The documentation set for this product strives to use bias-free language. For the purposes of this documentation set, bias-free is defined as language that does not imply discrimination based on age, disability, gender, racial identity, ethnic identity, sexual orientation, socioeconomic status, and intersectionality. Exceptions may be present in the documentation due to language that is hardcoded in the user interfaces of the product software, language used based on RFP documentation, or language that is used by a referenced third-party product. Learn more about how Cisco is using Inclusive Language.
An access control list (ACL) consists of one or more access control entries (ACE) that collectively define the network traffic profile. This profile can then be referenced by Cisco IOS XR softwarefeatures such as traffic filtering, route filtering, QoS classification, and access control. Each ACL includes an action element (permit or deny) and a filter element based on criteria such as source address, destination address, protocol, and protocol-specific parameters.
Prefix lists are used in route maps and route filtering operations and can be used as an alternative to access lists in many Border Gateway Protocol (BGP) route filtering commands. A prefix is a portion of an IP address, starting from the far left bit of the far left octet. By specifying exactly how many bits of an address belong to a prefix, you can then use prefixes to aggregate addresses and perform some function on them, such as redistribution (filter routing updates).
 Note |
For a complete description of the access list and prefix list commands listed in this module, refer to the IP Addresses and Services Command Reference for Cisco NCS 6000 Series Routers. |
|
Release |
Modification |
|---|---|
|
Release 5.0.0 |
This feature was introduced. |
The following prerequisite applies to implementing access lists and prefix lists:
All command task IDs are listed in individual command references and in the Cisco IOS XR Task ID Reference Guide.If you need assistance with your task group assignment, contact your system administrator.
The following restrictions apply to implementing access lists and prefix lists:
Layer 2/Layer 3 ACLs are not supported on Layer 2 interfaces.
IPv4 ACLs are not supported for loopback and interflex interfaces.
IPv6 ACLs are not supported for loopback, interflex and L2 Ethernet Flow Point (EFP) main or subinterfaces.
IPv6 ACL configuration on bundle interfaces (Ethernet LAG bundles only) is not supported.
If the TCAM utilization is high and large ACLs are modified, then an error may occur. During such instances, do the following to edit an ACL:
Note |
Use the show prm server tcam summary all acl all location and show pfilter-ea fea summary location commands to view the TCAM utilization. |
Video Monitoring is not supported through ACLs on IPv6 interfaces.
IPv4 and IPv6 egress ACLs are not supported on SDR interconnect (CSI) interfaces.
Per interface ACL statistics are not supported on CSI interfaces.
You can configure an ACL name with a maximum of 64 characters.
You can configure an ACL name to comprise of only letters and numbers.
The following restrictions apply to implementing ACL-based forwarding (ABF):
No support for IPv4 multicast traffic.
No support for ACL-based forwarding from a software switching path (for example, IPv4 option packets).
Support is only on physical interfaces, subinterfaces, and bundles.
ACL-based forwarding is an ingress-only feature.
ACL-based forwarding is not supported on SDR interconnect (CSI) interfaces.
When optional parameter interface-statistics is provided, the system pre-allocates a fixed number of contiguous statistic entries per ACE. The maximum number of contiguous statistic entries with unique counters for each ACL, of each direction of each line card, can be up to eight entries.
To implement access lists and prefix lists, you must understand the following concepts:
This section lists the feature highlights for access lists and prefix lists.
Cisco IOS XR software provides the ability to clear counters for an access list or prefix list using a specific sequence number.
Cisco IOS XR software provides the ability to copy the contents of an existing access list or prefix list to another access list or prefix list.
Cisco IOS XR software allows users to apply sequence numbers to permit or deny statements and to resequence, add, or remove such statements from a named access list or prefix list.
Note |
Resequencing is only for IPv4 prefix lists. |
Cisco IOS XR software does not differentiate between standard and extended access lists. Standard access list support is provided for backward compatibility.
Access lists perform packet filtering to control which packets move through the network and where. Such controls help to limit network traffic and restrict the access of users and devices to the network. Access lists have many uses, and therefore many commands accept a reference to an access list in their command syntax. Access lists can be used to do the following:
Filter incoming packets on an interface.
Filter outgoing packets on an interface.
Restrict the contents of routing updates.
Limit debug output based on an address or protocol.
Control vty access.
Identify or classify traffic for advanced features, such as congestion avoidance, congestion management, and priority and custom queueing.
An access list is a sequential list consisting of permit and deny statements that apply to IP addresses and possibly upper-layer IP protocols. The access list has a name by which it is referenced. Many software commands accept an access list as part of their syntax.
