Policy-based routing (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 by using several attributes and to specify the next hop or the output interface to which the packet should be sent. PBR also provides a basic packet-marking capability.
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Policy-based routing (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. Therefore, 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. For a simple policy, you can use any one of these tasks; for a complex policy, you can use all of them. 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 following forwarding paths:
Cisco Express Forwarding (formerly known as CEF)
Distributed Cisco Express Forwarding
Policies can be based on the IPv6 address, port numbers, protocols, or packet size.
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.
PBR allows you to classify and mark packets at the edge of the network. PBR marks a packet by setting precedence value. The precedence value can be used directly by devices 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 policy-based routing (PBR) enabled are passed through enhanced packet filters called 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, the device 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, 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 normal forwarding channels and destination-based routing is performed.
You must configure policy-based routing (PBR) on the interface that receives the packet, and not on the interface from which the packet is sent.
Policy-based routing (PBR) for IPv6 will match packets using the
matchipv6address command in the associated PBR route map. Packet match criteria are those criteria supported by IPv6 access lists, as follows:
Source IPv6 address (standard or extended access control 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
matchlength command in the PBR route map.
Match statements are evaluated first by the criteria specified in the
matchipv6address command and then by the criteria specified in the
matchlength 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 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
Policy-based routing (PBR) for IPv6 packet forwarding is controlled by 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 set statements in turn. PBR evaluates each set statement individually, 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 set path. 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 of a specified interface. This set statement is used only when there is no explicit entry for the packet destination in the IPv6 RIB.
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
When to Use Policy-Based Routing
Policy-based routing (PBR) can be used 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:
Routing based on interactive traffic versus batch traffic
Routing based on dedicated links
Some applications or traffic can benefit from Quality of Service (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.
To enable PBR for IPv6, create a route map that specifies the packet match criteria and the desired policy-route action. Then, 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.
Depending on your release, IPv6 PBR allows users to override normal destination IPv6 address-based routing and forwarding results. VPN routing and forwarding (VRF) allows multiple routing instances in Cisco software. The PBR feature is VRF-aware, which means that it works under multiple routing instances, beyond the default or global routing table.
In PBR, the
setvrf 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. PBR, through the
setvrf command, provides a single device with multiple routing tables and the ability to select routes based on ACL classification. The device classifies packets based on ACL, selects a routing table, looks up the destination address, and then routes the packet.
Identifies a route map to be used for IPv6 PBR on an interface.
Returns to privileged EXEC mode.
Enabling Local PBR for
Packets that are
generated by the device are not normally policy routed. Perform this task to
enable local IPv6 policy-based routing (PBR) for such packets, indicating which
route map the device should use.
Command or Action
privileged EXEC mode.
password if prompted.
Device# configure terminal
Device(config)# ipv6 local policy route-map pbr-src-90
PBR for packets generated by the device.
privileged EXEC mode.
Verifying the Configuration and Operation of PBR for IPv6
Command or Action
Enables privileged EXEC mode.
Enter your password if prompted.
Device# show ipv6 policy
Displays IPv6 policy routing packet activity.
Troubleshooting PBR for IPv6
Policy routing analyzes various parts of the packet and then routes the packet based on certain user-defined attributes in the packet.
In the following example, a route map named pbr-dest-1 is created and configured. The route map specifies the packet match criteria and the desired policy-route action. PBR is then enabled on Ethernet interface 0/0.
ipv6 access-list match-dest-1permit ipv6 any 2001:DB8:2001:1760::/32route-map pbr-dest-1 permit 10match ipv6 address match-dest-1set interface serial 0/0interface Ethernet0/0ipv6 policy route-map interactive
Example: Enabling Local PBR for IPv6
In the following example, packets with a destination IPv6 address that match the IPv6 address range allowed by access list pbr-src-90 are sent to the device at IPv6 address 2001:DB8:2003:1::95:
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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.
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support and Cisco software image support. To access Cisco Feature Navigator, go
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Table 1 Feature Information for IPv6
routing for IPv6 allows a user to manually configure how received packets
should be routed.
commands were introduced or modified:
debug fm ipv6
ipv6 local policy
set ipv6 default
set ipv6 next-hop
show fm ipv6 pbr
show fm ipv6 pbr