Implementing Policy-Based Routing for IPv6

Last Updated: December 5, 2011

This module describes policy-based routing (PBR) for IPv6. PBR in both IPv6 and IPv4 allows a user to manually configure how received packets should be routed. PBR allows the user to identify packets using several attributes and to specify the next hop or output interface to which the packet should be sent. PBR also provides a basic packet-marking capability.

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest feature information and caveats, see 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 document.

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 Implementing Policy-Based Routing for IPv6

The following restrictions for policy-based routing for IPv6 are implemented in Cisco IOS Release 12.2(33)SXI4 on the Cisco Catalyst 6500.

  • The match length command is applied in software and is not supported in hardware.
  • Packet marking is applied in software and is not supported in hardware.
  • The set interface command is applied in software and is not supported in hardware.
  • Packets that contain an IPv6 hop-by-hop header will be supported in software. Such packets will not be supported in hardware.
  • PBR policies that use access-lists matching on IPv6 flow label and differentiated services code point (DSCP) value, and extension headers such as routing, mobility, and destination headers, cannot be fully classified in hardware and will be applied in software after partial classification.
  • It may not be possible to classify traffic completely in hardware when access-list matching on noncompressible addresses are used. In such cases, PBR is applied in software.
  • IPv6 PBR on switch virtual interfaces (SVIs) will be applied in software. Hardware provides only partial classification on SVIs.

Information About Implementing Policy-Based Routing for IPv6

Policy-Based Routing Overview

PBR gives you a flexible means of routing packets by allowing you to configure a defined policy for traffic flows, which lessens reliance on routes derived from routing protocols. To this end, PBR gives you more control over routing by extending and complementing the existing mechanisms provided by routing protocols. PBR allows you to set the IPv6 precedence. It also allows you to specify a path for certain traffic, such as priority traffic over a high-cost link.

PBR for IPv6 may be applied to both forwarded and originated IPv6 packets. For forwarded packets, PBR for IPv6 will be implemented as an IPv6 input interface feature, supported in the process, Cisco Express Forwarding, and distributed Cisco Express Forwarding forwarding paths.

Policies can be based on IPv6 address, port numbers, protocols, or packet size. For a simple policy, you can use any one of these descriptors; for a complex policy, you can use all of them.

PBR allows you to perform the following tasks:

  • Classify traffic based on extended access list criteria. Access lists, then, establish the match criteria.
  • Set IPv6 precedence bits, giving the network the ability to enable differentiated classes of service.
  • Route packets to specific traffic-engineered paths; you might need to route them to allow a specific quality of service (QoS) through the network.

Policies can be based on IPv6 address, port numbers, protocols, or size of packets. For a simple policy, you can use any one of these descriptors; for a complex policy, you can use all of them.

PBR allows you to classify and mark packets at the edge of the network. PBR marks a packet by setting its precedence value. The precedence value can be used directly by routers in the network core to apply the appropriate QoS to a packet, which keeps packet classification at your network edge.

How Policy-Based Routing Works

All packets received on an interface with PBR enabled are passed through enhanced packet filters known as route maps. The route maps used by PBR dictate the policy, determining where to forward packets.

Route maps are composed of statements. The route map statements can be marked as permit or deny, and they are interpreted in the following ways:

  • If a packet matches all match statements for a route map that is marked as permit, then the router attempts to policy route the packet using the set statements. Otherwise, the packet is forwarded normally.
  • If the packet matches any match statements for a route map that is marked as deny, then the packet is not subject to PBR and is forwarded normally.
  • If the statement is marked as permit and the packets do not match any route map statements, the packets are sent back through the normal forwarding channels and destination-based routing is performed.

You specify PBR on the interface that receives the packet, not on the interface from which the packet is sent.

Packet Matching

PBR for IPv6 will match packets using the match ipv6 address command in the associated PBR route map. Packet match criteria are those criteria supported by IPv6 access lists, as follows:

  • Input interface
  • Source IPv6 address (standard or extended access list [ACL])
  • Destination IPv6 address (standard or extended ACL)
  • Protocol (extended ACL)
  • Source port and destination port (extended ACL)
  • DSCP (extended ACL)
  • Flow-label (extended ACL)
  • Fragment (extended ACL)

Packets may also be matched by length using the match length statement in the PBR route map.