An access list can be configured and named, but it is not in effect until the access list is referenced by a command that accepts an access list. Multiple commands can reference the same access list. An access list can control traffic arriving at the router or leaving the router, but not traffic originating at the router. Note that, traffic such as SSH, ICMP and telnet traffic are blocked by ACL, in spite of being originated from the router. This is because, those packets are not injected as high priority packets, and hence get subjected to ACL processing. At the same time, BGP traffic bypasses the ACL applied on the interface, as it is a control packet which is injected as a critical inject packet from RSP or LC. Such packets are handled in the system with high priority and do not get dropped.
Use the following process and rules when configuring an IP access list:
The software tests the source or destination address or the protocol of each packet being filtered against the conditions in the access list, one condition (permit or deny statement) at a time.
If a packet does not match an access list statement, the packet is then tested against the next statement in the list.
If a packet and an access list statement match, the remaining statements in the list are skipped and the packet is permitted or denied as specified in the matched statement. The first entry that the packet matches determines whether the software permits or denies the packet. That is, after the first match, no subsequent entries are considered.
If the access list denies the address or protocol, the software discards the packet and returns an Internet Control Message Protocol (ICMP) Host Unreachable message. ICMP is configurable in the Cisco IOS XR software.
If no conditions match, the software drops the packet because each access list ends with an unwritten or implicit deny statement. That is, if the packet has not been permitted or denied by the time it was tested against each statement, it is denied.
The access list should contain at least one permit statement or else all packets are denied.
Because the software stops testing conditions after the first match, the order of the conditions is critical. The same permit or deny statements specified in a different order could result in a packet being passed under one circumstance and denied in another circumstance.
Only one access list per interface, per protocol, per direction is allowed.
Inbound access lists process packets arriving at the router. Incoming packets are processed before being routed to an outbound interface. An inbound access list is efficient because it saves the overhead of routing lookups if the packet is to be discarded because it is denied by the filtering tests. If the packet is permitted by the tests, it is then processed for routing. For inbound lists, permit means continue to process the packet after receiving it on an inbound interface; deny means discard the packet.
Outbound access lists process packets before they leave the router. Incoming packets are routed to the outbound interface and then processed through the outbound access list. For outbound lists, permit means send it to the output buffer; deny means discard the packet.
An access list can not be removed if that access list is being applied by an access group in use. To remove an access list, remove the access group that is referencing the access list and then remove the access list.
An access list must exist before you can use the ipv4 access group command.
Consider the following when creating an IP access list:
Create the access list before applying it to an interface.
If you applied a nonexistent access list to an interface and then proceed to configure the access list, the first statement is placed into effect, and the the implicit deny statement that follows could cause all other traffic that needs to be permitted on the interface to be dropped, until you configure statements allowing the dropped traffic to be permitted.
Organize your access list so that more specific references in a network or subnet appear before more general ones.
To make the purpose of individual statements more easily understood at a glance, you can write a helpful remark before or after any statement.
Source address and destination addresses are two of the most typical fields in an IP packet on which to base an access list. Specify source addresses to control packets from certain networking devices or hosts. Specify destination addresses to control packets being sent to certain networking devices or hosts.
Address filtering uses wildcard masking to indicate whether the software checks or ignores corresponding IP address bits when comparing the address bits in an access-list entry to a packet being submitted to the access list. By carefully setting wildcard masks, an administrator can select a single or several IP addresses for permit or deny tests.
Wildcard masking for IP address bits uses the number 1 and the number 0 to specify how the software treats the corresponding IP address bits. A wildcard mask is sometimes referred to as an inverted mask, because a 1 and 0 mean the opposite of what they mean in a subnet (network) mask.
A wildcard mask bit 0 means check the corresponding bit value.
A wildcard mask bit 1 means ignore that corresponding bit value.
You do not have to supply a wildcard mask with a source or destination address in an access list statement. If you use the host keyword, the software assumes a wildcard mask of 0.0.0.0.
Unlike subnet masks, which require contiguous bits indicating network and subnet to be ones, wildcard masks allow noncontiguous bits in the mask. For IPv6 access lists, only contiguous bits are supported.
You can also use CIDR format (/x) in place of wildcard bits. For example, the IPv4 address 1.2.3.4 0.255.255.255 corresponds to 1.2.3.4/8
You can filter packets on the basis of transport layer information, such as whether the packet is a TCP, UDP, ICMP, or IGMP packet.
The ability to apply sequence numbers to IP access-list entries simplifies access list changes. Prior to this feature, there was no way to specify the position of an entry within an access list. If a user wanted to insert an entry (statement) in the middle of an existing list, all the entries after the desired position had to be removed, then the new entry was added, and then all the removed entries had to be reentered. This method was cumbersome and error prone.
