Configuring Policy-Based Routing
This chapter describes how to configure policy based routing on the Cisco NX-OS device.
This chapter includes the following sections:
Information About Policy-Based Routing
Policy-based routing allows you to configure a defined policy for IPv4 and IPv6 traffic flows, lessening reliance on routes derived from routing protocols. All packets received on an interface with policy-based routing enabled are passed through enhanced packet filters or route maps. The route maps dictate the policy, determining where to forward packets.
Route maps are composed of match and set statements that you can mark as permit or deny. You can interpret the statements as follows:
- If the packets match any route map statements, all the set statements are applied. One of these actions involves choosing the next-hop.
- If a statement is marked as deny, the packets that meet the match criteria are sent back through the normal forwarding channels and destination-based routing is performed.
- 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.
For more information, see the “Route Maps” section.
Policy-based routing includes the following features:
- Source-based routing—Routes traffic that originates from different sets of users through different connections across the policy routers.
- Load sharing—Distributes traffic among multiple paths based on the traffic characteristics.
This section includes the following topics:
Policy Route Maps
Route-Maps are used to filter routes that are distributed across various routing protocols and between different entities in a given routing protocol. Each entry in a route map contains a combination of match and set statements. The match statements define the criteria for whether appropriate packets meet the particular policy (that is, the conditions to be met). The set clauses explain how the packets should be routed once they have met the match criteria.
You can mark the route-map statements as permit or deny. If the statement is marked as a deny, the packets that meet the match criteria are sent back through the normal forwarding channels (destination-based routing is performed). If the statement is marked as permit and the packets meet the match criteria, all the set clauses are applied. If the statement is marked as permit and the packets do not meet the match criteria, those packets are also forwarded through the normal routing channel.
Note Policy routing is specified on the interface that receives the packets, not on the interface from which the packets are sent.
Set Criteria for Policy-Based Routing
The set criteria in a route map is evaluated in the order listed in the route map. Set criteria specific to route maps used for policy-based routing are as follows:
1. List of specified IP addresses—The IP address can specify the adjacent next-hop router in the path toward the destination to which the packets should be forwarded. The first IP address associated with a currently up connected interface is used to route the packets.
Note You can optionally configure the set criteria for next-hop addresses to load balance traffic across up to 16 IP addresses. In this case, Cisco NX-OS sends all traffic for each IP flow to a particular IP next-hop address.
2. List of default next-hop IP addresses—Route to the interface or the next-hop address specified by this set statement only if there is no explicit route for the destination address of the packet in the routing table.
Note You can optionally configure the set criteria for the default next-hop addresses to load balance traffic across a maximum of 16 IP addresses. In this case, Cisco NX-OS sends all traffic for each IP flow to a particular IP next-hop address.
3. NULL interface—Traffic that matches the match statement is dropped if you use the set null interface.
If the packets do not meet any of the defined match criteria, those packets are routed through the normal destination-based routing process.
Licensing Requirements for Policy-Based Routing
The following table shows the licensing requirements for this feature:
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Cisco NX-OS |
Policy-based routing requires an Enterprise Services license. For a complete explanation of the Cisco NX-OS licensing scheme and how to obtain and apply licenses, see the Cisco NX-OS Licensing Guide. |
Prerequisites for Policy-Based Routing
Policy-based routing has the following prerequisites:
- Install the correct license.
- You must enable policy-based routing (see the “Enabling the Policy-Based Routing Feature” section).
- Assign an IP address on the interface and bring the interface up before you apply a route map on the interface for policy-based routing.
- Because the default size of IPv4 and IPv6 TCAM regions is 0, you must carve the PBR TCAMs and reload the switch before applying PBR policy on an interface (see the Cisco Nexus 3000 Series NX-OS Security Configuration Guide.)
Guidelines and Limitations for Policy-Based Routing
Policy-based routing has the following configuration guidelines and limitations:
- A policy-based routing route map can have only one match or set statement per route-map statement.
- A match command cannot refer to more than one ACL in a route map used for policy-based routing.