Match statements are evaluated first by the criteria specified in the match ipv6 address command and then by criteria specified in the match length command. Therefore, if both an ACL and a length statement are used, a packet will first be subject to an ACL match. Only packets that pass the ACL match will then be subject to the length match. Finally, only packets that pass both the ACL and the length statement will be policy routed.

Packet Forwarding Using Set Statements

PBR for IPv6 packet forwarding is controlled using a number of set statements in the PBR route map. These set statements are evaluated individually in the order shown, and PBR will attempt to forward the packet using each of the of the set statements in turn. PBR evaluates each set statement by itself, without reference to any prior or subsequent set statement.

You may set multiple forwarding statements in the PBR for IPv6 route map. The following set statements may be specified:

  • IPv6 next hop. The next hop to which the packet should be sent. The next hop must be present in the Routing Information Base (RIB), it must be directly connected, and it must be a global IPv6 address. If the next hop is invalid, the set statement is ignored.
  • Output interface. A packet is forwarded out of a specified interface. An entry for the packet destination address must exist in the IPv6 RIB, and the specified output interface must be in the path set. If the interface is invalid, the statement is ignored.
  • Default IPv6 next hop. The next hop to which the packet should be sent. It must be a global IPv6 address. This set statement is used only when there is no explicit entry for the packet destination in the IPv6 RIB.
  • Default output interface. The packet is forwarded out a specified interface. This set statement is used only when there is no explicit entry for the packet destination in the IPv6 RIB.

Note
The order in which PBR evaluates the set statements is the order in which they are listed above. This order may differ from the order in which route-map set statements are listed by Cisco IOS show commands.

When to Use Policy-Based Routing

You might use PBR if you want certain packets to be routed some way other than the obvious shortest path. For example, PBR can be used to provide the following functionality:

  • Equal access
  • Protocol-sensitive routing
  • Source-sensitive routing
  • Routing based on interactive versus batch traffic
  • Routing based on dedicated links

Some applications or traffic can benefit from QoS-specific routing; for example, you could transfer stock records to a corporate office on a higher-bandwidth, higher-cost link for a short time while sending routine application data such as e-mail over a lower-bandwidth, lower-cost link.

How to Implement Policy-Based Routing for IPv6

Enabling PBR on an Interface

To enable PBR for IPv6, you must create a route map that specifies the packet match criteria and desired policy-route action. Then you associate the route map on the required interface. All packets arriving on the specified interface that match the match clauses will be subject to PBR.

In Cisco IOS Release 12.2(33)SXI4 on the Cisco Catalyst 6500, IPv6 PBR allows users to override normal destination IPv6 address-based routing and forwarding results. Virtual private network (VPN) routing and forwarding (VRF) allows multiple routing instances in Cisco IOS software. The PBR feature is VRF-aware, meaning that it works under multiple routing instances, beyond the default or global routing table.

In PBR, the set vrf command decouples the VRF and interface association and allows the selection of a VRF based on ACL-based classification using existing PBR or route-map configurations. It provides a single router with multiple routing tables and the ability to select routes based on ACL classification. The router classifies packets based on ACL, selects a routing table, looks up the destination address, and then routes the packet.

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    route-map map-tag [permit | deny] [sequence-number

4.   Do one of the following:

  • match length minimum-length maximum-length
  • match ipv6 address {prefix-list prefix-list-name | access-list-name}

5.   Do one of the following:

  • set ipv6 precedence precedence-value
  • set ipv6 next-hop global-ipv6-address [global-ipv6-address...]
  • set interface type number [...type number]
  • set ipv6 default next-hop global-ipv6-address [global-ipv6-address...]
  • set default interface type number [...type number]
  • set vrf vrf-name

6.    exit

7.    interface type number

8.    ipv6 policy route-map route-map-name


DETAILED STEPS
  Command or Action Purpose
Step 1
enable


Example:

Router> enable

 

Enables privileged EXEC mode.

  • Enter your password if prompted.
 
Step 2
configure terminal


Example:

Router# configure terminal

 

Enters global configuration mode.

 
Step 3
route-map map-tag [permit | deny] [sequence-number


Example:

Router(config)# route-map rip-to-ospf permit

 

Defines the conditions for redistributing routes from one routing protocol into another, or enables policy routing.

  • Use the route-map command to enter route-map configuration mode.
 