The IP Access List Entry Sequence Numbering feature allows users to add sequence numbers to access-list entries and resequence them. When you add a new entry, you choose the sequence number so that it is in a desired position in the access list. If necessary, entries currently in the access list can be resequenced to create room to insert the new entry.
The following details the sequence numbering behavior:
If entries with no sequence numbers are applied, the first entry is assigned a sequence number of 10, and successive entries are incremented by 10. The maximum configurable sequence number is 2147483643 for IPv4 and IPv6 entries. For other entries, the maximum configurable sequence number is 2147483646. If the generated sequence number exceeds this maximum number, the following message displays:
Exceeded maximum sequence number.
If you provide an entry without a sequence number, it is assigned a sequence number that is 10 greater than the last sequence number in that access list and is placed at the end of the list.
ACL entries can be added without affecting traffic flow and hardware performance.
If a new access list is entered from global configuration mode, then sequence numbers for that access list are generated automatically.
Distributed support is provided so that the sequence numbers of entries in the route processor (RP) and line card (LC) are synchronized at all times.
This feature works with named standard and extended IP access lists. Because the name of an access list can be designated as a number, numbers are acceptable.
Cisco IOS XR software can provide logging messages about packets permitted or denied by a standard IP access list. That is, any packet that matches the access list 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 command in global configuration mode.
Note |
ACL logging is not supported for ingress MPLS packets |
The first packet that triggers the access list causes an immediate logging message, and subsequent packets are collected over 5-minute intervals before they are displayed 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 |
ACL logging is not supported on SDR interconnect (CSI) interfaces. |
However, you can use the { ipv4 | ipv6 } access-list log-update threshold command to set the number of packets that, when they match an access list (and are permitted or denied), cause the system to generate a log message. You might do this to receive log messages more frequently than at 5-minute intervals.
 Caution |
If you set the update-number argument to 1, a log message is sent right away, rather than caching it; every packet that matches an access list causes a log message. A setting of 1 is not recommended because the volume of log messages could overwhelm the system. |
Even if you use the { ipv4 | ipv6} access-list log-update threshold command, the 5-minute timer remains in effect, so each cache is emptied at the end of 5 minutes, regardless of the number of messages in each cache. Regardless of when the log message is sent, the cache is flushed and the count reset to 0 for that message the same way it is when a threshold is not specified.
Note |
The logging facility might drop some logging message packets if there are too many to be handled or if more than one logging message is handled in 1 second. This behavior prevents the router from using excessive CPU cycles because of too many logging packets. Therefore, the logging facility should not be used as a billing tool or as an accurate source of the number of matches to an access list. |
In earlier releases, the non-fragmented packets and the initial fragments of a packet were processed by IP extended access lists (if you apply this access list), but non-initial fragments were permitted, by default. However, now, the IP Extended Access Lists with Fragment Control feature allows more granularity of control over non-initial fragments of a packet. Using this feature, you can specify whether the system examines non-initial IP fragments of packets when applying an IP extended access list.
As non-initial fragments contain only Layer 3 information, these access-list entries containing only Layer 3 information, can now be applied to non-initial fragments also. The fragment has all the information the system requires to filter, so the access-list entry is applied to the fragments of a packet.
This feature adds the optional fragments keyword to the following IP access list commands: deny (IPv4), permit (IPv4) , deny (IPv6) , permit (IPv6). By specifying the fragments keyword in an access-list entry, that particular access-list entry applies only to non-initial fragments of packets; the fragment is either permitted or denied accordingly.
The behavior of access-list entries regarding the presence or absence of the fragments keyword can be summarized as follows:
|
If the Access-List Entry has... |
Then... |
||
|---|---|---|---|
|
...no fragments keyword and all of the access-list entry information matches |
For an access-list entry containing only Layer 3 information:
For an access-list entry containing Layer 3 and Layer 4 information:
|
||
|
...the fragments keyword and all of the access-list entry information matches |
The access-list entry is applied only to non-initial fragments.
|
You should not add the fragments keyword to every access-list entry, because the first fragment of the IP packet is considered a non-fragment and is treated independently of the subsequent fragments. Because an initial fragment will not match an access list permit or deny entry that contains the fragments keyword, the packet is compared to the next access list entry until it is either permitted or denied by an access list entry that does not contain the fragments keyword. Therefore, you may need two access list entries for every deny entry. The first deny entry of the pair will not include the fragments keyword, and applies to the initial fragment. The second deny entry of the pair will include the fragments keyword and applies to the subsequent fragments. In the cases where there are multiple deny access list entries for the same host but with different Layer 4 ports, a single deny access-list entry with the fragments keyword for that host is all that has to be added. Thus all the fragments of a packet are handled in the same manner by the access list.
Packet fragments of IP datagrams are considered individual packets and each fragment counts individually as a packet in access-list accounting and access-list violation counts.
