit 172.25.7.7 1 packet list 2 deny 172.17.23.21 1 packet
Five minutes later, the console will receive the following log:
list 1 permit 172.25.7.7 9 packets list 2 deny 172.17.23.21 13 packets
Example: Limiting Debug Output
The following sample configuration uses an access list to limit the debug command output. Limiting the debug output restricts the volume of data to what you are interested in, saving you time and resources.
Device(config)# ip access-list acl1 Device(config-std-nacl)# remark Displays only advertisements for LDP peer in acl1 Device(config-std-nacl)# permit host 10.0.0.44 Device# debug mpls ldp advertisements peer-acl acl1 tagcon: peer 10.0.0.44:0 (pp 0x60E105BC): advertise 172.17.0.33 tagcon: peer 10.0.0.44:0 (pp 0x60E105BC): advertise 172.16.0.31 tagcon: peer 10.0.0.44:0 (pp 0x60E105BC): advertise 172.22.0.33 tagcon: peer 10.0.0.44:0 (pp 0x60E105BC): advertise 192.168.0.1 tagcon: peer 10.0.0.44:0 (pp 0x60E105BC): advertise 192.168.0.3 tagcon: peer 10.0.0.44:0 (pp 0x60E105BC): advertise 192.168.1.33
Additional References Creating an IP Access List and Applying It to an Interface
Related Documents
|
Related Topic |
Document Title |
|---|---|
|
Cisco IOS commands |
|
|
Security commands |
|
|
|
|
|
Filtering on IP options, TCP flags, or noncontiguous ports |
|
|
Controlling logging-related parameters |
Standards and RFCs
|
Standard/RFC |
Title |
|---|---|
|
No new or modified standards or RFCs are supported by this feature, and support for existing standards or RFCs has not been modified by this feature. |
— |
Technical Assistance
|
Description |
Link |
|---|---|
|
The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password. |
Feature Information for Creating an IP Access List and Applying It to an Interface
The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
|
Feature Name |
Releases |
Feature Configuration Information |
|---|---|---|
|
ACL—Access Control List Source and Destination Address Matching |
Cisco IOS XE Release 3.5S |
In the Cisco IOS XE Release 3.5S, support was added for the Cisco ASR 903 Router. |
|
ACL—ICMP Code |
Cisco IOS XE Release 3.5S |
In the Cisco IOS XE Release 3.5S, support was added for the Cisco ASR 903 Router. |
|
ACL Performance Enhancement |
Cisco IOS XE Release 2.1 |
This feature was introduced on the Cisco ASR 1000 Series Aggregation Services Routers. No commands were introduced or modified for this feature. |
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