Step 4
Do one of the following:
  • match length minimum-length maximum-length
  • match ipv6 address {prefix-list prefix-list-name | access-list-name}


Example:

Router(config-route-map)# match length 3 200



Example:



Example:

Router(config-route-map)# match ipv6 address marketing

 

Specifies the match criteria.

  • You can specify any or all of the following:
    • Matches the Level 3 length of the packet.
    • Matches a specified IPv6 access list.
    • If you do not specify a match command, the route map applies to all packets.
 
Step 5
Do one of the following:
  • set ipv6 precedence precedence-value
  • set ipv6 next-hop global-ipv6-address [global-ipv6-address...]
  • set interface type number [...type number]
  • set ipv6 default next-hop global-ipv6-address [global-ipv6-address...]
  • set default interface type number [...type number]
  • set vrf vrf-name


Example:

Router(config-route-map)# set ipv6 precedence 1



Example:



Example:

Router(config-route-map)# set ipv6 next-hop 2001:DB8:2003:1::95



Example:



Example:

Router(config-route-map)# set interface serial 0/0



Example:



Example:

Router(config-route-map)# set ipv6 default next-hop 2001:DB8:2003:1::95



Example:



Example:

Router(config-route-map)# set default interface ethernet 0



Example:



Example:

Router(config-route-map)# set vrf vrfname

 

Specifies the action or actions to take on the packets that match the criteria.

  • You can specify any or all of the following:
    • Sets precedence value in the IPv6 header.
    • Sets next hop to which to route the packet (the next hop must be adjacent).
    • Sets output interface for the packet.
    • Sets next hop to which to route the packet, if there is no explicit route for this destination.
    • Sets output interface for the packet, if there is no explicit route for this destination.
    • Sets VRF instance selection within a route map for a policy-based routing VRF selection.
 
Step 6
exit


Example:

Router(config-route-map)# exit

 

Returns the router to global configuration mode.

 
Step 7
interface type number


Example:

Router(config)# interface FastEthernet 1/0

 

Specifies an interface type and number, and places the router in interface configuration mode.

 
Step 8
ipv6 policy route-map route-map-name


Example:

Router(config-if)# ipv6 policy-route-map interactive

 

Identifies a route map to use for IPv6 PBR on an interface.

 

Enabling Local PBR for IPv6

Packets that are generated by the router are not normally policy routed. Perform this task to enable local PBR for IPv6 for such packets, indicating which route map the router should use.

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    ipv6 local policy route-map route-map-name


DETAILED STEPS
  Command or Action Purpose
Step 1
enable


Example:

Router> enable

 

Enables privileged EXEC mode.

  • Enter your password if prompted.
 
Step 2
configure terminal


Example:

Router# configure terminal

 

Enters global configuration mode.

 
Step 3
ipv6 local policy route-map route-map-name


Example:

Router(config)# ipv6 local policy route-map pbr-src-90

 

Configures PBR for IPv6 for packets generated by the router.

 

Enabling Cisco Express Forwarding-Switched PBR for IPv6

Beginning in Cisco IOS Release 12.3(7)T, PBR for IPv6 is supported in the Cisco Express Forwarding switching path. Cisco Express Forwarding-switched PBR is the optimal way to perform PBR on a router.

No special configuration is required to enable Cisco Express Forwarding-switched PBR for IPv6. It is on by default as soon as you enable Cisco Express Forwarding and PBR on the router.

Verifying Configuration and Operation of PBR for IPv6

SUMMARY STEPS

1.    enable

2.    show ipv6 policy


DETAILED STEPS
  Command or Action Purpose
Step 1
enable


Example:

Router> enable

 

Enables privileged EXEC mode.

  • Enter your password if prompted.
 
Step 2
show ipv6 policy


Example:

Router# show ipv6 policy

 

Displays IPv6 policy routing packet activity.

 

Troubleshooting PBR for IPv6

Policy routing looks at various parts of the packet and then routes the packet based on certain user-defined attributes in the packet.

SUMMARY STEPS

1.    enable

2.    debug ipv6 policy [access-list-name

3.    show route-map [map-name | dynamic dynamic-map-name | application application-name]] | all] [detailed


DETAILED STEPS
  Command or Action Purpose
Step 1
enable


Example:

Router> enable

 

Enables privileged EXEC mode.

  • Enter your password if prompted.
 
Step 2
debug ipv6 policy [access-list-name


Example:

Router# debug ipv6 policy

 

Displays IPv6 policy routing packet activity.