Note |
The fragments keyword cannot solve all cases involving access lists and IP fragments. |
Note |
Within the scope of ACL processing, Layer 3 information refers to fields located within the IPv4 header; for example, source, destination, protocol. Layer 4 information refers to other data contained beyond the IPv4 header; for example, source and destination ports for TCP or UDP, flags for TCP, type and code for ICMP. |
Fragmentation and the fragment control feature affect policy routing if the policy routing is based on the match ip address command and the access list had entries that match on Layer 4 through Layer 7 information. It is possible that noninitial fragments pass the access list and are policy routed, even if the first fragment was not policy routed or the reverse.
By using the fragments keyword in access-list entries as described earlier, a better match between the action taken for initial and noninitial fragments can be made and it is more likely policy routing will occur as intended.
You can include comments (remarks) about entries in any named IP access list using the remark access list configuration command. The remarks make the access list easier for the network administrator to understand and scan. Each remark line is limited to 255 characters.
The remark can go before or after a permit or deny statement. You should be consistent about where you put the remark so 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. Remarks can be sequenced.
Remember to apply the access list to an interface or terminal line after the access list is created. See the“Applying Access Lists” section for more information.
In Cisco IOS XR software, ACL counters are maintained both in hardware and software. Hardware counters are used for packet filtering applications such as when an access group is applied on an interface. Software counters are used by all the applications mainly involving software packet processing.
Packet filtering makes use of 64-bit hardware counters per ACE. If the same access group is applied on interfaces that are on the same line card in a given direction, the hardware counters for the ACL are shared between two interfaces.
To display the hardware counters for a given access group, use the show access-lists ipv4 [access-list-name hardware {ingress | egress} [interface type interface-path-id] {location node-id}] command in EXEC mode.
To clear the hardware counters, use the clear access-list ipv4 access-list-name [hardware {ingress | egress} [interface type interface-path-id] {location node-id}] command in EXEC mode.
Hardware counting is not enabled by default for IPv4 ACLs because of a small performance penalty. To enable hardware counting, use the ipv4 access-group access-list-name {ingress | egress} [hardware-count] command in interface configuration mode. This command can be used as desired, and counting is enabled only on the specified interface.
Software counters are updated for the packets processed in software, for example, exception packets punted to the LC CPU for processing, or ACL used by routing protocols, and so on. The counters that are maintained are an aggregate of all the software applications using that ACL. To display software-only ACL counters, use the show access-lists ipv4 access-list-name [sequence number] command in EXEC mode.
All the above information is true for IPv6, except that hardware counting is always enabled; there is no hardware-count option in the IPv6 access-group command-line interface (CLI).
Prefix lists can be used as an alternative to access lists in many BGP route filtering commands. The advantages of using prefix lists are as follows:
Significant performance improvement in loading and route lookup of large lists.
Incremental updates are supported.
More user friendly CLI. The CLI for using access lists to filter BGP updates is difficult to understand and use because it uses the packet filtering format.
Greater flexibility.
Before using a prefix list in a command, you must set up a prefix list, and you may want to assign sequence numbers to the entries in the prefix list.
Filtering by prefix list involves matching the prefixes of routes with those listed in the prefix list. When there is a match, the route is used. More specifically, whether a prefix is permitted or denied is based upon the following rules:
An empty prefix list permits all prefixes.
An implicit deny is assumed if a given prefix does not match any entries of a prefix list.
When multiple entries of a prefix list match a given prefix, the longest, most specific match is chosen.
Sequence numbers are generated automatically unless you disable this automatic generation. If you disable the automatic generation of sequence numbers, you must specify the sequence number for each entry using the sequence-number argument of the permit and deny commands in either IPv4 or IPv6 prefix list configuration command. Use the no form of the permit or deny command with the sequence-number argument to remove a prefix-list entry.
The show commands include the sequence numbers in their output.
To implement access lists and prefix lists, you must understand the following concepts:
Converged networks carry voice, video and data. Users may need to route certain traffic through specific paths instead of using the paths computed by routing protocols. This is achieved by specifying the next-hop address in ACL configurations, so that the configured next-hop address from ACL is used for fowarding packet towards its destination instead of routing packet-based destination address lookup. This feature of using next-hop in ACL configurations for forwarding is called ACL Based Forwarding (ABF).
Traffic engineering over an IP or MPLS backbone can be done without MPLS-TE. The ability to divert certain kinds of traffic on top of routing allows you to let only voice traffic travel over certain links, while allowing data traffic to be sent using regular routing.
ACL-based forwarding enables you to choose service from multiple providers for broadcast TV over IP, IP telephony, data, and so on, which provides a cafeteria-like access to the Internet. Service providers can divert user traffic to various content providers.