- An ACL used in a policy-based routing route map cannot include a deny statement.
- The same route map can be shared among different interfaces for policy-based routing as long as the interfaces belong to the same virtual routing and forwarding (VRF) instance.
- For Cisco Nexus 3000 Series switches, the maximum size of the IPv4 PBR TCAM can be 1024 by carving from other regions. For Cisco Nexus 3100 Series switches, this maximum size can be 2816 by carving from other regions.
- For Cisco Nexus 3000 Series switches, the maximum size of the IPv6 PBR TCAM can be 512 by carving from other regions. For Cisco Nexus 3100 Series switches, this maximum size can be 512 by carving from other regions.
Default Settings
Table 17-1 lists the default settings for policy-based routing parameters.
Table 17-1 Default Policy-based Routing Parameters
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Policy-based routing |
Disabled |
Configuring Policy-Based Routing
This section includes the following topics:
Note If you are familiar with the Cisco IOS CLI, be aware that the Cisco NX-OS commands for this feature might differ from the Cisco IOS commands that you would use.
Enabling the Policy-Based Routing Feature
You must enable the policy-based routing feature before you can configure a route policy.
SUMMARY STEPS
1. configure terminal
2. feature pbr
3. (Optional) show feature
4. (Optional) copy running-config startup-config
DETAILED STEPS
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Step 1 |
configure terminal Example: switch# configure terminal switch(config)# |
Enters global configuration mode. |
Step 2 |
feature pbr Example: switch(config)# feature pbr |
Enables the policy-based routing feature. |
Step 3 |
show feature Example: switch(config)# show feature |
(Optional) Displays enabled and disabled features. |
Step 4 |
copy running-config startup-config Example: switch(config)# copy running-config startup-config |
(Optional) Saves this configuration change. |
Use the no feature pbr command to disable the policy-based routing feature and remove all associated configuration.
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no feature pbr Example: switch(config)# no feature pbr |
Disables policy-based routing and removes all associated configuration. |
Configuring a Route Policy
You can use route maps in policy-based routing to assign routing policies to the inbound interface. See the “Configuring Route Maps” section.
SUMMARY STEPS
1. configure terminal
2. interface type slot/port
3. ip policy route-map map - name
or
ipv6 policy route-map map - nam
4. (Optional) exit
5. (Optional) exit
6. (Optional) copy running-config startup-config
DETAILED STEPS
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Step 1 |
configure terminal Example: switch# configure terminal switch(config)# |
Enters global configuration mode. |
Step 2 |
interface type slot/port Example: switch(config)# interface ethernet 1/2 switch(config-if)# |
Enters interface configuration mode. |
Step 3 |
ip policy route-map map-name Example: switch(config-if)# ip policy route-map Testmap |
Assigns a route map for IPv4 policy-based routing to the interface. |
ipv6 policy route-map map-name Example: switch(config-if)# ipv6 policy route-map TestIPv6map |
Assigns a route map for IPv6 policy-based routing to the interface. |
Step 4 |
exit Example : switch(config-route-map)# exit |
(Optional) Exits route-map configuration mode. |
Step 5 |
exit Example : switch(config)# exit |
(Optional) Exits global configuration mode. |
Step 6 |
copy running-config startup-config Example: switch# copy running-config startup-config |
(Optional) Saves this configuration change. |
This example shows how to add a route map to an interface:
switch# configure terminal
switch(config)# interface ethernet 1/2
switch(config-if)# ip policy route-map Testmap
switch(config)# exit
switch(config)# copy running-config startup-config
You can configure the following optional match parameters for route maps in route-map configuration mode:
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match ip address access-list-name name [ name... ] Example: switch(config-route-map)# match ip address access-list-name ACL1 |
Matches an IPv4 address against one or more IP access control lists (ACLs). This command is used for policy-based routing and is ignored by route filtering or redistribution. |
match ipv6 address access-list-name name [ name ... ] Example: switch(config-route-map)# match ipv6 address access-list-name ACLv6 |
Matches an IPv6 address against one or more IPv6 ACLs. This command is used for policy-based routing and is ignored by route filtering or redistribution. |