 
Step 3
show route-map [map-name | dynamic dynamic-map-name | application application-name]] | all] [detailed


Example:

Router# show route-map

 

Displays all route maps configured or only the one specified.

 

Examples

Sample Output from the show ipv6 policy Command

The show ipv6 policy command displays PBR configuration, as shown in the following example:

Router# show ipv6 policy
Interface                 Routemap
Ethernet0/0               src-1
Sample Output from the show route-map Command

The show route-map command displays specific route-map information, such as a count of policy matches:

Router# show route-map
route-map bill, permit, sequence 10
  Match clauses:
  Set clauses:
  Policy routing matches:0 packets, 0 bytes

Configuration Examples for Implementing Policy-Based Routing for IPv6

Example Enabling PBR on an Interface

In the following example, a route map named pbr-dest-1 is created and configured, specifying packet match criteria and desired policy-route action. Then, PBR is enabled on Ethernet interface 0/0. 

ipv6 access-list match-dest-1
  permit ipv6 any 2001:DB8:2001:1760::/32
route-map pbr-dest-1 permit 10
  match ipv6 address match-dest-1
  set interface serial 0/0
interface Ethernet0/0
  ipv6 policy-route-map interactive

Example Enabling Local PBR for IPv6

In the following example, packets with a destination IPv6 address matching that allowed by access list pbr-src-90 are sent to the router at IPv6 address 2001:DB8:2003:1::95:

ipv6 access-list src-90
 permit ipv6 host 2001:DB8:2003::90 2001:DB8:2001:1000::/64
route-map pbr-src-90 permit 10
 match ipv6 address src-90
 set ipv6 next-hop 2001:DB8:2003:1::95
ipv6 local policy route-map pbr-src-90

Additional References

Related Documents

Related Topic

Document Title

IPv6 addressing and basic configuration

" Implementing IPv6 Addressing and Basic Connectivity ," Cisco IOS IPv6 Configuration Guide

QoS for IPv6

" Implementing QoS for IPv6 ," Cisco IOS IPv6 Configuration Guide

Multicast Border Gateway Protocol (BGP) for IPv6

" Implementing Multiprotocol BGP for IPv6," Cisco IOS IPv6 Configuration Guide

Access control lists for IPv6

" Implementing Traffic Filters and Firewalls for IPv6 Security ," Cisco IOS IPv6 Configuration Guide

IPv6 supported feature list

" Start Here: Cisco IOS Software Release Specifics for IPv6 Features ," Cisco IOS IPv6 Configuration Guide

IPv6 commands: complete command syntax, command mode, defaults, usage guidelines, and examples

Cisco IOS IPv6 Command Reference

IPv4 Quality of Service

" Quality of Service Overview ," Cisco IOS Quality of Service Solutions Configuration Guide

Standards

Standards

Title

No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.

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MIBs

MIBs

MIBs Link

None

To locate and download MIBs for selected platforms, Cisco software releases, and feature sets, use Cisco MIB Locator found at the following URL:

http://www.cisco.com/go/mibs

RFCs

RFCs

Title

No new or modified RFCs are supported by this feature, and support for existing RFCs has not been modified by this feature.

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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.

http://www.cisco.com/cisco/web/support/index.html

Feature Information for Implementing Policy-Based Routing for IPv6

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.

Table 1 Feature Information for Policy-Based Routing for IPv6

Feature Name

Releases

Feature Information

IPv6 Routing--IPv6 Policy-Based Routing

12.2(30)S 15.1(1)S 12.2(33)SXI4 12.3(7)T 12.4 12.4(2)T

Policy-based routing for IPv6 in Cisco IOS software allows a user to manually configure how received packets should be routed.

The following commands were introduced or modified by this feature: debug ipv6 policy, ipv6 local policy route-map, ipv6 policy route-map, match ipv6 address, match length, route-map, set default interface, set interface, set ipv6 default next-hop, set ipv6 next-hop, set ipv6 precedence, set vrf, show ipv6 policy, show route-map

Cisco and the Cisco logo are trademarks or registered trademarks of Cisco and/or its affiliates in the U.S. and other countries. To view a list of Cisco trademarks, go to this URL: www.cisco.com/go/trademarks. Third-party trademarks mentioned are the property of their respective owners. The use of the word partner does not imply a partnership relationship between Cisco and any other company. (1110R)

Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental.

© 2011 Cisco Systems, Inc. All rights reserved.