ACL-based forwarding (ABF) enables you to configure filters for IPv4 packets. Each packet is based on the information from an IP source or destination address, TCP ports, precedence, DSCP, and so on. If a match occurs, ABF forwards the packet to one of the multiple next hops (up to three). ABF provides an alternative to regular routing by giving the ability to forward a next hop, based on packet content that extends beyond the destination IP address.
The ABF rule does not apply to “For Us” packets.
By implementing ABF, you can perform the following functions:
Specify up to three next hops in the ACL rules.
Forward IPv4 packets that are being forwarded on default routes to the next hop, as specified by the ACL rule.
Use the existing ACL matching functionality to pick up the next-hop IP address that is based on the ACE configuration. The highest preferred, active, next-hop IP address—which is based on the ACE configuration—is chosen.
Use the traditional destination IP address forwarding if the ABF next hops are not reachable.
Use ABF as an ingress-only feature; it is not available for packets switched or originated by the software.
Specify no rejection when both VRF and ABF configurations are applied on an interface. The ABF configuration is silently ignored by the forwarding software.
This section contains the following procedures:
This task configures an extended IPv4 or IPv6 access list.
| Command or Action | Purpose | |||
|---|---|---|---|---|
| Step 1 |
configure |
|||
| Step 2 |
{ipv4 | ipv6} access-list name Example:or |
Enters either IPv4 or IPv6 access list configuration mode and configures the named access list. |
||
| Step 3 |
[ sequence-number ] remark remark Example: |
(Optional) Allows you to comment about a permit or deny statement in a named access list.
|
||
| Step 4 |
Do one of the following:
Example:or |
Specifies one or more conditions allowed or denied in IPv4 access list acl_1.
or Specifies one or more conditions allowed or denied in IPv6 access list acl_2.
|
||
| Step 5 |
Repeat Step 4 as necessary, adding statements by sequence number where you planned. Use the no sequence-number command to delete an entry. |
Allows you to revise an access list. |
||
| Step 6 |
commit |
|||
| Step 7 |
show access-lists {ipv4 | ipv6} [access-list-name [sequence-number] [hardware {ingress | egress} [interface interface-path-id | sequence number | location node-id] | [usage {pfilter location node-id}] [summary [access-list-name]] [maximum [detail]] Example: |
(Optional) Displays the contents of current IPv4 or IPv6 access lists.
|
After creating an access list, you must apply it to a line or interface. See the Applying Access Lists section for information about how to apply an access list.
ACL commit fails while adding and removing unique Access List Entries (ACE). This happens due to the absence of an assigned manager process. The user has to exit the config-ipv4-acl mode to XR Config mode and re-enter the config-ipv4-acl mode before adding the first ACE.
After you create an access list, you must reference the access list to make it work. Access lists can be applied on either outbound or inbound interfaces. This section describes guidelines on how to accomplish this task for both terminal lines and network interfaces.
Set identical restrictions on all the virtual terminal lines, because a user can attempt to connect to any of them.
For inbound access lists, after receiving a packet, Cisco IOS XR software checks the source address of the packet against the access list. If the access list permits the address, the software continues to process the packet. If the access list rejects the address, the software discards the packet and returns an ICMP host unreachable message. The ICMP message is configurable.
For outbound access lists, after receiving and routing a packet to a controlled interface, the software checks the source address of the packet against the access list. If the access list permits the address, the software sends the packet. If the access list rejects the address, the software discards the packet and returns an ICMP host unreachable message.
When you apply an access list that has not yet been defined to an interface, the software acts as if the access list has not been applied to the interface and accepts all packets. Note this behavior if you use undefined access lists as a means of security in your network.
This task applies an access list to an interface to restrict access to that interface.
Access lists can be applied on either outbound or inbound interfaces.
| Command or Action | Purpose | |
|---|---|---|
| Step 1 |
configure |
|
| Step 2 |
interface type interface-path-id Example: |
Configures an interface and enters interface configuration mode.
|
| Step 3 |
Do one of the following:
Example: |
Controls access to an interface.