You can configure the following optional set parameters for route maps in route-map configuration mode:
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set ip next-hop address1 [ address2... ] { load-share } Example: switch(config-route-map)# set ip next-hop 192.0.2.1 |
Sets the IPv4 next-hop address for policy-based routing. This command uses the first valid next-hop address if multiple addresses are configured. Use the optional load-share keyword to load balance traffic across a maximum of 16 next-hop addresses. |
set ip default next-hop address1 [ address2... ] { load-share } Example: switch(config-route-map)# set ip default next-hop 192.0.2.2 |
Sets the IPv4 next-hop address for policy-based routing when there is no explicit route to a destination. This command uses the first valid next-hop address if multiple addresses are configured. Use the optional load-share keyword to load balance traffic across a maximum of 16 next-hop addresses. |
set ipv6 next-hop address1 [ address2... ] { load-share } Example: switch(config-route-map)# set ipv6 next-hop 2001:0DB8::1 |
Sets the IPv6 next-hop address for policy-based routing. This command uses the first valid next-hop address if multiple addresses are configured. Use the optional load-share keyword to load balance traffic across a maximum of 16 next-hop addresses. |
set ipv6 default next-hop address1 [ address2... ] Example: switch(config-route-map)# set ipv6 default next-hop 2001:0DB8::2 |
Sets the IPv6 next-hop address for policy-based routing when there is no explicit route to a destination. This command uses the first valid next-hop address if multiple addresses are configured. |
Cisco NX-OS routes the packet as soon as it finds a next-hop and an interface.
Verifying the Policy-Based Routing Configuration
To display policy-based routing configuration information, perform one of the following tasks:
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show [ip | ipv6] policy [name] |
Displays information about an IPv4 or IPv6 policy. |
show route-map [name] pbr-statistics |
Displays policy statistics. |
Use the route-map map-name pbr-statistics to enable policy statistics. Use the clear route-map map-name pbr-statistics to clear these policy statistics.
Displaying Policy-Based Routing Statistics
Use the show route-map rmap-name pbr-statistics command to display the statistics for policy-based routing. The statistics are maintained for each route-map sequence. It shows the number of packets that are policy-routed based on the match condition in a given route-map sequence. All other packets that are routed using the default routing table (could be due to unreachable next-hops in the set command) are also displayed. The PBR statistics collection must be turned on before any statistics can be shown.
This example shows how to display PBR statistics:
switch(config)# show route-map pbr-sample pbr-statistics
Clearing Policy-Based Routing Statistics
Use the clear route-map rmap-name pbr-statistics command to clear the counters maintained for PBR statistics of a route-map.
This example shows how to clear PBR statistics:
switch(config)# clear route-map pbr-sample pbr-statistics
Configuration Examples for Policy Based-Routing
This example shows how to configure a simple route policy on an interface:
ip access-list pbr-sample
permit tcp host 10.1.1.1 host 192.168.2.1 eq 80
match ip address pbr-sample
set ip next-hop 192.168.1.1
route-map pbr-sample pbr-statistics
ip policy route-map pbr-sample
The following output verifies this configuration:
n3000# show route-map pbr-sample
route-map pbr-sample, permit, sequence 10
ip address (access-lists): pbr-sample
n3000# show route-map pbr-sample pbr-statistics
route-map pbr-sample, permit, sequence 10
Policy routing matches: 84 packets
Related Topics
The following topics can give more information on Policy Based Routing:
Additional References
For additional information related to implementing IP, see the following sections:
Related Documents
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Policy-based routing CLI commands |
Cisco Nexus 3000 Series NX-OS Unicast Routing Command Reference, Release 6.x |
Standards
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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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Feature History for Policy-Based Routing
Table 17-2 lists the release history for this feature.
Table 17-2 Feature History for Policy-Based Routing
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Policy-based routing |
6.0(2)U2(1) |
This feature was introduced. |