This example applies filters on packets inbound and outbound from HundredGigE interface 0/2/0/2. |
| Step 4 |
commit |
This task applies an access list to a line to control access to that line.
| Command or Action | Purpose | |
|---|---|---|
| Step 1 |
configure |
|
| Step 2 |
line {console | default | template template-name} Example: |
Specifies either the console, default, or a user-defined line template and enters line template configuration mode.
|
| Step 3 |
access-class list-name {in | out} Example: |
Restricts incoming and outgoing connections using an IPv4 or IPv6 access list.
|
| Step 4 |
commit |
This task configures an IPv4 or IPv6 prefix list.
| Command or Action | Purpose | |||
|---|---|---|---|---|
| Step 1 |
configure |
|||
| Step 2 |
{ipv4 | ipv6} prefix-list name Example:or |
Enters either IPv4 or IPv6 prefix list configuration mode and configures the named prefix list.
|
||
| Step 3 |
[ sequence-number ] remark remark Example: |
(Optional) Allows you to comment about the following permit or deny statement in a named prefix list.
|
||
| Step 4 |
[ sequence-number] {permit | deny} network/length [ge value] [le value] [eq value] Example: |
Specifies one or more conditions allowed or denied in the named prefix list.
|
||
| Step 5 |
Repeat Step 4 as necessary. Use the no sequence-number command to delete an entry. |
Allows you to revise a prefix list. |
||
| Step 6 |
commit |
|||
| Step 7 |
Do one of the following:
Example:or |
(Optional) Displays the contents of current IPv4 or IPv6 prefix lists.
|
||
| Step 8 |
clear prefix-list {ipv4 | ipv6} name [sequence-number] Example: |
(Optional) Clears the hit count on an IPv4 or IPv6 prefix list.
|
This task configures a standard IPv4 access list.
Standard access lists use source addresses for matching operations.
| Command or Action | Purpose | |
|---|---|---|
| Step 1 |
configure |
|
| Step 2 |
ipv4 access-list name Example: |
Enters IPv4 access list configuration mode and configures access list acl_1. |
| Step 3 |
[ sequence-number ] remark remark Example: |
(Optional) Allows you to comment about the following permit or deny statement in a named access list.
|
| Step 4 |
[ sequence-number ] {permit | deny} source [source-wildcard] [log | log-input] Example:or |
Specifies one or more conditions allowed or denied, which determines whether the packet is passed or dropped.
|
| Step 5 |
Repeat Step 4 as necessary, adding statements by sequence number where you planned. Use the no sequence-number command to delete an entry. |
Allows you to revise an access list. |
| Step 6 |
commit |
|
| Step 7 |
show access-lists {ipv4 | ipv6} [access-list-name [sequence-number] [hardware {ingress | egress} [interface interface-path-id | sequence number | location node-id] | [usage {pfilter location node-id}] [summary [access-list-name]] [maximum [detail]] Example: |
(Optional) Displays the contents of the named IPv4 access list.
|
After creating a standard access list, you must apply it to a line or interface. See the Applying Access Lists” section for information about how to apply an access list.
This task copies an IPv4 or IPv6 access list.
| Command or Action | Purpose | |
|---|---|---|
| Step 1 |
copy access-list {ipv4 | ipv6}source-acl destination-acl Example: |
Creates a copy of an existing IPv4 or IPv6 access list.
|
| Step 2 |
show access-lists {ipv4 | ipv6} [access-list-name [sequence-number] [hardware {ingress | egress} [interface interface-path-id | sequence number | location node-id] | [usage {pfilter location node-id}] [summary [access-list-name]] [maximum [detail]] Example: |
(Optional) Displays the contents of a named IPv4 or IPv6 access list. For example, you can verify the output to see that the destination access list list-2 contains all the information from the source access list list-1. |
This task shows how to assign sequence numbers to entries in a named access list and how to add or delete an entry to or from an access list. It is assumed that a user wants to revise an access list. Resequencing an access list is optional.
| Command or Action | Purpose | |||
|---|---|---|---|---|
| Step 1 |
resequence access-list {ipv4 | ipv6} name [base [increment]] Example: |
(Optional) Resequences the specified IPv4 or IPv6 access list using the starting sequence number and the increment of sequence numbers.
|
||
| Step 2 |
configure |
|||
| Step 3 |
{ipv4 | ipv6} access-list name Example:or |
Enters either IPv4 or IPv6 access list configuration mode and configures the named access list. |
||
| Step 4 |
Do one of the following:
Example:or |
Specifies one or more conditions allowed or denied in IPv4 access list acl_1.
or Specifies one or more conditions allowed or denied in IPv6 access list acl_2.
|
||
| Step 5 |
Repeat Step 4 as necessary, adding statements by sequence number where you planned. Use the no sequence-number command to delete an entry. |
Allows you to revise the access list. |
||
| Step 6 |
commit |
|||
| Step 7 |
show access-lists {ipv4 | ipv6} [access-list-name [sequence-number] [hardware {ingress | egress} [interface interface-path-id | sequence number | location node-id] | [usage {pfilter location node-id}] [summary [access-list-name]] [maximum [detail]] Example: |
(Optional) Displays the contents of a named IPv4 or IPv6 access list.
|
If your access list is not already applied to an interface or line or otherwise referenced, apply the access list. See the “Applying Access Lists” section for information about how to apply an access list.
This task copies an IPv4 or IPv6 prefix list.
| Command or Action | Purpose | |
|---|---|---|
| Step 1 |
copy prefix-list {ipv4 | ipv6} source-name destination-name Example: |
Creates a copy of an existing IPv4 or IPv6 prefix list.
|
| Step 2 |
Do one of the following:
Example: |
(Optional) Displays the contents of current IPv4 or IPv6 prefix lists.
|
This task shows how to assign sequence numbers to entries in a named prefix list and how to add or delete an entry to or from a prefix list. It is assumed a user wants to revise a prefix list. Resequencing a prefix list is optional.
Note |
Resequencing IPv6 prefix lists is not supported. |
| Command or Action | Purpose | |
|---|---|---|
| Step 1 |
resequence prefix-list ipv4 name [base [increment]] Example: |
(Optional) Resequences the named IPv4 prefix list using the starting sequence number and the increment of sequence numbers.
|
| Step 2 |
configure |
|
| Step 3 |
{ipv4 | ipv6} prefix-list name Example: |
Enters either IPv4 or IPv6 prefix list configuration mode and configures the named prefix list. |
| Step 4 |
[ sequence-number ] {permit | deny} network/length [ge value] [le value] [eq value] Example: |
Specifies one or more conditions allowed or denied in the named prefix list. |
| Step 5 |
Repeat Step 4 as necessary, adding statements by sequence number where you planned. Use the no sequence-number command to delete an entry. |
Allows you to revise the prefix list. |
| Step 6 |
commit |
|
| Step 7 |
Do one of the following:
Example: |
(Optional) Displays the contents of current IPv4 or IPv6 prefix lists.
|
This section contains the following procedures:
Perform this task to configure ACL-based forwarding with security ACL.
| Command or Action | Purpose | |
|---|---|---|
| Step 1 |
configure |
|
| Step 2 |
ipv4 access-list name Example: |
Enters IPv4 access list configuration mode and configures the specified access list. |
| Step 3 |
[ sequence-number ] permit protocol source source-wildcard destination destination-wildcard [precedence precedence] [[default] nexthop1 [ipv4 ipv4-address1] nexthop2[ipv4 ipv4-address2] nexthop3[ipv4 ipv4-address3]] [dscp dscp] [fragments] [log | log-input] [ [ttl ttl [value1 ... value2]] Example: |
Sets the conditions for an IPv4 access list. The configuration example shows how to configure ACL-based forwarding with security ACL.
|
| Step 4 |
commit |
|
| Step 5 |
show access-list ipv4 [[access-list-name hardware {ingress | egress} [interface type interface-path-id] {sequence number | location node-id} | summary [access-list-name] | access-list-name [sequence-number] | maximum [detail] [usage {pfilter location node-id}]] Example: |
Displays the information for ACL software. |
| Command or Action | Purpose | |
|---|---|---|
| Step 1 |
configure |
|
| Step 2 |
{ipv6 } access-list name Example: |
Enters IPv6 access list configuration mode and configures the specified access list. |
| Step 3 |
[ sequence-number ] permit protocol source source-wildcard destination destination-wildcard [precedence precedence] [default nexthop [ipv6-address1 ] [ipv6-address2 ] [ipv6-address3 ]] [dscp dscp] [fragments] [log | log-input] [nexthop [ipv6-address1 ] [ipv6-address2 ] [ipv6-address3 ]] [ttl ttl value [value1 ... value2]][vrf vrf-name [ipv6-address1 ] [ipv6-address2 ] [ipv6-address3 ]] Example: |
Sets the conditions for an IPv6 access list. The configuration example shows how to configure pure ACL-based forwarding for ACL.
|
| Step 4 |
commit |
Perform this task to configure pure ACL-based forwarding for ACL.
| Command or Action | Purpose | |
|---|---|---|
| Step 1 |
configure |
|
| Step 2 |
{ipv4 } access-list name Example: |
Enters IPv4 access list configuration mode and configures the specified access list. |
| Step 3 |
[ sequence-number ] permit protocol source source-wildcard destination destination-wildcard [precedence precedence] [default nexthop [ipv4-address1 ] [ipv4-address2 ] [ipv4-address3 ]] [dscp dscp] [fragments] [log | log-input] [nexthop [ipv4-address1 ] [ipv4-address2 ] [ipv4-address3 ]] [ttl ttl value [value1 ... value2]][vrf vrf-name [ipv4-address1 ] [ipv4-address2 ] [ipv4-address3 ]] Example: |
Sets the conditions for an IPv4 or an IPv6 access list. The configuration example shows how to configure pure ACL-based forwarding for ACL.
|
| Step 4 |
commit |
|
| Step 5 |
show access-list ipv4 [access-list-name hardware {ingress | egress} [interface type interface-path-id] {sequence number | location node-id} | summary [access-list-name] | access-list-name [sequence-number] | maximum [detail] [usage {pfilter location node-id}]] Example: |
Displays the information for ACL software. |
This section provides the following configuration examples:
The following example shows access-list resequencing. The starting value in the resequenced access list is , and increment value is . The subsequent entries are ordered based on the increment values that users provide, and the range is from 1 to 2147483646.
When an entry with no sequence number is entered, by default it has a sequence number of 10 more than the last entry in the access list.
ipv4 access-list acl_1
10 permit ip host 10.3.3.3 host 172.16.5.34
20 permit icmp any any
30 permit tcp any host 10.3.3.3
40 permit ip host 10.4.4.4 any
60 permit ip host 172.16.2.2 host 10.3.3.12
70 permit ip host 10.3.3.3 any log
80 permit tcp host 10.3.3.3 host 10.1.2.2
100 permit ip any any
configure
ipv4 access-list acl_1
end
resequence ipv4 access-list acl_1 10 20
show access-lists ipv4 acl_1
10 permit ip host 10.3.3.3 host 172.16.5.34
30 permit icmp any any
50 permit tcp any host 10.3.3.3
70 permit ip host 10.4.4.4 any
90 permit ip host 172.16.2.2 host 10.3.3.12
110 permit ip host 10.3.3.3 any log
130 permit tcp host 10.3.3.3 host 10.1.2.2
150 permit ip any any
In the following example, an new entry is added to IPv4 access list acl_5.
show access-lists ipv4 acl_5
ipv4 access-list acl_5
2 permit ipv4 host 10.4.4.2 any
5 permit ipv4 host 10.0.0.44 any
10 permit ipv4 host 10.0.0.1 any
20 permit ipv4 host 10.0.0.2 any
configure
ipv4 access-list acl_5
15 permit 10.5.5.5 0.0.0.255
end
show access-lists ipv4 acl_5
ipv4 access-list acl_5
2 permit ipv4 host 10.4.4.2 any
5 permit ipv4 host 10.0.0.44 any
10 permit ipv4 host 10.0.0.1 any
15 permit ipv4 10.5.5.5 0.0.0.255 any
20 permit ipv4 host 10.0.0.2 any
The following example shows how an entry with no specified sequence number is added to the end of an access list. When an entry is added without a sequence number, it is automatically given a sequence number that puts it at the end of the access list. Because the default increment is 10, the entry will have a sequence number 10 higher than the last entry in the existing access list.
configure
ipv4 access-list acl_10
permit 1.1.1.1 0.0.0.255
permit 2.2.2.2 0.0.0.255
permit 3.3.3.3 0.0.0.255
end
show access-lists ipv4 acl_10
10 permit ip 1.1.1.0 0.0.0.255 any
20 permit ip 2.2.2.0 0.0.0.255 any
30 permit ip 3.3.3.0 0.0.0.255 any
configure
ipv4 access-list acl_10
permit .4.4.4 0.0.0.255
end
show access-lists ipv4 acl_10
10 permit ip 1.1.1.0 0.0.0.255 any
20 permit ip 2.2.2.0 0.0.0.255 any
30 permit ip 3.3.3.0 0.0.0.255 any
40 permit ip 4.4.4.0 0.0.0.255 any
The following sections provide references related to implementing access lists and prefix lists.
|
Related Topic |
Document Title |
|---|---|
|
Access list commands: complete command syntax, command modes, command history, defaults, usage guidelines, and examples |
Access List Commands module in IP Addresses and Services Command Reference for Cisco NCS 6000 Series Routers |
|
Prefix list commands: complete command syntax, command modes, command history, defaults, usage guidelines, and examples |
Prefix List Commands module in IP Addresses and Services Command Reference for Cisco NCS 6000 Series Routers |
|
Terminal services commands: complete command syntax, command modes, command history, defaults, usage guidelines, and examples |
Terminal Services Commands module in System Management Command Reference for Cisco NCS 6000 Series Routers |
|
Standards |
Title |
|---|---|
|
No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature. |
— |
|
MIBs |
MIBs Link |
|---|---|
| — |
To locate and download MIBs, use the Cisco MIB Locator found at the following URL and choose a platform under the Cisco Access Products menu: https://mibs.cloudapps.cisco.com/ITDIT/MIBS/servlet/index |
|
RFCs |
Title |
|---|---|
|
No new or modified RFCs are supported by this feature, and support for existing RFCs has not been modified by this feature. |
— |
|
Description |
Link |
|---|---|
|
The Cisco Technical Support website contains thousands of pages of searchable technical content, including links to products, technologies, solutions, technical tips, and tools. Registered Cisco.com users can log in from this page to access even more content. |
Feedback